GTO Drivetrain

This page highlights work performed on several systems of my 1967 GTO:

  • Engine
  • Quadrajet Carburetor
  • Exhaust
  • Rear axle

Pontiac 400 YS 335HP Engine

October 24, 2012

1967 Pontiac V8 400 335HP

During a lull over the winter of 2012/2013, I turned my attention to the engine of the GTO. I believe the GTO sat dormant for a while in the 70's before the previous owner purchased it, so during the car's first refurbishment, he had an overhaul performed on the engine to get it running good. I did not get any details on what work was performed when I bought the car, but it did run good for me when I used the car as my daily driver for a few years.

Crusty Pontiac 400 engine

But, a couple decades have passed since then and it's time to take it apart for a good inspection.

So, during a few evenings I tore the intake, heads and oil pan off the engine. What I found inside this 133K motor were the original pistons, rods, cam and valves. The main caps and rod caps were off next and the crank was removed. The crank and all the bearings looked real good, and the cylinder bores looked really nice with almost imperceptable ridges.

Pontiac crankshaft

It looked like the bearings, timing chain and valve seals had been replaced but there was no evidence of any machine work. All the measurments are stock spec. It probably had a ring job with a honing of the bores.

Pontiac 400 cast aluminum pistons

Since the inspection results were good news, nothing will get replaced but I will clean it up and re-seal everything.

Before putting it back together, I tackled a few broken studs on the various engine parts. I managed to carefully extract a broken exhaust bolt, the manifold choke stove screw, and a valve cover screw without cutting into the original threads. This was accomplished with creative fixturing and the use of a milling machine. It's nice to have end mills for these jobs.

I took the opportunity to scrape the tops of the pistons clean, and the heads were also taken apart and the valves and combustion chambers were de-carboned and cleaned up also. Incidentally, I cc'd the 670 heads and found the volumes ranged from 72 to 74 cc's.

CC'ing Pontiac heads with plexiglass and syringe Installing the Graph-tite rear main seal in Pontiac V8Engine block ready for crankshaft installation

For the rear main seal, I purchased the Best Gasket brand "Graph-tite" rope seal. The installation is pretty easy with the engine on an engine stand. 

The old bearings were reinstalled into the saddles and rods, and the crank was reinstalled.

I also installed a pilot bearing into the rear of the crank. I was happy to find it was machined for a pilot bearing even though it was born an automatic car. Some automatic spec engines are allegedly not machined to accept a pilot bearing. Rather than stake the bearing into the bore, I used Loctite 620 which is a bearing retaining compound. 

The oil pan was very carefully massaged to get the flange nice and flat, and it was installed onto the block with Utltra Black RTV and cork gaskets.

Waterpump gap

Building up the waterpump back plate with weldment

The timing cover required some heli-coil work to repair some stripped out and corroded bolt holes, but it was salvagable. I also spent a bit of time on the water pump divider plates. These sat too far into the cavity which allowed a pretty fair sized gap between the plate and waterpump impeller. I never had an overheating problem, but it's a well known issue with Pontiac V8 engines and good practice to minimize the gap.

adjusting Pontiac waterpump plate for correct seating

In this case, the excess gap was probably due to some corrosion on the plates where they bear against the backside of the timing cover cavity, so I welded up the contact points on the plates to add thickness and filed them down to restore the intended gap. I used a straight edge to make sure the plates didn't stick out beyond the face where the waterpump and gasket sit.

Distributor Rebuild

GTO points distributor with Standard blue streak points GTO points distributor with Standard blue streak pointsGTO points distributor with Standard blue streak pointsGTO points distributor with Standard blue streak points

In my experience, points distributors have always been trouble free, so I'm keeping the points distributor on this car. I don't mind at all checking and adjusting the dwell a couple times a year.

Upon removal, the distributor exhibited sticky rotation, so disassembly was in order to investigate. With the guts on the bench it was obvious that the upper bearing (bushing actually) was dirty and sticky. The shaft had actually galled up a little bit. There is a grease well around the upper bearing, but it was pretty dry. I cleaned the well out, then used a wire to clean out the wicking holes that feed into the bushing, and refilled the well with my own grease concoction. It is simply some gear oil, assembly lube and lithium grease. 

The distributor shaft required some polishing to smooth the bushing surface, and after reassembly, it spins beautifully. I tested the vacuum advance and it works fine, so it was screwed back on. The Standard "Blue Streak" cap I bought in the 80's topped it all off.

Final assembly

slipping in the GTO engine GTO 400 YS engineAfter cleaning and painting, the engine was united with the flywheel, clutch and transmission. The heads were left off to ease installation into the car. Installation was pretty easy with no front end sheet metal to get in the way.

From there, assembly continued with installation of the heads, intake, fuel pump, exhaust manifolds and starter. The crank pulley mounting holes were wallowed out from being loose in the past, so I welded the damaged holes, ground down the bumpy welds and CNC'd the six mounting holes so the alignment would be right on.

I've got an early 70's quadrajet that came with the car, but I also have a '79 unit that I might go with and tune it up according to the Cliff Ruggles book. 

This engine is pretty much bone stock, so I anticipate it might not run very good with available gas. Depending on how bad it will be, I'll keep a lookout for some different heads with bigger chambers. We'll see.

First Start

March 2013

Over the course of some weeks I got all the wiring done, and then found the old waterpump leaked like a sieve. Rather than fuss with trying to find a good rebuilt pump, I bought a new Flowkooler pump. It's got an interesting impeller.

Pontiac Flowkooler waterpump impeller

The only carb I had was an ancient, choke-less Olds quadrajet that I've never rebuilt. So that means it's never been apart for at least 25 years. Yah. (Keep reading farther down for details of a replacement carb.)

I managed to put on the wrong year intake gaskets during assembly which resulted in a massive hole in the intake exhaust crossover. I also wired the exhaust crossover butterfly valve closed instead of open. This made for noisy, cantankerous operation for the first start. And power was pretty low down! In addition, the vacuum advance was inadvertently connected to a ported vacuum source rather than manifold vacuum. Still, I forged ahead with the initial firing.

My son took some video of the first startup, and he posted it on Youtube. It's not edited much, so avoid viewing the middle few minutes. We took it for a spin around the block. It's cold with no windshield. But it was fun.

After the first run, I fixed all the glitches, gained probably 80 horsepower and the car was a relative screamer (keeping in mind the car was in strippo mode with no glass, seats, carpets, top, etcetera.) Since then, the car has been loaded up with all it's accouterments, and it's back to it's heavy old self. But it runs really nice and has decent power. It's a time machine in a way, since the engine has never been rebuilt and is in it's 1967 configuration.

The engine compartment looked pretty good at this point. I still needed to work on more correct brake booster vacuum hoses, and vacuum advance lines. Here's the engine configuration in 2013:

1967 GTO engine compartment

I used the original pitted and scratched valve covers and air cleaner. I like them because they are original to the car. And yes, I'm saving pennies for a correct radiator cap too.

Quadrajet Carburetor Rebuild

January 8th, 2015

Dirty old Quadrajet

Rebuilding a late 70's Quadrajet to a Cliff Ruggles recipe

After running the GTO for a few months, the crusty, clapped out Olds Quadrajet that was just not up to my standards. It was cantakerous when trying to start cold. If it sat for a few days I would routinely have to pop the hood, take off the air cleaner and partially block the primaries to choke it a bit to get it to start up. So with the body restoration done, it was time to get the fuel system to work like it was meant to.

A few years ago I picked up a complete Quadrajet (with an intact choke system) at a swap meet for 5 dollars. I had no clue what it was except that it had a front facing fuel inlet that Pontiacs use. I finally looked up the numbers and found that it is a 1979 Oldsmobile 403 Quadrajet for a Trans Am. Closer inspection revealed that, despite the dirt, it was in excellent condition. 

I picked up a Quadrajet book written by Cliff Ruggles: How to Rebuild and Modify Rochester Quadrajet Carburetors. According to Ruggles, these late model QJ's are good "core" carbs to work with for almost any application. As I found out, it would need modification to optimize it's performance for a car from the previous decade.

In addition to the book, I purchased a complete rebuild kit from the Cliff Ruggles website for a stock rebuild. The Ruggles kit is quite comprehensive, and had everything needed to do a complete rebuild.

Carb teardown was straight forward and all parts were organized and cleaned with lacquer thinner. These late 70's carbs have hardened caps over the idle mixture screws in the throttle plate to prevent "tampering". The throttle plate has to be slit with a saw so that a punch can catch an edge and knock the plug out. The hacking results in an ugly throttle plate, but it's necessary in order to have adjustable idle mixture screws. In retrospect I should have cleaned up the hack marks and made it pretty, but I can pretty it up at another time. In the photo below, you can see the crude slits at the edges above the small primary bores on the throttle plate:

Cuts necessary to remove idle mixture caps Quadrajet

Initial Tests

To get a baseline, I rebuilt the carb to stock '79 specs with the intention of performing mods/upgrades one at a time. 

To bolt this "late' carb to the unique '67 only intake, I fabricated an aluminum plate to block off the front heat passage. (No, I didn't want to tap those passages for pipe plugs.) 

Custom 1967 Pontiac Intake heat passage block off plate

So the custom plate is sandwiched between a stock '67 gasket and a later model gasket on top that matches the '79 Olds carb.

Rebuilt Pontiac Quadrajet first iteration

My first road tests with the '79 spec carb yielded a surging idle, and pretty weak acceleration performance. Attempts at adjusting the idle mixture screws had no effect on the surging idle. According to the Ruggles book, if idle mixture screw adjustment yields no change, this indicates that the idle mixture circuit is too small. 

To fix this problem, the carb had to come completely apart. It became obvious the carb was pretty far off from optimum tune, so I decided to just perform all the mods called out in Ruggles book for a "stock performance" rebuild. 

So here's what I did:

Enlarge Idle Mixture Circuit

As mentioned above, the late Quadrajet idle mixture circuits are likely undersized, so I basically used the settings called out in the middle column on page 94:

Idle Tube ID: left stock at 0.035" (recipe calls for 0.036")

Idle Down Channel enlarged from 0.041" to 0.046"

Upper Air Bleed left stock (0.069")

Lower Air Bleed left stock (about 0.070")

Holes behind Mixture Screws enlarged from about 0.074" to 0.089"

Bypass Air Holes

This "late" Quadrajet had no bypass air holes, probably because these later carbs get their bypass air from their hot air choke housing...since this application will not use a hot air choke, I plugged the vacuum/air hole in the choke housing and drilled 0.055" dia holes into the throttle plate as shown in the picture above (I'm pointing to one of the holes with the x-acto knife). 

Main Jets

I did not change out the stock #73 jets or #55P rods. The jet/rods size ratio is a bit skewed from the optimum ratio recommendation but I'm sticking with them for now. I also left the power piston screw in its stock location at this time.

Road Test #2

The carb was reinstalled and the idle mixture screws now had an impact on tuning. There was a vast improvement on idle quality and low speed cruise. Full throttle blasts still seemed rather sluggish however, so I took the carb off for work on the secondary system.

Secondary System

I ordered Edelbrock "CE" secondary rods and installed them. 

I drilled out the secondary discharge holes from stock 0.029" to about 0.033". Don't be fooled like I was initially; these discharge holes have a large ID visible, but deeper in these holes the ID is smaller, and this is what you want to modify...the holes are in the main body casting of the carb; I'm pointing to these holes in the photo below.

In addition, I also added small cutouts (see Ruggle's book page 106) to the air flaps. This helps atomize the fuel when it is initially discharged from the secondary circuit and the flaps arent' quite opened up yet.

Modified secondary air flaps on Quadrajet

I also did a minor adjustment to the air valve spring for quicker opening. 

Road Test #3

The performance was better, but I still had some suspicions about the primary side of things.

Tip in Test....Lean or Rich

I did the fast idle "tip in" test described on Ruggles book page 99. This test indicates whether you are running on the lean or rich side for the primary circuit. Basically, you set the idle speed screw on the throttle linkage to run the engine about 2200 rpm (engine warmed up) then choke the engine a bit either with the choke flap or your hand over the primaries. An RPM increase of about 100 RPM indicates a borderline lean condition that is considered good. If the RPM's increase much more than 100 RPMs, your engine is running too lean. If the RPMs don't change or go down, pull a vac hose somewhere to introduce more air and see if the RPM's go up. If so, this indicates a rich condition.

In my case, when I choked it a little bit, RPM's went up about 250 RPM, so I was running a bit lean. I'm not quite ready to swap jets or rods, so I decided to adjust the power piston that (on these late 70's Quadrajets) offers some range of adjustment for tuning fuel flow.

Power Piston

The power piston screw can only be reached when the carb air horn is removed. This is obviously labor intensive when tuning. But a small aluminum plug/cap can be modified to allow power piston adjustments without taking the carburetor air horn off. You can see the plug at the lower part of the air cleaner mounting surface, just forward of the float bowl vent:

Power piston plug on a Quadrajet

With the airhorn off, simply tap the plug out and modify it with a blind, tapped hole. I went with a 4-40 thread. Now, with the carb back together, the plug can be removed by simply inserting a 4-40 screw and using it as a puller to pop the plug out and do adjustments.

Power piston plug with tapped hole Quadrajet
Quadrajet power piston modified plug installed airhorn

I turned the power piston out 1.25 turns CCW to richen up the part throttle operation. Embarassingly enough, I still haven't re-tested it with the tip in test. I did do more road testing however:

Final Test Comments

More road testing indicated that short acceleration blasts don't last long enough for the secondaries to really kick in. The slow-to-respond secondaries problem seems exacerbated by having a 4 speed with the associated vacuum spikes whilst shifting...(I don't speed shift...it's a cream puff for cripes sakes.) The stock 1979 vintage choke pull off diaphram bleed rate is just too slow for a speedy kick in of the secondary system.

[The old carburetor I used had NO choke pull off, and surprisingly, I never had a bog problem. I don't know what that really means as far as how good the tune was in that situation, but I sure did like the almost instant engaging of the 4 "barrels".]

So, I still think there is more power lurking in my tuning. My intention is to modify the choke pull off for faster action. I purchased a new "Standard" brand choke pull off for 10 bucks (Amazon!) and soon I will modify the bleed rate on it and try it out. Ruggles book describes methods for doing this. I'll post the results when I get to it.

Choke

The orginal '67 carbs used a "divorced" choke which basically means the temperature sensative element (bimetallic spring) is mounted directly to the intake manifold exhaust crossover for direct heating. A rod connects the spring to the linkage on the carb. Later carbs, like the Trans Am carb I have now, use a choke housing mounted to the side of the carb, with the bimetallic spring inside. These later housings get their heat by having a small vacuum "leak" inside the housing which pulls air through a tube inside the intake manifold exhaust crossover. The air gets heated up on its trip through the tube. 

There isn't an easy way to adapt this late style choke housing requiring hot air to an early divorced choke manifold car which uses direct heating. A 20 dollar solution is to convert to an electric choke. These are available all over the place, and I got one from eBay. Here it is installed into the choke housing:

Electric choke conversion on Quadrajet

The electric choke requires a constant 12V source which is not supplied on an old fashioned GTO engine harness, so, a popular solution to this problem is to tap into the nearby wiper motor harness. 

Electric choke tapping wiper motor harness GTO Quadrajet

I popped out the existing power lead from the connector, and tapped off of it by soldering on a new pigtail, added some heat shrink, put the lead back into the connector and reinstalled it into the wiper motor terminals. The other end of the pigtail was terminated with a simple female spade and installed onto the new electric choke. Purists will immediately notice the non-stock choke, but for me, it beats trying to find a 60's divorced choke Pontiac Quadrajet.

Techniques for adjusting the choke linkage is a simple matter of inspecting all the parts, installing them, and then tuning them to specification. The subtleties of how a choke works is something I never really paid attention to until now. The most important thing I think is to have the choke pull off adjusted correctly, so that it pulls the choke open by the specified amount (about a 1/4 inch in my case) immediately upon starting. It's equally important to have the choke flap completely closed during the cold start for maximum choking. 

After careful setup and adjustments, it WORKS. It works fantastic! In all my days of driving 60's cars, I never really had a good working choke.
It's amazing that I can leave the car sitting for a few weeks, get in, pump the carb once to "set" the choke and it fires right up. In fact, over this winter, after sitting undisturbed for 3 months, I got in the car, pumped the pedal twice and it started right up and fast idled. Shocking. The GM engineers knew what they were doing!

Ugly yet wonderful performing Quadrajet on GTO

1967 GTO Exhaust Installation

January 31, 2013

These are dark days for car work in the cold northeast, but with my little 5kW heater buzzing away, I managed to install a new exhaust system onto the GTO in tolerable comfort.

Hovering GTO undergoing Pypes exhaust installation

There are a bunch of options for dual exhaust systems for GTO's nowadays. I would have preferred a totally stock type system, but those are too much money, so I decided to go with a Pypes X system with a pair of Dynomax 17749 long case mufflers. I think this combo will give me a pretty quiet system which will be fitting with my stock restoration.

While the price for the Pypes A-body pipes wasn't too spendy, an additional "cost" that some folks may want to consider is the labor required to tweak this universal-type system for a better fit. I have the tools and time to put into it, so with some trimming, cutting and welding, I got the system to fit pretty decently.

Downpipes

67 GTO log type pypes downpipes

I started with the downpipes (headpipes). I am using plain old "log" manifolds, and Pypes does make downpipes to fit these. These downpipes were the best part of the whole system. They fit perfectly and required no work. There was no indication which pipe was for which side, but it was clear in my situation that they fit best only one way. When bolted on, there was plenty of room around the starter, control arms and oil filter, and they don't hang down too low.

1967 GTO with log manifold Pypes downpipes

The downpipes must be cut to length depending on where you want the "X". The "X" is made assuming the downpipes are parallel to the centerline of the car, but in my case the driver side pipe angled toward the centerline by about 10 degrees. So, I made my first modification to the short 45 degree elbow that adapts to the "X" section. The 45 degree elbow on the driver side was notched and then welded to change the angle to about 55 degrees. The photo below shows the slice and weld job on the elbow closest to the bottom. 

Pypes X pipe adapter sliced and re-welded at shallower anglePypes X section clamped in place on 1967 GTO

Welding was very easy with just plain ol' steel wire on my MIG. It works great on the stainless. The resulting mystery alloy of weldment will eventually rust, but I'm sure it will last for a very very long time.

I used Walker stainless band clamps to clamp the "X" on. They worked pretty well despite the huge bolts being in the way on some of the joints.

Tailpipes

With the "X" in place, and before tackling the intermediate pipes, I began working on the tailpipes and mufflers. The car was boosted up on blocks (under the wheels) and there was enough room for the tailpipes to be slipped over the axle with the suspension at ride height. This made the constant fitting and re-checking pretty easy.

67 GTO up on blocks to perform Pypes exhaust intallation

Trial fitting the tailpipes showed that the tailpipe inlet ends in front of the axle hung too low (for my taste anyway). If I attempted to move the tailpipes higher, the tops of the loops over the axle hit the trunk pan.

To compensate, a little over an inch was cut out of the front part of the tailpipe to effectively raise the inlet up 1 inch. The new inlet location raised the mufflers up nicely and closer to where a stock system would have them.

Pypes tailpipe modification to inlet side for GTO Welding modified Pypes tailpipe inlet for GTO application

With the front part of the tailpipe modified, a second problem revealed itself which is typical of these Pypes systems: The rear part of the tailpipes are straight, and the pipes make a straight shot out the back to exit under the bumper. This makes the tailpipes plainly visible from the side of the car, which I really dislike. So some more mods were necessary.

To address the drooping tailpipes, I sliced a wedge out of the tailpipes at the forward part of the straight section (just after it passes under the frame) and bent the pipes exits up 3 inches. In the photo below, the tailpipe has already been sliced and the exit end moved up. Before modification, the exit end was even with the stack of 1x3 wood scraps to the right.

Slicing Pypes tailpipe and bending ends up on 67 GTO exhaust

This mod tucked the tailpipe up in between the frame and the rear quarter so it was now hidden from view from the side. You can see the gas tank peeking out under there, as well as a "U" clamp for the hanger.

Modified PYPES tailpipe for 1967 GTO

To get the exhaust exit pointed down and away from the bumper, and since I am using exhaust extensions (stock style trumpet tips),  I fabricated downturns for the ends of the tailpipes.

Downturn fabricated for PYPES tailpipes on 67 GTO

These downturns were fabricated with a simple angle cut and weld modification on some extra straight pieces included in the Pypes kit. Fortunately these extra pieces feature swaged ends to fit over the end of the tailpipes. 

I'll put a slice into the trumpet and use some homemade band clamps to hold them onto the downturns.

Intermediate Pipes

Finally I worked on the intermediate pipes that connect the "X" to the muffler inlets. These sections are supplied as straight pipes with very short 45 degree elbows at the forward ends to connect to the "X".

These intermediate pipes have to hang low a bit to get by the lowest part of the floorpans and the exits failed to meet up very close with the mufflers. So I fabricated "jogs" into the intermediate pipes that moved the pipe outlets up higher and a little outboard to meet the muffler inlets. 

Below is a picture of the "jogs" I put into the outlet ends.

Intermediate pipes modified with jogs for GTO exhaust

Here they are installed. The "jogs" let the mufflers sit up higher and keep them a comfortable distance from the driveshaft.

Customized PYPES intermediate pipes on 1967 GTO

Detailing the Undercarriage

While the car was boosted up in the air, I took the opportunity to install the emergency brake cables (new manual trans lengh cables), a manual trans driveshaft, gas tank, rubber lines and gauge wiring. 

I also re-created the inspection dabs of paint that I found during disassembly. These included a big yellow dot under the differential housing, red and orange marks on the spindles, and markings on the rear frame rail.

To recreate the frame markings, I made a stencil from a sheet of paper and cut out the text, and used a mini roller with white paint.

Here's the stencil I found under the undercoating in 2005:

1967 GTO convertible frame part number stencil

It's an upside down stencil with "PPS" for Parish Pressed Steel, "9788786" which is the part number (for an automatic convertible frame), and the date which was "2 14 67". Since I'm not undercoating, I'm letting it all hang out:

Restored GTO frame part number stencil.

And here's the final glamour shot: (I fitted the old bumper at this time to fit the exhaust)

View of tailpipe, trumpet exhaust tip fitted to GTO

I'm going to get rid of the big "U" clamps on the hangers also and use some more homemade band clamps.

Here's a couple shots of the completed undersides:

Front undercarriage detail of 67 GTO
Modified tailpipe detail of Pypes installation on 67 GTO

EDIT: I ended up removing the driver side pipe and muffler again to move that side up a bit more....to make it even with the passenger muffler. Much better...perhaps a picture soon...

Rear Axle Refurb on the GTO

December 30, 2012

Even though it's been decades since I've driven this car, I do remember the rear end making a racket. So when I was doing the frame refurbishment a while back, I removed the axle cover and looked around in there. I noticed the differential case had side to side movement within the axle housing. I should have fixed it then, but I didn't have the gumption. So one day this week I jacked up the car and removed the axle assembly so I could see what could be done.

BOP differential case

The differential case has tapered bearings pressed onto each end, and the outer cups are clamped into the housing with caps and bolts. An intentional bearing pre-load should be present by having an interference fit of the case into the axle housing so there should be no side to side movement. However, I measured a side to side movement of 0.020", and the ring gear backlash was 0.023". Both numbers were not good and something was bad here.

After removing the axles, the differential bearing caps were removed. I was careful to keep the caps marked so they could go back into the same side, position and orientation. If the caps are mixed up, the matching machine tolerances will be disturbed and potentially destroy the rear. The case typically must be lightly pried out, but in this situation it just lifted right out.

Differential bearing races with shims on the outboard sides

Under the caps and between the races and housing are custom machined spacers from the factory that set the side to side position of the diff case in relation to the pinion gear. As built by GM, these spacers are cast iron, and they are intentionally a few thousands too thick on each side. This introduces pre-load onto the differential case bearings. When taking the rear apart, take care not to mix these spacers up as they will be a good reference when reinstalling the case.

Upon removal of the case, it was evident that the bearings had worn down significantly. The rollers for both bearings looked fine, but the outer races were severely galled and had some deep pitted areas.

GTO differential case bearing damage

I pulled the bearings off of the diff case and it appeared that one of the bearings also spun on the diff case which slightly galled the surface.

Differential case bearing boss

Despite the damage, it looked like it was repairable. The pinion looked good and spun nice with a bit of drag like it should. The ring gear looked good, and the spider gears looked okay.

A search was undertaken to find bearings and seals. I learned that finding these kind of parts locally on a shelf is not very likely. I did find the diff bearings at a NAPA, but I could not find axle seals, or axle bearings. I ended up buying parts from Amazon of all places. 

I installed the new bearings onto the differential case with a hammer and bearing driver. (I don't have a hydraulic press. Yet.) Bearing retaining compound was used as an extra measure.

For installation of the diff case into the axle housing, PMD service procedures recommend new steel shims instead of re-using the original cast iron units. Since I kept the originals for reference, it was a simple matter to stack some steel shims to match the originals. A cast iron spacer is shown next to the new shims.

Differential case shim kit for GTO rear axle

Initially, you subtract a few thousandths on each shim stack so the case can go in and out with no interference, but you don't want free-play either. Initial measurements can be made more easily this way.

Checking backlash of the ring and pinion on a Pontiac GTO rear axle

I measured 0.007" backlash on the ring and pinion on the first try with the new shims set to original specs. I then added 0.005" to the shim stack on the passenger side which introduced the required pre-load. Putting the extra shim thickness on the passenger side also pushed the ring gear a bit further away from the pinion, and a re-measure of the ring and pinion backlash indicated 0.009" which is probably a better number for used gears. I did not go to the length of getting compound and checking the gear contact. I figured since the new shim stacks ended up being within a couple thousands of the original shims, I should be okay.

After torquing on the caps, the axles were installed along with a new wheel bearing and seal on one side. (I did the other side a couple decades ago) I also took the opportunity to re-detail the housing and clean up the bodywork dust and overspray. The new-to-me 4 speed frame brackets were also installed when the control arms were re-installed.

New wheel bearing on old GTO axle shaftCleaned up GTO 8.2 axle assemblyRepaired rear axle assembly being installed into 67 GTO convertible

In the spring of 2013, the car was taken on it's maiden voyage after the restoration. I'm happy to report that the rear axle is super quiet and functions perfectly!

Driveshaft

April 23, 2014

I drove the Goat a couple hundred miles in the summer of 2013, with just a little time on the highway, but I did notice a vibration at high speeds. I kind of suspected the driveshaft because of the high-ish frequency. I should have known because when I bought it off of ebay years ago, it had a shredded u-joint on one end. Sure enough, when I put the car on jackstands, I could see that the driveshaft was running eccentric by a good 0.060". I had no idea if this was fixable, so I did a search for a local driveshaft shop and found CT drive-shaft in East Hartford. I was hoping they could just balance it. 

Chris, the owner of CT Drive-shaft, told me to bring it down. After explaining my problem, he mentioned some details about driveshafts running truer than 0.010", and my heart sank; I knew my unit was toast. And yep, that's what he told me later that day when I called back.

So, after thinking about it, I decided I didn't want to mess with another used driveshaft. Chris explained that he could make a really nice steel unit that would be much better than the original unit. So he whipped one up in mere hours after I asked him to proceed.

New driveshaft for GTO from CT Driveshaft East Hartford

It's 3.5" steel with Neapco yokes. He re-used my new Spicer 3R (saginaw) u-joints and Neapco slip yoke.

I bolted it on and wow it sure runs nice. I thought about putting the factory type stripes on, but since it's obviously a replacment unit, I just clearcoated it. So the jittery convertible is a little less jittery.

Any questions or comments? Send an email:

squid@squidsfabshop.com

SFS

Links:

Jeep Forward Control "Mighty FC"

Here's a really cool something Jeep engineers and marketing people came up with that they will never build. I'd buy a Jeep pickup if they would just make one. Oh well. Above is a link to an FC concept hype-mobile.

Here's another cool Jeep Pickup concept from about 2012:

1967 GTO Original Owner

These two videos feature an original owner GTO. This car was featured in Hemmings Muscle Cars magazine a couple years ago. Part 2 has inside and outside shots of the owner driving the car. Very nicely done.

Blues Maker

"Mississippi" Fred McDowell. One of the great Bluesman. This is a documentary made in 1969.

Pinstripes

Pinstriping the ol' fashioned way. Pretty nice.

Blues Traveler. Wow.

Blues Traveler plays often on the Dave Letterman show. Here they are playing a toe tapper with Paul Schaffer.

Pepsi Throwback

Pepsi Throwback with Sugar!

Pepsi has put out a "limited edition Throwback" version of Pepsi with REAL sugar, instead of high fructose corn syrup which has been used since the 80's. Holy cow there IS a difference; it's WAY better. Find some quick!

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