Monthly Archives: August 2019

Pontiac renovations, part 25.

I continued to work on the parts of the gearbox, stripping everything down. A large volume of swarf, metal chips and bits of burned friction material from the clutches had found its way into the hydraulics.

Front drum

I managed to clamp down and disassemble the clutch packs. All the friction material (an organic fibrous material and come cork) on the friction rings was gone, burned to a crisp. The six light spots are bright patches worn into the metal.

Rear drum

The rear drum was significantly more difficult to take apart. It is not internally spring loaded and is a tight interference fit. It was less badly worn but still unserviceable.


With the drums apart, I checked the thickness of the thrust washer shims. They were below limits.

I ordered a pair of new ones. The copper is completely worn through on one of the old ones.

Valve block

The cleaning continued. I disassembled the valve block, which was all partially jammed up with dirt and swarf. The bores and pistons were all in good shape, and upon reassembly all move well.

Servo spring

I started to disassemble the rest of the hydraulics. The front servo relinquished a fractured spring. This is going to be the main causal reason the gearbox failed, with this slipping there is extra stress on the clutches.

4-3 downshift valve

I invested in a large screwdriver and was able to remove all the plugs from the front servo. The 4-3 downshift valve (above) is a good example of how dirty the hydraulics in the system were.

I had a little difficulty disassembling the front oil pump, because the thing was held together with 4 Fillister head screws, all of which were stuck fast with sealant and all had been previously rounded off. One needed to be sawn down and another drilled. The pump itself was in surprisingly good shape inside, considering the amount of swarf in the rest of the pipes. The overpressure relief valve (the dark circle on the bottom right of the right hand assembly above) was also jammed, so that was freed up and cleaned out.

Rear servo, in pieces

The rear servo is fully spring loaded. It holds the rear band on when the gearbox is not pressurized, meaning that if reverse is engaged it has both reverse and 3rd gear selected simultaneously. This effectively locks the gearbox solid and acts as a parking brake.

Rear servo, assembled

I managed to reassemble the rear servo without losing any parts or breaking any of the oil rings. There’s enough tension in the spring to launch the thing into orbit.

Reverse gear

Finally, the reverse gear assembly.

The reverse gear cone is a little scored- turns out there’s been some swarf stuck in it and that’s caused hotspots. I picked all the steel out of the alloy. Thankfully this mechanism only comes into contact with the drum when reverse is engaged, and only slips of the vehicle is moving when that is done.

A good drum

In contrast, a new drum is fairly smooth. (Above).

Special tool

The annular piston that forms the central drum cone is held in by a disc and a snap ring. The disc needed to be pushed down, compressing the springs so the snap ring could be removed.

Modified valve core

I trimmed the base of a valve core flat so it would seal against the case.

Reverse cone removed

Application of compressed air saw the piston removed. Surprisingly, this was the only part of the system not full of swarf and dirt. The seals were fairly new (though in bad condition) and the roller bearing at the back is quite new also. The reason for this became apparent when I found half of the wavy washer under the retainer in the drum. It appears that fractured, came loose and jammed the reverse gears, causing a bit of damage. Someone had taken it apart, done half a job to pull the pieces out and thrown it back together.

Removing seal

I overhauled the reverse mechanism. Removed the seals, cleaned the grooves they sit in. Whoever was inside the gearbox previously neglected to do this.

Cleaning sealing surfaces

The sealing surfaces were not very clean so I rubbed then back with 1000 grit paper until they were smooth.

New seals were applied.

Reverse gear assembly

I reassembled it all, having to improvise another special tool to get the outer lip seal to be able to get past the step the static outer cone sits in. Now awaiting new bearings.

Governor and rear oil pump

The governor assembly was also in need of cleaning. The smaller governor weight would stick at the bottom of it’s bore because it was worn. I lapped it carefully with some metal polish and now it doesn’t jam- the piece it used to get hung up on doesn’t need to seal, it simply needs to prevent the piston bottoming out.

The governor is two parts- the left hand one has a large weight and opens up that valve at low road-speed. That engages the reverse gear lockout pin. The smaller of the two pins is thrown out at higher speed, and provides pressure to the valve block to engage different gears as the speed of the car increases. If the pin sticks then it will change gear too late each time.

Pontiac renovations, part 24.

Strip-down of the gearbox began in earnest. With the service manual in hand, I was able to determine the correct procedure to dismantle it.

Upside down

The manual states the first thing to do is to upend the gearbox and mount it in the gearbox holding jig. I don’t have a jig so it just sat upside down on my new bench instead.

A volume of dirt

First impressions upon removing the oil pan were not good. There was a lot of black gunge, which draining the fluid belied, being rather clean red when it came out.

Dirt flushed

I flushed a lot of the dirt out, which left behind a lot of metallic swarf and a few molten globules of metal. Not a good start at all. I was hoping at this point it was merely remnants of a burned up clutch plate.

Clean oil pan

I thoroughly cleaned the oil pan and leveled the gasket surface with my orbital sander.

Clean steel

I then cleaned the old paint and rust from the exterior of the oil pan. Originally the pan was zinc coated and not painted; somebody had painted it gray in the past.

Painted oil pan

The original color is battleship gray, but I opted for Solstice Blue again.

Oil filter

I removed the gauze oil filter. Somebody had added blue sealant to the rear pump pickup point. This made me cringe.


I began to follow the manual to remove the control block, reverse control and band servos.

Planetary sets and reverse

That left the core of the gearbox in place; the front and rear planetary sets and the reverse mechanism. I removed the reverse gear assembly and undid the main bearing cap holding the two planetary gear sets in.

Rear assembly removed

I removed the snap ring holding the rear assembly in place and pulled it off the fluid delivery sleeve (the section that provides hydraulic pressure to the clutches). At this point I was able to determine the source of the swarf and metal shavings in the oil pan.

Oil delivery sleeve

One oil control ring was fractured and the sleeve itself was very badly scored. The sleeve should not make contact with the drum at all where the rings are.

Overheated bearing

The bearing surface showed it had overheated and worn away significantly, allowing the drum band system to pull it off center and force contact with the oil delivery sleeve.

Main bearing

Removing the snap ring from the front assembly showed similar damage to the bearings, allowing it to be well off center and tear up the fluid delivery sleeve on this side also.

Main driving shaft

The main driving shaft (output of the primary epicyclic to the fluid coupling torus) is made of much tougher metal than the fluid delivery sleeve and has escaped much in the way of damage.

Thankfully, parts are available and I will be able to rebuild all the damaged sections. I need to take the assemblies apart and check the clutches for condition.

Pontiac renovations, part 23.

August rolled around again, and as it is wont to do, has been warm.

Warm in the garage

Having spoken to a radiator shop and been quoted a significantly higher price than I could afford for repair, I decided to set about and attempt a repair on my radiator myself.

Filler neck

The filler neck had what looked like some sort of putty or mastic spread all around it in a messy fashion.


I pried at it a little with a screwdriver and a large chunk fell off, showing it to actually be lead solder. Whoever put it on did it badly.

Filler neck removed

I decided to cut my losses, and while holding the cap in my big pliers, I heated it up with my gas torch. It popped off with relative ease, showing a lot of dirt where it had split away from the top tank, and was being held in place around about one fifth of it’s circumference.

Cleaned with wire brush

I used a steel wire wheel to clean both the top of the tank and the filler neck. I then added soldering flux, heated them both and tinned them by adding solder to each face, ensuring good adhesion.

Filler cap soldered in place

I then lined the two pieces up and heated them so the solder flowed and melted together. Hopefully a permanent repair.

Big gas flame

The radiator had been leaking along the seam between the fins and the top tank. I cleaned it up and attempted to solder it up with my gas torch, which proved to have a flame too broad and too hot to easily work with.

Soldering with big flame

I was able to make a good seal, but it wasn’t the tidiest of work. I went to the store and bought a torch with a much tighter flame pattern, adjustable temperature also.

Small torch

The tighter flame allowed me to control the heat better, and so I soldered up the rest of the seam.

Seam soldering complete

This method allowed me to improve my technique and make a much more tidy repair.

Pressure testing

I built a rather Heath-Robinson testing rig, consisting of the garden hose and some duct tape.


With the seam no longer leaking, the pressure testing identified a small crack in the top tank.


I cleaned the area around the crack mechanically with a wire wheel, then chemically with acid flux.


I soldered the crack up and tested it again. This time it didn’t leak.

A bit of black paint

I cleaned the metal down of old flaking paint and gave it a coat of semi gloss black. I ran out of paint, will continue the rest with a new can.

GM Hydra-Matic notes

As a side-note, the gearbox is specified in a strange way compared to automatic gearboxes I am used to. Most modern automatics have the engine drive the torque converter housing, which turns the pump, and the inner vanes of the torque converter drive the mainshaft. The output of that is then passed through the reduction gears.

Pontiac specified that the vehicle should not creep at idle, in Dr (drive) position. Even with the engine idle specced lower than the manual gearbox version (375 versus 550 RPM) the fluid coupling imparts enough force at 375 RPM to move the car forwards. At a guess the rationale for this was to not alienate their customers who had never experienced an automatic gearbox before.

Get in, sit down, start up and put it into gear, look there, the car does not move.. gently squeeze on the gas pedal sir.. there, the car begins to move- press a little harder, and just take your foot off the gas and onto the brake to stop. Yes, just like that sir, isn’t that a fantastic marvel of modern technology?

To stop the car from creeping yet retain an acceptable idle (the engine gets a bit unhappy as it approaches 300 RPM or lower) the engine drives the outer coupling housing directly (which is not connected to either inner torus) and that is taken inside the gearbox and through a 1.45:1 epicyclic reduction gear. The output of that is then sent back to the driving torus at 7/10 the speed of the input. As a result the driving torus is turning at about 260RPM at idle. At this speed it does not impart enough torque into the driven torus to move the car.

The output of the driven torus goes back deep inside the gearbox and drives a second epicyclic reduction gear of 2.63:1 ratio. The two gears driving each other in reduction results in an overall gearbox ratio of 3.82:1 in first gear.

The epicyclic reduction gears can be locked by the internal clutches to either reduce the output speed or be locked solid at 1:1 ratio. Combining the 2 clutches in a binary style fashion (00 01 10 11) provides 4 reduction options- 3.82:1, 2.63:1, 1.45:1 and 1.00:1 (direct).

The final drive passes through a third epicyclic gear, which, by holding the planet set still with a clutch will reverse the motion of the output shaft and provide a reverse gear. It is also locked out internally to first gear full reduction only- without that there would be 4 speeds in reverse with a top speed of about 60mph. Not ideal!

The gearbox also has a few interesting design features- two oil pumps, one on the engine driven side, the other on the output shaft. This is to allow oil pressure to be built up as the vehicle is towed, for two reasons. First, it provides lubrication without the engine running, second it provides oil pressure so that if the transmission is dropped from N to Dr it will engage a gear and be capable of bump starting the engine.

The oil pumps are designed to provide high pressure at low speed. This pressure is kept constant by a spring relief valve. The gears are selected by valves with varying strength springs. A governor valve (centrifugal weight that spins with road speed) increases pressure on the valves as the road speed changes, initiating gear changes. The throttle pedal is attached to the gearbox and serves two functions. First, it opens a valve that applies main pressure to the opposite side of the gear shift valves, meaning greater governor pressure needs to be built up before the valves will move and gear changes occur. Second, as the gears are changed it adds boost pressure to the servos so the bands clamp more firmly and quickly. This makes low speed, light throttle gear changes smooth to engage at low speed, and hard acceleration changes to snap tight quickly at higher road speeds.

It all sounds good but there are a lot of moving parts that all need to move in synchrony. If something jams, it’ll either disengage drive fully or attempt to engage two gears at once which causes undesirable operation, neck-snapping jerks in the drive or a redline-flare of the engine. In this case, it would change gear at a much higher RPM/roadspeed than it should have, and only when the throttle was snapped shut. Hopefully that can be remedied.

Pontiac renovations, part 22.

I started to strip down the parts of the gearbox I knew how to take apart, having ordered the service manual but still waiting for it to arrive.

Fluid coupling driving torus

The fluid coupling is all held together with a large nut, secured with a tab washer. The tab washer was a good idea by the engineers because the nut, initially torqued to 50 lb/ft, was loose.

Fluid coupling parts

The large drum section connects directly to the engine flywheel (and represents a significant rotating mass to act also as flywheel) and the two torus sections sit inside and drive each other.


The inside of the bellhousing was fairly clean, though it is easy to see where the O-ring has been leaking past the torus housing. The inner part of the torus is kept full of fluid by the pump and at about 40psi by a pressure relief spring. The mainstay of the oil is kept in by two piston rings on the inner edge.

Gearbox, bare

The bellhousing came off easily. I cleaned the machined faces up and inspected the seal.

Side pan

I removed the side oil pan from the gearbox. It was rusty and the previous keeper(s) had painted it gray over rust and dirt. I cleaned it up with orbital sander and wire wheel.

Painted pan

It then received a couple of coats of Solstice Blue paint, as a test. I see no reason why engine parts cannot be any particular color. It won’t last but it’ll start out looking nice.

Ignition timing clamp

I cleaned up the distributor clamp, which has a moderately helpful pointer (which will need to be reset) to show degrees of advance or retard against TDC (Top Dead Center).

Timing marker

There’s a cast vee in the case of the engine to refer against, and the distributor also has a knurled wheel to fine tune the timing.

Service manual

The service manual arrived. It’s in good condition, printed in May of 1951. It gives a good explanation of how the gearbox actually works.

Measuring main shaft endfloat

I clamped my dial gauge to the gearbox and measured the endfloat. This is set by a bronze thrust washer buried deep down at the back end of the gearbox. 19 thou’, slightly over limit. If I can get a replacement shim I’ll fit it, else that’s on the next big service.

Engine, in turquoise green

I decided to finish up something I had started a good while back. I cleaned the engine down and gave it a coat of paint.

Other side

It is meant to be something close to Brunswick Green, but I cannot find that color anywhere, and the nearest green (Hunter Green) is horrible. So, I went slightly out of the box and painted it a color called Deep Turquoise. It’s close to the mid sixties Pontiac V8 color, And goes well with black parts attached.

Harrison 3127575

I brought the radiator to a shop in town, and their main guy took a look, measured it up and said it would need to be recored, at $460 for the core and about 6 hours of labor to total approximately $900. I am going to clean it up and attempt to plug the hole and make do for now. Sometimes these things price themselves out of the market.