Projects Mild custom '51 Pontiac Chieftain

Here we go again!


"You know you car is low when ..."


Pulled the valve block completely apart.


Ultrasonic bath to flush any particles out.


All bores clearanced and the thing reassembled. Let's see if that works now.

Phil

 

Fingers crossed...

 

It's better. But it's still occasionally sticky.

I'll try it like this for a while and see. It's all adjusted up. I have 4-3 downshift back so that's a bonus.

Phil

 

Actually, this only happens when the gearbox is hot. I might be seeing problem with the oil being too thin.

Edit: I'm going to see about getting a pressure gauge to put on and run the tests in the service manual. It'll be interesting to see if it's losing pressure at any point. May well be back down to the pressure regulator.

 

I need to poke my nose into the book.
If it doesn't cycle to 4th gear, it hangs in 1st repeatedly then dumps to 3rd.

Once it's made 4th it's as smooth as can be.

Phil

 

Just ordered a gauge, that should be here before the end of the week. I can compare the book values and do a road test then and see if it's within spec.

Phil

 

Ought to be able to see that while driving!

I'll get the fittings for it when I can, needs a downsize and an extension plus a flexible line- I'm thinking a brake pipe.

Phil

 

Thing regulates nicely to 60psi. Front oil pump easily sees it to that pressure on the starter motor.
In gear, stationary it holds pressure.
Driving, the pressure modulates directly with throttle position, from 60-100psi so the 8-cylinder variant TV valve is working.


Reverse, the high pressure line is engaged and the valve shuttles giving a wobbly 130-160psi as it should.

It did act up one time, and the main line pressure was perfect, which narrows the issue down to the 1-2 valve getting stuck.

That is a bit of a problem as there is no real recovery from that fault other than valve block replacement.

Thankfully spares are available (not cheap though) and I can try to massage a few more miles out of this one before I have to stump up for a new one.

Phil

 

So Phil, where is the 1-2 valve located? How much of a project is that replacement?

 

After all your work now you can be an expert consultant or re-builder of the transmissions for others.

 

The selector valve consists of the two arrowed pieces that go into the valve block (circled).
Takes about 40 minutes to pull down, stripdown doesn't take long.

I've got a headband with magnifying loupes on it coming so I can inspect better, the pieces are small and are made to very fine tolerance.

It was designed with maintenance in mind.

Phil

 

I'll pass on the rebuilding part- one was enough but I'm trying to gain a better understanding of the thing so I can fix it when it inevitably causes problems. I don't mind giving advice though.

Phil

 

Does that 1-2 valve have a spring and or check ball in it's path that could be sticking?

 

No, in the Dr position there's 4 things that dictate the engagement of gear 1 vs gear 2.
There's:
42: The governor piston, which has modulated pressure against it based upon road speed
37: The selector piston, which the governor piston pushes against
36: The spring, that the governor pressure has to overcome to change the gear
35: The throttle position piston, which boosts the spring to make the change later if the throttle is pressed down.



I have s feeling the governor piston is getting stuck at the bottom of the bore when it's warm when the spring pushes it back.

That can be remedied in the short term but it's an effect of being quite worn, that bore gets the most workout of all of them and it's slightly oval with age.

I've got some magnifying glasses coming in the mail, I'll be able to eyeball the parts better with them.

Phil

 

I am constantly amazed at your skill and tenacity. Keep at it; I'm sure you'll get it eventually.

 

Me too. You are a machine at troubleshooting.

Sidebar: I lol'ed at the giant pressure gauge. That should get it!

 

The gauge was bought in mind that it would be by my ankle when driving. I wanted something that would be fine enough to see down to 2psi on the graduation but still be large enough to get an at-a-glance easily.

The more I try to fix it, the better I understand it. "Clean the whole thing and hope" only goes so far, as shown by the last 2 efforts.

Phil

 

Gotta give you credit for plinking away at it... Most guys would have swapped in a Chevy by now... LOLOL

I'm curious... Would it be possible to sleeve that bore to bring it back into spec?

 

A long time ago my dad helped me rebuild a 60 Pontiac hydramatic that had some sticking valves.
We used a tiny brake cylinder hone, only spun for a few seconds to clean the bore. It was no doubt the wrong thing to do perhaps losing some seal in the valve, but it worked, no more sticking valve for the few years till it was sold. Good luck, those old trannies are a hoot. Some amazing engineering back then.

 

Possibly but there's not a large amount of material in the body, that being part the reason for it being temperature sensitive.

Phil

 

Yeah, this has done so many miles I think the wrong thing may fix it.

Phil

 

Did the missing test this afternoon. Got up to 20, dropped the car into N and switched the engine off; then put on the ignition and engaged Dr.
The rear pump makes about 30psi and is enough to bump start the car reliably.

Waiting for my microscope lenses to arrive before I take it apart again.

Phil

 

Had more to do so finished up the body of the other horn.


Got a couple coats of paint on it, that can dry overnight and I'll get the other side tomorrow.

Phil

 

Took an hour out tonight to do noisy things.


120 grit to get rid of the rust.


Clean enough to see and then beat out the dents.


220 grit to finish.


Finally, first coat of black.

Phil

 

I have to ask; what kind (brand) of paint did you use? When I first saw it, I thought it was chrome!

 

It's a really specialized type of paint, really expensive, imported, made from..


Wait no




Rust-Oleum black enamel. $7 from the hardware store.


I like enamel for jobs like this, it lays on well enough straight out of the can for non-bodywork (slight orange peel) shiny, but rubs down very well with fine grit and polish if you want it a little more smooth.
It's not a bad black; it's not the deepest ever but it's what I call respectable. You just gotta watch it- it's 66 out here at the moment and about 70% rH- I lay a coat on then give it as gentle waft of hot air from my heat gun to get it to form a skin and seal, which tightens it up a little and stops it from sagging, as enamel is quite runny stuff.
Good prep, lots of coats and patience, with 600 grit paper between each coat to keep it flat.

Phil

 

I am going to pull the gearbox valve block out again. My lenses arrived!

Phil

 

those right there are some spooky looking glasses!

 

WE ARE THE BORG.. WE ARE HERE TO ASSIMULATE YOU!

 

Okay then. Let's eyeball the valves.


Yup. They've got a lot of miles on. Found a couple burrs and high spots and carefully tried to take them down.
First drive was good, we'll see if that trend continues.

Phil