Okay, so either the front seal on the trans or the pan gasket is leaking on my car. Standard TH350, came with the car. I'd like to change every seal I can without pulling the trans. Otherwise, the trans shifts fine, no noise or bumping, just loses fluid and I have to put more in, and it akes a mess on the driveway. Annoying.

Can anyone list these or point me to a thread with them, with locations and descriptions? Your help would be much appreciated.

 

Crawl under, wipe the leaks off well and check it again in a day or so to try to find the exact point of leaking.
On mine, the shifter shaft and speedo cable seals are leaking. Both make the pan and front seal look bad, as the fluid seeps that direction. Both of these can be done with the tranny in the car, but should be on a lift or 4 ramps to get some room.
Replacing the shift shaft seal requires the pan to be dropped.

I think the modulator seal can be replaced while in the car, as well as the kickdown cable seal.
I have a box full of seals to put in my tranny but have not had time to do it yet.

 

Trans pan gasket
Kickdown cable o-ring
Modulator o-ring
Shifter shaft seal
Governor cover seal
Output shaft seal (after pulling the driveshaft)
Dipstick tube o-ring
Extension housing seal
Speedo gear holder o-rings (yeah, there are two)

Note what's missing...

 

Yeah, that was my luck when my 350 was leaking.

 

Alright, so assuming I want to do a trans fluid change anyway, which of these require the pan to be off besides the shift shaft seal? (including those where the pan being off even helps) I'm on kind of a tight budget but since I know the trans fluid hasn't been changed, I'd like to do it...and while I have the pan off, it's a good time to replace the seals that require access that way.

 

I am thinking the shift shaft seal is the only one that requires it just to be able to replace it. Having the sump drained may help prevent spills on some of the other low ones... Just a logical guess though.

 

Is draining the sump something covered in the factory manual? I'm not really familiar with where that part is in the transmission, even having just watched a video about rebuilding the THM350.

 

Yes. Remove the pan bolts and drop the pan, spilling fluid all over you and the ground, despite all efforts to avoid doing so...

That is the reason I have not done mine yet...

I am wondering if most can be sucked out the dipstick tube first................

 

Hmm, a really long, thin piece of flexible tubing, stick it down there and then use a hand pump...you could be on to something.

 

Exactly. Like one of those suction oil change kits...

 

They make them. There are kits available for like $50. but a small handheld compressor and a rubber tube would work fine, sucking it into a small jug. Just don't go over like 25psi.

 

Hey Joe,

This is great information, I'm dropping my pan to change my fluid in my 72 th-350 very soon. Also to verify the kickdown cable since it's inoperable.

My question being, does the CSM cover the changing of the shift-shaft seal? It's been leaking a little bit (drop by drop) so i'd like to change it at the same time. Is it a hard job?

Thanks!

-Tony

 

It is well instructed - about the hardest outer seal to replace. There is some internal disass'y that is needed, as well as the outside linkage.

 

I was hoping it would be easier than that.... Do you know where it is in the CSM? I can't seem to find it.. flipping throught the Hydramatic section..

Thanks Rob!

-Tony

 

What is the shift shaft seal?

Also, obviously I have a seal leaking, and I know I am more than capable of changing it myself, but, are there advantages to taking it to a shop. Are there adjustments that a show could make by dropping the pan that might improve performance? Bands and such? Lately my car seems like it doesn't downshift like I remember it used to. It feels like its bogging down before it'll shift. I guess it could be the carb, I did play with it a bit,

 

The shift shaft is also called the manual shaft. It is whats connected to the shifter, either on the column or the floor.
The 72 CSM documents the 350's shaft on pages 7-248 and 249.

 

Wow. I don't think mine is that. It's leaking quite a bit worse. I fear I've got a leaky torque converter or something.

 

So i'm looking at the pages you referenced in the CSM. It seems that there is ALOT of dissasembly in order to get that shift shaft seal out..

Do all these things need to be removed in order to get at the shaft seal?? Governor, vacuum modulator, valve body??? List goes on..

Can someone offer me a good process to removing this seal??

 

No, they are discussing a general tranny dissassy.
The shift shaft removal is discussed within that section.
The shifter linkage has to be disconnected on the outside, then the corresponding linkage inside (pan dropped) so the shift shaft can be pulled "into" the tranny so that the seal can be extracted. A pain, but what else...

 

Okay phew! Thanks rob,

I'm going to be changing the filter anyway since i'll be under there changing the fluid and shaft seal. I actually got my seal in the mail yesterday, the box looks like it's from the 80's and it says made in USA! So i'm guessing it's a good one.

I will disconnect the outside linkage and drown it in WD-40. when i was working on my suspension i noticed a couple drops of red on the floor. Looks like it's coming exactly from the shaft seal. The seal cost 5 bucks so i might as well get it done.

Any ideas what colour the pan should be painted? I'm probably going to wire brush it and paint it at the same time.

Cheers,

Tony

 

Shift shaft seal...... say that fast 3 times, lol!

 

LOL, somtimes i need a pick-me-up when dealing with transmission trouble, thanks sandy!

Hey, speaking of which, you have a beautifully painted car. Sandy, what colour is your transmission pan? I would like to paint mine.

 

I thought the pan was left in natural steel, or were plated in a similar color. There are paints that mimic that look...

 

Well thanks for the compliment, lol! I think it's oil colored from her little leaks under there! To be honest, I really don't know. I've never looked. Now I'm curious.....

 

Mine is naturally rusted :P

My policy so far is every part i take off my car, i clean and paint. (even my voltage regulator cap, and i have an internally regulated alternator)

 

Paint it pink, where is Mdmechanic (Eric)!!! LOL! I painted mine silver! When you drop your pan make sure there is not a bunch of grayish gunk in there! If there is then you may want to consider a rebuild and all those seals will be replaced during that process.

 

By golly you better not forget them screws, too!
Frame-off starting soon it sounds....

 

Agreed this is going to be a pain, but im finally getting around to it.

Rob, so I see the section where it describes the shaft removal. Why parts do I need to get 'out of the way' in order to remove the manual shaft?

I don't want to disassemble too much and risk messing up gaskets or parts... Especially since the previous owner installed a shift kit apparently..

Thanks in advance for the help

 

Tony, you said your kickdown is inoperable? What exactly do you mean? You might not need to take your tranny apart if you give me the right answer. You KNOW you want to give me the right answer now...

a) Can you shift the car manually up and down through DSL LSD (hey LSD is DSL backwards - Olds musta been onto something)

b) If you're at say 30mph and you walk on the throttle, does it shift or does the engine bog? Waiting for answer to this and other fun projects.....

 

Hey Al,

I can definitely answer... The cable appears to be stuck, it is in the fully extended position and I can't push it in or out...

I'm guessing perhaps It's not connected? I've never opened up this tranny.

At 30mph, If I romp on the gas, the engine just bogs, it doesn't downshift...

 

There is a fairly pricey tool that extracts the shifter shaft seal w/o dropping the pan, but for your needs at this time, you need to do the pan and filter anyhow. This tool is like an inverse of a twist socket like one might use on a rounded nut.
With the pan off, and the stuff removed from the outside of the selector shaft, it should be pretty obvious what you need to do to remove the shaft. It's easy. Clean and polish your shaft nicely before re-inserting it of course.



I can definitely answer... The cable appears to be stuck, it is in the fully extended position and I can't push it in or out... I'm guessing perhaps It's not connected? I've never opened up this tranny.
===========
It's common for the lower end to not be connected to the z-ended wire within the trans. It can fall off if not careful during the install. At the top end of the cable, you should be able to move it with your fingertips. The cable might be bad too... Early models - 71/2? run the cable to the firewall and the gas pedal. This cable is harder to find but not impossible. The other type runs up to the carb. Much more common.

 

But it will shift by manually moving the shift lever, right? If your car shifts up normally under normal driving, the modulator is not likely the problem. You should check to see that the rubber vacuum line to the modulator (runs to the long metal line on the PS of the intake) is not leaking. IIRC you replaced your vacuum lines a while back didn't you?

Take a look at this thread pic of my car. The downshift cable should match yours. Since you played with the carb and the throttle cable, you more than likely just need the trans cable to reseat itself to the proper position. I had exactly the same problem when I switched to 4bbl q jet. Simple fix on the shift (hopefully). Even though the cable may be already seated, you're going to need to free it, then release and pound the gas to the floor. That should set your kickdown linkage cable to WOT.https://classicoldsmobile.com/forums...tml#post352299

For info on the actual 'how to' adjust? Look in the CSM on page 7-243. There's a really good write up and adjustment pic (fig 7-640) at the bottom of the page. Hope this solves your shifting problem as it did mine.

Any other leaks on the tranny you'll have to still probably replace seals.

 

Hey Al,

The car will definitely shift manually if i use the column shifter. And it upshifts great. I'll have to take a picture, but when i look at my pedal assembly. The downshift cable doesn't move in or out. It's kind of stuck in the fully extended position. Should i try rocking it back and forth to see if it'll reseat?

 

There is one more seal that can be replaced with transmission in car. It is the accumulator cover o-ring. This little guy, if bad, can cause major leaks while driving, as the accumulator is used when 2nd gear band is active.

So if you are intending on sealing up the transmission you may want to grab some snap ring pliers and replace this critter too.

 

I sure hope my cable is alright! It is the same version as Allan has ( supposedly all 68-72 Th350's had it on the gas pedal. ).

That sounds good, I sure hope I won't have to remove any complicated components to get the shift shaft seal out..

So my detent cable seems pretty stuck, is this Z shaped shaft actually inside the transmission? Or is it accessible where the cable hooks up to the transmission?

That tool sounds really interesting, any ideas on what it's called??

Thanks,

Tony

 

These will be the absolute best resources you can use to do any transmission work.

TH-350 Rebuild DVD

TH-350 Exploded view & parts
At the top of this page you will see a PDF small thumbnail of the big exploded view......click it, and save.
I printed my 2004R in 11x17 and laminated it at kinko's.

 

Thx for the link Aces. I was looking for one of those recently.

 

Not to hyjack the thread.....but...... I was ready to post a new thread and this was soooo similiar. Where are the 2 o-rings for the seedo gear assembly? One for the outer casing where the complete assembly goes into it, and one for the speedo cable goes? I looked on the CSM on Wildabout cars, but didn't see them.

Thought I only had a leak at the cooling lines (prev owner created rubber hoses with steel ends), but when I changed the motor mounts, which raised the motor about 3/4 inch. (Front end up on jack stands too) She started leaking tranny fluid all over the floor. Could it be that just this difference in hight/angle allowed a good amount of fluid to drain into the rear housing and start leaking out, or do I need to be looking for another problem? Fluid appears to be leaking and running down the speedo cable.