Original 68 Buick th400 just failed

[brave sir robin]

190k miles on original st400 (th400).
Stopped off to let dogs out in middle of a trip. Left rest stop and noticed large white clouds of smoke trailing behind. Look under car and transmission fluid (dex 6 and maxlife atf) pouring out from behind torque converter. Now currently stuck in side of the road 50 miles from home waiting for tow truck.

Before this happened the only oddities were occasional slow downshifts when slowing down. It would feel like it took a little bit too long to downshift when approaching stop lights.

Will not move forward or reverse as I'm typing this.
All is poop

 

[skyactiv]

I rebuilt one of those and put in a shift kit along with a higher stall converter. Cheap and easy transmission to rebuild. Don't be afraid to tackle it yourself if your on the fence about it.

 

[brave sir robin]

Don't have much interest in shift kits and definitely not a different converter. This is a cruiser daily driver type car and this is the first time in five years it's left me stranded....grrr

This almost could not cone at a worse time for me.

 

[BigD1]

Just recently had a turbo hydramtic 125C, also known as 3T40, rebuilt for $850 out the door, and that included new converter. It's in a 92 Olds Cutlass Supreme. When I am riding shotgun, I don't notice that it is shifting. It is one smooth shifting trans.

I have had very good luck over the years with turbo hydramatic trans mainly the 350 and 400. Around here it does not cost an arm and leg to rebuild them.

Good luck with it!

 

[brave sir robin]

I'm probably looking at rebuilding it myself at this point but will need to get it home first. Never had a transmission open aside from filter and gasket before...ugg

 

[brave sir robin]

Question for the transmission guys on this forum.

what type of rebuild kit should I be looking for?
keep in mind that this is a stock (ish) Electra and not a full on race car so no real need for fancy valve bodies and whatever.
Do I get just a basic rebuild kit? or should I replace the steels and clutches too? etc...

could it be as simple as just needing to replace the front seal?


I have an original chassis service manual as well as a sizable collection of tools but do live in an apartment so everything will be done on my kitchen floor lol.

 

[andyd]

could it be as simple as just needing to replace the front seal?

Maybe, it could be a lip seal on the torque converter. When that failed in the '88 528e, that was the only part I replaced Used a gallon of ATF to drive it 20 miles to the shop.

 

[casamagana]

There are several levels of rebuild kits available. Each one adds more parts. The transmission ideally should be diagnosed and, if needed, disassembled to determine what it needs.

For instance, last month I rebuilt a TH350 out of 1967 Firebird which hadn't moved in 13 years. It was leaking everywhere after start up. After disassembly, all it need was a basic overhaul kit which does not include fiber clutches or steels. Just soft parts in the kit; seals and gaskets.

Prior to that I did a C4 out of an old Comet had a burnt direct or front clutch. It got a master overhaul kit which includes steels and fiber clutches.

 

[brave sir robin]

I should probably include more information.

up until this failure while no longer my daily driver it did get driven at a minimum once but usually twice a week. It gets used every time it rains or any day thats going to like 105* or higher. It was not leaking noticeably before this happened but has always had a slight seepage around the transmission pan. Never enough to leave any drips or anything and I had not needed to top off fluid in years.

The only hint it gave me was the last few days I had noticed it was taking slightly longer to downshift when approaching stop lights. A few days ago I did accidentally disconnect the kickdown switch while messing with ac ducts under the dash and it got driven like that for two or three days before I noticed.

The leak is for sure coming from behind the torque converter and is almost pouring out of it while the engine runs.

I'm not transmission expert but I am guessing the bearing has torn up the front seal and thats the problem.

 

[AVB]

There is no bearing, just a bushing. It sounds like you just need a new seal, maybe a converter if it is grooved.

 

[brave sir robin]

I ordered a new front seal and bushing and should have them in by noon tomorrow. Already have three quarts of maxlife and will pick up another gallon of it too. Debating whether or not I should replace the pan gasket and filter as well.

 

[joegreen]

I'm currently rebuilding my th400. It sounds like yours won't move because it ran out of fluid. A member named clinebarger Is the resident transmission specialist. I'm sure he will chime in.

 

[AVB]

I don't think that you can replace the bushing without pulling the pump. May as well replace the rear seal too.

 

[ragtoplvr]

Do try not to use Dex 6. The old dex 3 is still widely available, and the higher viscosity is better for that vintage.

But the dex 6 did not cause your failure.

Rod

 

[casamagana]

Originally Posted By: brave sir robin
I ordered a new front seal and bushing and should have them in by noon tomorrow. Already have three quarts of maxlife and will pick up another gallon of it too. Debating whether or not I should replace the pan gasket and filter as well.


To reseal the pump, you will need a seal, the bushing, the pump to case gasket, the pump to case o-ring, and the sealing washers that fit on the pump mounting bolts.

 

[brave sir robin]

Originally Posted By: casamagana
Originally Posted By: brave sir robin
I ordered a new front seal and bushing and should have them in by noon tomorrow. Already have three quarts of maxlife and will pick up another gallon of it too. Debating whether or not I should replace the pan gasket and filter as well.


To reseal the pump, you will need a seal, the bushing, the pump to case gasket, the pump to case o-ring, and the sealing washers that fit on the pump mounting bolts.


yeah I was noticing that.

Going to attempt at least the front seal tomorrow morning because I will need to move the car to my normal parking spot asap. Cant have it sitting where it is for a week while I figure out how the dang thing works.

I am not terribly confident this is going to fix the issue. I have never had one of those lip seals fail and pour out this much fluid. Usually they sort of seep and leak in drips not nearly pour out a couple qts of fluid within two blocks. I thought they were mostly a dust seal and not under that kind of pressure.

Will take pics and post them tomorrow for funsies

 

[brave sir robin]

Change of plans.
Ordered a front pump reseal kit online because auto parts stores do not seem to carry the special pump bolt sealing washers and I'm gonna need to buy a new jack since my good one was stolen. Waiting until next weekend to start tearing into it.

 

[clinebarger]

The sealing washers are not special, Most GM/Hydramatic transmissions built before 1987 used the same washer. I hope they send you 8 of them as TH400's built prior to 1970 have 8 pump bolts vs the later ones using 7.

If this trans has never been rebuilt before.....It really needs ALL the rubber parts/seals replaced. If the pump busing is tore up/worn......Close inspection of the Pump Gears, Converter Hub, Converter Pilot Hub, And Flexplate are required!

Out of curiosity.....Is this "Switch Pitch" TH400?

 

[dorcheat]

Originally Posted By: clinebarger
Out of curiosity.....Is this "Switch Pitch" TH400?


Close: the 1967 Buick models used the THM 400 switch pitch transmissions and included the Electra 225, Riviera, and Wildcat models. The Skylarks, Specials, and LeSabres with automatics used the Super Turbine 300.

Brave Sir Robin, I own a 1969 Riviera so I can empathize with you. My transmission leaks a bit as well and probably needs all the seals replaced.

 

[MolaKule]

It only makes sense to also replace the pump innards since they are most likely worn.

You want full internal pressures for smooth operation.