TH350C Transmission and a Mild 455

[1984Oldsmobile442]

Good morning,

I have a 1984 Oldsmobile with a Mild 455 and TH350C Transmission. The transmission has failed to the point where it will not engage in either forward or reverse. I am considering removing the TH350 C myself for the purpose of having a local shop for a re-build it. It is my understanding a TH 350 C should have stall capabilities. This was working when the old 307 was on board. However, this was abandon and not dealt with when the 455 was installed. (Maybe that is part of the problem with the TH 350 C since it was not allowed to lock up as designed?) It may be important to note the TH350C was installed in the early 1990s after the old Turbo 200 failed.

Questions:
Can a correctly built TH350 C handle a mild 455?
What should be done to make the transmission lock up correctly?
I suspect the torque converter is trashed since I believe it came from the old Turbo 200? What would a proper touque converter set up be in terms of stall etc?

Thought:
The rear gears are standard highway from the original vehicle set up. The rear end may or may not handle the power of the 455. I really don't have the money for a 12 bolt or a ford 9 inch. I wish I could upgrade this.

I appreciate any thoughts or input. Thank you for reading this post.

 

[RustRocket]

I don't have any information for you, but your questions are almost the same as mine. I have a TH350C and a 3.8, and my brother offered to give me his also mild 455.

 

[rustyroger]

A 455 in stock form will eat a 350 built for a G Body if you don't spend some money beefing it up. Unless you feather foot it everywhere, but why put a 455 in if you do this?.
A 200r4 built to deal with 455 torque is what I would do, a 700r4 or th400 would be second best choices for me.
The rear end and chassis will need work as well to live with torque they were never designed to deal with.

Roger.

 

[1984Oldsmobile442]

Thank you for your thoughts. Are you thinking trying to beef up a TH350C is throwing good money at an iffy solution?

What type of modifications should I expect with the drive shaft on a 200r4 700r4 or the th400? I suspect the 400 may have the same tail length as a TH350C?

Work on the rear end and frame scare me a bit. I'm not sure where there is room to really weld in meaningful structural support for the frame with the body on. Maybe I am missing something? I see what you mean when looking at the frame in terms of design. The gauge of the steel does not seem to be the same as what you would find in a late 1960's or early to mid 70's Olds.

RustRocket: From what I know you will most likely need to install front springs designed for the added weight. That may be a good time to do a full evaluation of your suspension set up. If your on a low budget you may be able to hit a local junk yard for sway bars etc.

 

[RustRocket]

Yeah that's what I was thinking, My 3.8 is a paperweight compared to those BBO's

 

[lilbowtie]

84 - where do you live? I have a 350 I'll sell for $100.00 (53,000 mi) . What do you need to weld in the back??

 

[Mike P]

There is a reason that GM put TH400s behind 455s ……anything else is on borrowed time.

 

[1984Oldsmobile442]

Hmm. It sounds like I should at least be looking for a BPO TH400. I'm guessing I need to do my homework on tail length of this unit?

I also spent some time looking thru the frame/ handling upgrade thread. Trolling local salvage yards will certainly be in my future.

Thanks for the offer Lillbowtie. I am going a different direction than a TH 350.

 

[lilbowtie]

Educate yourself before you make your decision. I'm a 400 person but either trans will handle what you are doing. The 400 will bolt in and the biggest things that need addressing is a yoke change on the driveshaft (which should fit) and you might need a special universal. The tail shaft mounting will change, and you should already have a dual pattern flywheel. No matter which trans you put in you should go through it. If you use a 350 I would install a good shift-programing kit, a wide direct clutch-drum bushing, and hardened intermediate roller clutch outer race at min. There are more mods which would only help esp. a 36 sprag intermediate clutch. If you go w/ a 400 try to buy a 70 or earlier w/ an 8 bolt front pump. Once again you should install a good programing kit and install a 34 element intermediate roller/spag clutch. There are also a lot more mods to help. These transmissions are very easy to work on and I would advise a book - How to work with and modify the turbo 400 by Ron Sessions and he also has one for the 350. Oh yea, I assume you are already using a trans cooler.

 

[olds307 and 403]

The TH200C converter will NOT fit a TH350C. It has a unique converter that only fits the TH250/350C, the regular TH350 converter IS different. You can get higher stall converters. Also make sure you don't have a TH250C, much more common in the BOP version and not worth building. A band adjustment stud near the cooler lines is a dead give away for the TH250C. If you are going to bother cutting the driveshaft for TH400, why not find a 4L80E? They are $600-$800 used here. You will need a manual shifter or controller and a bell housing adapter. The TH2004R will need considerable beefing and don't bother with the useless 700R4. The spider gears will be the first to go in that rear end.