TH400 BOP Transmission to 350 SBC

[monsolo]

I have been very lucky with my t-bucket build so far... I've had very generous people give me some fairly expensive drivetrain components and I'm very grateful, since I don't have a whole lot of $$$. So here's my issue... a good friend gave me a 350 SBC and a transmission. The engine is very straightforward but the transmission was a mystery to me, not being a transmission guy and all. But I could visually see that the tranny bolt-hole pattern wasn't going to match up with my SBC. After much internet searching and education, I've come to find out that I have a TH400 BOP (Buick, Olds, Pontiac) transmission which happens to be in very good shape. I've also learned that I need to buy an adapter to make it mate up with my SBC. Have any of you had this issue and used this type of adapter? Summit Racing sells a nice thick adapter that seems would work ok, especially since I have not yet welded my engine and tranny mounts onto my frame. Since the adapter pushes the tranny back about 1/4" to 3/8" from the engine, is there anything I need to worry about with regard to the torque converter and all? As I mentioned, I really don't have the $$$ to be swapping this tranny out with a Chevy version so I really want to make this tranny work on my t-bucket. Thanks for the help!

 

[Mike]

The adapter will do what you want it to do, but it can also create problems down the road. Since you are spacing the trans back, then you will also need to space the convertor away from the flexplate. As long as you are prepared to make and remember the changes, then you will be good to go. With the caveat that the more parts you start adding, the more chances you are creating for parts failures down the road.

You might be able to swap that B-O-P T-400 for a Chevy T-350. The T-350 is lighter and will offer less internal drag, so the swap would benefit you. A PowerGlide loses about 18 horsepower to parasitic drag, a T-350 comes in at about 38 horsepower and a T-400 requires about 45 horsepower.

 

[monsolo]

Mike, that makes perfect sense and jives with what I've been reading. Now for my secret weapon! I have a late 80's Chevy 4.3L V6 with a 700R4 tranny still mated to it out in my barn. What you're telling me and what I'm reading on the internet is making me think this TH400 isn't the best option for my t-bucket. So, now the question becomes, how hard is it for a guy who is an engineer and a pretty good gear head to rebuild a 700R4 himself? I'm seeing rebuild kits going between $250 and $350. That's almost doable when the end product is a nice rebuilt tranny!

 

[badbowtie]

there are good dvd's available for 700r4 rebuilds and only a few special tools needed that aren't to hard or expensive to get, I was going to do one a few years ago but decided to go with a turbo 350 which I built myself (first time ever doing one) and it worked fine, if you are self confident get the dvd and the rebuild book both available on ebay and go for it. good luck, also as far as the turbo 400 in the t bucket you want to make sure of overall length the t 400 is about 6 inches longer than the std t350 if I recall correctly

 

[Screaming Metal]

As Mike told you, the 350 or the PG is the better choice. The 400 really is only needed when you go to survivability mode, running a big, powerful motor. Then, you'll want a 400.
There are kits that make the 350 almost as bulletproof as the 400's/

Putting a kit into a 700R4 isn't hard, the kit has all the pieces parts, gotta be mechanically inclined, keep a clean work area, and you have to pay attention to details. Follow the directions to the letter....and you should be fine.
Use good sockets and wrenches you don't want to round off any bolts that you'll be needing to torque down. And you may want to pick up a inch-pound torque wrench....look at your directions and read

 

[Mike]

Meh, I cannot see the reasoning behind using T-400 for anything. I think people tend to think along the lines of bigger being better and that just isn't the case. Bigger only means heavier and heavier means it is going to require more power to make the car perform as well. I don't care how much money you have, you are never going to spend enough to be able to ignore the first half of Newton's First Law of Motion, as well as his Second Law of Motion. There are very, very few people who recognize the fact that a wheel will never start rolling without the introduction of an outside force.

Sweeping and generalized statements about big, powerful motors mean absolutely nothing in a street T-Bucket that is never going to be able to grab hold of the ground in the first place. And even then, the sprag in the convertor is still the weakest link, not the transmission. With the right shaft materials, a PowerGlide will happily live behind well over 2,500 HP. But it isn't going to live with a $200 torque convertor. And let's face it, we can count the number of street-driven T-Buckets capable of making and applying just 25% of that power on exactly no hands.

 

[Francis Blake]

Good info here, I didn't know a t400 took that much power to run. my car has been widened enough to have room for a clutch pedal SO I am thinking of a stick. I assume chevy has used a five speed tranny similar to ford. Because I need an overdrive with the 4.10 danna rear end in my car I am considering going that way, right now I am just thinking, but I have to do something because at highway speed my car turns way to many revs.

 

[Joe-405]

Sticks are cool and I thought about using one. But you gotta remember these cars are so light that it would make it violent if you ever shifted fast or hard.

If you have a Chevy engine and need overdrive a 700r4 will be just right with those gears.

 

[Francis Blake]

I have a Chevy 350, and a 700r4 is probably what I will end up with. I need something that will get my engine speed down on the road and the o.d. will do just that.

 

[blyndgesser]

A 700R4 or 200-4R will do a wonderful job for you behind a small-block. Swap that TH400 to someone who wants to stuff a Caddy motor into a full-size pickup.

 

[409T]

A 700R4 or 200-4R will do a wonderful job for you behind a small-block. Swap that TH400 to someone who wants to stuff a Caddy motor into a full-size pickup.

My wife has a TH400 in her car behind a 327 and I wish I (she) had taken blyndgesser's advice. A 5 speed stick would be nice too, but the slow traffic here would wear out your leg.

 

[monsolo]

Great stuff here! Based on all of these responses, my mind is made up and I'm going with the 700R4. I talked it over with a good friend of mine and he is anxious to start the rebuild with me so I'm ordering a kit asap. Which brings me to my next questions... what rebuild kit is the best and where should I go to get it? Summit Racing has a kit as does Speedway Motors... or is there somewhere else better?

 

[monsolo]

FYI, this 4.3L V6 / 700R4 (4L60) came from a Chevy S-10 pickup in the 1988 through 1993 model year range. All I need to do is figure out whether it is the 4L60 or the 4L60E model... by the way, I'm also using the solid axle rear end from that pickup for my t-bucket.

 

[monsolo]

Anybody know of a good reputable provider of transmission rebuild kits? Especially for the 700R4/4L60(E)?

Thanks!

 

[badbowtie]

jegs or summit racing have tci kits, they work for me, transgo is another good one, look on ebay you can find some there if you're not in a big rush, even try a local rebuild shop in your area, with the 700r4 when it comes to the torque converter they are some 27 spline and some are 30 spline if I remember correctly and a trans newer than 1988 has better oil passages than earlier ones

 

[2old2fast]

I can tell you first hand what happens when you powershift a T , it generally jumps sideways about 1/2 lane , if you're ready for it it's "controlable" , I'd hate to think of someone who wasn't !!!
dave

 

[Screaming Metal]

B

Anybody know of a good reputable provider of transmission rebuild kits? Especially for the 700R4/4L60(E)?

Thanks!

B&M, TransGo, Walker, TCI, TransMissionPartsUSA, MakcoTransmissionParts, just to name a few....Jegs and Summit carry the ones mentioned, not all of them, but the more commercial ones....