[Ozzmann]

So I had my th400 rebuilt around 7000 miles ago, using good parts and a semi manual shift kit installed. I have since put it behind my 494 stroker and continental 13'' Pontiac special convertor.
I can't jump on the throttle till I'm moving a bit, so I don't kill the old 8.2 diff, but once going I go WOT, this is where the th400 lets me down and just leaves the engine free reving, till I get off the gas, and hit it again, then it'll go. Is it my convertor or box failing me, I think it's too much torque, it made over 640 ft/lbs on the dyno.
It'll do this regardless if I shift manually or leave it in 3rd and just let the box shift itself.
What do I need to do to fix this??

[Big Mike]

Converter. The turbo 400 can handle that much torque nearly stock.

[Cliff R]

Is it missing the 1-2 upshift, or 2-3 upshift, or both?

Not quite sure what "semi-manual" means when it comes to setting up the TH400?

Did the builder modify the 1-2 shift valve and block the bleed hole in the VB for manual control of the 1-2 upshift?......Cliff

[Ozzmann]

Originally Posted by Cliff R

Is it missing the 1-2 upshift, or 2-3 upshift, or both?

Not quite sure what "semi-manual" means when it comes to setting up the TH400?

Did the builder modify the 1-2 shift valve and block the bleed hole in the VB for manual control of the 1-2 upshift?......Cliff

It's missing the 1-2 shift, from standing start, if I stand on the throttle once cruising at 30-35mph it shifts perfectly.
it's got a Transgo shift kit that I can shift manually and hold each gear till I up shift, or I can leave it in drive. the miss happens in both manual and auto shifting.
Im' not sure, but I guess he did the mods you ask about Cliff, cause I can shift manually.
I actually got my convertor off you to suit my engine when it was close to a standard 400, so I'm not sure if it's really suited to the new motor now.

[mchell]

Sound like you rolled the sprag?

Assuming you have first gear and when shifting into second under power there is essentially nothing ...

[JSPONT]

Originally Posted by mchell

Sound like you rolled the sprag?

Assuming you have first gear and when shifting into second under power there is essentially nothing ...

This^^^^ I rolled a 34 element beging of the year, went to a 36 element. Torque and heavy cars are hard on parts

[Half-Inch Stud]

add 2 more Quarts , and see how she runs. Report back.

[kyle_blake]

my tranny would complete the 1-2 shift 90% of the time, the 10% it would complete then fly right out of gear , rpm's would climb so of course you let off gas and it falls back into what ever gear, there were 3 rollers in the sprag that fell out or were bent. that's it.

[Ozzmann]

Originally Posted by kyle_blake

my tranny would complete the 1-2 shift 90% of the time, the 10% it would complete then fly right out of gear , rpm's would climb so of course you let off gas and it falls back into what ever gear, there were 3 rollers in the sprag that fell out or were bent. that's it.

Yea, mine doesn't do it every time either...... mmmmm

[QUOTEadd 2 more Quarts , and see how she runs. Report back. ][/QUOTE]

I checked the level, it looks ok, are you saying to add more fluid anyway?

So I'm guessing by most of the replies, I can discount the converter as the cause??

[Cliff R]

Most likely inside the transmission and not the converter.

Rolled 34 element sprags are rare but do happen on occasion. I've seen a couple here in a all the years I've been building TH400's. The roller type sprag is actually impossible to roll as the drum is "notched". They just explode instead, if/when the torque capacity is exceeded.

A sprag type clutch can also loose holding ability and not be rolled over, have seen a few slipping with damaged inner/outer races. I've also seen a number of them kick the snap ring off the drum, and why GM upgraded to a spiral lock ring on the 4L80E instead of a standard snap ring.......Cliff

[Formulajones]

That's exactly what my brand new TCI 400 would do when I bought that thing 30 years ago.

Drove fine everywhere, but as soon as I went full throttle on the 1-2 shift, it would just free wheel and bang the rev limiter. Let of the gas and it would grab 2nd gear and take off again. It was especially bad when the transmission was warmer.

Tore that trans down no less than a dozen times diagnosing it for TCI. In the end they were no help and wouldn't warranty it. I educated myself on transmissions at that time and found out myself it was exactly as Cliff described, damaged races on the sprag.

I've built my own transmissions ever since.

[mchell]

I’ve destroyed several 34 element sprags .....they are not immune to damage. With mine, the sprag rollers basically skipped on the direct drum surface damaging the direct drum and locking the sprag rollers in a position that rendered them inactive (no second gear under power)

I’ve since changed to a full manual valve body so I can burn out in second or third gears....I also Avoid first gear when running street tires....so far so goodness

[TCSGTO]

I just had a 400 built by a very respected high profile shop last year that did the same thing. They "fixed" it once and it still acted the same way. It ran fine on the shops' trans dyno but wouldn't work in the car. They couldn't figure it out and ended up giving me a full refund + a little extra for my time. It had a Transgo shift kit also.

[Formulajones]

Originally Posted by TCSGTO

I just had a 400 built by a very respected high profile shop last year that did the same thing. They "fixed" it once and it still acted the same way. It ran fine on the shops' trans dyno but wouldn't work in the car. They couldn't figure it out and ended up giving me a full refund + a little extra for my time. It had a Transgo shift kit also.

At least they stood by their work and gave you a refund. I can't say the same for TCI.

[Cliff R]

There are ways to be easier on the sprag so they lead a long life. Window shattering shifts will kill the best set-ups, so we are more conservative here with the 1-2 shift program, leave the accumulator functional, and use and prefer at a minimum waved frictions or at least a waved apply plate in the intermediate clutch pack.

Using the spiral lock over the retainer is also a must, and "tac" welding the stock type snap ring in place is asking for problems. I've seen enough of those kicked off the drum to avoid that deal completely.

As far as function goes the roller type in the notched drum is far better as it's impossible to "roll" it over. It doesn't have nearly the apply area as the 34 element deal, so tends to be a little harder on the outer race when locked up as it's only applying force to a few areas.

As an experiment quite a few years ago I set up a full race TH400 with a notched drum and roller sprag set-up. I used waved frictions, a waved apply plate for the intermediate pack, very conservative hole size in the separator plate, and functional accumulator. That transmission did fine in a very quick full race application (foot brake). Never did hear about it failing and it's probably still working fine today. Even so it never gave enough of a "warm and fuzzy" to do all of them in that fashion, so I've stuck to the smooth drum and 34 element set-ups instead......Cliff

[TCSGTO]

Originally Posted by Formulajones

At least they stood by their work and gave you a refund. I can't say the same for TCI.

Agreed. I was pleasantly surprised the way it was handled. Stand up guy for sure.

[JSPONT]

Heavy cars, sticky tires that still spin will kill a 34 element sprag in no time. spinning 1st and pulling second hurts it.
If you compare a 34 element to a 36 ,there is a huge difference. No one I know with decent power and street races has ever had a 34 element live.
My friend just put a Chevelle together with a big big block. 1st test ride he rolled the 34 element sprag.
To me, put the best parts in that you can so you have no issue's. As Cliff said it also depends on how you drive. If you have a full manual valve body you, you can do your burn out in second. That 1-2 shift is what hurts the sprag, and as Cliff said, a real hard 1-2 shift does not help either.
I added a 36 element sprag, been beating the car all season, so far so good.

[JSPONT]

Here is my old 34 element, vs a 36 element

[Ozzmann]

Originally Posted by Formulajones

That's exactly what my brand new TCI 400 would do when I bought that thing 30 years ago.

Drove fine everywhere, but as soon as I went full throttle on the 1-2 shift, it would just free wheel and bang the rev limiter. Let of the gas and it would grab 2nd gear and take off again. It was especially bad when the transmission was warmer.

Tore that trans down no less than a dozen times diagnosing it for TCI. In the end they were no help and wouldn't warranty it. I educated myself on transmissions at that time and found out myself it was exactly as Cliff described, damaged races on the sprag.

I've built my own transmissions ever since.

This describes it perfectly!

[Ozzmann]

So, I know nothing about the internals of a th400, if I was to drop the pan would I be able to tell what the problem is, or is it a complete tear down?
How hard is to rebuild an auto on your own, do you need any special tools?