Technical Question for the Turbo 400 re-builders

The very early versions (64-66) of this unit used a sprag between the planetary drum and center carrier. Versions after went to a roller clutch, and this sprag has not been available for some time. I am trying to put together a Nailhead case unit. My options include re-using the sprag, using a roller drum assembly (I have a later BOP unit lying around), or see if another sprag will work. Research and contacting transmission shops have not produced anything definitive. Anybody?

 

What is the question?

 

If the sprag clutch is not worn re-use it

you can try contacting Lawrence transmissions up here in rexdale ( Toronto) he’s the guru for vintage transmissions and helped me with the Dyna-leak in my 55 Buick , helpful and knowledgeable guy . If there are parts available he would know where to get them .

 

The question for the experienced guys is what did they do?

 

I always keep old hard parts in the transmission, if they're in good condition. Don't fix what ain't broke.

 

I’ve rebuilt transmissions , differentials and drive units in everything from a car to a 100,000 lbs capacity forklift .

like @squirrel said , transmission hard parts if not worn or broken can be reused indefinitely.

there is nothing wrong with a sprag clutch , although not considered “new technology “ anymore they are still used in a lot of applications .

And again , why are you looking to replace it ?

 

When I taught auto trans rebuild, I had a student rebuild the ST400 in his Pontiac Gran Prix. He wanted more aggressive shifts especially 1-2. Since he didn't have too much money, I suggested drilling the orifice in the separator plate. He asked what would happen if he left the check ball out by that orifice. I said the shift would be very aggressive, but not to do that. He ignored my recommendation. A full throttle shift without the orifice check ball resulted in the sprag going over center and broke a bunch of pieces. For some reason he was mad at me.

When I went through the transmission on my Model A, 1965 Buick version of the 400, I left the sprag in it. It already performed for over 100K miles and had no discernable wear. In fact, when I went through the transmission all friction plates and steel plates looked brand new. The small intermediate band normally has some darkening on its edges, but the one in my transmission looked as new as all the clutches. I ended up only replacing the seals, both hard and soft.

 

Thanks for the replies guys. Seems the consensus is to re-use the sprag. I actually have two, both used 1964 units. One has 133K on it, but was working fine when the Electra 225 was parked. The other has unknown mileage, but along with the races look OK. Both these transmissions have the one year only valve body, so a hard 1-2 shift unlikely.
I was mainly interested to see if someone had used a sprag from another application in its place. The issue with that is this sprag has retainer on it because of the way the unit has to be assembled.