9000th01ss

iTrader: (10)

I bought a 1998 trans with 60,000 miles on it about 5 years ago, reverse didn't work. I tore it down, didn't find much wrong, replaced the band anyway.
It worked maybe 100 miles. Come to find out the servo piston was slamming the case on apply and cracked it.

I got a whole reverse servo set up from a hardparts supplier, it had a longer apply pin. It's worked great for 5 years and about 30,000 miles.

Now today it just started slipping again. I never do anything in reverse except back out of parking spots. Maybe other things, it's in a dually and I know it would spin the tires in reverse before.
It's got good pressure, I think, its 60psi in reverse but it responds to throttle more than the other gears it'll go up to 300 psi in reverse at 4000 rpm (slipping) and the gauge flutters a lot.
It's got a Sonnax pressure limiting boost valve.

I guess I'm just going to see whats in the pan and put a longer pin in it. Is this unusual to have to do this almost as maintenance?

tptransmission

It is mainly due to the pressure spikes. It is normal for pressure to increase reverse boost is usually in the 300 psi range. The fluttering is just the pressure being released above the 300 psi.

9000th01ss

iTrader: (10)

Thanks.
Hopefully it's just the apply pin, any idea why it's come up short twice now?
Maybe it was on the loose side the last two times it was set up?

tptransmission

There is always variation in the parts, machining of the band lugs ,band diameters etc. I have seem the piston crack in the center mainly around the pin. If the piston is bottoming in the case, It is most likely parts that are out of dimension or on the high end of the spec.

9000th01ss

iTrader: (10)

I realize that is why there are different apply pin lengths. But I thought they were for set up only.
My transmission seems to need a longer one every xx,xxx miles.

I just changed it today, 1/8" longer. Works great.

I tried that old th400 trick for measuring pin length by putting the second accumulator o-ring in the servo cover, if the cover goes on, the clearance is not too tight.
I put a 3/16 washer in there and the cover just went on, thats why I went with a pin .125 longer.

Other than that, I found the regular crap in the filter.
I found the exact same thing last year. This filter has 6,000 miles on it running full load towing my 2002SS on a trailer, plus about 5,000 miles running empty.
The reverse band I put in it at 60,000 was green.
These chips look red. For some odd reason I've always suspected my converter clutch is dragging.
Who knows

tptransmission

I have set the pin dimension and then ran the vehicle for a few hundred miles and checked he dimension, Only to find that I needed a longer pin. There are numerous variables that play into this. When we set the dimension we apply 25 ft lbs and choose the right pin. The rear band is subjected to reverse boost pressure along with the heat and wear of the band and the reaction carrier. It is not to difficult to see that this dimension will change rather quickly.

9000th01ss

iTrader: (10)

Thanks for the info.