This is my first post after years of lurking! I'm trying to figure out what I did wrong so I can take the appropriate course of action to fix it. The background: A stock 1995 Corvette LT1/4L60E with 78,000 miles lost the 3/4 clutch. I did my best to meticulously rebuild it using the transmission bench video series and information I have gleaned elsewhere - mostly here. The transmission was in very good shape other than the 3/4 clutch. In addition to the normal frictions, steels, bushings, thrust washers, etc.; I put in the following upgrade parts:

Sonnax Smart Shell
Sonnax Performance Pack Shift Kit
Dynamic 396's suggested 3/4 clutch stack

After reinstalling everything, with the car still up on jack stands, I refilled it, started it up, and with the brake on, went through all of the gear positions one at a time, carefully filled it to full again, and then went through the gears. The forward gears seem to work although I didn't try much over idle. Reverse does not move, but it will try to move if you blip the throttle. There is no discernible load when you move it into reverse.

I air tested what I could. The input drum clutches seemed perfect. I did not replace any of the Teflon rings, but they seemed OK. I wasn't happy with the reverse input clutch but eventually convinced myself that it was OK.

I air tested the reverse input clutch with it on the pump and stator shaft. With air pressure at about 40 psi, I could hear quite a bit of leakage and the clutch would not engage. It seemed like the leakage was coming out of the pump spool cavity. The small filter screen popped out of the hole when I applied the air pressure but it stayed after I pushed it back in. The reverse input drum seemed to be in good shape- did not appear to have overheated, the rings and stator shaft were smooth, and reverse originally worked fine. I just added the new piston seals, clutches, and steels. I have the two special seal protector tools (like this: https://www.toolsource.com/clutch-se...-p-111845.html), although I suppose I still could have folded one of the seals.

After watching a couple of YouTube reverse input clutch air test videos, I upped my pressure to about 100 psi and the clutch applied, although there was still a lot of leakage.

I did install the pump spool and springs like mrvedit shows: https://ls1tech.com/forums/automatic...rse-4l60e.html post 4.

I'm pretty confident that I properly torqued the reinforcement plate on the valve body like performabuilt describes: https://ls1tech.com/forums/automatic...o-reverse.html post 6.

I'm thinking that I screwed up one of the reverse input piston seals or something in the pump isn't right. How should the air test of the reverse input drum work - pressure, leakage, clutch apply, etc?

The car is still up in the air, waiting for me to take the trans back out if that is what I need to do...

Thanks for all the help you have all ALREADY given me with the other posts here!

Advice?

 

The reverse clutches should apply with 40 psi of air. You could have rolled a piston seal on installation or you could be losing pressure at the 2 Teflon rings that seal the pump to the reverse drum. It wouldn’t hurt to check the 3 reinforcement plate bolts before pulling the trans back out.

 

You also might want to check the center ring on the reverse input drum we actually ran across a couple kits a while back that had the wrong seal not immediately visual but the ring rubber was just a bit smaller and it made no reverse. other than that the plate mentioned, The stator rings and of course the low reverse clutch seals and piston.

 

The trans is back out. The reinforcement plate was torqued down. The stator seals were smooth with no nicks or cuts. The clutch housing fit snugly on the stator. The piston seals were not rolled and seem to fit fine. 40 psi doesn't even make the clutch twitch. I put a resizer on the stator seals and applied pressure - lots of air is coming out of the spool bore; is that normal?

 

I found the problem. It was stupid and it cost me a lot of time, but maybe it will help someone in the future.

The boost valve was sure enough stacked right, but it wasn't pushed in to the point where the snap ring was in its groove. The Sonnax sleeve has O-rings to help give it a tight seal but the friction also allow it to stay in and make me believe it was in the right place! I was wrong!!

I put it back in, pushed it in far enough to get the snap ring in the right place and the reverse input clutch works fine at 40 psi now.

 

Glad you found it!

 

Just got it back in the car today - works great! It's good to have all the gears again!!

 

Excellent work!

 

Interesting and unexpected problem , Good you found it ,

 

thanks for posting.

 

For anybody else who might come across this, make sure when you were rebuilding your 3–4 clutch, you had the correct stacking arrangement. I found out the hard way, that, depending on the kit that you use, and whether or not you use heavy duty clutch packs, you can sometimes have anywhere between six and nine friction plates. if you do a bit of research, according to the type of clutch pack, you are installing, you should find the exact stacking arrangement. walk-through videos like to tell you nine, for example, but my stacking arrangement only required eight.

 

Thats some really old thread you revived here.
i dont think i have seen a pre-configured clutch, steels and plates.

Performabuilt uses 0.020" clearance with unknown specs for steels and clutches. They push it to the limit.

I decided to target 0.030" clearance as the pros here recommended.

And.. Whats heavy duty clutches? Im in a facebook forum of 4l60e and people tend to use beautifull names like : Alto red eagle!!!! Red band!!!!! Top tier clutchesss!!! Like these old "sh*t ricers say" videos.

im glad this forum brings people back proportions.

1. There are no better clutches than Raybestos GPZ or Borg Warner HEG.

2. Its better to have thicker steels and thinner clutches

3. Do not buy gimmick stuff with cool names. Thats the very first thing that this forum teached me.

4. Read this forum before watching build videos.

 

This is one of the few applications where a "Kolene"/ Nitro-Carburized or Nitrided Steel Plate is beneficial...

These Steel Plates reduce the Friction Coefficient (Normally not a desirable characteristic) and allow for a very tight Tolerance Clutch Stack.
The desired Shift Feel and Timing (along with the 2-4 Band and Corresponding Clearance/ Timing) can be achieved without the excessive Clutch Drag that would normally occur without use of the "Kolene" Steels.