Posted this in another forum, but want to get other opinions
and options. I'm open to all options, from repair to replacing
the tranny with a stock or aftermarket "performance" unit,
as I'm also considering beefing up the engine (neighborhood
of 300-400HP). Anyway ... here's the prob:

===========================================
1995 z28, 150k miles, auto

Driving home after work, stopped for gas, then pulled out and
accelerated, not aggressively (yet slightly spirited) heard a
hard "clunk" coming from the tranny (when shifting from 1-2)
and immediately (it has 1-2-d-D) lost forward movement.

Checked the fluid today, thinking it was so low on fluid that
possibly the torque converter wasnt doing it's job. The fluid
level was 1 (one) quart low. Anyway, here's some test
feedback:

* R(everse) - backs up fine - no hesitation from the tranny.
Shifts right into R and backs up.
* 1 - pushes forward fine, no hesitation from the tranny.
Shifts right into 1 no hesitation and pushes forward.
* 2 - pushes forward fine, no hesitation from tranny.
From standing start, pushes forward/shifts from
1st -> 2nd with no issues.
* d - no forward movement from standing start. However,
if I start with 1st, then to 2nd (or start in 2nd) and get
above 20-25, then shift into 'd', it will shift into 'd' (3rd?),
but when the car gets below 20 MPH, it "slips" and
there is no forward movement, yet engine revs.
* D - no forward movement whatsoever. Can't
manually shift through the gears up to any speed
and get the car to shift into 'D' (4th?)

Any ideas or suggestions?
===========================================

 

The input sprag has grenaded. When you pull it to manual 1st or 2nd, you're using the over-run clutches to take off, instead of the forward clutches. This is a common problem with the extremely fragile SKF input sprag GM used. This is why we ALWAYS replace them with the much stronger Dual Cage Borg Warner sprags.

Yes, it's probably time for a rebuild. Your choices? There's really only ONE, if you want it to be right, and take some abuse. Our web link is below. Don't take my word for it, though. There's a few open threads right now about our transmissions.

Frank
CPT

 

I would think the low roller clutch. heres why, the overun clutch is on in auto 1 st gear in the D position. .IMO

 

Low roller only holds in Manual 1st. I'm still betting on forward clutches or input sprag.

Frank
CPT

 

I think you mean the low/reverse clutches only hold on manual low one the low roller is 1st gear and holds in D and OD

 

If the low roller clutch fails, it won't move in manual 2nd.

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What are we applying in manual 2nd that will make the car move, that's not applied in manual 3rd?

Frank
CPT

 

Actually you will notice that in manul 2nd / 2nd gear the low roller is not holding , Now On this particular car I cannot say however some of the cars have the ability to do second gear start. Meaning when placed in the second gear position the actually start in second and not first. And since the low roller is not used in second gear , In that case the car would take off in 2nd gear in the second position with the low rollr clutch failed . Now also notice the overun clutch is on it all gears in D so if it were the sprag or the forward clutch the car would still move in D from the overun clutch being on. The exception would be if the sprag.forward clutch and the overun clutch or hub were destroyed then the car would not move forward at all in any position. IMO

 

Yeah Calderclay, dont feel bad, my 95 Z28 is down with the same symptom, loud clunk, no go in D, drivin it manually. Its time for a new one, some things to remember if you dont go high performance.

1. A 3.4L. 6 banger 4l60e will not fit on your Z28, same insides different case.

2. A used tranny for your z28 is near impossible to find on ebay.

3. Junkyards charge top dollar for this tranny.

4. If your in or around texas and wanna save big bucks on a rebuild, give this guy a ring, Phil 469-366-5271 or email him at Hart1550@aol.com, he will sell you a rebuilt tranny for $650 provided he has a core built and if you get your ride to him he will install it for an extra $100.

 

Thanks for the replies. I will check out a number of transmission builders, such as CPT and PerformaBuilt, among others.

Parts_changer - yes, I am in Texas (Cypress - outside of Houston), so I will check with Phil. However ...

Since I will be replacing the tranny, I am now seriously considering replacing the engine with an LS1 (versus the LT1) - quite possibly the GM Performance 350HP crate engine. If I decide to do this, I suspect I have to change out the tranny to one that mates to the LS1.

 

Yep and as a matter of fact i saw a used LS1 and tranny on ebay earlier today if you possibly wanted to go that route, but yeah if u got the $$$$ go crate and and a tranny that will handle it. Good luck.