Hi all
4 months ago my 94 Z28 would only reverse - no forward gears
I then purchased a rebuild DVD by Paul Zank & proceeded to strip the tranny. As predicted buy the forum ( Frank CPT) the forward piston was
cracked ,band, overrun & forward clutches were toast & the input sprag bearing had collapsed damaging the gear & the release springs.
The 3/4 clutches , reverse clutches , bushings & planetaries looked good.

I then purchased the following:
1) Steel forward piston - moulded seals
2) 13 vane rotor kit
3) Alto carbonite powerband in standard width
4) Transgo release spring kit
5) Complete clutch rebuild kit & gasket set
6) Beast sunshell
7) Universal Poly Trans mount
8) Rebuilt input sprag with double cage bearing
9) New filter & assembly lube.

I followed the DVD checks & air test procedures , did not cut input drum & pump teflon seals , leak tested servo check ball , removed reverse check ball in cage, ground clearance for beast sunshell.
forgot to replace big servo spring from kit, did not replace torque converter to heavy to import.

Problems after installation:
slippage under load in all gear except 4th
Hunts between 3rd & 4th at constant speed & throttle.
Stopped slipping in reverse under load ,now cannot ingage reverse

Please assist with some faultfinding ideas, as removing & installing tranny is not fun without proper facilities.

Thanks
Patrick

 

Unfortunatly if you can engage reverse and the othe complaints you have you will likley end up pulling it back out and down You could check the valve body bolts maybe particulary the ones that hold the plate at the back, Sorry your having issues there , When you tacked again feel free to holler at me even live on yahoo messenger I am on most of the time day and night

 

Sorry, I can't be here all day...I'm up to my ears in 4L60E's, in the shop.

Does this thing act the same (slipping) in manual ranges?

Reverse doesn't try to apply at all? Does it try to apply before the transmisson heats up?

Are you sure it's not slipping in everything except when it goes into lock-up, not 4th gear?

You did put a slide spring back in the pump, right? Years ago, I worked at a shop where a builder forgot them in several pumps, and it slipped under heavy throttle.

Frank
CPT

 

You said you installed the steel molded rubber forward piston, did you replace the aluminum overrun piston with a molded rubber overrun piston? If you have it in "1", "2", or "D" position, will it slip from the start? If you have it in "OD" postion, does it slip from the start also? Dana

 

Dana brings up a good point. If you replaced the forward piston with a stell one, you've also got to use use a steel over-run piston and the proper spring pack. We've seen others try using the aluminum over-run pistons in the steel forward pistons, because they use a sleeved input drum. This won't work, because the lip seal is in a different location between the 2 . The sleeve is really worthless anyway. The steel over-run piston has no locators for the forward spring pack, so the later pack with the retainer/locator on the bottom has to be used.

Frank
CPT

 

To answer Dana's first question yes I did replace the overrun piston with a new steel moulded piston,but the original combination was a steel overrun & a aluminum forward ??
My spring pack is the retainer type for the overrun
I air tested these clutch packs for operation before assembly.
The tranny slips in 1,2,D & OD
When moving forward in 1 under light throttle their is slip then movement on releasing the throttle the tranny almost stalls the motor as it dips below the normal idling rpm.

The only part of the reassembly of the tranny I was uncomfortable with was when the DVD
said use the scuff markings on the valve body plate to determine the spring/piston order on the 1/2 & 3/4 accumulators

Hope my descriptions are making sense

Thanks
Patrick

 

I found the 3/4 accumulator's piston/spring order to be incorrect for a 94

Can this cause fluid pressure loss to rest of tranny ?

 

No

Frank
CPT

 

I investigated the input drum pistons & found that I was confusing the 3/4 piston with the overrun piston . Therefore I am using a steel forward with a aluminum overrun & correct me if am wrong , because the overrun fits into the forward piston it's lip seal does not work in the steel forward , would this cause the car to slip in reverse ? I also found that at the base of the neck of my new filter is cracked ( must have been damaged in transit) So I need to order more parts for this rebuild to work?

 

If you have the steel forward piston with the aluminum overrun, then you must have the steel sleeve installed in the input drum. If this is the case, then you will need the modified steel forward piston to make it work. I can send you one of these modified steel forward pistons if you want, just let me know? If you do not have the steel sleeve, then replace the aluminum overrun with a steel molded rubber overrun piston. This will not cause your problem with reverse. A crack in the neck of the filter could possibly cause your reverse problem, as the pump could be seeing air which can cause an immediate slip.

 

My original pistons at dissassembly were steel 3/4 aluminum forward & overrun

Is the steel sleeve in the input drum standard in a stock 94 tranny?

If not can someone supply me with a steel molded overrun piston & correct spring pack?

I have found plenty of steel overrun pistons online but not the modified spring pack

Thanks
Patrick

 

The steel sleeve is a "band-aid on a bullet wound". It serves absolutely no purpose. The only thing that will break the input drum is using a converter without a lock-up damper. In 18 years, I've only had 1 transmission (700/4L60E) break an input drum. The steel input piston set is a much better option, because they DO break aluminum pistons! You simply can't use an aluminum over-run piston in a steel forward piston.
BTW, if you use one of those "mickey mouse" sleeved drum's, with a converter without a damper, it'll break the whole center out of the drum.
Please build this transmission right. Get a stock drum, with all 3 steel pistons and correct spring packs.

PM me, and I'll get you some information on where to order them from. We're not really geared to sell parts.

Frank
CPT

 

Hi All

At last I replaced Aluminuim overrun piston & spring pack in forward drum, with steel piston & later spring pack.

The tranny really performs well in the forward gear, with quick & tight upshifts & downshifts even at WOT
Thanks to Frank & Dana for excellent faultfinding diagnosis.
But unfortunately this saga is not over, when selecting reverse the drive goes soft & it seems to shudder/grab & release in reverse.
After a bit more reading, I ran the tranny at 30mph in 2nd manual & then did a manual downshift to first - no engine braking or forward drive.

There seems to be a mechanical drive problem in reverse , I did not pull that part of the tranny out when I did the steel overrun piston

Please assist with what could be wrong & what parts may be required for a repair.

Any ideas on best pan drain plug location would also be appreciated.

Thanks
Patrick

PS: if I lived in the States I would definitely have sent the tranny in to a pro for a performance rebuild

 

Just curious on reverse did you tighten the little steel plate with the three bolts at rear of the trans?