1991 Z28 TH700R4 2-3 shift clunk
 

Happy New Year!

I have a 1991 Z28, with factory original Th700R4, that has had a 'clunk' sound & feel on the 2-3 shift since the day I brought it home, brand new (7 miles on it when I bought it from Scott Irvin Chevrolet in Valencia, California).
Two Chevy dealers, Scott Irvin and Rally in Palmdale looked at the problem.
Scott Irvin Chevrolet took the car in (service manager drove the car and said, 'Yep, the car has a problem.') and R&R'd the ring and pinion setup twice to address the issue, with no change in the clunk issue, then they passed me onto the Corporate Warranty folks who told me there was no problem with my car; the clunk was normal. This was in 1992.
Rally Chevrolet in Palmdale took the car in (service manager drove the car and said, 'Yep the car has a problem.') to address the 2-3 shift clunk issue.
They changed the ring & pinion, with no change in the clunk. When I picked up the car, drove it, and reported no change in the problem I brought the car in for, they again attempted a repair. I picked up the car again, and the 2-3 shift clunk wasn't as noticeable, but shifts were mushy soft and slow. I brought it back and the 'mechanic' said he 'adjusted' the TV Cable to address the clunk. I told him the trans was going to burn itself up in that configuration, and again I was referred to the Corporate Warranty folks, who told me there is nothing wrong with the car.

Both Chevy dealer repairs were done under warranty; no charge.

Next, the car went to Mike's Transmissions in Lancaster, Ca. The same Mike's that now only does mail order transmissions like full race TH400's.
Mike did this and that (replaced 3-4 clutch pack, raised line pressure, and installed a shift kit, not B&M, not TransGo, a Superior brand s/k). On the test drive, there was no change to the 2-3 shift clunk, so Mike didn't charge me for the 'repair.'

The trans was later rebuilt with Dana's Street / Strip kit. NICE TRANS, but still had the 2-3 shift clunk.

What else should I look at to address the now well-known TH700R4 2-3 shift clunk?

Thanks in advance for any help.

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Unless it has already been changed, maybe you have had a bad tranny mount since 1991.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

It is a timing issue within the transmission. On the 2-3 shift the 2/4 band gets released while the 3/4 clutch pack is applied. Have them both engaged for a split second and the trans locks up and the pinon gear clunks against the ring gear.

The opposite can also occur, release the band too soon and the 2-3 shift flares as 3rd isn't engaged yet. This is the more common issue on the 2-3 shift.

It has been quite a while since I've studied the 700R4 shift mechanism, so I can't offer exact advice other then the above. The servo has a lot to do with the timing, along with the feed orifices.

Since this was an issue from new it may be that the transmission was built incorrectly. Maybe the wrong separator plate or valve body was used. Or the servo wasn't set up correctly.

RBob.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Thanks red rock and RBob.

Transmission mount is unrelated.

Been all through 'whys' and 'hows' it clunks so many times I've forgotten more than than I know about it.

I'm looking for a remedy to the situation.

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

has the driveshaft/u-joints/yoke been checked? did dana rebuild your transmission for you or did you just buy one of his kits? perhaps it is time to send it off to a builder that is going to spend the time to go over the whole trans in detail.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Buy a new transmission and rear end.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Thanks, morgsie.

Thanks again red rock.

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Here is how I fixed the 2-3 shift clunk after a Trans-Go shift kit install:

https://www.thirdgen.org/forums/tran...ift-clunk.html

RBob.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Thanks much, RBob.

That definitely gives something to chew on.

Anesthes?

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

I think your 3/4 clutch pack is engaging too quickly.

If you follow RBob's thread, from post 35 onward.

I don't know what differs from his plate/vb mods and the transgo kit. You may want to check with Transgo. But I'm under the impression it's one of the 'fixes', and my Corvette didn't have the 2-3 clunk after doing the transgo kit.

-- Joe

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Thanks, Joe.

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Something interesting I can relate:
My slightly modified 700 had a sluggish WOT 2-3 shift. Cruise shift was "normal" I would say.
The TransGo Jr kit addresses some the shift timing associated with these transmissions and one of them is the 2-3 shift.
List of upgrades are the ususal: .500" boost valve, Corvette servor, modified valve body and seperator plate, most of which is included in the Jr kit.
Now here's the interesting part, after installing the kit, WOT 2-3 shifts are now crisp and instantaneous however at light throttle, there's a distinct "binding" that occurs which shows itself as a "clunk". It seems to me that's the backlash in the drivetrain being taken up momentarily. It definitely an application of two circuits in the transmission being active at the same time which results in a brief lockup. The more throttle that's applied, the less distinct this event is.
How are your WOT shifts? Could be something to consider.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Yes, I agree with all on the timing of the band-release / 3-4 clutch apply; with the band released w/o 3-4 clutch apply, the trans is in first gear, with band applied and 3-4 clutch applied, trans is in forth. So in either of these scenarios, instead of going 2-3, it kinda goes 2-1-3, or 2-4-3.....kinda sorta.
The trans has the modified TransGo kit from Dana / Pro built, and had the Street / Strip Rebuild kit installed by someone recommended to me by an engine builder. I had to have it rebuilt again after 20k pretty hard miles; frictions and steels looked about the same! But the shift kit is still there. Chirps third occasionally. Moderate to heavy throttle shifts are niiiiiiice! Only clunks on light throttle shifts, like most people here are saying.

Thanks again for the help. Dana, you got your ears on:)?

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

As I said before. even with all the modifications that TransGo has you do and with what I do it will mostly eliminate the clunk. Some transmissions will have it more or less even with the same transmission modifications. The main reason that is does it is that the overrun clutches are on when in 1, 2 or 3 shifter position. Usually in overdrive, it will not do it. That is why GM eliminated the overrun clutches being on in when the shifter was in Drive (3) until it shifted to drive (3rd). They did this to lessen the complaints. Without going into the separator plate and changing hole sizes which will affect the shifts, there really is not much that can be done.

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Thanks, Dana.

Bill

Re: 1991 Z28 TH700R4 2-3 shift clunk
 

Sounds like.someone did not reinstall a check ball back into the trans from new and did not notice because of the shift kit? Or the trans circuit in the itself has a narrow or not big enough and the fluid dont have enough time to fully engage, disengage the cluch packs. Only way would be a full tear down and inspect very carefully. Sounds like a dud from birth so find a.replacement before you break something else