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Old 07-18-2007, 10:56 AM   #1
Ausome vet
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Default Help with '96 6 speed transmission

Help! The 6 speed (ZF?) transmission in my '96 is toast. I hear rumors that this was a bad transmission and GM stopped making it or selling parts. Does anyone have any experience with this transmission, recommendations for replacement (parts, new, rebuild),etc? I would really appreciate the help.

Thanks
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Old 07-18-2007, 11:16 AM   #2
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The ZF tranny is not a POS as you may have heard. GM never made it. It was made by ZF in Germany. Browse on over to ZFDoc.com and read some of the FAQ. Contact them and they will take care of your tranny.

BTW Post the actual symptoms. You never know what people here can suggest as a fix until you give them a chance.
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Old 07-18-2007, 11:22 AM   #3
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And while you're about it, you might just add a little to your skimpy profile so someone might know what city, first name, etc. That could be added to your edited post which would tell more about your current car, as well as the symptoms or diagnosis of what is wrong with it.
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Old 07-18-2007, 11:37 AM   #4
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The ZF tranny in the C4 corvette is an excellent transmission.

They do break occasionally, but it's usually due to abuse or neglect.
The cost to replace the dual mass flywheel and clutch material are the main complaints I hear.

The Doug Nash 4+3 transmissions in early C4s were the ones prone to problems, and that is not a rumor, it's fact.

Give us some more details about the problems you are having with your ZF trans and maybe we can help you.
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Old 07-18-2007, 01:02 PM   #5
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Default more info on '96 transmission

I'm new to the forum. Didn't know how much info to put in. It is a '96 Collectors Edition that I purchased used with about 15000 miles on it. I put an additional 15000 on it. Mostly Sunday driving but a few harder drives (1 trip to the drag strip, 2-3 to the race track) but it should seriously be able to handle it. While driving it became 'sluggish' when accelerating from a stop and a little difficult to get in gear. Seemed to do better with a little more speed so I immediately headed for home. Within 10 minutes of the initial problems (driving about 40mph) the rear end locked up on me. I couldn't move the car in or out of gear, on/off, etc. (had to drag it up on the flat bed). I can't get the gear shift into any gear, stays in neutral. With the rear end on jack stands the rear wheels don't turn if I have the clutch but if I let the clutch out the wheels start to turn and it makes a bad noise. On the ground it won't budge even with the gear shift in neutral and clutch in or out even when being dragged. A friend is working on it and has pulled the transmission and says it has already been rebuilt once (not good since I got it with only 15000 miles). Hope this helps. Again I appreciate any help. PS I added to my bio.
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Old 07-18-2007, 01:20 PM   #6
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Quote:
Originally Posted by Ausome vet View Post
I'm new to the forum.
Welcome to the forum. I'm sorry we are 'meeting' when you are having trouble. If your friend isn't familiar with these gear boxes then I think it would be wise for him to assist only with the removal and reinstalation and ZF doc should do the repair work. There is some chance of finding a ZF used but as you know, you are rolling the dice when buying used parts.

A bit of time on the strip and the driving you do isn't supposed to cause any trouble with these gear boxes. It may be that the PO drove differently than you do and that the first repair was done under less than ideal circumstances.

Do a forum search on ZFDoc. I think you will find people here generally have a great appreciation for them.

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Old 07-18-2007, 01:26 PM   #7
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There are alot of new in the box transmissions available, many on EBAY for about $1500. Or about the same as replacing a syncro in one. If you did in fact have catastrophic failure, it probably isn't worth rebuilding. The stories you hear are because first, they wouldn't release parts to the rebuilders, and when they did, they let one company sell them, and second, now they charge BMW prices (BMW made the trans in partnership with GM as temporary solution to the lack of a strong enough GM overdrive transmission). ZFDoc is very good at repairing them if you decide to go that way, but you may be able to find some one locally. This is one of the reasons that (outside of this forum) they are not so well thought of, and generally are a harder sale. They are good transmissions, but when they go........
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Old 07-18-2007, 10:30 PM   #8
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how difficult is it to replace a ZF6 with a T56? will everything bolt up?
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Old 07-18-2007, 11:40 PM   #9
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Very difficult, and you wouldn't be gaining anything, the ZF6 is at least as good/strong.
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Old 07-19-2007, 06:15 AM   #10
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Quote:
Originally Posted by zr1fred View Post
There are alot of new in the box transmissions available, many on EBAY for about $1500. Or about the same as replacing a syncro in one. If you did in fact have catastrophic failure, it probably isn't worth rebuilding. The stories you hear are because first, they wouldn't release parts to the rebuilders, and when they did, they let one company sell them, and second, now they charge BMW prices (BMW made the trans in partnership with GM as temporary solution to the lack of a strong enough GM overdrive transmission). ZFDoc is very good at repairing them if you decide to go that way, but you may be able to find some one locally. This is one of the reasons that (outside of this forum) they are not so well thought of, and generally are a harder sale. They are good transmissions, but when they go........
Yes, but how can you be sure that they are "new and in the box" and not used and cleaned up? Not doubting your word, it's just a little hard to ck one out from 500 or 1500 miles away, don't you think? And then there's the whole paypal and who gets what, when, issue.

Ausome, not questioning your friend doing the repair/replacement, but what exactly is his experience with man trans, and more specifically, ZFs?
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Old 07-19-2007, 08:35 AM   #11
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Have you removed the driveshaft and tried moving the rear tires? You may have a differential problem and not a transmission problem. Did you notice any increase in noise prior to the rear wheels locking?
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Old 07-19-2007, 10:04 AM   #12
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few years ago, GM sold all of their stock of brand new ZF's, and there still is alot of them in the secondary market (all though the numbers are declining monthly). Most of the ZF sellers on EBAY are businesses and guarantee their product, and don't charge a core (shipping can run up to $500). The ZF only fits the corvette, so there isn't much demand for them other than corvette owners as replacements and spares, hence the low (comparably) price. There is a difference in the regular ZF's and the ones for the ZR1's. I would be carefull of buying a used one off EBAY (alot of them are the ones people who have replaced their trans with a new unit and now are selling their core). I also, when I first read the thread thought that it might be the rear end!
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Old 07-19-2007, 10:09 AM   #13
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Quote:
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Have you removed the driveshaft and tried moving the rear tires? You may have a differential problem and not a transmission problem. Did you notice any increase in noise prior to the rear wheels locking?
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Old 07-19-2007, 03:41 PM   #14
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Quote:
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The transmission is off and the case is cracked along with some nice bits of metal that used to be parts (have not seen it with my own 2 eyes yet) so I don't think it is a question of not being the transmission. The guy doing the repair is a friend that has been a mechanic ofr yrs (20?) and currently is working primarily on big trucks but transmissions are a hobby.

Thanks again for everyones input.
Jennifer
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Old 07-19-2007, 03:54 PM   #15
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Quote:
Originally Posted by Ausome vet View Post
The transmission is off and the case is cracked along with some nice bits of metal that used to be parts (have not seen it with my own 2 eyes yet) so I don't think it is a question of not being the transmission. The guy doing the repair is a friend that has been a mechanic ofr yrs (20?) and currently is working primarily on big trucks but transmissions are a hobby.

Thanks again for everyones input.
Jennifer
Be VERY careful, the ZF tranny used in the Corvettes requires MANY special tools to take apart and put back together properly, if your friend does not have these I would not have him attempt to get it done, it'll cause more problems than it fixes. Although it sounds like yours is completely toast, if the case is cracked it's scrap. How's the bell-housing?

Give Bill at ZFDoc a call, he's very helpful even if you're not a paying customer!! He'll get you going in the right direction. And I think he has a good line on some new ZF transmissions that are still available, if you get one from him I would highly recommend having him blueprint it, it's a little more expensive but you'll have a 100% flawless transmission if you do.

www.zfdoc.com

He's done a lot of work on mine and I've been nothing but satisfied.
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Old 07-19-2007, 04:20 PM   #16
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Welcome to the Forum. Good advice here.
There is a good Corvette club in Lansing called Capitol City Corvette Club (I think).
I hang out with the West Michigan Crew and we have attended some of the events put on by the Lansing group. Go to the Events and Regional section of the Forum and post your questions too. You will probably find someone local who would be willing to give you a hand. They are also a fun bunc to cruise with when you get her back on the road.
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Old 07-19-2007, 05:07 PM   #17
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Quote:
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I would highly recommend having him blueprint it, it's a little more expensive but you'll have a 100% flawless transmission if you do.
Explain what exactly he does "blueprinting" a transmission.
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Old 07-19-2007, 05:21 PM   #18
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Quote:
Originally Posted by RWD_tech View Post
Explain what exactly he does "blueprinting" a transmission.
Here is a quote from the ZFDoc site;

"Each unit is built to race-ready standards and is backed by our 1-year/unlimited mileage warranty. We provide solutions for extreme power applications (up to 700 ft. lb.). ZF re manufactured transmissions are built to provide long life smooth operation in even the most severe operating conditions."

He dis-assembles the entire transmission, check all clearances, polishes the synchros, etc and rebuilds the transmission and sends you a sheet with all the information. Also, at this time he can weld 2nd gear onto the shaft for extra strength (if this is going to be a racing transmission, or one with a lot of power being put through it).

You can download this video from his site;

Right-click and save as;

www.zfdoc.com/SyncTes-med.WMV

Listen to the difference

Last edited by Zix; 07-19-2007 at 05:27 PM.
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Old 07-19-2007, 08:30 PM   #19
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lol listen to the difference?....give a transmission 200 miles and it will sound exactly the same as the "detailed" gear. im sure this guy does good work in other areas of the trans, but the whole detailing thing seems like a waste. i dont understand the benefits of polishing a synchronizer either
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Old 07-19-2007, 08:42 PM   #20
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Well, I've felt the before and after effects, and it's night and day. There is no slop/rattle in the shifter, it just clicks in and out of gear very smoothly. It's actually very impressive and I've had quite a few people comment on it when I let them take my car for a spin.

Also, Bill is very meticulous in his work, if there is the smallest thing wrong he spends the time to make it 100%...he has the kind of work ethic and service ethic that is second to none.

Oh, and he doesn't polish the synchros, that was a mistake on my part!
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Old 07-19-2007, 08:42 PM
 
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