ZF6 Question/Help
Thread Starter
Advanced
Joined: May 2012
Posts: 51
Likes: 0
ZF6 Question/Help
Hello all,
So I just purchased a 91 Corvette 6 speed with 85K on it. When I accelerate from first gear I get a slight grind when I go to put it in 2nd gear. If I really baby it and shift under like 17MPH it will shift into 2nd gear perfectly fine. I have seen some information on this forum about air in the system and needing to bleed. I have also seen information about the synchronizer for 2nd gear being shot. Also, the CAGS has been jumped out, could this have anything to do with my issue???
Has anyone else experienced this issue and found an easy fix. If the Trans does need to get rebuilt, does anyone know of a place in the Boston area that is knowledgeable working on the ZF6?
Thanks
So I just purchased a 91 Corvette 6 speed with 85K on it. When I accelerate from first gear I get a slight grind when I go to put it in 2nd gear. If I really baby it and shift under like 17MPH it will shift into 2nd gear perfectly fine. I have seen some information on this forum about air in the system and needing to bleed. I have also seen information about the synchronizer for 2nd gear being shot. Also, the CAGS has been jumped out, could this have anything to do with my issue???
Has anyone else experienced this issue and found an easy fix. If the Trans does need to get rebuilt, does anyone know of a place in the Boston area that is knowledgeable working on the ZF6?
Thanks
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Hello all,
So I just purchased a 91 Corvette 6 speed with 85K on it. When I accelerate from first gear I get a slight grind when I go to put it in 2nd gear. If I really baby it and shift under like 17MPH it will shift into 2nd gear perfectly fine. I have seen some information on this forum about air in the system and needing to bleed. I have also seen information about the synchronizer for 2nd gear being shot. Also, the CAGS has been jumped out, could this have anything to do with my issue???
Has anyone else experienced this issue and found an easy fix. If the Trans does need to get rebuilt, does anyone know of a place in the Boston area that is knowledgeable working on the ZF6?
Thanks
So I just purchased a 91 Corvette 6 speed with 85K on it. When I accelerate from first gear I get a slight grind when I go to put it in 2nd gear. If I really baby it and shift under like 17MPH it will shift into 2nd gear perfectly fine. I have seen some information on this forum about air in the system and needing to bleed. I have also seen information about the synchronizer for 2nd gear being shot. Also, the CAGS has been jumped out, could this have anything to do with my issue???
Has anyone else experienced this issue and found an easy fix. If the Trans does need to get rebuilt, does anyone know of a place in the Boston area that is knowledgeable working on the ZF6?
Thanks
http://www.rsgear.com/
George if he's still at it is as good as there is in the vicinity. I'd say that's somewhat "local". There very well could be a local that does a quality build also.
You do need to confirm the clutch and the hydraulics are sound and I believe I'd spend a good bit of time with the diagnostics of that first. There's a good bit to check before "over-reacting" maybe.
Racer
Joined: Apr 2010
Posts: 372
Likes: 23
From: Harper Woods MI
I also have a '91 with the ZF6 speed with 99k. It started to make similar noises after I got stuck in a traffic jam for 30 mins. I had a new clutch put in after getting the noise and it's been great ever since.
Thread Starter
Advanced
Joined: May 2012
Posts: 51
Likes: 0
I did a trans fluid change with the ZFdoc BMW 10w-60 as well as replace the clutch master and slave cylinder so as far as I know I have done all that I can do with the clutch hydraulics.
When replacing the trans fluid, I noticed that there were some brass metallic specs in the oil. I am led to believe these are pieces of syncros. Has anyone else seen something like this when replacing trans fluid with bad syncros?
When replacing the trans fluid, I noticed that there were some brass metallic specs in the oil. I am led to believe these are pieces of syncros. Has anyone else seen something like this when replacing trans fluid with bad syncros?
Pro
Joined: Oct 2003
Posts: 550
Likes: 0
From: Hesperia California
About ten years back, my son took out the syncros in 1st and 2nd in my 89. I then pulled my engine and trans for a rebuilt of both. I live on the West coast and everyone said that zf doc in Arizona was about the only way to go for a rebuild. I did not want to go through the trouble of shipping the trans. I talked to a local very reputable trans shop that I have dealt with for a long time. They said that their standard trans guy was very familiar with zf. Ford trucks have been using them for years. I was told that the zf was a good trans. A little noisy and very pricey to rebuild. That was almost ten years ago and the trans shifts like new still. Look around for a good shop.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Intermediate
Joined: Jan 2014
Posts: 47
Likes: 0
I've got a factory brand new ZF6 for sale I'd make you a deal on if you're interested in just swapping your tired one out for a new one, instead of going the expensive rebuild route. I'll ship it free if it'll help.. I was going to install it into my '95 if/when it ever needed it, but as I get older, my ambition to tackle the job is waning... 
PM if interested.
-J
PM if interested.
-J
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
Working with Bill, ZFdoc, now, as I get ready to convert to a ZF6-40. He says the synchros are the weak part of the unit and that the best way to kill the ZF is to not have a perfect clutch. If bleeding fixes it; superb, but don't delay getting it up to snuff.
Parts are high; any foreign parts are + not all shops will tackle the ZF.
Parts are high; any foreign parts are + not all shops will tackle the ZF.
Race Director
Joined: Sep 2001
Posts: 14,678
Likes: 751
From: NEwhere Ohio
I did a trans fluid change with the ZFdoc BMW 10w-60 as well as replace the clutch master and slave cylinder so as far as I know I have done all that I can do with the clutch hydraulics.
When replacing the trans fluid, I noticed that there were some brass metallic specs in the oil. I am led to believe these are pieces of syncros. Has anyone else seen something like this when replacing trans fluid with bad syncros?
When replacing the trans fluid, I noticed that there were some brass metallic specs in the oil. I am led to believe these are pieces of syncros. Has anyone else seen something like this when replacing trans fluid with bad syncros?
Im sorry, but i dont agree with bill b about that being acceptable or desireable for the zf6.
I had so much problems with the synchros, under wot, that the shift lever physically would not move into the next gear.
When i went to change that crap out, there was all kinds of bronze glitter in my fluid. (when changing the correct fluid out, the old fluid is virtually clear)
Bill (who has been very helpful to me except for this case) told me to check clutch hydraulics and if those were good then i need to get the zf6 rebuilt at a cost of thousands)
The solution was simply replace the bmw castrol 10w_60 crap with gm syncromesh which is what gm recommends for zf6.
Once i did this, the grinded shifts went away. And also as i mentioned, trans oil changes were clear, free from bronze specs, when the correct stuff is used.
There has been some dumb advice on this forum, and putting bmw motor oil in your zf6 ranks near the top
Pro
Joined: Aug 2007
Posts: 668
Likes: 38
From: Austin TX
This seems to be a heavily debated topic. I am currently running Amsoil Synchromesh. I am not very happy with the product. It works fine in the cold weather. But in the warm weather, it works fine until the fluids get hot. Then I get grinding going from first to second. I am checking this post to see if there are any updates on recommendations. I did a search on Rockland Standard Gear and they recommend GM 1062931 and Castrol RS only. It looks like the ZF Doc is being vague on recommendations at the moment.
Dizwiz.. What GM part number Synchromesh are you using?
Dizwiz.. What GM part number Synchromesh are you using?
Last edited by mixalive; Feb 13, 2014 at 11:45 AM.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
In my case, it wasnt the synchros Or hydraulics that was the problem, it was using the bmw 10w-60 crap instead of the fluid that the factory says should be in there.
Im sorry, but i dont agree with bill b about that being acceptable or desireable for the zf6.
I had so much problems with the synchros, under wot, that the shift lever physically would not move into the next gear.
When i went to change that crap out, there was all kinds of bronze glitter in my fluid. (when changing the correct fluid out, the old fluid is virtually clear)
Bill (who has been very helpful to me except for this case) told me to check clutch hydraulics and if those were good then i need to get the zf6 rebuilt at a cost of thousands)
The solution was simply replace the bmw castrol 10w_60 crap with gm syncromesh which is what gm recommends for zf6.
Once i did this, the grinded shifts went away. And also as i mentioned, trans oil changes were clear, free from bronze specs, when the correct stuff is used.
There has been some dumb advice on this forum, and putting bmw motor oil in your zf6 ranks near the top
Im sorry, but i dont agree with bill b about that being acceptable or desireable for the zf6.
I had so much problems with the synchros, under wot, that the shift lever physically would not move into the next gear.
When i went to change that crap out, there was all kinds of bronze glitter in my fluid. (when changing the correct fluid out, the old fluid is virtually clear)
Bill (who has been very helpful to me except for this case) told me to check clutch hydraulics and if those were good then i need to get the zf6 rebuilt at a cost of thousands)
The solution was simply replace the bmw castrol 10w_60 crap with gm syncromesh which is what gm recommends for zf6.
Once i did this, the grinded shifts went away. And also as i mentioned, trans oil changes were clear, free from bronze specs, when the correct stuff is used.
There has been some dumb advice on this forum, and putting bmw motor oil in your zf6 ranks near the top
Instructor
Joined: Jan 2014
Posts: 213
Likes: 4
From: San Francisco California
Oftentimes it is the simplest of things that cause us grief so always good to start with the basics...have you rechecked your clutch fluid level recently? That one, low clutch fluid level, gets even the best of us sometimes. On mine, I had to slide the ECM over to get at it and the cap was a real bear to get off with quite a bit of concern that it might snap the brittle plastic neck below, but once I did, that did the trick for me.
Pro
Joined: Aug 2007
Posts: 668
Likes: 38
From: Austin TX
Oftentimes it is the simplest of things that cause us grief so always good to start with the basics...have you rechecked your clutch fluid level recently? That one, low clutch fluid level, gets even the best of us sometimes. On mine, I had to slide the ECM over to get at it and the cap was a real bear to get off with quite a bit of concern that it might snap the brittle plastic neck below, but once I did, that did the trick for me.
Last edited by mixalive; Feb 14, 2014 at 10:26 AM.
Thread Starter
Advanced
Joined: May 2012
Posts: 51
Likes: 0
Does anyone have a part # for the GM Syncromesh trans fluid? Seems like GM makes 2 types.
I had pretty much given up on the trans but I figured it would be worth it to try to remove my BMW 10w-60 fluid (which obviously had mixed reviews) before I go through the expense of replacing the trans all together.
I had pretty much given up on the trans but I figured it would be worth it to try to remove my BMW 10w-60 fluid (which obviously had mixed reviews) before I go through the expense of replacing the trans all together.
Team Owner
Joined: Feb 2006
Posts: 23,198
Likes: 117
From: San Antonio Texas
When I drained the BMW 60 weight muck out of my balky ZF6, a lot of brass sparkle came out. AmsOil made it shift like butter. It contains an additive to treat brass synchros so the dont wear so much. I've done road racing and long distance travel too so I change it yearly and have had nothing but praise for the product.😍
Thread Starter
Advanced
Joined: May 2012
Posts: 51
Likes: 0
Hmmm that's interesting. I have been flip flopping on either getting the GM Syncromesh or the Penzoil Syncromesh (which seemed to be the same thing just cheaper). I still haven't fully diagnosed my issue but I'm wondering if I put this Amsoil product in my car, if I will still getting the slight grind on 2nd gear?? I don't know at what point the syncros get to the "point of no return".
Instructor
Joined: Sep 2012
Posts: 125
Likes: 5
I'm not sure if this is true or not but I have been told that GM oil is the exact same as penzoil syncromesh . I am finishing up my Zf swap into my 93 this weekend from the 700r4 and plan on using the penzoil lube.I will post updates on how it feels when I take it for its maiden voyage