96 LT4 6spd
12-25-2017, 02:43 PM
#1
96 LT4 6spd
Ok. So when under heavy acceleration, the 1 to 2 shift always has gear buzz. 2 to 3 is smooth and so on. So i made sure the clutch was pinned to the floor. Still, gear buzz. So then i jammed clutch in, paused, then shifted. BUZZ.
This never hapoens under normal driving. But if you wind the 1st gear all the way up, it happens. I also noticed that when moving into reverse, there is sometimes a false lock in resulting in gear buzz until you actually get her locked into reverse.
Anyone have any clues?
This never hapoens under normal driving. But if you wind the 1st gear all the way up, it happens. I also noticed that when moving into reverse, there is sometimes a false lock in resulting in gear buzz until you actually get her locked into reverse.
Anyone have any clues?
12-25-2017, 03:32 PM
#2
Race Director
You need thicker countershaft shim washer (from zfdoc).
this is a well known problem not specific to zf.
factory dual mass flywheel did a better job dampening the noise vs aftermarket single mass flywheels.
but to me, the factory dual mass flywheel is a boat anchor its so heavy.
You need to remove transmission to do this, so its prob also good time to replace clutch and engine rear main seal (if leaking).
Be sure to use a sprung hub clutch if going away from heavy dual mass flywheel or else you will have a lot of noise
good luck !
this is a well known problem not specific to zf.
factory dual mass flywheel did a better job dampening the noise vs aftermarket single mass flywheels.
but to me, the factory dual mass flywheel is a boat anchor its so heavy.
You need to remove transmission to do this, so its prob also good time to replace clutch and engine rear main seal (if leaking).
Be sure to use a sprung hub clutch if going away from heavy dual mass flywheel or else you will have a lot of noise
good luck !
12-25-2017, 10:00 PM
#3
The noise is as if you do not have the clutch in at all. You can feel the gears not meshing in the gear shifter.
This is even though you have the clutch pedal pinned to the floor. Now, if you really hesitate and let trans speed or engine rpm drop, bingo, no grinding (gear buzz) and a smooth shift.
So if this is normal, this gear box is not capable of the all important high rpm1 to 2 shift. That rules out drag racing for sure.
This is even though you have the clutch pedal pinned to the floor. Now, if you really hesitate and let trans speed or engine rpm drop, bingo, no grinding (gear buzz) and a smooth shift.
So if this is normal, this gear box is not capable of the all important high rpm1 to 2 shift. That rules out drag racing for sure.
Last edited by MikieG1971; 12-25-2017 at 10:01 PM. Reason: Spelling
12-25-2017, 11:06 PM
#4
Le Mans Master
The issue of sometimes not fully engaging Reverse is normal, and not just for a ZF6. Just move it back to the neutral gate and try Reverse again. No worries.
The problem between 1st and 2nd is not normal, and does not sound like the normal chatter in neutral caused by the countershaft shim clearance. If I'm understanding your description correctly, it sounds like a failing synchro to me. You can try double clutch: after leaving 1st, with the lever in Neutral and engine revs rapidly falling, let the clutch out in Neutral for a moment; then push the clutch in again and move the lever to 2nd. That should rapidly allow the countershaft to match speed with 2nd gear. But if that helps, it means your 2nd-gear synchro is suspect. This does not seem to be a common issue for these transmissions, but synchros are wear items, so it isn't impossible.
The problem between 1st and 2nd is not normal, and does not sound like the normal chatter in neutral caused by the countershaft shim clearance. If I'm understanding your description correctly, it sounds like a failing synchro to me. You can try double clutch: after leaving 1st, with the lever in Neutral and engine revs rapidly falling, let the clutch out in Neutral for a moment; then push the clutch in again and move the lever to 2nd. That should rapidly allow the countershaft to match speed with 2nd gear. But if that helps, it means your 2nd-gear synchro is suspect. This does not seem to be a common issue for these transmissions, but synchros are wear items, so it isn't impossible.
12-25-2017, 11:10 PM
#5
I have strong suspicions you are right. So now i am wondering how much $$ this repair is.
Also, at 21 years, is it not wiser for complete tranny rebuild and what will that likely cost?
Also, at 21 years, is it not wiser for complete tranny rebuild and what will that likely cost?
12-25-2017, 11:14 PM
#6
Le Mans Master
I don't know, but it won't be cheap to have someone else do it. I also have never done this work myself, so I can't advise you there either. I'd ask ZF Doc. My concern wouldn't be the age as much as the mileage on your tranny, along with wondering what really caused ihat one synchro to crap out. These trannies are not known for high failure rates, so this problem would concern me.
12-25-2017, 11:18 PM
#7
Prepare for 2,500 or more. If you are going on, you are going to want to rebuild the entire thing. It will be a minimum of 2k just to fix your issue without addressing additional problems in the rest of the box.
12-26-2017, 10:13 AM
#11
Le Mans Master
Before pulling the trans and going nuclear on it with a rebuild, it would be a very good idea to drain the fluid and refill with a good fluid (there are several good threads here about which fluids work well). That alone can help a worn synchro work a lot better. Id oubt your clutch hydraulics are the problem, since all the other gears appear to work normally. But just in case, make sure your clutch master cylinder is full with clean fluid. IOW, start with the basics and then reassess that 1-2 shift. If it's still a problem, then it's time to start thinking about going inside the transmission.
PS - I forgot to mention above that the reason the Reverse gear is different is that it isn't synchromeshed. It is intentionally unsynchromeshed in order to make it difficult to engage accidentally while moving forward.
PS - I forgot to mention above that the reason the Reverse gear is different is that it isn't synchromeshed. It is intentionally unsynchromeshed in order to make it difficult to engage accidentally while moving forward.
12-26-2017, 11:08 AM
#12
Race Director
Before pulling the trans and going nuclear on it with a rebuild, it would be a very good idea to drain the fluid and refill with a good fluid (there are several good threads here about which fluids work well). That alone can help a worn synchro work a lot better. Id oubt your clutch hydraulics are the problem, since all the other gears appear to work normally. But just in case, make sure your clutch master cylinder is full with clean fluid. IOW, start with the basics and then reassess that 1-2 shift. If it's still a problem, then it's time to start thinking about going inside the transmission.
PS - I forgot to mention above that the reason the Reverse gear is different is that it isn't synchromeshed. It is intentionally unsynchromeshed in order to make it difficult to engage accidentally while moving forward.
PS - I forgot to mention above that the reason the Reverse gear is different is that it isn't synchromeshed. It is intentionally unsynchromeshed in order to make it difficult to engage accidentally while moving forward.
This is why im asking if the car is new to him.If some dummy took stupid advice to put in bmw castrol 10w-60 engine oil into their transmission - the result could be what is being experienced here
12-26-2017, 09:22 PM
#13
Pro
I know I'm late to this party but, I agree that a ZF transmission with old or the wrong lube in it will not shift properly and trying a fresh fill before an expensive pull and rebuild is a good plan. My own '96 benefitted from a fluid change.
12-26-2017, 11:34 PM
#14
So the plan for tomorrow is as follows..
1 Oil change to Mobil 1
2 clutch solenoid flush
3 trans gearbox lube changed to Penzoil synchromesh synthetic
4 rear axle serviced with fresh synthetic with additive
5 realigned (cannot stand an uncentered steering wheel)
6 title and registration
Maybe even new keys.
Next events will be.
1 new wheels (ZR1 size)
2 new tires Goodyear Eagle F1 GS-D3
3 brake upgrade with system flush
4 power steering flush
1 Oil change to Mobil 1
2 clutch solenoid flush
3 trans gearbox lube changed to Penzoil synchromesh synthetic
4 rear axle serviced with fresh synthetic with additive
5 realigned (cannot stand an uncentered steering wheel)
6 title and registration
Maybe even new keys.
Next events will be.
1 new wheels (ZR1 size)
2 new tires Goodyear Eagle F1 GS-D3
3 brake upgrade with system flush
4 power steering flush
12-28-2017, 09:07 AM
#15
Got it all done. Even ordered new GM key sets!
But sadly. After driving the car the rest of the day, the 1 to 2 synchronizer is stil not working during high rpm driving.
But sadly. After driving the car the rest of the day, the 1 to 2 synchronizer is stil not working during high rpm driving.
12-28-2017, 09:51 AM
#16
Race Director
How much bronze flecks (the synchro material) did you see in the old fluid? A couple? Or did the old fluid look like metallic paint when it came out? (Full of sparkles).Also. You might want to check out the master and slave cylinder clutch hydraulics to make sure its not a clutch hydraulic issue1. Check clutch fluid level make sure its not low2. Id bleed them - the fluid will probably be black3. Id check to make sure these are oem parts and not the chinese cast universal slave cylinders that autozone and advance auto parts sell for the cars.Rule these out before saying you have a synchro problem !This is all Assuming you put the syncromesh fluid in the trans that you said.Again, there has been some bad advice that bmw motor castrol motor oil works well in the zf trans. (stemming from zfdocs outdated website - needs updated. Zfdoc usually has good advice. ) a lot of dummies over the years (including me) tried this with bad results and similar results to what you describe.
12-28-2017, 09:59 AM
#17
Clutch fluid was bkack. Flushed with new dot 4. The trans lube didnt really look that old. This is a red flag.
Clutch works perfectly. Its just, if i hold 1st gear under massive accelleration over say 20 mph, the shift will not be smooth. If i drive like a normal person, everything is smooth.
Who buys an LT4 6spd Corvette to drive it lika a Cavalier?
Clutch works perfectly. Its just, if i hold 1st gear under massive accelleration over say 20 mph, the shift will not be smooth. If i drive like a normal person, everything is smooth.
Who buys an LT4 6spd Corvette to drive it lika a Cavalier?
12-28-2017, 11:04 AM
#18
I would think the fact it's only doing it on the 1-2 shift is a clear sign of it being a mechanical issue and not a fluid issue. The fact the fluid didn't look that old might indicate the previous owner tried to solve the problem with fluid and when that didn't work being faced with a possibly expensive repair decided to sell.
12-28-2017, 03:29 PM
#20
Safety Car
I'm going to put this out there with the understanding I know nothing about it, don't know the seller or anything else on it.
I saw this on the local craigs list: https://minneapolis.craigslist.org/w...424370257.html
It doesn't list price or anything else. I do not know if it's complete or not or even if it's a legitimate ad. Just showing it as it might be of use to someone if it is real. I think it's been out there a while so who knows?
I saw this on the local craigs list: https://minneapolis.craigslist.org/w...424370257.html
It doesn't list price or anything else. I do not know if it's complete or not or even if it's a legitimate ad. Just showing it as it might be of use to someone if it is real. I think it's been out there a while so who knows?