Hi, I have a 88 Z51 with 65k miles in otherwise near mint condition, and it grinds going into reverse unless I wait 10 or so seconds. Lately, it sounds like some of the gears are grinding extremely bad. Sometimes I have to shut off the motor to get it to quit grinding. Sounds like plates are slipping badly. Don't know much about history as I've only had it for 2 years so I don't know if the od has been cared for every 10k miles as recommended, or if ever. Anyways, with all the problems with these pos dn 4 + 3 trannies, I'm thinking not to spend the money having it overhauled, and instead putting that money towards a quality 6 speed. I don't race or need a high performance tranny, just one that works. What 6 speed tranny would you advise, what all is needed, and approximately what kind of money would it take?
Help! replacing Doug Nash 4 + 3 with 6 sp
- Thread starter BlueZ51
- Start date
- Thread starter
- #2
Thank you very much vetteoz. That's a lot of useful info with investigating my options. Ultimately, I'm going to have to take my Vette to a pro to have this done and everything I learn on this site will help me know and understand the best options. My Vette is still driveable, but it seems the tranny problems start after it's warmed up. Does anyone out there know of a tranny pro in the Minneapolis/St Paul area with experience with these 4 + 3 who can diagnose the problem and advise options? Anybody know what kind of total money for parts & labor it would take to swap out the 4 + 3 for either a new or rebuilt 6 speed? I don't want to risk having a used one put in. Any advice will be appreciated.
xfirez51
Well-known member
I did this swap on my 84 Z51. Completely changed the car IMO. Loved it. It's a bit involved and I can't imagine what the cost would be if I hadn't done it myself. Mainly it's parts swapping
except for cutting the tunnel and grafting the ZF tunnel piece on. Just a little glass work.
You'll need ZF yoke and drive shaft. Later I installed a D44. The ZF is quite a bit heavier than
the Nash unit which I think lowers the center of gravity and gives it a more planted feel IMO.
I also installed a Fidanza flywheel. BTW, make sure the ZF is for an L98 car and not ZR-1.
ZR-1 has longer input shaft.
except for cutting the tunnel and grafting the ZF tunnel piece on. Just a little glass work.
You'll need ZF yoke and drive shaft. Later I installed a D44. The ZF is quite a bit heavier than
the Nash unit which I think lowers the center of gravity and gives it a more planted feel IMO.
I also installed a Fidanza flywheel. BTW, make sure the ZF is for an L98 car and not ZR-1.
ZR-1 has longer input shaft.
John Robinson
Gone but not forgotten
To go along with vetteoz. When you try to shift do you push the clutch pedal all the way to the floor? Like most clutches you probably push it down tell you feel the clutch disengage which is the normal way to use a clutch. You might try to push it all the way to the floor the next time you want to shift into reverse and see if that makes any difference. If it does then it is a pretty good chance the clutch is either out of adjustment for the engage point or it is worn out.
Hib Halverson
Technical Writer for Internet & Print Media
I agree with "vetteoz" and "John Robinson"....I'd verify your clutch and the clutch hydraulics are operating properly before I'd go buy a new trans.
If you do find the transmission is the problem, not only is the ZF S6-40 upgrade a choice, but Richmond Gear makes a bolt-in kit which adapts one of its "ROD" six-speeds to the 84-88 Corvette. One good thing about the Richmond Gear conversion is you don't have to change the axle ratio.
If you do find the transmission is the problem, not only is the ZF S6-40 upgrade a choice, but Richmond Gear makes a bolt-in kit which adapts one of its "ROD" six-speeds to the 84-88 Corvette. One good thing about the Richmond Gear conversion is you don't have to change the axle ratio.
xfirez51
Well-known member
BTW, when was the last time you either checked or changed your clutch fluid? If its black, change it. If it gets black again quickly, cylinder seals may be bad so you may want to replace the master and slave cylinder. I that doesn't do it, then it may be time for a clutch.
One other thing to consider. The clutch pedal will bend and straighten over time. If the clutch pedal is not resting somewhat forward of the brake pedal, the pedal may be bent which shortens up the travel and does not the clutch to fully disengage. If you need to push clutch pedal completely to the floor, this may be the cause. You should feel clutch resistance beginning near top of stroke not half way down.
douglas foster
Well-known member
- Joined
- Aug 18, 2005
- Messages
- 226
- Location
- minnesota usa
- Corvette
- 1984 C4 Gold coupe, Z51, 4+3 manual, BBS rims,
- Thread starter
- #8
Grinding only starts at 185 degrees and above
Hello, I'm still saving up to do this right. I have 2 additional things to add which may give better hints about what's wrong. First, and weirdly, the gear grinding only starts after the coolant temp reaches 185 degrees. Why would gear grinding only start after this particular temp? Also, and this may be unrelated, I have to wait about 10 seconds to shift into reverse or else it grinds, although a totally different grind than the sound described above. Is it normal for a 1988 Corvette to grind when shifting to reverse?
Hello, I'm still saving up to do this right. I have 2 additional things to add which may give better hints about what's wrong. First, and weirdly, the gear grinding only starts after the coolant temp reaches 185 degrees. Why would gear grinding only start after this particular temp? Also, and this may be unrelated, I have to wait about 10 seconds to shift into reverse or else it grinds, although a totally different grind than the sound described above. Is it normal for a 1988 Corvette to grind when shifting to reverse?
boomdriver
Well-known member
Remember...the trans is as cold as anything and thicker grease cushions loose parts better....once warm it thins and the excessive play becomes more obvious.
Sounds like a clutch not completely disengaging and a worn syncro. The syncros are what allow a shift from any gear to any gear without the growling and grinding as they make certain that all the gears are turning at the same speed...syncronized. Timed, in other words. When you find one that grinds thats eventually going to wear out the mating surface that has a very nice sharp edge normally...until it gets rounded off grinding. Then, no gear at all.
Sounds like a clutch not completely disengaging and a worn syncro. The syncros are what allow a shift from any gear to any gear without the growling and grinding as they make certain that all the gears are turning at the same speed...syncronized. Timed, in other words. When you find one that grinds thats eventually going to wear out the mating surface that has a very nice sharp edge normally...until it gets rounded off grinding. Then, no gear at all.
Hib Halverson
Technical Writer for Internet & Print Media
This is unlikely a synchro problem because the trans grinds going into reverse and, the gearbox section of the Doug Nash has no synchronizer for reverse. That also is why, if the trans is going to grind, it does so in reverse.
Is the trans hard to shift into first when sitting at a stop light.
What kind of lubricant is in the trans?
I still think this is a clutch problem. Either the clutch itself is faulty and dragging or the clutch hydraulics are faulty.
As for the problem occurring mostly when the powertrain warms up, I can only guess:
1) Clutch disc expands slightly
2) Clutch hydrauilc lines running too close to exhaust such that heat affects fluid.
I would start by changing the clutch fluid then bleeding the clutch hydraulics per the service manual.
Is the trans hard to shift into first when sitting at a stop light.
What kind of lubricant is in the trans?
I still think this is a clutch problem. Either the clutch itself is faulty and dragging or the clutch hydraulics are faulty.
As for the problem occurring mostly when the powertrain warms up, I can only guess:
1) Clutch disc expands slightly
2) Clutch hydrauilc lines running too close to exhaust such that heat affects fluid.
I would start by changing the clutch fluid then bleeding the clutch hydraulics per the service manual.
- Thread starter
- #11
Resolution: new little balls!
I took my Vette to the local Chevy dealer and paid just $10 per hour more than other local tranny shops and it turned out to be good. It seemed to me that a very qualified & professional mechanic with many years of real experience worked on my beloved Vette and he found the problem was a failed pilot bearing, so he replaced the pilot bearing and the throwout bearing and resurfaced the flywheel. He also flushed & filled the transmission (both the main box & the overdrive box). He said the performance clutch was in near new condition (I found in the file that this was done in a performance shop about 10k miles ago by the previous owner - which changes my earlier story of it being the original clutch. Too bad they didn't notice the worn bearings at that time). The mechanic said the tranny worked perfectly. The pilot & throwout bearings cost under $100 but there was a lot of labor costs of course - but I'm convinced the true problem was honestly fixed. Just thought I would let you all know about the this in case it helps somebody.
I took my Vette to the local Chevy dealer and paid just $10 per hour more than other local tranny shops and it turned out to be good. It seemed to me that a very qualified & professional mechanic with many years of real experience worked on my beloved Vette and he found the problem was a failed pilot bearing, so he replaced the pilot bearing and the throwout bearing and resurfaced the flywheel. He also flushed & filled the transmission (both the main box & the overdrive box). He said the performance clutch was in near new condition (I found in the file that this was done in a performance shop about 10k miles ago by the previous owner - which changes my earlier story of it being the original clutch. Too bad they didn't notice the worn bearings at that time). The mechanic said the tranny worked perfectly. The pilot & throwout bearings cost under $100 but there was a lot of labor costs of course - but I'm convinced the true problem was honestly fixed. Just thought I would let you all know about the this in case it helps somebody.
Hib Halverson
Technical Writer for Internet & Print Media
Boy...was I off on this one.
I kept thinking it was the clutch, but never considered a faulty pilot bushing. The old pilot must have been really bad to make that much noise.
Even those of us who know a little about cars need to be reminded occasionally how easy it can be to diagnose something wrong when trying to do it by Internet.
I kept thinking it was the clutch, but never considered a faulty pilot bushing. The old pilot must have been really bad to make that much noise.
Even those of us who know a little about cars need to be reminded occasionally how easy it can be to diagnose something wrong when trying to do it by Internet.
John Robinson
Gone but not forgotten
What is missing by Internet is the smell, the sound , The feel of the engine running.
I had a miss with my vette and one day I was driving by my neighbors house and he stopped me and told me he could hear a high voltage snap when I went by. Since he was a builder of Hot Rods. I felt he might know something so I changed my search from the ECM Opti mentality and looked and found I had a spark plug with a cracked porcelan that was jumping to ground. Then I fired it up in a very dark spot and was able to see the spark jumping from the wires to the closest ground. Off came those new wires and back to the parts store for another set. So yes Hib it is hard sometimes to get the correct diagnosis without the hands on see it smell it feel it factor. If I had not been told about the hgh votage snapping (which I could not hear inside the car) and he could hear when I drove by I might still be looking for that miss. But at least the advice is free and the op can pick and chose what to accept at no cost. What the Internet does do is give someone a broader look at their problem .
G Winter
Well-known member
If the pilot bearing was a needle bearing style and it started to come apart it could bind on the shaft and spin the trans with the clutch disengaged.
I will share an experience with my 90 clutch. For those that don't know it has the ZF 6 speed. The flywheel failed and I replaced everything to do
with the clutch. With the OEM kit a new bronze pilot bushing was included. Not having installed a clutch for a very many yrs I put grease on the pilot
bushing and the input shaft like we always did in the old school. Turned out to be the wrong thing to do. About 2000 miles later when pulling into the
drive downshifted to first and had the a grinding sound like a bad bearing in the transmission. Nobody seemed to know what the problem was so I
called the ZF Doc. A great guy would love to meet him. He told me it could be the shaft in the reverse /first gear idler. Was able to check this by
removing the complete exhaust and the cover plate. Everything looked ok. Another phone call. In the conversation I mentioned having installed a
new clutch. He was quite a moment and asked it a bronze pilot bushing was installed. Then asked if I had put grease on it. Turns out that is a no
no . He said the grease glazes and seals up the internally lubricated bushing, causing it to wear. The ZF is so sensitive to this it causes it to
make all kinds of noises. I replaced the bushing with a bearing and have had no farther problems.
I shared this in hopes someone else don't make the same mistake.No matte how experienced we are, things slip past us, or in my case just make a
stupid mistake.
Glenn
I will share an experience with my 90 clutch. For those that don't know it has the ZF 6 speed. The flywheel failed and I replaced everything to do
with the clutch. With the OEM kit a new bronze pilot bushing was included. Not having installed a clutch for a very many yrs I put grease on the pilot
bushing and the input shaft like we always did in the old school. Turned out to be the wrong thing to do. About 2000 miles later when pulling into the
drive downshifted to first and had the a grinding sound like a bad bearing in the transmission. Nobody seemed to know what the problem was so I
called the ZF Doc. A great guy would love to meet him. He told me it could be the shaft in the reverse /first gear idler. Was able to check this by
removing the complete exhaust and the cover plate. Everything looked ok. Another phone call. In the conversation I mentioned having installed a
new clutch. He was quite a moment and asked it a bronze pilot bushing was installed. Then asked if I had put grease on it. Turns out that is a no
no . He said the grease glazes and seals up the internally lubricated bushing, causing it to wear. The ZF is so sensitive to this it causes it to
make all kinds of noises. I replaced the bushing with a bearing and have had no farther problems.
I shared this in hopes someone else don't make the same mistake.No matte how experienced we are, things slip past us, or in my case just make a
stupid mistake.
Glenn
Hib Halverson
Technical Writer for Internet & Print Media
The "ZFDoc" is Bill Boudreau, a pal of mine from way back. He got started doing ZFs for the ZR-1 folks a number of years ago and has expanded that in to a very successful business. With the ZF S6-40 going out of producction in 96, there are fewer and fewer folks who really understand that transmission.
Bill is one of them.
Bill is one of them.
- Joined
- Jun 13, 2010
- Messages
- 234
- Location
- Surprise, AZ
- Corvette
- 87 Callaway Cpe 87-070 & 68 Cpe 427, 4spd A/C
WhalePirot
Well-known member
4+3 is just fine
Another lesson here, is the DN 4+3 works fine, IF understood and maintained. The logic is complicated and differs in the '84 from the others, tho many have altered the wiring to a simple On/OFF, bypassing the Open/Closed loop aspect and the rest of the logic of the ECM.
I had mine rebuilt in Boca many years ago and it works just fine, even with all the power I thrust through it; just as Paul at 5-speeds promised. I have more worries about the T10, super or not
and the cryo-hardened Dana 36.
Glad 2C the OP is smiling again.
Another lesson here, is the DN 4+3 works fine, IF understood and maintained. The logic is complicated and differs in the '84 from the others, tho many have altered the wiring to a simple On/OFF, bypassing the Open/Closed loop aspect and the rest of the logic of the ECM.
I had mine rebuilt in Boca many years ago and it works just fine, even with all the power I thrust through it; just as Paul at 5-speeds promised. I have more worries about the T10, super or not
and the cryo-hardened Dana 36.Glad 2C the OP is smiling again.
Similar threads
Corvette Forums
Supporting Vendors
Dealers:
