1985 Corvette

Well I didn't think it was possible but I got another problem with my recent new stroker ZF six speed combo. Engine runs just fine but the clutch when pushed in some bogs down the engine at idle. If I push it in all the way the engine drops down to 400 rpm and tries to die if I don't let off it. Didn't dare try a gear with this problem. Caged roller bearing in crank, new clutch slave and master with brand new SPEC stage 3+ clutch kit. Almost ready to throw in the towel on all this. One thing after another...

don hall

Sounds like you installed the mods, so my suggestion to ask the installer for help is worthless.

crowz

This is reaching but Ive seen this with a bad ground harness that attaches to the motor. Pushing the clutch in caused the motor to bog or die completely. Again its a longshot but has happened before.

1985 Corvette

True, but hey, here's to increasing your post count on the forum.


I'll look into it to see where clutch neutral safety switch grounds out to, sure beats yanking parts out. I guess I'll try anything at this point but goddamn do I not want to pull that trans and clutch out. I'll recheck the clutch slave to see if it's properly torqued down.

Trans in car when I installed engine with clutch and bellhousing bolted on. Everything came together great. Bellhousing fully seated. Car starts with clutch pedal fully depressed but pressing it in while idling in neutral is almost like a kill switch if I try to press clutch pedal in again. Manual transmission indicated in the chip programming. Burned out on this car....

1985 Corvette

Okay this is reaching, but I received the clutch pedal assembly with an attached clutch neutral safety switch, which had cut wires but left about four inches off each one. Both wires are black, as are both wires from a donor dash harness I received to connect to the switch's plug. I installed quick disconnect male/female plugs on the wires just in case I had to switch them around if I didn't "wire" it back up correctly.

I always looked at the switch as it didn't matter which wire coming out of the switch went to which wire on the dash harness because it was closing a circuit to allow voltage to the starter but if I have the wires crossed, is it possible me pressing in the clutch with crossed wires on the neutral safety switch is creating a draw/drag on the electrical to bog down the motor? I know it's reaching but the thought crossed my mind. The gauge of wire on the neutral safety switch wiring is decent sized.

don hall

Post count is not important to me.... I erased about 2000 about 10 years ago in protest to posters getting the same count for posting an icon, compared to posters helping with a multi-paragraph solution.

chadk

throw-out bearing? Im just trying to think mechanically what would cause this. To prove your theory on electrical drain you could watch the voltage gauge on dash when depressing the clutch. Do you have a scan tool. Im guessing as well but with keys in run position and engine off I would press and release the clutch while watching the scan tool for any relays/solenoids/or whatever changing state. Maybe your clutch input is going to wrong input on computer. In return the computer is trying to compensate with fuel air mixture.

cv67

Youll never start the car in gear, bypass the switch

Does the car want to slip in gear Ok other than the rpm thing?

Dont give up on the car your way down the homestretch! I understand though after fooling with one taken apart for 10 yrs.
Hoping all is well so you dont have to pull your trans back out (I had to twice in the first 50 mi if that makes you feel any better)

Edit: have someone depress the clutch then watch the balancer see if it moves forward

ghoastrider1

Does it grind at all when trying to engage gears at an idle? Can you try an bypass the clutch relay? Man, don't give up. What happens when you try to start the car with it in gear but clutch pressed in?

1985 Corvette

Ron, good call on watching the balancer. I didn't get to that but I bypassed the clutch safety switch per your recommendation. Started in neutral and clutch pedal travel isn't a lot and the gear selection is nice and smooth. Maybe it was the switch? No rpm drop when I press the clutch down a few inches. However if I try to put the clutch pedal all the way to the floor it bogs. I wouldn't have to pedal to the floor to change gears but it still irks me it's doing this. Maybe some type of stop to put in place? I know stock vettes don't have this problem.



Hi Ghoast, it engages all gears very well with minimal pedal press down. No grinding it's buttery smooth. There's chatter on disengage of clutch in neutral but have been told it's perfectly normal for this type of clutch. Only issue I'm having now is if I try to put the pedal all the way to the floor, it bogs. Car moves with clutch engaged.

Little head scratcher but it's a bit of good news after yesterday. I talk a big game but I've cooled of since yesterday. You just hate to spend money like this on new parts for years and have to fight it every other step. Preaching to the choir. That's hotrodding.

cv67

Did you do a ZF conversion?

May wanna give ZFDoc a call tell him what parts you used bet he could tell you in a minute whats going on.

1985 Corvette

Yeah, ZF conversion. That doesn't sound like a bad idea.

chadk

I have never had one of these transmissions removed from car nor am I an expert or even a novice but I do remember changing a clutch in a car several years ago with a buddy. I remember something about installing the disk the correct way. Is there springs on the clutch disk? Could you have installed this backwards?

1985 Corvette

I'm no expert either but when the clutch was installed, I noticed SPEC had raised sprung hub side labeled to face the trans and the flat side to face the engine. That didnt seem to coincide with the deep dish recess in the flywheel but I tried it. Not even close to bolting together so I flipped it over so the raised hub fit in the flywheel recess and everything came together perfectly.

The clutch slave is a cast iron piece I actually found based off a recommendation from LD85 in one of his old posts. Maybe the pushrod or component as a whole is over extending.

chadk

Does anyone have a diagram of what he is talking about? Let me get this straight. The clutch disk had labels or markings on it to install "this side towards trams" and it wouldn't work so you disregarded this and flipped it over?

1985 Corvette

The flywheel is an aftermarket steel one piece unit with a deep dish recess in the center. It's the exact size for the raised sprung hub to rest inside. However, the raise sprung hub side had a "trans side" sticker on it, while the flat side had "Flywheel side". It didn't seem right but I attempted this way first and the pressure plate mating surface was a good 1-1/2'' away from the flywheel with me pressing firmly on it. Flipping the disc over so the raised sprung hub went inside the recess of the flywheel allowed the pressure plate to properly mate to the flywheel to be bolted up. I did a google search on the issue and apparently there have been a few clutch discs sent out with the stickers labeling which side went which way swapped. Email sent and voicemail left for ZF Doc. Guess we'll see what he has to say.

chadk

Oh. Ok. Not picking on you or anything like that. I have a zf as well and one day will be changing clutch. Im just trying to understand and help you as well. Maybe someone will post a diagram (at least for my understanding).

-=Jeff=-

So with the trans in neutral, no foot on clutch it idles fine, but when you push in the clutch with your foot the ides drops and it wants to die?

could you post some more info and pictures of what you used for the clutch and flywheel?

bjankuski

Sounds to me like the throughout bearing is bottoming out against something and putting pressure against the crankshaft which is putting pressure on the thrust bearing and bogging the engine down. I would study the clutch, throughout bearing, pressure plate, and flywheel that you used and make sure they are installed correctly and that they are the correct parts.

1985 Corvette

Code for the clutch kit is: SC423FZ Spec Stage 3+. Flywheel is steel unit: SC05S Your description is exactly what's happening. Maybe I'll try to grab some video this weekend. Again, two or three inches of travel and it allows for perfect gear selection....no grinding....nothing. Engagment of gear after release of pedal like normal. It's when I'm the last two or so inches away from fully "bottoming out" the pedal against the firewall is when I get the bogging of idle and eventual engine stall in process. ZF Doc warned against silent accelerated wear of synchros if the pedal was not fully going to the floor during gear shifts.

https://www.corvetteforum.com/forums...t-another.html

If you check that thread and scroll down to Armysnipe's pictures he posted, same setup I have, except mine is a blue pressue plate.



You may be right. There's a lot of noises going on from the engine, open trans tunnel due to install, to the chatter of the friction disc but I will keep a better ear out this next start. One thing I will say is the friction disc had stickers on it labeling which side faced which way. The raised sprung hub was labeled to face the transmission, with the flat side labeled to face the flywheel. I tried this arrangement but pressure plate would come nowhere near close to mating up to the flywheel.

The flywheel has a deep dish recess in it that looks made for the hub, so when I flipped it over it went together perfect and the pressure plate actually would mate to the flywheel to bolt together. I even have ZF Doc a little puzzled on this one. He suggested I have a helper press the pedal in while I watch the flywheel from underneath for any shift in movement noticeable by eyeballing it.

I'm praying I don't see it when I try it but we'll see. Clutch pedal feels great, I never feel any "feedback" or weird vibrations through it when pressing down. Third time is the charm for checking it this weekend guess.....