Grinding When Shifting

[jas280z]

Finishing a restoration on my '78 280z with a 3.9 R200 out of a 280zx and a stock 5 speed. Took it for the first drive today and experienced some trouble. After about a quarter mile I experienced a very slight grind upshifting into 2nd, which I attributed to poor clutch control on my part. Taking it out of the neighborhood onto a faster road I experienced a noticeable grind up shifting into 3rd, shifted slowly into 4th and got no grinding, and shifted normally into 5th when the **** hit the fan. MAJOR grinding, I instantly jumped on the clutch and threw it in neutral, kept grinding until the car slowed to about 20 mph, even with the tranny in neutral and the clutch fully depressed. For the record the tranny grinded slightly occasionally when shifting into rev, but never at any other time, 80k on it.

 

Strange thing was the grinding sounded like it was coming from the diff. The car was driven after the diff was swapped, and it wasn't touched during the restoration, so I don't think it was causing the problem. Also the fact that the grinding only came after a shift leads me to believe it isn't the diff, as if I correct, the differential spins at the same speed when you are travelling at X mph, no matter what gear you are in. The thought I have on how the diff would act up after a shift it from the increased load put on it when shifting from one gear to another. But for now I believe it was not the differential, and that the fact that the car has no interior minus seats and seatbelts causes the whole thing to be an echo chamber and it is quite hard to pinpoint where any specific sound is originating.

 

In my research of the problem I came across a few threads that said the throwout bearing could cause this problem. When I had the engine out I replaced the clutch and pressure plate, as well as had the flywheel resurfaced. The clutch I ordered was an OE style replacement. I replaced the pilot bushing, but the throwout bearing that came with the kit was a bit shorter than the one that was on the car, which I am fairly certain was the original. I put the one that was on the car back on, as I knew it worked with the old clutch.

 

Could my throwout bearing be causing this problem? Or could it be something as simple as the clutch travel needing to be adjusted? The fact that the grinding continued when the clutch pedal was fully depressed has me thinking it has to do with the clutch not engaging properly; either it is not being fully actuated, or the throwout bearing is not doing its job. Do my conclusions make sense, or is there something else I may be missing?

 

EDIT: I should add that limping home I was able to get going with minimal grinding, but by the time I traveled the mile or so back to my house the grinding was pretty bad in all gears at anything above idle.

Edited June 30, 2010 by jas280z

[Geking]

just checking, but you did put gear oil in the trans and diff?

[jas280z]

Yup, redline, has maybe 400 miles on it.

[jas280z]

After doing a bit more research on clutches at How Stuff Works, I think that the throwout bearing collar may not be my problem. The one I used, the original, was the longer of the two. My symptoms tell me that the clutch may not be being fully actuated. Using too long of a throwout bearing would cause the clutch to not come all the way back from actuation, using a collar that is too short would cause the clutch not to disengage the flywheel and cause grinding. So using the longer of the two would not cause this, it might cause slipping if too long, but not grinding. my symptoms seem to indicate that the slave cylinder is not going through its full range of motion. I am in the middle of replacing it, and will also adjust my clutch pedal travel to ensure full actuation. Do these conclusions make sense to you guys?

[hoov100]

Three things you replace while you are replacing the clutch. clutch M/C, clutch S/C and the throwout bearing. I would be looking to see how much travel the S/C has and making sure the clutch is completely disengaged when you press the pedal to the floor.

[NewZed]

After doing a bit more research on clutches at How Stuff Works, I think that the throwout bearing collar may not be my problem. The one I used, the original, was the longer of the two. My symptoms tell me that the clutch may not be being fully actuated. Using too long of a throwout bearing would cause the clutch to not come all the way back from actuation, using a collar that is too short would cause the clutch not to disengage the flywheel and cause grinding. So using the longer of the two would not cause this, it might cause slipping if too long, but not grinding. my symptoms seem to indicate that the slave cylinder is not going through its full range of motion. I am in the middle of replacing it, and will also adjust my clutch pedal travel to ensure full actuation. Do these conclusions make sense to you guys?

 

Poor clutch action should only cause grinding during shifting. One grind per shift, then no abnormal sounds.

 

You described constant grinding while in gear which sounds more like a bad bearing or something rubbing somewhere.

[jas280z]

If I am recalling correctly the grinding would occur after I put the car into gear, as I was releasing the clutch. Don't know if this helps, and I may be mistaken, it all happened very quickly. And the grinding at first only happened for about a second immediately following a shift, had me thinking syncro's possibly too (didn't think to double clutch, kinda wish I hand tried that), it wasn't until I shifted to 5th that the grinding stayed constant. Would a bad bearing start grinding off only when being shifted and the progressively get worse (obiously it is only going to get worse, but I am guessing maybe the increased load after being re-engaged after a shift might cause a bearing on the brink to grind then)?

[NewZed]

If I am recalling correctly the grinding would occur after I put the car into gear, as I was releasing the clutch. Don't know if this helps, and I may be mistaken, it all happened very quickly. And the grinding at first only happened for about a second immediately following a shift, had me thinking syncro's possibly too (didn't think to double clutch, kinda wish I hand tried that), it wasn't until I shifted to 5th that the grinding stayed constant. Would a bad bearing start grinding off only when being shifted and the progressively get worse (obiously it is only going to get worse, but I am guessing maybe the increased load after being re-engaged after a shift might cause a bearing on the brink to grind then)?

 

I am not a transmission expert but there are a few things you could do to separate whether it's transmission or clutch. If you can start the car while in neutral, pressing the clutch pedal in will push the throwout bearing against the diaphragm spring on the pressure plate. If the throwout bearing is bad it will grind then, whether you are in gear or not (assuming the clutch linkage and hydraulics are working correctly).

 

If it stays quiet then try to put it in to gear. If it goes in to gear, especially reverse, without grinding then the clutch is disengaging sufficiently to take the load off of the transmission main shaft. You should be able to sit there with the clutch pedal in, car in gear, and hear no strange noises. If so then clutch is disengaging correctly.

 

Put it in first gear and slowly release the clutch pedal. This will engage the clutch and put engine load on the mainshaft. If the problems are in the transmission or differential, this is (most likely) when you will start to hear the bad noises, as you start moving. Just putt around in first gear and listen.

 

Just a few ideas on isolating the noise to one component. Before you start changing parts out.

[jas280z]

Thanks for the procedure, I will most likely try this once I change the slave. I was already planning on changing it so I had it on hand and that is my first course of action. I really hope it is just a problem with the clutch engaging via pedal or slave, I really don't want to have to pull the transmission right after installing the engine, and then of course I would have to find a replacement before July 11th when I plan on taking it for a few laps of Watkins Glen, or else I'm going around the track in a Jeep Liberty.

 

Just a thought, could this possibly be a wheel bearing? I have never actually heard one go bad, but I understand that they grind. The sound did sound as if it was coming more from the rear end and I am fairly certain it is not the differential. Although I will look into the diff as well to rule it out.

Edited June 30, 2010 by jas280z

[jas280z]

Solved!

 

Turns out that the prop shaft is hitting the rear sway bar under acceleration, I am thinking it may have to do with the car squatting under acceleration. I am probably going to replace the diff mount at well as possibly fabricating up a spacer to put under the diff mount to raise it 3/8 of an inch or so.

[NewZed]

If things are that loose you should check your moustache bar bushings and the nuts holding the housing to the bar also. To get that much movement from just a bad front diff mount would be unusual, I believe.

 

I have an essentially stock 76 and with a pretty bad diff mount all I got was a bad clunk. Not even a hint of grinding under hard acceleration.

 

And you should consider the RTz style diff mount. It is an improvement over stock, for about the same or less money.

[jas280z]

I have new mustache bar bushings with the master kit I got from MSA, just need to install them. I'll look into the RTz mount, but for now I REALLY just want to get on the road, been working on this car for about 10 months and I need to remind myself why I am doing all this work .