Clutch draging issues Stock or Spec?

Before my headgaskets went my clutch started to drag a bit. Or, when I was stopped at a light with the tranny in gear it would creep forward if I took my foot off the brake. After thinking about it, I realized the most probable cause was the clutch disc was dragging against the flywheel. I didn't have this problem when the tranny was rebuilt last and the clutch replaced. That was over 3 years ago. The dragging clutch only developed over the last few months before the headgasket blew.

Might the dragging clutch have been caused by the clutch springs getting worn out?

Since the motor was out I took the opportunity to have the tranny rebuilt and toss in a new slave cylinder. But I am worried that the problem will remain.

The engine shop hasn't said anything about the flywheel being out of spec yet. I would like to save the 400 bucks and not have to buy an aluminum flywheel yet (next tranny rebuild). I am also not all that secure with the idea of shimming the slave cylinder or the flywheel to make up for the space.
But if it needs to be done which is better to shim, flywheel or slave cylinder?
How far can it safely/reliably be shimmed?

I bought a Spec Stage I clutch and want to use it with the stock flywheel. Anyone have the dragging clutch problem with the Spec Stage I clutch?

SPEC Stage III

I Love my Stage III & alum. flywheel. No sticking or dragging. It grabs like hell & doesn't slip at all.

The SPEC flywheel has a replaceable steel friction surface for the clutch. If it wears out, you just have the friction surface replaced.

68COUGAR

I have dissasembled a couple of clutches that had this problem.
A couple of pointers.
1) make sure that the hydraulics are in good condition and properly bled.
2) make sure that the input shaft on the tranny is properly shimmed. There should be only very slight play. If it wobbles it's too loose.
3) take a 1/2 hour and clean the splines of the input shaft. dirt/clutch dust gets beaten into the grooves of the splines until it is so hard it seems like metal. It's not. I use a couple of new razor blades and really scrape into it. The clutch disc should move freely the full length of the splines, usually it won't and there will be some binding at some point along the length of it.
4) Make sure the pilot bearing is in pristine condition. Replace if in doubt.

On our XR7 I measured the distance on my aluminum flywheel from the block mounting surface to the face of the friction surface. I discovered that it was about .100" short. I made a simple shim out of sheet metal to go behind the slave cyl. to compensate. There is no possible drawback or reliability issue in doing this. I can say that after performing the procedures listed above I have never had an issue with clutch drag again.

The Drag

Both of the stock SC's I've owned had this problem. Even after a stock clutch replacement. I just didn't know any better then to tinker with it.

When I put in my last clutch (a Stage II) I put in a Spec flywheel too. It was just a little too much, the clutch would not fully disengage, I had to deal with it. I bled it many times. All the stuff was new too.

Then I followed Mr XR7 Dave's advice with the slave shim and I could not be happier with the decision! Zero drawback. Now my clutch releases in the middle of travel. It has never slipped.

It would probably be a little easier to shim the flywheel, I just figured shiming the slave would be less intrusive.

I firmly believe my previous stock setups would have benefitted from a shim too. They were always down to the floor and never far enough.

Cheers
MB

XR7 Dave said:

On our XR7 I measured the distance on my aluminum flywheel from the block mounting surface to the face of the friction surface. I discovered that it was about .100" short. I made a simple shim out of sheet metal to go behind the slave cyl. to compensate. There is no possible drawback or reliability issue in doing this. I can say that after performing the procedures listed above I have never had an issue with clutch drag again. [/B]

Click to expand...

Dave, you wouldn't happen to know what the distance between the face of the flywheel and the crankshaft mount is supose to be?
My manual is currently at the engine builders shop and I'm at work.

On the shims, did you machine them to completely fit the bottom/mounting surface of the slave cyclinder?
Did you measure the slave cyclinder with the throwout bearing in place, if so what kind of numbers did you get?

When I measured the old slave/throwout I think I got about 0.040 taller than the new one.

No, I sure don't remember. I only did that on my aluminum flywheel because I wondered about the precision of the aftermarket part. I have not had problems with any stock flywheels. I would suggest that if the flywheel has been turned at all, shims be used to compensate.

On the slave shim I did not machine anything at all. It is not a high tech operation to shim the slave cylinder. I simply cut out the shim from a sheet of metal I got from Home Depot with a pair of tin snips. I just made a circle and drilled the necessary holes in it.

I also noticed that my aftermarket slave seemed to sit the TO bearing higher than the one I took out. I let it go that way because I wanted to raise the engagement point. It seems to have worked out fine.

Hey XR7 Dave do you have any pics of what you did ?? i had my clutch/pressure plate/ TO bearing replaced not too long ago, but i am having problems with the clutch, its hard to get it in first when its at a stand, and it wants to drag a bit. I have to sit at lights witht the clutch in 1st. i tried bleeging it and it doesn't do anything... i am tired of this... i get fustrated at times.... please help me.....

Well, short of pulling back apart and doing what I suggested, you have to understand what is happening that is causing the problem. Then you can try some "remedies" that will help you deal with it.

Picture this scenario. You are stopped, engine is running. The output shaft is connected to the wheels, so it is not turning. Now the input shaft has a lot of bearing surfaces with which to create friction as all the gears ride on the output shaft. In normal circumstances, this friction stops the input shaft from spinning when you have your foot on the clutch. Also realize that all forward gears are constantly meshed with one another, so if one turns, they all turn.

Now in the above setting, the output shaft is not turning, and to turn the gears (input shaft) against the friction of the bearings requires a certain amount of force. In the absence of clutch or pilot bearing drag, the friction between the gears and the output shaft will stop the input shaft from spinning. When all gears are stopped moving, it will theoretically be as easy to shift as it is when the motor is off. Obviously this is not happening in your case.

So what is happening is the input shaft is spinning and it shouldn't be. Now if you compare the friction surface area of a dragging clutch vrs the friction area of a blocker ring, it is easy to see that the blocker is going to lose.

Now if the clutch were engaged, certainly you wouldnt' be able to shift at all, but since it is only dragging, you are able to shift somewhat. Also realize that when the input shaft is released, (say you just pulled it out of gear) the input shaft only begins to accelerate. How quickly it accelerates depends on how badly your clutch drags. When shifting under these conditions, you must be careful or you will destroy your syncro rings.

If I have been able to paint a picture of what is going on in there, it remains only to find ways to minimize the problem. First of all, remember that when the car is in gear the input and output shafts are locked in a ratio that matches the gear ratio of the gear. Assuming 1st gear ratio of 3.75:1, you can see that there will never be more than that speed ratio differential for the syncro to overcome. Once you stop, and put the car into neutral that speed differential goes to 800:0. That is why it is much easier to shift into first before you stop. After you stop and let the dragging clutch accelerate the input shaft to motor speed it becomes almost impossible to shift. Higher gears will be easier to get into when idling in neutral because a) the ratio is more favorable and b) because the syncro's are typically in better shape.

So from a driving standpoint, make your shifts quickly, and don't sit with the car in neutral. If you do sit in neutral, then try 4th gear before first to stop the input shaft from spinning. Never force it into gear by putting extreme pressure on the shifter (I know it's tempting).

Now one other thing you can do to help overcome the dragging of the clutch is to run a heavier transmission fluid. By increasing the drag of the bearings, the transmission might be able to overcome the dragging clutch to a degree by itself. I have run as much as 85w140 gear oil in the transmission. It makes shifting a little stiff when cold but it works wonders when the tranny is warm.

That's about it I guess.

Thinking out loud, sorry for the long post

Looks like I have some driving habits to alter, I always jump straight into 1st after idling in neurtal. Until it was too late. Thanks Dave.

I was looking at the tranny input shaft, throwout bearing and slave cyclinder last night. It looks like the throwout bearing constantly rides against the clutch finger or springs due to the coil spring behind the throwout bearing over the slave cyclinder housing. Does this seem right you everyone?

I'm having a hard time picturing how the shim effects the release point. My thinking is that since the clutch is hydraulic it should adjust itself. Within reason.

What follows is a very long list of questions of me thinking out loud;
In trying not to get into a masters disertation on hydraulics I'd put it this way. The amount of movement in the slave cyclinder is in propotion to the slave cylinder area and the master cyclinder area. But there is a starting volume. When wear ocurrs on the throwout bearing surface or the fingers on the clutch start to sag, this wear isn't being compensated for somehow. But it should.
Maybe a non-true flywheel is causing the throwout bearing to wobble and push the cycliner back in the bore farther than it should? Does this sound far fetched?
Or for some other reason the slave cyclinder is being forced back farther than it should in the bore?

I would think that the throwout bearing and slave cyclinder should only be forced back as far as the clutch springs would push it. Does that seem right?
Or, when we release the clutch pedal is the master cyclinder pulling the slave cyclinder back in the bore, which I would think isn't the master cyclinders job???
So, do most of us have a combination of a bad slave cyclinder and a bad master cyclinder? God I hope not. Even with the engine out I don't want to even try and remove the master cyclinder.

Damn, this could drive someone nuts. oops, already did.

This is a simple hydraulic system, it shouldn't be this hard to figure out.

It's the spring!!!!!

I feel like an idiot. But The coil spring on the slave cyclinder determines the release position. How many of us replace or re-temper that spring when we do a clutch job, I know I usually don't.

The throwout bearing rides on the clutch springs. The clutch springs should be the only thing that pushes the slave cyclinder back in it's bore when we release the clutch. So how much spring constant you take away from the clutch springs with the slave cyclinder spring determines your release position, as felt though the pedal.

Dave's shim in essance increases the spring constant of that coil spring.

I think it might be possible that some of our dragging clutch problems are being caused by an old slave cyclinder coil spring.

I may re-temper that spring before the tranny goes back in and see what happens.

Could be that has an effect, but I did used a new slave/TO assembly on mine when I was having the worst trouble. On others I did not replace the slave or any part of it and everything works fine.

May I suggest that this thread be moved to the FAQ forum when it drops off the first page. Either that, or move it to one of the archive member forums. This is good information provided by Dave, and I think it should remain on record in an appropriate forum.

Nice work, Dave!

First off like to say that i agree with bill and that this is some nice work Dave, very informative. second, i have a question for you.
you say that all slaves (or flywheels) should be shimmed right, well do you recommend a 0.100" for all applications, or is that just a ballpark figure which should be fined tuned according to the application (ie. the amount of material removed from flywheel, brand of flywheel and such)
the reason i ask is that im having all these clutch problems and was recommended to install a slave shim. my flywheel has been resurfaced and right now it is 0.977" thick. i was told to install a 0.100" shim to bring my system up to par, but im not sure if that 0.100" would be overdoing it or not. since you seem to be the expert here on this topic, i thought you might have a little insight.
thanks Dave.

The shim I chose was based on the measurements of the aftermarket flywheel that I am using. I would recomend that the shim match the amount of material removed although I don't see a problem with using a larger shim than the material that you removed from the flywheel. Do you have the stock thickness specification? I can't seem to find it in my Helms.

The slave cylinder has a lot of available travel and it will self adjust in (it just doesn't seem to adjust out very well). You will need to open the bleeder port to get the motor and trans back together after shimming the slave.

David

spec stage 1

bought a Spec Stage I clutch and want to use it with the stock flywheel. Anyone have the dragging clutch problem with the Spec Stage I clutch?

just to put my 2 cents in, i have the spec stage 1, and it works great, no sippage or dragging, course i have yet to see how it does at the track. (putting a ramanned engine in, cracked head !)

ok guys,
i yanked my tranny, shimmed my slave 0.875", put it all back together and rebled the system and it shifted like a dream....for about 2 days.
now, its back to the same way it was. heres my symptoms:
1 it occassionally does not want to go into first (or any gear for that matter) from a stop, not always, but more often then not.
2 once im moving it shifts ok, but not great.
3 the clutch seems to be doing its job until i start moving VERY slow, then it grabs even when the clutch pedal is to the floor. (doesnt always do this, but more often then not). like if im rolling to a light with the clutch in, i can fell a slight "clunk" when it grabs and the clutch barely does its job.

what is going on here? why did it work perfect for 2 days and now it sucks again? anyone have any ideas, im starting to lose hope.

livn...

a clutch spring wasn't doing it's job...I had the same clutch dragging issue and only changed the clutch and the slave cylinder. Problem fixed, and as you already replaced the slave it really sounds like the clutch.

My clutch looked real good when I pulled it out, but apparently something was wrong with it (I assume one spring was dead).

BTW take XR7 Dave's advice and take a razor blade to the input shaft, clean out the splines, and repack the pilot bearing with grease, or replace it altogether.

I don't think my flywheel was ever resurfaced. I held a measure tape up to it (not too accurate) and it looked to be about 1", not much more if any. So I don't know if I hold with the whole shim theory, but it seems to work for some people. My car didn't need it though. Just my .02

Brian

Maybe ...

Maybe loose pressure plate bolts, the same symptom. It happened to me. I yanked it all back out and the pressure plate bolts had all backed off about 1/8 of an inch, it had become undrivable and it was getting worse.

I used loctite when I put it back together and made a slave shim too. It's been perfect since.

You may be able to determine if your pressure plate bolts have backed off by taking out the starter and getting a little mirror in there to make sure the pressure plate and flywheel are snug. I couldn't get a good enough look by just removing the inspection plug.

good luck
Bob

Could it be possible that the slave shim i used was too small and that the reason the car shifted great for those 2 days and crapppy after that is because my clutch is finally breaking in?
BlackSC and Bob, what your saying would make sense for what i was experiecing before the shim operation, but it doesnt explain the good shifting for the two days, then gradually getting worse. good shifting getting worse seems like a hydraulic leak somewhere, but then again if that were the case, id probably have no clutch pressure at all by now.
im thinkin that i need a even bigger shim. any thoughts?

livn,

Have you resolved this clutch dragging/hard to get in gear issue yet? If so, what was your fix? My car is in the shop now trying to fix this problem.
I replaced master cylinder, re-bled. Slave cylinder has about 20k on it, no leaks.