Intentionally burning clutch to remove glaze and stop slipping issues?


#1

I have a 1994 Geo Metro that I picked up a little over a year ago. I had to swap engines and replaced the clutch at the same time. This included a turned flywheel and new pressure plate. I also replaced all seals and gaskets except for the distributor O-ring and the head gasket. This included the crank and cam seals on the front and rear of the engine as well as the seal housing gaskets/oil pump gasket. I drove it for several months and then the distributor O-ring began to leak oil profusely which is a common problem with these cars. The distributor is keyed directly into the camshaft on the rear side of the engine so it sits sideways directly above the transmission/engine interface. Some of the leaking oil went right down into the clutch area. Being that adding a cup of synthetic oil every day was still cheaper than driving one of my pickups, I just kept driving the car until the new O-ring arrived and added oil. Once the O-ring was replaced, the oil leak stopped.

I had a couple episodes of clutch slipping not long after the leak was fixed and then everything seemed fine. I figured that some oil got down there and wore off after the clutch stopped slipping. The car drove fine for about a year until I began noticing the clutch slipping under load in 4th and 5th gear. I had some suspicions of this for a week or so before it became more obvious that the clutch was most definitely slipping. I have a new clutch kit and a spare flywheel that I plan to have machined in the next few days. I have been driving it a couple weeks around town and just babying it so the clutch won’t slip.

I was also told by some that I should intentionally burn the clutch some to remove any glaze buildup on the clutch disc or flywheel/pressure plate surfaces. They told me to put the parking brake on or put the front bumper up against a tree and burn the clutch. I originally figured this was a bad idea but decided to try it yesterday, figuring I had little to lose. I did it just until I began to see smoke and smell it and then stopped. I let everything cool off for an hour and then took the car for a drive. The clutch was no longer slipping at all so I am wondering if this fixed the problem for now or simply delayed the issue for a short while. Anyone here have an opinion on this situation? I am sure I took some life off the clutch by doing this but…


#2

I used to do this “back in the day” to restore the clutch. The problem is that it usually only works for a short period of time. If you are extremely lucky you may get a little more life out of the clutch. Putting on the parking brake or putting the bumper against the tree is a bad idea. Just go out on a deserted roadway, rev the engine and pop the clutch.


#3

+1 to missileman’s post.
IMHO it’s worth trying. You’ve nothing to lose and might extend the clutch life a bit.


#4

If you are getting oil on the disc, a good heating would vaporize the oil and reduce the lubrication on the disc. My method for cleaning the disc and/or flywheel and pressure plate is to start out in the highest gear of the transmission; get the engine up to 3-4k RPM and slip the clutch while holding the RPM until the car is up to 30 or 40. A couple of applications does a pretty good job of getting rid of shudder and grabbing.

This will sometimes work for a clutch that is dragging to where first engagement is stiff and reverse grinds. After a few 'burns" you can tell the clutch engagement is less crisp but the drag is more manageable.


#5

I’ve heard Ray say on the show that to test a clutch for slipping, put the brake on or up against a tree, then put it it 4th or 5th gear and get the rpm pretty high then let out the clutch.

I always wondered when he said this, yes, I can see how it tests for slipping, but if it didn’t slip and the engine stalled, wouldn’t this test be sort of hard on the engine? It seems like in 5th gear and high rpm and the clutch suddently stopping the engine from turning there would be some pretty big forces on the crankshaft and bearings. Is that something to be concerned about, or any engine can handle it, and not a big deal?


#6

I can’t imagine this putting any more stress on an engine than someone revving it up and dumping the clutch to do a burnout. While I wouldn’t want to do this everyday, I don’t think a little will hurt the engine as it will be a lot more gradual and at lower RPMs. I was most worried about destroying the clutch to the point where I couldn’t get home so this is why I did it at my house with the parking brake method. Of course it was slipping anyway so I figured it could just be replaced if nothing else. I have all the parts and just need to get this spare flywheel turned.

These cars have a mechanical clutch adjuster where you have to turn a nut on a threaded rod to make sure you don’t start riding the clutch as it wears from time to time. I have this so there is a small amount of play when disengaged. You don’t have this option in a hydraulic setup.

The car will get a good 25 mile run tomorrow and I will see how it does under load at higher speeds. It seemed that the smallest headwind would cause it to start slipping if I was in a higher gear.


#7

I’ve found that a marginal clutch will first start to slip in a higher gear, wide open throttle, near the rpm’s of the engine’s max torque.


#8

The puzzling part is your saying the clutch worked fine for about a year after you fixed the oil leak. If the slippage was due to oil, I’m at a loss to understand why it took a year to begin slipping.

As for the technique you used to dry/deglaze the clutch, there’s always the concern that the excessive heat generated causes fatigue in the pressure plate springs - which may provoke early failure.


#9

I am pretty much resigned to replacing the clutch and have the parts required to do so. The clutch kit is a Sachs which come highly recommended for these little cars. This includes the alignment tool, pressure plate, throw out bearing, clutch disc, etc. While I figure what I did is probably a Band-Aid, we will see how long it works.

I also thought it was strange how long it took to come back as a major issue for me after the oil leak was fixed. I am wondering if the oil leak started the clutch glazing and it just continued from there. Maybe it was slipping just a tiny bit for a while and I never noticed. There were quite a few times within the week or two before it became definite such as when getting on the highway or climbing a hill at highway speeds that I began to wonder about the clutch. It seemed like it was slipping some but by no means freewheeling almost as if in neutral like it did later on.

I am almost wondering if there might be another oil leak somewhere that showed up recently. Maybe the rear main let go or the seal around the input shaft of the manual transmission is seeping. I am thinking about a hidden oil leak that isn’t obvious without taking it apart.

I have a spare flywheel from another one of these cars I junked and am going to have it turned in the next few days when I get a free moment. I want everything ready for when it is needed.


#10

@circuitsmith,

That hasn’t been my experience, probably because my clutch is self-adjusting. The first symptom I noticed was it shifting roughly into first gear. I never noticed any problems in high gears.


#11

I have tested a clutch by putting the car against an immovable object. But the object is your parking brake and the tree is just a precaution. Plus, you don’t rev it way up. Idle speed or slightly above will do. If your parking brake can’t hold a car in top gear when you let the clutch out to make it stall, your parking brake needs work first. 3k to 4 k rpm is asking for trouble and you can make a slipping clutch out of a good one, fast.

Or, while traveling in high gear at a lower speed, floor the accelerator. If it accelerates slowly without slipping and revving up, it’s ok. If it slips, doing it several times accomplishes the same deglazing thing without stressing the drive train by popping the clutch against a tree or gun starting it at high rpm. It’s an older car. Don’t break anything more !

Agree with @circuitsmith and @JoeMario. You don’t have to be an animal about this.

Or, find several heavyweights, load them into the car, and do the same things at lower speeds. Just ask for volunteers in the MacDonalds parking lot.

@Whitey Isn’t that a master/slave cylinder or gear synchronizer or throw out bearing problem ? Worn clutch plate should shift easier.