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Sudden slipping clutch
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jeremypbeasley
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PostPosted: Fri Nov 08, 2019 11:21 pm    Post subject: Sudden slipping clutch Reply with quote

Alright, people. Hereís the story.

Iím just a year into this Vanagon madness as well as being a proud YouTube certified mechanic. After numerous issues with my factory engine, I got another stock 1.9 in good shape and swapped it. In addition to a full refresh of everything above the block and heads, I installed a brand new Sachs clutch kit while I was in there. Been running really well since.

Last week, I narrowly avoided a collision happening in front of my and slammed the breaks harder than I ever have. Thankfully, I didnít collide with anyone or anything. About a mile down the road after I took off again, I noticed a loss of power to my wheels despite the engine sounding just fine. By all accounts, what I experienced was my clutch slipping. It behaved as if, even though Iíd fully removed my foot from the clutch pedal, the clutch was still partially disengaged. Only a few miles from home, I slowly drove it about 20mph back.

I had to leave town for a week the next morning. When I returned, I cranked the engine without issue, sounds just fine. When I put it in gear, the same issue remained. I could put it in 1st and floor it, barely moving up the street. No matter the great, I canít top 15mph. Iíve only driven it a few hundred feet since.

I noticed that my brake fluid reservoir was lower than before. Previously the fluid was just above the top of the ĒmaxĒ triangle. Now itís just below the triangle. Not a huge shift but clearly somethings leaking. My dash happened to already be off, so I inspected all around for leakage. The only thing I could find was that the outside of the clutch master cylinder was wet with oil. Not dripping at all, just wet.

To rule out issues with brakes, I fully removed all four wheels and the rear drums. Nothing suspicious whatsoever.

Iíve got a new master cylinder and hose from van cafe on their way. I plan to replace both units, bleed the lines, and hope this fixes my issue. That said, Iíve got a hunch that the issue, at least in part, is the friction disc itself. Why the sudden issue with engaging the flywheel? Why did this follow a brake slam? I can pull the gearbox if needed, but itís a lot of work and Iíd rather more fully diagnose the issue before I commit to yanking it off.

If anyone would care to lend some wisdom here, Iíd sure appreciate it.


Last edited by jeremypbeasley on Mon Nov 11, 2019 2:40 pm; edited 1 time in total
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the joker
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PostPosted: Sat Nov 09, 2019 6:02 am    Post subject: Re: Sudden slipping clutch Reply with quote

wet slave replace and bleed Idea you should be all set
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MarkWard
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PostPosted: Sat Nov 09, 2019 7:04 am    Post subject: Re: Sudden slipping clutch Reply with quote

How does it roll? Sounds like the brakes are dragging big time. The brakes are way more powerful than the engine.
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PostPosted: Sat Nov 09, 2019 8:28 am    Post subject: Re: Sudden slipping clutch Reply with quote

A simple test to check for clutch slippage is to set the hand brake, select first gear and then ease out the clutch pedal.

That should kill the engine, if it doesn't then the clutch is slipping.
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PostPosted: Sat Nov 09, 2019 8:32 am    Post subject: Re: Sudden slipping clutch Reply with quote

Your clutch is slipping and the quicker you stop driving it the cheaper the repair bill will be.

The slipping clutch is making \loads of heat and that will destroy the flywheel and pressure plate if you keep driving it.

Iíll guess that brake fluid has worked its way onto the clutch lining
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jeremypbeasley
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PostPosted: Mon Nov 11, 2019 12:29 pm    Post subject: Re: Sudden slipping clutch Reply with quote

MarkWard wrote:
How does it roll? Sounds like the brakes are dragging big time. The brakes are way more powerful than the engine.


Seems to roll just fine, but that said my frame of reference is minimal given I haven't rolled a Vanagon a lot in N.

Ahwahnee wrote:
A simple test to check for clutch slippage is to set the hand brake, select first gear and then ease out the clutch pedal.

That should kill the engine, if it doesn't then the clutch is slipping.


Great call. Did this. When I ease out on the clutch, the van vibrates quite a bit, but doesn't stop. The engine sounds like it's slightly slowing down, but I can't know for sure given my tach is not operational.

When I let off the handbrake, the van creeps forward but rather pathetically.


Last edited by jeremypbeasley on Mon Nov 11, 2019 2:29 pm; edited 1 time in total
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jeremypbeasley
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PostPosted: Mon Nov 11, 2019 1:02 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Here's a photo of my master cylinder and a video of the slave in action here: https://www.youtube.com/watch?v=uIvFC2bjGEg

A leaking master and a slave that, while not leaking, doesn't seem to be moving the clutch arm/lever as far as it should, suggests that the mechanisms outside the bellhousing arent't giving enough pressure to DISENGAGE the clutch disc sufficiently.

This is confusing. Even if I were to remove the slave entirely, wouldn't a functioning clutch always be engaged? Is it not the sole job of the master/slave to provide a way to disengage an otherwise entirely engaged clutch?

If I'm understanding this correctly, then even if I replace my master and slave, my clutch disc will still slip and is likely damaged. Is this correct?


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MarkWard
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PostPosted: Mon Nov 11, 2019 4:01 pm    Post subject: Re: Sudden slipping clutch Reply with quote

I have seen engaged and disengaged interchanged. Bottom line if the clutch is slipping, engine revs up in gear, but no real movement, the pressure plate is no longer clamping the clutch disc with enough pressure. A few reasons for this, but unlikely external.

There is a recent thread about a wonky clutch. Ended up being a seizing cross shaft.

Whatís interesting is that this happened after a heavy brake application. I still think the original problem was a stuck brake and trying to drive it burnt the clutch up.
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jeremypbeasley
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PostPosted: Mon Nov 11, 2019 6:42 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Well, shit.

I just removed the master and slave. Hard to tell where the leak was because it's so filthy. I'll replace both tomorrow.

I'm propbably going to just suck it up and pull the transmission to inspect the internals. Mating the engine and gearbox without a lift is my personal hell, but it seems foolish to ignore it at this point.
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PostPosted: Tue Dec 17, 2019 3:18 pm    Post subject: Re: Sudden slipping clutch Reply with quote

@jeremypbeasley - did you figure it out?

i just came back from a month away and my clutch was slipping. the clutch is only a few years in with minimal miles. i had a sticky front caliper this summer, which i replaced.

i would really rather not pull the engine/transmission to check for leaks. nothing obvious dripping from the bottom of the bell housing indicating an oil leak inside, but that seems to be the most obvious answer.

perhaps a rodent made a nest, and ground it up when i drove? more far fetched.
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PostPosted: Wed Dec 18, 2019 10:17 pm    Post subject: Re: Sudden slipping clutch Reply with quote

jeremypbeasley wrote:
if I were to remove the slave entirely, wouldn't


Yes you are correct. If you removed the slave, the clutch (if ďproperĒ) would be fully engaged, not slipping.
The test could Be similar by opening the bleeder screw.

Difficult to test drive though.
Requires a hill to start rolling.
And ďadvanced methodsĒ

Can you wiggle the little clutch rod thats in the slave? Make sure itís ďlooseĒ?
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Wildthings
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PostPosted: Thu Dec 19, 2019 1:16 am    Post subject: Re: Sudden slipping clutch Reply with quote

I am going to guess that for some reason when you did your panic stop you got lubricant all over your clutch, either engine oil or tranny fluid. Can't ever remember hearing of this happening before though.
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jeremypbeasley
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PostPosted: Thu Dec 26, 2019 7:03 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Thanks for checking in on me, folks.

Today was the first day in a month Iíve had to work on the van. I pulled the transmission off shortly after the original post. I also removed the master and space completely. I have since received my replacement master and slave cylinders. Even if theyíre not the culprit, I figured Iíd replace them once and for all.

Today I removed the pressure plate and disc from the flywheel. Theyíre toast. Photos below. I also removed the flywheel and dropped it off for resurfacing.

Thankfully Iíve got a brand new SACHS clutch kit in the garage that I can throw on, but I remain perplexed as to how this happened.

Iím donít really care about finding the mystery as if itís some map on the back of the Declaration of Independence. However, I can only assume this will happen again if something is left in the same way that caused this in the first place.

Checking boxes: The wheels spin freely and I have no reason to believe the brakes have ever seized to the point that it would overwork the engine. The flywheel end play is just above spec at .006Ē, but that shouldnít be a big deal. Everythingís been torqued to spec.

The only suspect thing here is the leaky master cyclometer. However that doesnít explain a slipping clutch at all.

Any help would be much appreciated. I really need this van back up and running again for a trip with the kiddos soon.


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Lastly a comparison between the disc I just pulled and a brand new one, just for kicks.


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E1
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PostPosted: Thu Dec 26, 2019 7:42 pm    Post subject: Re: Sudden slipping clutch Reply with quote

I'm curious if during your panic stop the engine went so low in revs as to stall with the clutch engaged -- and/or too much was demanded of the parts while working the clutch.

Just a thought. I've mentioned heel-and-toeing here several times but have yet to get a reply from others knowing or using this (and Mark Ward surely does).

Also, the pressure plate seems to have a chunk of clutch on it as if ground off by a ton of stress. It looks very similar to a clutch drum after toasting a clutch on a small race motor when caused by heat and/or chatter.

Glad you nailed it regardless.
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Last edited by E1 on Thu Dec 26, 2019 7:53 pm; edited 1 time in total
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PostPosted: Thu Dec 26, 2019 7:52 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Clutches are not damaged on the low end of the torque curve.

That clutch is burned up from slippage while the engine is turning fast and putting out max torque..

It could look like that from either a malfunction such as a stuck cross-shaft bushing, or improper use (which you have not mentioned).

I saw some van-folks at Descend on Bend trying to tow-start a diesel van.
At some point, the tow-van clutch belched out a thick puff of smoke.
His disc looks like yours (like a piece of carpet) but he didn't know it (yet) because he didn't take it out and look.
But when we left Descend on Bend his van was still there, almost the last one in the camp.
Poor guy had a California license plate... (600 miles?)
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PostPosted: Thu Dec 26, 2019 7:57 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Kinda did mention improper use. Wink

Any downshifting without matching revs is improper technique, as would be stopping in gear without dumping the clutch at some point.

Just didn't want to come off as accusing the driver. Wink
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PostPosted: Thu Dec 26, 2019 10:43 pm    Post subject: Re: Sudden slipping clutch Reply with quote

For the record, Iím entirely open to this being improper driving/operating. Damage is done. I would just want to know what Iíd need to do differently.

I drove five miles home at about 20mph immediately following the heavy braking incident. I stopped 3 times along the way just to let it rest. Once home, a week later, I drove it around the block just once. Maybe Iím ignorant, but could I really fry a disc as bad as Iíve shown in under 6 miles of driving?

Besides what Iíve described just now, what would be improper use?

PS, I donít think thereís any malfunction in the cross shaft. It appears to operate flawlessly despite its age.
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PostPosted: Thu Dec 26, 2019 11:05 pm    Post subject: Re: Sudden slipping clutch Reply with quote

Right attitude, good. 👍🏼

Per the sudden braking, did you bring it to a complete stop? In gear? Clutch in or out? Did it stall?

It's okay if you're not sure, recording such details in one's memory aren't exactly priority compared to safety considerations "in the moment." Cool

Intriguing issue all-around...
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PostPosted: Fri Dec 27, 2019 12:57 am    Post subject: Re: Sudden slipping clutch Reply with quote

jeremypbeasley wrote:
For the record, Iím entirely open to this being improper driving/operating. Damage is done. I would just want to know what Iíd need to do differently.

I drove five miles home at about 20mph immediately following the heavy braking incident. I stopped 3 times along the way just to let it rest. Once home, a week later, I drove it around the block just once. Maybe Iím ignorant, but could I really fry a disc as bad as Iíve shown in under 6 miles of driving?

Besides what Iíve described just now, what would be improper use?

PS, I donít think thereís any malfunction in the cross shaft. It appears to operate flawlessly despite its age.


I would have expected the clutch to stink like crazy if you suddenly got it hot enough to do that kind of damage. If no stink, I would be inclined to say it happened previously when pulling a hill with the pedal down and for some reason you just didn't notice the stink. Maybe you were having a strong cross wind or something at the time the damage was done.
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PostPosted: Fri Dec 27, 2019 6:36 am    Post subject: Re: Sudden slipping clutch Reply with quote

Kinda along Wildthings' idea, I am wondering if the clutch had been slipping off and on for some time, but had gone largely unnoticed?

For example, I had an old Cabriolet that had a slipping clutch. It would mostly only happen if I were to try to power up a particularly steep hill. I let off and it would quit slipping. But frequently the slippage could be minimal and perhaps not be noticed if things catch up with themselves pretty quickly.

Another time, with a different Cabriolet, I had decided to change the clutch for one reason or another. I drove to my friend's house in Wichita (two hours away) and we changed the clutch with a part he'd gotten locally. Everything seemed fine, but when I was about halfway home, going up a steep hill on the interstate, the brand new clutch gave out. It was slipping so badly the car couldn't go up that hill and I had to get a tow. I swapped in a new one at home and all was fine.

So sometimes stuff is just bad off the shelf.

One other thought I just had is, you might want to really flush out the hydraulic lines before replacing the slave cylinder. There could be some kind of crud in there that was preventing the fluid from returning fully, which would show up as being like you were halfway pushing the pedal. (I don't recall, on a Vanagon are there rubber lines in the system? If so, I'd get a new one-they can fail internally.)
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