View original topic: Sudden slipping clutch Page: Previous  1, 2
MarkWard Fri Dec 27, 2019 10:54 am

I'll emphasize this again. You did a major panic stop prior to the clutch starting to slip. The brakes must have stuck partially on and that caused the clutch to burn up.

I worked for Audi in the mid 80s with the run away 5000. "The harder I pressed the brake pedal, the faster the car went".

It was determined the new owners, especially short women backing up, would get their feet mixed up, believing they were on the brake pedal not the accel pedal. Audi had so much bad press, they let it go. The recall was to add a shift lock to train owners how to "find" the brake pedal. There was nothing wrong with the car other than the brake pedal was close to the accel pedal to make room for the clutch pedal.

Anyhow I mention this because the brake are about 3x as powerful as the engine. There is no way the engine can overpower the brakes. I would suggest you examine your brakes very closely. It could be either the front or rear hanging up. In normal application, you may not notice this. It may need the "extra force" to cause this to happen.

If it's not the brakes as I suggest. It is just a coincidence that it happened after a panic stop and unrelated to the failure.

Sodo Fri Dec 27, 2019 12:13 pm

MarkWard wrote: I'll emphasize this again. You did a major panic stop prior to the clutch starting to slip. The brakes must have stuck partially on and that caused the clutch to burn up.

Mark I think that would be noticeable driving the van. How would you even get into 2nd gear if the van decelerated (braked) whenever you press the clutch?

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

I'm in this camp.
Clutches survive enormous amounts of abuse.
Such as kids (and now millennials) learning how to drive stick.
This abuse happens at the higher revs, when the engine is making torque.
--->Gasoline is being burned.<---- foot on throttle.
Rotational energy is departing thru the crankshaft, some thru the wheels, some being "wasted" at the slipping clutch.
When the heat adds faster than the clutch's ability to shed the heat, the pressure plate and flywheel get red hot, and it roasts the friction disc.

The braking incident does not remotely qualify as abuse, it's a very short event, at low RPM, low torque.
Well within the clutch's capacity.

I have a hard time believing the braking event is related ...... other than coincidentally at the same time as the clutch problem coming to light.
And I don't see any oil anywhere on the clutch.

Look for a 'slipping' fault.
Either clutch mechanism stuck, or driver error, or a pressure plate spring failure.
Maybe someone roasted this clutch awhile ago (like that feller I wrote about at Descend on Bend), and it still was able to move the van.
But it was damaged, slipped a lot and finally "gave out".

Can you post pics of the 'spring fingers' of the pressure plate?
If the 'fingers circle' is 'uneven' that suggests a broken diaphragm spring, which would certainly result in a slipping clutch, which would then roast the disc to look like your pic.
Press down on them with something 'round', how much spring pressure is there?
It should be "difficult" you have to "stand on it".
Much harder, like about six times harder than pressing the clutch pedal.
You have a new pressure plate, right? (I hope so)
Compare spring pressures between the old and new pressure plates.

E1 Fri Dec 27, 2019 1:27 pm

As I've said, this is a very intriguing case.

But if there's one thing I read on Samba over and over, it's claims of coincidental parts failures. I may not be a mechanic, but odds of such things are *extremely* remote.

I hope the result of this thread is definitive. Quite a mystery to be solved.

MarkWard Fri Dec 27, 2019 3:26 pm

Sodo, Then my vote is "Coincidence".

jeremypbeasley Fri Dec 27, 2019 3:31 pm

Right on. Appreciate all the great points and examples.

Flywheel came back resurfaced today. Iím gonna flush out those clutch hydraulic lines real good before installing the new master and slave. Since Iím in here, I might as well replace the felt seal, rubber seal, and pilot bearing. Loads of fun when youíre working on the street in the winter.

In lieu of a clear silver bullet, Iím going to acknowledge that thereís a huge margin for my own error here and do some research to clearly know I can sense if/when clutch slips slightly in the future. Iíve only been driving a Vanagon for a year so itís entirely possible that there was slippage before and I didnít notice. I donít recal any stink any any time.

Hoping when I put this all back together, I can get this puppy running till next summer without having to pull the damn gearbox off again!

Who knows, maybe Iíll be lucky enough to even have time for some body work!

jeremypbeasley Fri Dec 27, 2019 3:32 pm

Whoops. I missed the whole second one of replies. Catching up...

E1 Fri Dec 27, 2019 6:51 pm

Once all's good, you shouldn't have to do a clutch for quite a long time.

Ours on our first bus chattered a fair bit upon purchase. I was able to (carefully) "burn" the glaze off and it went over 40,000 trouble-free miles before replacement. And I only replaced it because the tranny was getting rebuilt.

I know some/most think downshifting by using "engine braking" is fine, but really it's "clutch braking" and it ain't fine. Brake pads are cheap, and good technique is free.

jeremypbeasley Tue Jan 21, 2020 11:42 pm

Hey folks,

We're back on the road! New clutch, new slave cylinder, new master cylinder, all new fluid.

When I flushed out the hydraulic lines, there was a ton of greenish black crap in there that looked like mold and rust combined. I'm sure this wasn't helping!

Test drove it for 30 mins tonight without issue. There's definitely a big different in how sensitive the clutch is. Maybe this whole time I was driving on a shit clutch and just didn't realize it was as bad as it was. Definitely learning a ton here.

I'm also looking into "double clutching" as a way to better operate.

Appreciate all your help and support.

Abscate Wed Jan 22, 2020 4:21 am

There is a natural tendency to associate failures with recent activity.

If the clutch disc was not contaminated with oil or brake fluid, it is just a worn out clutch.

Things that commonly get done incorrectly on a clutch job, other than cheap parts:

Cheap parts
Not resurfacing the flywheel in three places
Flywheel inspection
Pilot bushing
Cheap parts
Checking that disc slides cleanly in splines
Fingers on PP
Release bearing inspection
Cheap parts

old_man Wed Jan 22, 2020 8:53 am

jeremypbeasley wrote:

I'm also looking into "double clutching" as a way to better operate.

Double clutching is generally used to save syncros. I only really use it when the transmission is really cold (0F sort of thing). Maybe heaving downshifting. Just my personal preference.

dobryan Wed Jan 22, 2020 9:35 am

No need to double clutch except maybe in very cold weather when starting out until the trans warms up some.

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