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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 17155
Location: Retired South Florida
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 Posted: Fri Dec 27, 2019 10:54 am Post subject: Re: Sudden slipping clutch |
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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.
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Sodo
Samba Member
Joined: July 06, 2007
Posts: 9616
Location: Western WA
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| Posted: Fri Dec 27, 2019 12:13 pm Post subject: Re: Sudden slipping clutch |
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| 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.
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'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
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E1
Samba Member
Joined: January 21, 2013
Posts: 6567
Location: Westfalia, Earth
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| Posted: Fri Dec 27, 2019 1:27 pm Post subject: Re: Sudden slipping clutch |
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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.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 17155
Location: Retired South Florida
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| Posted: Fri Dec 27, 2019 3:26 pm Post subject: Re: Sudden slipping clutch |
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Sodo, Then my vote is "Coincidence".
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jeremypbeasley
Samba Member
Joined: September 18, 2018
Posts: 164
Location: Seattle, WA
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| Posted: Fri Dec 27, 2019 3:31 pm Post subject: Re: Sudden slipping clutch |
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Right on. Appreciate all the great points and examples.
Flywheel came back resurfaced today. I’m gonna flush out those clutch hydraulic lines real good before installing the new master and slave. Since I’m in here, I might as well replace the felt seal, rubber seal, and pilot bearing. Loads of fun when you’re working on the street in the winter.
In lieu of a clear silver bullet, I’m going to acknowledge that there’s 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. I’ve only been driving a Vanagon for a year so it’s entirely possible that there was slippage before and I didn’t notice. I don’t 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 I’ll be lucky enough to even have time for some body work! |
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jeremypbeasley
Samba Member
Joined: September 18, 2018
Posts: 164
Location: Seattle, WA
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| Posted: Fri Dec 27, 2019 3:32 pm Post subject: Re: Sudden slipping clutch |
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| Whoops. I missed the whole second one of replies. Catching up... |
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E1
Samba Member
Joined: January 21, 2013
Posts: 6567
Location: Westfalia, Earth
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| Posted: Fri Dec 27, 2019 6:51 pm Post subject: Re: Sudden slipping clutch |
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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.
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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jeremypbeasley
Samba Member
Joined: September 18, 2018
Posts: 164
Location: Seattle, WA
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| Posted: Tue Jan 21, 2020 11:42 pm Post subject: Re: Sudden slipping clutch |
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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. |
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Abscate
Samba Member
Joined: October 05, 2014
Posts: 22670
Location: NYC/Upstate/ROW
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| Posted: Wed Jan 22, 2020 4:21 am Post subject: Re: Sudden slipping clutch |
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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
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old_man
Samba Member
Joined: June 19, 2018
Posts: 1382
Location: Newfoundland
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| Posted: Wed Jan 22, 2020 8:53 am Post subject: Re: Sudden slipping clutch |
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| jeremypbeasley wrote: |
I'm also looking into "double clutching" as a way to better operate.
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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. |
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dobryan
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Location: Brookeville, MD
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