Clutch failure on trail. Need help.

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ChickenPinz
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Clutch failure on trail. Need help.

Post by ChickenPinz » Mon Jun 29, 2020 3:49 pm

At Hollister hills and clutch will no longer engage. Just before the failure it was slipping progressively more and more. Now it won't engage at all. Plenty of fluid in the reservoir. Pedal resistance feels normal. Before this we were at the top of the mountain and doing a long downhill largely with engine braking.

Anyone have any good ideas of a possible repair here on the trail? Otherwise I need to figure out a trailer and tow vehicle and bring it home. Of course after towing it off the mountain.
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rmel
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Re: Clutch failure on trail. Need help.

Post by rmel » Mon Jun 29, 2020 5:28 pm

Almost sounds like the slave is hung up holding the clutch open.
But then your peddle feels normal. If the hydraulics fail it's typically
going to be a clutch engaged. You probably would have know it if the
pressure plate failed. I guess one thing to try would be to loosen the
slave from the bell and see if it engages. If it does, then you know
what's wrong. Y'd have to pull the plunger out unless you have a spare
slave laying around.

Good luck.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Mon Jun 29, 2020 5:55 pm

We tried bleeding the clutch circuit on the trail, and it didn't help. My sense is it's hanging up internally. Maybe the slave cylinder. Waiting for my rescue vehicle to arrive with a U-Haul trailer....
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hatzlibutzli
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Re: Clutch failure on trail. Need help.

Post by hatzlibutzli » Tue Jun 30, 2020 7:27 am

Sounds like a worn out clutch lining ... the Pinz is known to be there quite quick without true prior "announcements". Hydraulic failure usually results in failure to disengage! With that one can "limp" home.

The good thing: if you have a new clutchkit it can be done also on a trail while its raining ... which is not the case with most other cars.

regards ... Simon

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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Tue Jun 30, 2020 7:43 pm

Well...a good samaritan helped me trailer it home, and I see pulling the transmission in its future. At this point, my prediction is that the disc is be more or less non-existent. As to warning, there were maybe half a dozen clutch engagements before essentially no power was getting to the transmission. Sometimes I can turn the driveshaft by hand, and other times not -- the amount of drag can vary a bit.

I have one vote for bad disc. Any other votes before I drop the tranny and reveal the results?
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rmel
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Re: Clutch failure on trail. Need help.

Post by rmel » Tue Jun 30, 2020 9:13 pm

Pull the slave cylinder and inspect that first.
Considerably easier if that's the problem.

You could also get a boreoscope in the bottom hole
of the Bell housing and should be able to see the
edge of clutch and perhaps some telltale signs.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Tue Jun 30, 2020 9:46 pm

@rmel -- the hole I see on the underside the bell-housing is maybe 2mm diameter at most -- not sure who has that small of a borescope!

Yes, of course, the slave cylinder will be inspected/pulled first. As well a complete visual inspection as much as possible, which includes things like fluid checks.

Pulling the transmission is a likely task, but it's certainly not my first one. Sorry I didn't spell out the whole process in detail for each step along the way as I assumed most folks would expect a progressively more invasive assault on the problem, but perhaps some might have misread my statement as "just pull the tranny first".
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rmel
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Re: Clutch failure on trail. Need help.

Post by rmel » Tue Jun 30, 2020 9:51 pm

Hmm, interesting. I have a 710 and a 712, both have an opening at least 7mm in diameter
at the bottom of the Bell housing. You could also try sticking a borescope into the slave
cylinder hole.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Tue Jun 30, 2020 10:58 pm

Even if one could look inside such a hole, I don't think it'd change the course of action no matter what is seen.

If removing the slave cylinder doesn't yield improvement, the next step is transmission removal since that puts the problem in the clutch itself and access will be required to resolve the issue. I can't imagine an issue which could be resolved through the slave cylinder opening or the hole on the underside.
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Re: Clutch failure on trail. Need help.

Post by VinceAtReal4x4s » Wed Jul 01, 2020 1:23 am

My guess is a worn disc as well. Pulling the tranny is very easy and can be done anywhere with basic tools so don't sweat going after it.
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rmel
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Re: Clutch failure on trail. Need help.

Post by rmel » Wed Jul 01, 2020 8:30 am

I don't want to belabor the point but you are missing the point.

Observation if possible -- is more information. If you see debris or
suspicious looking issues at the edge of the clutch then you know
with 100% confidence that's the baby. If you don't and the slave
removed also did not resolve the issue then it's still high confidence
but now your hoping just a wee bit. I always look for ways to get
more data for any given problem. BTW I agree the slave is not
likley the problem but it's so easy to eliminate. And I did have one
Master that locked up due to internal debris that wedged it to no
avail, couldn't even get it apart to rebuild.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Wed Jul 01, 2020 9:17 am

I think you are missing the point, actually.

More data is good, but engineers often get lost in collecting data that isn't actionable or is irrelevant. My contractor friend has a great phrase: "Solutions, not problems"

In this case, after removing the slave cylinder, if the situation can't be resolved there's no other option that pulling the transmission to collect more data inside. Sticking a borescope into the underside hole might collect some data, but nothing that would change the next course of action. And it would thus be time and effort wasted that'd be better spent getting toward a solution. And you won't learn anything with the borescope that won't be learned more completely with the transmission out.

As a pilot/engineer, I use borescopes all the time on cylinders and valves, so I recognize their value.

But I'm open to ideas, so please suggest what different courses of action might result depending on what one would see by looking inside with a borescope.
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ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Thu Jul 02, 2020 10:43 pm

ChickenPinz wrote:
Mon Jun 29, 2020 3:49 pm
At Hollister hills and clutch will no longer engage. Just before the failure it was slipping progressively more and more. Now it won't engage at all. Plenty of fluid in the reservoir. Pedal resistance feels normal. Before this we were at the top of the mountain and doing a long downhill largely with engine braking.

Anyone have any good ideas of a possible repair here on the trail? Otherwise I need to figure out a trailer and tow vehicle and bring it home. Of course after towing it off the mountain.
After pulling the transmission, the failure was obvious and as expected: clutch disc disintegration.

The whole pressure-plate side of the clutch disc was without friction material. Minimal injury to the pressure plate, but I am replacing all the standard parts (disc, cover, bolts, throw-out bearing) regardless.

Oh, and the drain/inspection hole on the bottom of the bell-housing? It's 5.0mm diameter.

For anyone wanting to diagnose this failure in the field, symptoms are:
- No, or minimal, power through the clutch
- Clutch worked fine not more than six cycles previous
- Good pedal pressure

Removing the inspection cover on the top right of the bell-housing for the ball-and-socket slave cylinder connection, and running the engine briefly resulted in a scattering of clutch disc detritus on the ground -- that'd be an easy confirmation in the field of this type of failure.
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newtopinz
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Re: Clutch failure on trail. Need help.

Post by newtopinz » Thu Jul 02, 2020 11:24 pm

Since there is not much warning, is there a way to check how much wear on the clutch friction disk before this happens on the trail or road? Would a borescope through the inspection hole or slave cylinder hole show this before it fails?

ChickenPinz
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Re: Clutch failure on trail. Need help.

Post by ChickenPinz » Fri Jul 03, 2020 1:34 am

I don't think the drain hole on the underside is going to help much. It's only 5mm and likely very little clearance on the inside. Your best inspection point is to remove the two nuts over the slave cylinder ball-and-socket joint.

All that being said, it wasn't particularly obvious that the failure had occurred on my truck even after half the disc had disintegrated. You might be able to stick a borescope in there, but it's not clear that there would have been any visual warning signs.

The transmission was just out within the last 100 miles or so, and both Jim and Andre saw it and neither saw anything that looked wrong at that time. My take from that is: There are no visual early warning signs. And there was no hard use of the clutch anytime from when Jim/Andre saw it until it failed. Oh, and the truck has about 50,000km/1500hr on it.

All that being said, if you're really worried about a failure on the trail, you could bring a spare disc since a clutch swap is 100% doable in the middle of nowhere with just the on-board toolkit. Me? I'll just make sure I'm with pals who could leave me some water and whiskey while they drive back to civilization to return with a new clutch.
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