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91 Syncro Clutch Slipping...
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benandmj
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PostPosted: Thu Feb 22, 2018 12:10 pm    Post subject: 91 Syncro Clutch Slipping... Reply with quote

Posted this in an old thread that was quickly buried but I think its worth its own discussion as I can't find much related info here.

In early January I picked up a van with a fresh transaxle rebuilt ($ept ‘17). I drove it across the country and after about 2000 miles I felt the clutch slip while accelerating in 4th. This only happened once. I've been driving it regularly since and the slipping has gotten progressively worse. Once hot, the clutch slips around 3600 rpms. I initially see it in 3rd or 4th but it happens in all forward gears under load. Van has a GoWesty 2.3. Syncro trans was rebuilt by a reputable builder. Reputation of shop that installed it is unknown.

A few things to consider since I bought the van after the recent work was done:

I spoke with the shop that did the rebuild and they do use a bronze cross shaft bushing.

We are assuming a new clutch and good condition flywheel were used when tranny was installed. New man seal/ no oil on flywheel. ??

Brand new clutch master cylinder.

Previous owner is awesome but not at all mechanically inclined.

I plan to pull the tranny and see wtf is going on in there but I’m going to replace the slave first which leads to the reason I started this post:

Does the “clutch engagement lever” that the slave actuates operate from limit to limit? When I remove the slave shaft there is range of motion left in the lever. Like the pressure plate isn’t fully releasing?

I have a worn clutch pedal with too much free play. Could an elongated clevis pin hole on the clutch pedal somehow cause this slipping I'm experiencing? Tackling that one before trans removal as well.

I guess I’m just looking for a reason to not pull a brand new transaxle from a van i just bought. I’ll report back. #vanlife
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MarkWard
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PostPosted: Thu Feb 22, 2018 12:47 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

I don't believe you will find the slipping clutch is related to the cross shaft or clutch slave cylinder. To clarify, the slipping clutch symptom is the engine rpms are increasing, but the van is not accelerating? If so, you have a clamping force issue with the pressure plate/clutch disc package.

If the clutch has been slipping, you will find heat spots on the flywheel and pressure plate. If the disc is worn too thin, you also lose some clamping force. If the flywheel has been machined, but the step for the pressure plate was not machined correctly, that will also affect clamping force.

You can look at the slave if you want, but in the end, I'd plan on pulling the transmission and taking a look see.
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PostPosted: Thu Feb 22, 2018 5:32 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

Other possibility would be oil has made its way onto clutch disc or flywheel surface from leaking engine or transmission oil seal.

Or just a flat worn-out clutch disc.

I don't think an issue with the hydraulic system would cause clutch slippage, if anything it would cause incomplete disengagement of the clutch and therefore crunchy/difficult shifting.

The clutch disc is clamped between the pressure plate and flywheel friction surfaces by the spring tension of the pressure plate. Clutch hydraulics, cross shaft etc don't have any bearing on that clamping force.
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PostPosted: Thu Feb 22, 2018 5:48 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

This was happening to me last summer with my '86 Syncro. It turned out to be a bad oil slinger that was leaking oil onto the clutch plate.
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benandmj
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PostPosted: Thu Feb 22, 2018 5:52 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

sjbartnik wrote:
Other possibility would be oil has made its way onto clutch disc or flywheel surface from leaking engine or transmission oil seal.

Or just a flat worn-out clutch disc.

I don't think an issue with the hydraulic system would cause clutch slippage, if anything it would cause incomplete disengagement of the clutch and therefore crunchy/difficult shifting.

The clutch disc is clamped between the pressure plate and flywheel friction surfaces by the spring tension of the pressure plate. Clutch hydraulics, cross shaft etc don't have any bearing on that clamping force.


This is my logic. It’s very frustrating to have so many unknowns but it’s obviously not hydraulic.... the shifting is great.

My plan is to have a new flywheel pressure plate and clutch on hand and crack it open. Seals etc while I’m in there. I really don’t think it’s oil contamination but we shall see.
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PostPosted: Thu Feb 22, 2018 5:53 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

calfredson wrote:
This was happening to me last summer with my '86 Syncro. It turned out to be a bad oil slinger that was leaking oil onto the clutch plate.


I had this issue on another van! I think I can rule that out as this gear box was just rebuilt by German Transaxle in Bend.
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PostPosted: Fri Feb 23, 2018 6:48 am    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

Agree with above - if it was wear in the clutch pedal, or a slave problem you would see disengagement issues, not issues once engaged. All of the other possibilities are likely, including poorly installed pressure plate with bent tines
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PostPosted: Thu Mar 01, 2018 2:59 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

Well I’ve been under the van a lot while waiting on new clutch and flywheel to come. R&R on the CV’s, new exhaust, engine and gearbox oil changes. I’m starting to think the clutch slip is a main seal leak. The undercarriage was pretty clean when I bought the van and it’s looking pretty wet with oil now just a month or so later. Sleeping at the bell housing. Hoping to pull the transmission this weekend or next. Stay tuned.
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PostPosted: Thu Mar 01, 2018 5:37 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

I know you're already unbolting stuff, but....might do this before it comes apart. How does the clutch "feel"? Normal pedal pressure compared to a van with a good clutch?

This question for the old-timers. Is there ever any condition where the slave fails to release fully?
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PostPosted: Thu Mar 01, 2018 5:50 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

Once you mentioned a new master cylinder I thought of this thread. Give it a good read. Was my problem with a new master cylinder and this thread solved slippage issue

https://www.thesamba.com/vw/forum/viewtopic.php?t=598908&highlight=
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PostPosted: Thu Mar 01, 2018 5:56 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

the nature of hydraulic clutches are that they self-adjust. on my '87 with 225K miles and the original slave, while it was a SOB to get off, the piston was still free and working. i think slave issues are going to be more leaking than hanging up.

that said, any wetness under the van that is centered around the bottom opening of the bell housing is a good sign of a seal problem, which there are plenty of.

it COULD be a poorly machined flywheel, with only the clutch face done and the machinist didn't also lower the mating face for the clutch plate. fairly cheap to get either a GW rebuilt FW or i see they now sell a new Asian one. my rebuilt FW from GW came below the specs to return it as a core, tho i'm confident it was machined just fine keeping the mounting face to clutch surface distance in correct proportion. which BTW, is a hard measurement to find.
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PostPosted: Tue Mar 20, 2018 1:42 pm    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

In the interest of preventing yet another insightful yet unresolved thread here, I am back with an update.

For the first time in 6+ years of Vanagon ownership, I've paid someone to work on my van. I recently moved and no longer have a paved flat area to work. After replacing my exhaust system and both rear axles while laying on a gravel hill, I determined that pulling the transaxle was not a smart idea in these conditions.

The clutch slipping was caused by a failed main seal. While I couldn't detect any major oil consumption, the clutch surface and flywheel were both apparently pretty trashed with oil. I'm hoping to post pictures of both when I pick the van up tomorrow. I'm now confident and comfortable with the workings of the hydraulic clutch system having replaced the clutch master, adjusted the pedal freeplay and bled the system. I also have a new pedal assembly to install as my high mileage van has some elongating of the clutch pedal clevis pin hole. Once again this forum and the responses to this thread have proven extremely helpful.
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PostPosted: Thu Mar 22, 2018 11:08 am    Post subject: Re: 91 Syncro Clutch Slipping... Reply with quote

I had a similar problem with a known new clutch, no oil on clutch, new clutch master and slave. It seemed to only happen on longer drives and when it was really hot out. My guess was that the fluid between clutch master and slave was heating up due to driving AND very hot ambient (110F here) and the expansion was pulling the clutch away slightly. This was caused by the clutch master on the pedal being adjusted so tight that there was no pedal free play to take up the fluid expansion. After adding the Bentley free play (a couple mm at the pedal if I remember correctly) problem went away for good. There's a lot going on here with my assumptions but the adjustment solved it. I had the clutch out at a later date and it was dry FYI.
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