Vacuum Assist Hydraulic Clutch slips when hot!? Why?

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Scantek
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Vacuum Assist Hydraulic Clutch slips when hot!? Why?

Unread post by Scantek » November 27th, 2017, 9:08 pm

Hi all

Problem with a clutch that slips in hot climate. When the Ute has been working hard or under load in warm weather it starts to slip.
It has been adjusted to have correct free play at the pedal but when the fluid gets warm and expands in the system it pushes the rod behind the pedal till there is no free play then because the pressure has to go somewhere it operates the slave cylinder and the clutch slips. I know this because when it happened to me last time I felt the slave cylinder and it was hot. I poured water on it from the garden hose and it went straight back to normal. It's not releasing the pressure back to the fluid reservoir.

I have got sick of the dealer adjusting it and not fixing anything so I have had to adjust the free play at the pedal to about 40mm to get it to work properly.
I took it to a service center the dealer nominated in my area and they agreed it has a problem and because the dealership brushed me off and didn't fix it early it will now need a complete new clutch and machined flywheel.

Has anyone had a clutch issue like this and what could be the problem?

Russ

Peter Aawen
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Re: Vacuum Assist Hydraulic Clutch Problem

Unread post by Peter Aawen » November 27th, 2017, 9:36 pm

Hey Russ, how long since the clutch fluid was bled & replaced?? Clutch fluid in good condition is pretty much identical to brake fluid, and warm weather SHOULD NOT EVER make it expand or do things like that you mention!! Hey, it should be able to handle temps up over 400 deg C (well over!) without any issues!! So if it is expanding, something is probably wrong WITH THE FLUID!! :eek:

Brake (& Clutch) fluid is hygroscopic which means it will absorb moisture/condensation out of the air over time, & water WILL expand when it gets hot - in the brake lines this actually boils off when the brakes get hot, causing steam which compresses & makes for brake fade & a very spongy pedal; but clutch fluid shouldn't ever get that hot, altho it certainly might get warm enough to expand with hot ambient temps!! On top of that, water contaminated fluid will turn the seals spongy & stop them working properly too!! :purplex:

So, bearing all that in mind, I'd guess you need to very carefully bleed the clutch fluid & replace ALL the fluid in there to get rid of the water/condensation contaminated fluid so this no longer happens. Check anything & everything that has a seal or o-ring in there too, you might need to replace the lot! And bear in mind that bleeding these systems can be extremely difficult to get done properly, a power bleeder is almost essential, or you might need to let gravity work on it for at least 24 hours!! Last time we did one of my Patrols vac assisted clutch system it took 24 hours AND a power bleeder and I still hadta do it again/properly to get it right after the (award winning) dealer had had a couple of goes!! The vacuum assist bit seems to add lotsa hidy spots & lengths of tubing where the fluid can pool. :mad:

If you haven't already replaced your clutch fluid, give it a go, it does sound very much like your fluid is contaminated & full of water.... If you have already changed the fluid, then I reckon you need to have another go at bleeding the system properly - it takes a loooong time to let the air/contaminated fluid get right out of the system, generally about TWICE as long as you feel HAS to be more than enough!! So go til you think you're done, then double that time, and THEN add some more time again just to be sure to be sure in cases!! Good Luck! :thumb:
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cbd
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Re: Vacuum Assist Hydraulic Clutch Problem

Unread post by cbd » November 27th, 2017, 9:37 pm

G'day
I've had 2 twin cabs over the last 27 years. There is no provision in any maintenance to replace the fluids like you would for brakes. Runs the same type of fluid and like brakes fluid they attract water. Water that expands and turns bubbles of steam when hot. Be worth while to consider a master and slave rebuild or at least a fluid change before a full clutch replace.
Just saying

Scantek
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Re: Vacuum Assist Hydraulic Clutch Problem

Unread post by Scantek » November 29th, 2017, 11:05 pm

Hi all
Thanks for comments. The vehicle is not 18 months old yet and was brought new. The dealer has tested and checked the fluid and all A ok.
The brake and clutch fluids have same reservoir and no issues with brakes.
When Ultratune and Foton get their **** together or I get to Perth in Jan it will be going in to have clutch replaced etc and the ECU update done so they will replace the fluid then (one would think that).
The guy at UT said flywheel will need machining too as it's been slipping for so long and clutch replaced not adjusted.

Apparently UT are going to do the warranty work on Fotons where there is no dealership

We shall see

Scantek
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Joined: October 29th, 2008, 6:55 pm
Location: Geraldton, WA

Re: Vacuum Assist Hydraulic Clutch Problem

Unread post by Scantek » November 29th, 2017, 11:10 pm

Sorry
Thanks Peter for your comments. I agree totally with what your saying.

I think I may have to yank the chain of the Perth dealership a bit on this. They seem to want to sell these vehicles but just brush you off when it comes to warrantee work

Cheers

Russ

mydmax
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Re: Vacuum Assist Hydraulic Clutch Problem

Unread post by mydmax » March 22nd, 2018, 11:11 am

I think the thing that is wrong is the bolting of the clutch master cylinder is not locked to a frame which holds the pedals and an extraordinary amount of distance change is happeneing between the clutch pivot frame and the master cylinder.
All to do with engine heat on the firewall I would imagine.
Is the master cylinder base and clutch pivot area braced tgether??? If not I would run a brace there to check.

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