Vauxhall Caterham Dry Sump clutch slave seals

[Paul McKenzie]

My mate's Caterham dry-sumped HPC suffered total clutch failure and loss of fluid the other day. So reading up in the archives, and seeing that people's attempts to replace the slave cylinder seals alone have often led to another early seal failure, we took the advice and ordered a new complete slave cylinder with seals (not cheap ).

 

Today we pulled the engine out, and removed the failed slave cylinder from the DS bell-housing. The seals were well gone. However, we then scratched our heads and wondered why the hell just a change of a few pennorth of seals wouldn't result in equally as good a job as replacement of the whole unit. This should be logical as the seals are the only part of the unit which make contact with the cylinder bore in the DS bell housing.

 

A bit more scratching of head and I think I might have the answer, but I would like to hear from others who have had this problem as to what they think. The slave sits in an ally bore machined into the bellhousing. When we examined the surface of the bore it's obvious both visually and by touch that the soft ally has been marked by very small movements of the slave in the bore. This I think has been caused by dirt getting between the seals and the bore wearing away the surface of the ally bore. If this is the case and people have not rectified it before fitting either a new slave assembly or just new seals, then this would explain the subsequent rapid failure of the seals that many have seen.

 

Please let me know what you think, as the next step would be to find a fix for the problem. I'm already thinking along the lines of having the bore machined out, and an insert put in (maybe in more resistant metallurgy) and then machined to properly fit the new slave.

[captain chaos]

Sounds as though you may have point here Paul.

 

Mine started leaking and I took the motor out beofre total loss occured. I never checked the bore of the bellhousingcome to think of it but I ditched this method anyway for a hydraulic unit.

[Paul McKenzie]

Thanks, Captain, but do you mean you ditched it for a non-hydraulic unit or a different type of hydraulic clutch?

 

BTW do you K series guys have this same problem with DS hydraulic clutches?

 

Paul

[Chelspeed]

K series bell housing / dry sump tank has been arranged to still use a cable.

 

No seal problems but the arm is fabricated as there's no room to use the normal Ford arm and the fabricated ones crack and fail so different problem.

[captain chaos]

Paul,

i ditched the unit for another hydraulic unit (same as Arnie and Paul Gibb). It's a ford unit from burton power or Super clutch, and you can buy different thickness spacers to bring it up to the clutch face. if you want pics I can mail them to you.

[Paul McKenzie]

Captain,

 

Can't seem to Blatmail you, but I'd appreciate pictures of the installation you use plus details of the spacers I need etc.

 

 

Thanks,

 

Paul

 

Edited by - Paul McKenzie on 26 Mar 2005 18:33:49

[Rob Walker]

Paul,

 

I used to maintain a drysumped VX for a mate. I replaced the seals three times in one year. IMO the seal fails due to the seal sticking/bonding to the bore after getting very hot ( engine oil temps) and the car being left to stand for weeks between use, the next time the clutch is depressed a tiny bit of seal is removed. I then tried the system filled with Dot 4 SILICON brake fluid, the rational being that this would act as a lubricant/release agent and may prevent the seal sticking to the bore. Well its seemed to work as the car ran a full year without failure and now has a new owner so I do not know if its still Ok.

 

I concur with you on the bore scratches, these need to be sorted to stand any chance of the seals lasting. Sleeving the bore would be a good move.

 

Chellspeed the K drysump clutch fork is not a Ford item its a bespoke Fork made from guage plate and is a different shape and is not interchangable with the standard fork which is use along with the wet sump system ( this may be a Ford pattern).

 

Rob

 

Edited by - Rob Walker on 26 Mar 2005 08:29:10

[Paul McKenzie]

Thanks, guys, good info.

 

The Captain's route is a fairly radical one involving junking the Caterham DS bellhousing and installing an after-market hydraulic release bearing in a conventional wet sump bellhousing with an new external DS tank. The result is superb, but probably not a cheap fix.

 

I think we'll probably have a shot at sleeving the bore in a decent metallurgy, together with a switch to silicone based fluid. We'll have a word with our engine builder next week and see what he thinks about this approach. I'll report back when it's done if it appears to be a reasonable approach.

 

Paul

[Chelspeed]

> the arm is fabricated as there's no room to use the normal Ford arm

 

> the K drysump clutch fork is not a Ford item its a bespoke Fork made from guage plate and is > a different shape and is not interchangable with the standard fork

 

Isn't that exactly what I said? It's what I meant.

 

The hydraulic unit sold by Burtons isn't a Ford unit it's a bespoke unit made by Titan Motorsport. Ford do make one now, fitted to some of the duratech cars I think, but the Titan ones have been around for at least 10 years or so. The Titan one fits to the front of the gearbox in place of the seal carrier and "trumpet" bit which the release bearing slides along. To fit this you need to use the wet sump bellhousing and a remote tank as there will not be enough room inside the dry sump tank / bellhousing. This is what I use and it certainly works well. I didn't mention it before because, as you say, changing bellhousings and going to a remote tank is a big step.

[Foxy Smith]

Paul,

 

I've just put my engine back in. That's the third time in about four years of ownership. I've replaced seals, upgraded to the "latest" (steel piston) slave and use the recommended hydraulic fluid. As you can imagine I've put a lot of thought into solving this problem. The thing is I reckon the concept is brilliant just that it has not been executed well, which is what you allude to in your post above. I also thought about the possibility of resleeving and considered making up a stainless sleeve. What has prevented me from doing this however is the difficulty in achieving a tight seal where the drillings from the hydraulic feed and the bleed nipple would breach the new sleeve. I am pretty sure that however well fitted with the pressures likely to be generated fluid would find its way between the new sleeve and the bore in the bell housing so no better off the before. To be honest I think that if there is a way forward with this it is with improved materials for the o rings. I tried to source some Viton rings but have just run out of time and resigned myself to trying this next time which will be in another 11-12 months.

 

I think what is a great shame about this is that Caterham have obviously "washed their hands" of this concept. Other wise why would they have gone back to the less competent clutch fork for the K series dry sump bell housing.

[Paul McKenzie]

Foxy,

 

Yes, I've been thinking about that as well. I am guessing (at the moment) that with careful choice of sleeve metallurgy (expansion coefficient etc) and bonding agent a good seal will be possible. We'll see what the engineer has to say later this week.

 

BTW I agree with you that it's a great concept, but badly executed.

 

Paul

[Foxy Smith]

Paul, if you do turn up something useful be sure to let us know.

 

Thanks,

 

Alan