My 1988 Vanden Plas has been leaking fluid that appears to come from the green reservoir that contains the mineral oil. All of the hoses connected seem to be tight but I can't determine where the leak is coming from. It has been leaking for months but I haven't noticed any difference in how the car runs. Is this leak of vital importance? I've considered purchasing another reservoir but don't know what it's called. Anyone have any ideas or a solution?

Thanks,
Big E

 

My '88 XJ40 was leaking mineral oil from the brake Low Pressure Switch. Located under the passenger right side front of the car.

 

Thanks Frankie, I'll check it out.

 

I've done some checking and found that the mineral oil andbrake low pressure switchare designed to work in conjunction with the high pressure hydraulic system used for brake boost and the self-leveling of the rear suspension.Mycar's rear suspension was reverted to conventional shock and spring many years ago.Since this is the case, should I still worry that the brake low pressure switch is leaking mineral oil? My mechanic, unaware that the rear suspension has been reverted, keeps filling the reservoir.

 

Yes, other systems depend on the mineral oil. The 88/89 cars use it more than the 90-94 models. I have new switches for $342.42. Yikes!

 

I also have a detailed diagram of the hydrolics on our cars. If you want it send me your e-mail and I will attach the document.

 

Frankie,
I'd appreciate the diagram of the hydraulics. Here's my e-mail hrdknox88@aol.com
Thanks,
Big E

 

could you send it to me too please? carguy101@cfl.rr.com

 

I had a similar problem with my vehicle when first purchased. I ended up topping off the mineral oil reservoir but it still leaked....apparently from beneath the main cap where the two feed hoses are located. I thought that the reservoir was not under high pressure however that may not be absolutely true. There must be some pressure relief hole beneath the cap that allows mineral oil to leak if the reservoir is over filled. After topping off the reservoir with fluid several times, she would still leak. I then decided...maybe I'm over filling the reservoir. So I removed some of the mineral oil, making sure that the green level indicator on the reservoir was still green (that means its full) and the leak eventually stopped. BTW, the hoses were in fine shape so they were not suspect in my leaking problem.

What it comes down to is this....since you've already converted to standard shocks from the SLS system (hopefully your valve block has been adjusted for this conversion, your next step is to convert your braking system to an after market brake booster system. This will remedy your "low brake pressure" VCM code as well as eliminate future braking concerns. The best part is that after the conversion, the hydraulic components: valve block, accumulator, reservoir and all associated piping can be removed. This will give you ample space within the engine bay for accessing any engine components not available before. I am in the market of doing that conversion to my car hopefully by spring.

Alot of information has been posted in other Jaguar forums regarding this conversion (check out Jag-Lovers archives). In the interim, my "low brake pressure" light keeps popping up perodically when I brake alot however goes away when I accelerate the vehicle. (This VCM waring is probably due to the accumulator, which is not worth replacing).

If you're serious about keeping your vehicle and not upset in trying to keep everything OEM, the brake booster conversion is the way to go.

Good luck ; )

 

I thought 1992 was the last year the XJ40 came with the self leveling suspension? I had a 93 and it didn't have it.

 

93 and some 94's still had. All 1994 XJ12's had it. You get into a real mess with the 94 models, because the later ones had the X300 suspension so the standard conversion kit doesn't work.

 

Thanks Fritterfran, I didn't know it could be converted...I'm on it.

 

Hey thanks for sending that to me it was really helpfull!!

 

Hi guys I'm having the same problem. can you pls send the diagram to me as well.
Cheers Peter
e-mail ptt8170@bigpond.net.au

 

Hey there Frankie, I realize this post is over 4 years old, but I sure would like and appreciate the diagram of the hydraulics you have for my 88 XJ6. If you are still here on this site! Thank you joenatola@gmail.com

 

I actually found this today while looking at 'How To' threads under download section.

S73 hydraulics publication xj40.pdf

This forum rocks.

 

Hi All,

I thought I would add to this timely post with my experience of the hydraulic system. I have an '88 xj40 3.6 and funnily enough I've just been down in the garage attending yet again to this system.

I had the dreaded green "blood" leak when I purchased the cat a few years ago and having previously replaced both pressure switches along with a new (aftermarket) accumulator, some tinkering with the valve body, replacement of the hoses from the reservoir to the pump (the top hose had deteriorated and cracked with age on the underside which wasn't easily detectable) and also re-soldered the relay in the trunk with those nasty little hairline fractures in the circuits which are responsible for the most of the VCM anti lock failure messages.

I thought after all that work I had the issue beaten..... until yesterday when I spotted some drops of oil on my shoes after a drive and more in the foot well.... so I grab my torch and do my best Houdini act under the dash and low and behold the brake pedal box was dripping with the green stuff...another wonderful Jag feature which lets you know that it's broken by pissing all over your feet!!! A quick check of the haynes, a phone call to Gary at JagAyre in Melbourne and I now have a replacement sencod hand Brake Servo on it's way via the mail (And I thought the accumulator and switches were expensive...anyone looked up the price on a new one of these!!!! and apparently they can't be overhauled???).

For those not in the know, the brake servo is the hydraulic part located between the brake pedal box and the master cylinder and the part most people throw away when they do the vacuum conversion......which I should have done in the first place!!!!!

Oh well, the benefit of hindsight but I'm too far in to getting it sorted now to turn back.... so with that said I have one question for which I cannot for the life of me find an answer to anywhere.... does anyone know if the green "blood" system (Castrol HSMO or Penrite LHM+) needs to be bleed? If so, how?

Thanks all for your pending input!

 

I was told that the servo could not be rebuilt, and had no luck in locating one. Hating to be told something could not be done, I found some similar seals and rebuilt mine. Lasted about a year before it started leaking again....

I picked up a vacuum booster for a later model Jag but have not made the change yet. I am in the process of relocting, so it will likely be spring before I can get back to work on my VDP. I am wanting to paint it at the same time I paint my Bel Air. Finding a place with adequate shop space has been the challenge! I will also be modifying the rear suspension to remove the SLS.

 

The mineral oil system has got to be the biggest technical/engineering blunders ever done by Jaguar on the XJ40. Even Jaguar come up with technical fixes/addendum's to replace the system(s).

If the purpose for your XJ40 is for daily use, then get rid of the SLS and covert the brake system!

If your vehicle purpose is for concourse shows, then maintain the original equipment, and buy every spare part you can for the SLS and brake systems.

These systems will fail even at low milage, my first repair the the SLS was at 45K miles, and I was dumb enough to fix it two more times after that!!!

Shame on me.