My 1988 Vanden Plas uses the hydraulic mineral oil system for the brake booster. Recently the brakes became soft when pushing on the pedal, and the “Low Brake Pressure” warning appears on the Vehicle Control Monitor (VCM). When I checked, it needed mineral oil. After I filled the reservoir with mineral oil I soon discovered a leak from the plug on the side of the reservoir. I repaired the leak by replacing the plug, and then filled the reservoir again with mineral oil.
The brakes are still soft, and the “Low Brake Pressure” warning still appears on the VCM. Although now when I pump the brake pedal twice I get good pressure on the second pump.
I am thinking that air might have gotten in the system from the leak in the reservoir, and that bleeding the brake system will get brake pressure back to normal. What do you think?
Can’t do any harm. Try it and report back.
The reservoir for the mineral fluid is self bleeding. The system you are about to bleed was unaffected by the work you did, the fault is on the hydraulic side I.E. brake booster or your accumulator
John W., Thanks for your reply. I get good pressure after pumping the pedal once. If the brake booster were bad would I get good pressure after pumping the pedal?
the most common problem in your 88 is the accumulator, most owners have converted their cars to vacume brakes. you may need to read up on the Ebooks area of the site regarding brake issues and accumulators.
wish I could find a straight forward answer to the conversion, part numbers and such, mine has been out for far too long! If my engine dies so do my brakes, not good.
Yes I agree. I’ve decided to have the system converted. There is just too great a chance of problems mounting with the hydraulic system.
If you find all the parts let me know exactly what you used. I really want to upgrade but just to lazy to locate the various parts.
That helps alot, thanks.
I decided to purchase the conversion kit that has instructions and everything needed to do the conversion. The only extra things I had to purchase were two nuts and lock washers to fasten the booster to the master cylinder, and four hose clamps. My biggest concern was drilling and tapping into the manifold to make a vacuum port for the booster. Luckily everything worked out to perfection.
The accumulator/switch was difficult to remove from underneath the car as it is in a tight spot with little room to maneuver. It was easier to remove by cutting the hydraulic lines rather than trying to remove them with a wrench. I am not a mechanic and this is by far the most complex thing I have done on an car, but it wasn’t as hard as I expected.
I just ordered the kit from jaguar specialties they claim it is all inclusive, hope they are right!
who did you get the kit from?
I purchased the kit from Jaguar Specialties. The nuts and washers to the master cylinder are not included. The instructions that came with the kit don’t list them as included. The nuts and lock washers I bought that fit were M10-1.50.
I just had the brake fluid changed…It had to be 10+ years since it was changed. All I can say now is wow! The brakes feel as good as the ones in my 2021 vehicle. I would strongly suggest changing the brake fluid after doing the conversion.
did you do it yourself?
No. Had a shop do it. I made sure they used DOT4 fluid.