1991 vanden plas thanks new to site sorry if i posted wrong.
The rear sls raises about a minute after car is started to the top clicks a few times and then lowers all the way back down and is very bouncy the mineral fluid was low a qt filled that even tried the rear level sensor with no luck same thing please if you have a idea it would be greatly appreciated Joe njoeandjen@comcast.net Thanks in advance!!

 

The SLS sytem in these cars is prone to failure which is why Jaguar issued a TSB encouraging all owners to remove the SLS and replace the system with "conventional" shocks and springs.

The SLS on the '88 and '89's is also connected to the ABS braking systems so removing the SLS still leaves the braking system in tact. Over time components in the hydraulic system deteriorate and fail in which case you have two options assuming you have already removed the SLS...

1) replace the components one by one and try and eliminate the problem. Each component is expensive, the accumulator (which is located at the front of the car inside the right front wheel well, not at the rear as someone suggested), high and low pressure switches, hoses and lines and the Hydraulic Brake Servo (which is the girling part between the master cylinder and the brake pedal box) Haynes says this part cannot be overhauled and new ones cost just under $1000.

2) Completely remove the hydraulic system and replace it with a conventional vacuum booster which is a much cheaper and less frustrating option. The kits are readily available on line and easily installed by any competent DIY'er for a few hundred $'s. The Vacuum booster replaces the Hydraulic Brake Servo mentioned above.

When the Hydraulic Brake Servo fails you can usually tell this by looking for the green mineral fluid dripping from the brake pedal box in the foot well under the dash.

It must be noted that most of the ABS and Low Pressure Warnings that appear on the VCM are either caused by a leak somewhere in the system or a faulty relay located in the trunk. The relay can be opened and checked for hairline fractures in the circuit board with a magnifying glass, and if needed, re soldered. I strongly recommend disconnecting the battery when removing/installing this relay (or any relay for that matter) as it is incredibly easy to short out the circuit and melt connecting wires!!!

I know that this doesn't answer the question of how to fix and retain the SLS... unfortunately it is not a gremlin worth chasing.

Also note that clunking in the rear end is often a sign of the top of the shock absorber strut wearing through the bushings and the metal of the upper spring pan.

 

Some years later I am about to finish my SLS overhaul and will let you know if I manage to get the combination of struts, levelling sensor and valve block to work together..
My goal is to end up with a fully working SLS.

 

Gunnar, you aren't alone in this endeavor. I have recently purchased a 1990 US spec. Vanden Plas (Dailmler) Majestic. It is a very nice car in very good condition. As soon as I can get the stripped out hulk of my '96 out of my garage I'm going to give the '90 a full service and conduct a complete examination of whatever parts of the SLS may still be still left in the car. I have the original invoice for conversion to ordinary shocks and springs in the rear, and the car still has the original green mineral oil in it. I want to see what's left and if it is possible to reconvert the car and if it makes sense to do so.

 

I fixed my Anti-lock light by pulling the overvoltage relay in the trunk, big white relay.
It was as they say , just a cold solder joint or two. I also replaced the diode in it.
Problem solved!


I have an accumulator assy with switches available on Ebay right now. I coverted to Vacuum assist.

 

What is the name of the kit I need to switch to conventional

 

Jailter,

Go to the first page of this thread topic and see the post by Motorcarman. It contains the TSB attachment with the proper part numbers for the conversion.

 

Some years passed. : That URL is now outdated. You can find the indispensable Hydraulic Manual here.

It can be of great help to someone wanting to try to keep their levelling system operating.

Those levelling struts consists of two sections: A ride levelling part, and a conventional gas shock damper. Usually the shock part is what fails.
On my car the shocks froze and would not move at all. So it was like riding horse and carriage. For other people they simply lose any damping effect.
I still have the conversion project unfinished. Few people have been letting such a thing drag on for several years. But I was too busy at work.
So the car still in 2019 sits with brand new SLS shocks installed, waiting for me to do the final bleeding of the system and take a ride.

 

I am curious how the project will end up. I was actually looking at an '88 XJ6 recently and the seller said that other than some leaky hose the system works fine. Makes you wonder how troublesome these systems really were, hence the conversations, if one is still working fine on a 32 year old car. Being a stickler for originality I would absolutely keep the system going if I had an XJ40 with one.