On my '88 VDP, I converted my brake system from the original troublesome hydroboost system to a vacuum brake booster,using one from a Series III XJ6. I removed all the old hydraulic parts including the tank and accumulator,etc. The new system works great but the issue I'm having is that I'm getting fault codes for low brake pressure and power fluid low. If I recall,isn't there something that has to be bypassed by jumping a wire across one of the connectors to the old hydroboost system? I also keep blowing a Circuit 2 and Circuit 3 fuse for Power Brakes and Ride Leveling. I assume this is somehow connected. Any help or suggestions?

 

Very interesting post. I would like to rid myself of these system but it probably will stay in the car for a while. How did u manage to pull off the retrofit? Do you have a link to a write up or something?

 

It's a pretty straight forward swap. The only thing you'll need to fabricate is an adaptor plate using 1/4" think aluminum plate (about a 5" square piece). You also need to adjust your brake light switch and relocate your coolant tank about 1 1/2" further forward. Finding a good used Series III booster isn't too hard as they still pop up at salvage yards. I know others here have used different boosters.Here is a write up that may help......Jag-lovers' Ebooks

 

Hi, this is Andrew from Jaguar Specialties. Just a side note here on your thread- back in 2008 we designed and currently still sell the kit to convert the early XJ40 brake servo system to vacuum style. It's a great conversion and we have well over 400 of them out in the field ( which is a big number for the Jaguar community), all over the world. Our customers love it and it's a proven, reliable, safe solution. No fabrication is required by the end user.

The kit includes the key special mechanical components and very detailed installation instructions, including (among other things) information on where to get a proper size vacuum source on the engine, what to do with the (now disabled) hydraulic pump and also how to disable the "low hydraulic pressure" and low hydraulic fluid" warning messages on the dash. Installation does not require any special tools and takes about 3 hours

We have a short write-up on our website:

Jaguar XJ40 Vacuum Brake Servo Upgrade

For more info, please Email me or send a PM ....

Thanks

Andrew
408 839 5569
Jaguar Specialties Website

 

Ahhh I see that it will not work on late XJ40s... Im sure the future will hold promising advances in technology and my cat will someday be less complicated in the braking department.

 

I'm not positive but I believe the only difference between the earlier models and later models was the style of the coolant tank.

 

Although the braking system changed around 1990/91,the later system should also be able to be converted. Like I said,an earlier coolant tank may be required. Another option may be fitting the whole brake assembly from an X300 to a later system. It may work since the later XJ40's and X300 are similar.

 

At the moment there are no kits out there to convert the later (90-94) XJ40 brake systems to a standard style master/vacuum brake booster configuration. And it would not be a simple procedure- on these models the ABS is integrated into the main control of the brakes (the master cylinder, if you will) so changing anything there loses the ABS entirely.

Also. the new system, made by ATE in Germany, is very reliable and should not need the major changes/upgrades of the earlier cars. All that is required is an occasional change of the brake accumulator unit (they slowly fail over time) and changing the brake fluid (Dot 4 only) every 2-3 years. That's it.

If you have a later car, you're stuck with the later system, which should be fine.... Putting in an X300 master/booster may be an option, but again all ABS function is lost......

 

I'm considering changing my second brake accumulator in 20,000 miles. The red "Brake" warning light is flashing. I'll change the fluid to see if that helps and I do have a spare accumulator in my parts drawer.
However, I have the complete ABS system from the '96 VDP I scrapped out a few years ago. I'm not an enthusiast of ABS brakes. In the 30 years or so they've been in cars I've never used them - not once. I guess I know how to drive...?
I'm considering removing the ABS from my '90 Majestic entirely and just having the "old" vacuum assisted brakes. As these cars get older spare accumulators, pumps and pressure switches will become more problematic and pricey. My car is 28 years old with a build date of '89 and I can see a major PIA may not be that far in the future.

 

I recently did the conversion. I’ve seen that everyone that has done this has removed all of the hydraulic system. What do I do with the hydraulic pump?

 

If the SLS has been replaced, then the pump can be removed from the front of the engine.

If it has no fluid, it could seize and damage the engine?

Jaguar used to offer a plate to cover the drive mechanism. A plate with 3 holes will work fine.

bob