Hello,

I have a 1988 Jaguar XJ40. I recently completed the conversion to the vacuum servo and have ditched the hydraulic system all up. I replaced all rotors and calipers, master cyl and I am attempting to bleed the system.

I am able to push out clean fluid when I bleed the brakes and have done this a number of times.

No matter what, I cannot get a pedal and the system seems to have air. I can get a pedal if I pump it up, but of course will be soft after a minute.

The system has frustrated me and I just cannot put my finger in it? I am not losing any fluid and the ABS I have not touched.

This should be easy, it is just a simple hydraulic system and the ability to bleed the system seems like I am missing something.

Could the ABS be an issue? Is there are procedure for that.

Any help and pointers are appreciated.

Larry

 

Have you tried to bleed in stages???

Pump pedal and bleed Master.
Pump pedal and open each line to Bosch ABS block.
Pump pedal and open each caliper.
(note) the rear should only have one line to bleed as both calipers share it but ensure that both calipers have no air.

You could also try to 'pressure bleed' the system with a proper low pressure bleeder.
You might try to Vacuum bleed the system to PULL the fluid through the system.

bob gauff

 

The air can get trapped in new calipers. Try hitting the calipers with a hammer to dislodge any air bubbles. As mentioned previously bleeding in stages is a good idea.

 

Hi Larry,

Bob and icsamerica have given some very logical responses.

I'm no expert on the vacuum servo conversion, but the one additional possibility I can think of is that the master cylinder pushrod may need to be adjusted so it moves further into the master when the pedal is depressed (assuming there is any adjustment available).

What else is there besides air in the system and the master pushrod adjustment? If the vacuum source to the servo was inoperative or the vacuum was insufficient, I'd assume you'd have a high, hard pedal, so your vacuum is probably fine.

A good mystery - hope you solve it soon.

Please keep us informed.

Cheers,

Don

 

You can eliminate an airlock as the cause if you do a vacuum bleed. Rent or buy a hand-pump vacuum bleeder like a mityvac and suck it through like Bob Gauff suggests. Start with the caliper furthest away from the master cylinder and work your way forward. Hopefully you'll get some bubbles!

Good luck with it

Larry

 

Larouex,

I don't know if you follow jag-lovers.com, but here is an interesting and relevant thread to your current endevour:

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You will have to join to view, but it's a free site as well and the discussion in the thread is relevent to your conversion. It would be worth reading and perhaps joining the discussion since the participants have either converted in the past or very recently to vacuum. The title of the thread is [xj40] Vacuum brake booster conversion , in the XJ40 forum, it's currently the first thread listed.

I converted mine about 10 yrs ago, but had a mechanic do the work (I bought the parts) and have never regretted the conversion. Been flawless.

 

Larouex,

I tried to send you a private message advising you of the jag-lovers thread, but evidently you didn't turn on that feature. This forum does notify a person of thread updates, but it's slow in doing so, usually 12 or 18 hours later at the earliest.