XJ12L 1975 SOFT BRAKE PEDAL

[bccanadaguy]

28,090 Miles One owner (Me)
Always kept indoors. Some year,when taken out brakes were bad. Since 1998 the car has new master cylinder, 4 remanufactured calipers,new reservoir,new rubber hoses,silicone fluid, new proportioning valve.. Rotors are good. Booster works.Repair shops have given up. I have given up. Car gets brought uot, worked on and put away, as it's unsafe to use. This has been going on for years.

NEED HELP!!!! /ubbthreads/images/graemlins/canpatriot.GIF

 

[Steve]

Firstly, welcome to the forum.....we will get you sorted out between us with any luck. My first thought was "old fluid", then I read about you changing to silicone. My next thought was that the rubber hoses are expanding under pressure. Were all of the hoses replaced? Next thing is if there is a leak, evident or not. Does the fluid go down at all when you pump the brakes? Where's Jack when we need him?

 

[piman]

Hello BCC,
presently, what actually happens when you drive the car? Does the pedal, on initial application, go straight to the floor and pressure can be found by pumping or is the pedal just low and feel soft?
I know you say the repair shops have given up, but what have they tried. I think we need a lot more information to try and find the problem. By the way, is it dual circuit?

Alec

 

[Webserve]

I know you are going to hate to hear this, but the problem is not an uncommon one when silicone fluids are used. Most of the owners I have run into with this problem have flushed the silicone and gone back to DOT 4 and the problem went away. You need to flush the system WELL. For some reason silicone, while a superior product generally, does not work well with these braking systems. I thought about using it on my 1967 Jag 420 until I read the problems others were having.

I used the DOT 4 and I have not yet had a problem with the re-build and my brake system is very similar to yours.

Webserve

 

[John S Farrington]

Canada guy, I have refrained from answering your brake problem since it must be serious, and with respect to brake hydraulics, it is hard to totally communicate without on the spot observations. I will try to make sense of your predicument. First of all, your Jaguar with properly operating brakes, will have adequate stopping power with only the front two calip[ers operational. These are easy to work on and the rear two calipers are a nightmare. Considering this, I would concentrate all initial efforts to be with the master cylinder and brake power servo and the front two calipers/pads/rotors. If the rear calipers appear to be free of leaks, then ignore them. If they are wet, then block off the hydraulic line going to the rear from the master cylinder. Now find out if you have any brake fluid leakage on the calipers or the master or in the lines. I would flush the system and go with dot 4 spec fluid. Next, inspect the front calipers and determine that they are installed with the bleed port on top, not on the bottom. If the bleed port is on the bottom, someone has crossed the left with the right caliper and installed them upside down. They will never be able to be bled successfully in that position. If all is go and the front cylinders are bled but still no brakes than let me know and I will give you more advice. I think this is adequate for your first homework assignment.

 

[bmurphy7369]

As Webserve, Jack and Steve have recommended, I think the idea of reverting back to Dot 4 fluid sounds like the inexpensive and logical first step to eliminate the fluid as the possible source of the problem. Silcone fluid is by nature slick and is often used as a lubricant as well. It would seem that these attributes would cause a possible "find any small pinhole" scenario which could be drawing air into the brake lines. The Jaguar you have was made to use a heavy fluid and I would think that the silicone fluid could definitely be the source.... Jack's troubleshooting suggestions are perfectly lined out, but hopefully the first step, the DOT 4 fluid, will eliminate the other steps. I had the opposite problem, the hard brake pedal with a bad servo, which eventually caused a friend to total the '86 XJ6.. I guess it could also be possible that the servo could operate properly but with a bad seal or diaphragm, could cause a pedal to be too soft, but not to the point of having almost no stopping power... just my guess on the servo, correct me if I am wrong, guys.

Brian /ubbthreads/images/graemlins/cheers.gif

 

[bmurphy7369]

Sorry, by the way, Welcome to the forum!

Brian /ubbthreads/images/graemlins/patriot.gif

 

[sparkydave]

It sounds like you've got most of the bases covered, and despite my being a supporter of silicone fluid, you might consider going back to DOT 4 and seeing if it makes a difference. I've been using it in my Midget for a while, and I didn't notice any different feel in the brakes when I switched over. Then again, I don't know how a Jaguar's brakes are supposed to feel.

-Dave

 

[maynard]

I agree with the rest or the listers about going back to DOT 4, preferaably Castrol LMA.

When you replaced the master, did you bench bleed it? Master cylinder rebuilders all recommend it.

 

[vettedog72]

This problem leaves me on the cliff. It's not enough to go through the trouble of getting the "best" brake fluid for the brakes but after that trouble and expense to have no real suggestions to resolve the all new brake components and the "best" brake fluid to only find you should have kept DOT 4, 5 or the fluid to will ruin the brake system if not changed on a periodic basis.

Did you get the problem resolved; if so, how? If not, I suggest you to find a web site that promotes the silicon fluid and they may resolve those users may resolve the problem.

 

[John S Farrington]

Canada guy, Did you check to see if the front calipers were installed correctly as per my previous message?? You seem to have a problem that goes beyond brake fluid and needs some fundamental trouble shooting.

 

[vettedog72]

Canada Guy:
Did you get the brakes sorted out?