Submitted by alan.barc@veri… on Sun, 10/06/2013 - 13:35

I've recently had problems with dragging brakes. This seemed to be the front pistons not retracting so I rebuilt the calipers. Problem solved - or so I thought. Then I experienced classic servo issues with the brakes binding even more severely at times. Disconnecting the vacuum line seemed to be a solution, so I replaced the servo system with a new unit. Problem solved again, or not. Driving from Dallas to San Antonio via I-35 on a hot Friday to attend a Concours this weekend I encountered heavy stop and go Austin traffic. Before long the brakes locked up and I was lucky not to get rear-ended. Just managed to get over to the shoulder, where I bled some fluid from a caliper until the pressure reduced enough to free the brakes. This was repeated on feeder roads. Waiting a few minutes had the same effect of freeing the brakes.
The consensus seems to be that the Reaction Valve is sticking when hot. It and the Master Cylinder were replaced 18 months ago due to the original(?) leaking. This morning I drove from S.A. back to Austin in cooler weather and with minimal braking with no problems.
Comments, ideas and similar experiences/solutions would be much appreciated. Do I need to replace the entire Master Cylinder set up, or just the Reaction valve? In view of the likely heat in the system, what about the brake fluid? Thanks

Submitted by lbc.resto@veri… on Thu, 10/24/2013 - 18:27

Too much to list here, but in detail on JL.

I recently found that my MC IP o-ring was 4 thou bigger than a new one that came in a "genuine Jaguar" MC repair kit. I changed it out, added lots of red grease and it was much better; but I could still feel a change once the car got really hot. The brakes didn't stick, but the pedal action changed and some pedal slop appeared, though not as bad as before.

Since then, I moved the vertical heat shields back as far as they will go to minimize hot air spillage round the back onto the MC.

The hot weather has now disappeared, probably until the Spring, so I can't confirm that it is fixed, but it is all behaving properly at the moment. We will see.

Submitted by mr.jwhey@rocke… on Thu, 10/24/2013 - 17:18

If you figure it out, please let me know as mine has been doing this for a while- when hot sticks and then releases after a few seconds. No pull to either side. I've tried everything including:

New master
Rebuilt servo, then bought new servo
Added servo heat shield
replaced all flex lines w/ s.s
Installed vaccum gage mounted to hood to check rv operation while underway.

At this point the only thing left to replace is the hard lines running fore and aft.

Submitted by alan.barc@veri… on Mon, 10/21/2013 - 09:43

I replaced the master cylinder in Austin a week ago, drove the 200 miles back to Dallas then to Houston and back this weekend (550 miles) with no braking issues at all. Although the weather has been cooler I believe the new master cylinder from Welch has solved my problem of dragging and locking brakes.

Submitted by alan.barc@veri… on Mon, 10/07/2013 - 15:17

Disconnecting the vacuum hose from the inlet manifold (plugged with good old duct tape) only gave me temporary relief after 200 miles of hot driving. Ordered a new "better quality" master cylinder/RV today. We'll see if that cures the issue this Sunday on my 180 mile trip back from Austin to Dallas.

Submitted by lbc.resto@veri… on Mon, 10/07/2013 - 13:38

It also seems to be repeating my posts as well; perhaps JCNA is running hot as well.

What has helped me is my discovery this weekend that the brakes release instantly when the RV is pulled and lock up again when it is released. It is looking more and more like the intermediate piston in the MC, but I don't know what else to do with it that I haven't already done.

I wonder if the IP bore on this newish MC is the correct dimension: I tried lightly polishing it before with very fine finishing paper? Is the supplied seal the correct size and material? How do we find out if one hydraulic fluid has more lubricity than another same spec brand?

Submitted by NE40-48370 on Mon, 10/07/2013 - 12:45

Sorry for the repeat Ian, it resent it automatically just now when I came back to check this lunch time.

I guess by 'never' I'm just checking that the incidence is so overwhelmingly different with/without vacuum hooked up, that we can definitively say (or as near as makes no difference) that it is a vacuum-related problem.

Without making that crystal clear demarcation, you could keep chasing your own tail.

Submitted by NE40-48370 on Mon, 10/07/2013 - 12:40

Must say I prefer Ian Sharkey to 'Smeg99' or whatever you're called over there! :-)

Just to confirm, if you disconnect the vacuum at the engine and plug the manifold, you can drive around for as long as you like, as hot as you like and the brakes never, ever, stick. Correct?

Pete

Submitted by NE40-48370 on Mon, 10/07/2013 - 10:03

Must say I prefer Ian Sharkey to 'Smeg99' or whatever you're called over there! :-)

Just to confirm, if you disconnect the vacuum at the engine and plug the manifold, you can drive around for as long as you like, as hot as you like and the brakes never, ever, stick. Correct?

Pete

Submitted by lbc.resto@veri… on Mon, 10/07/2013 - 09:33

I referred to seal stiction to cover all hydraulic seals, including those in the calipers. That said, if you had this on a caliper then both the left and right side brakes would have to start sticking at the same or you would notice the pulling while driving.

On my car, with the brakes sticking and parked on a slight slope with the handbrake off, the brakes will release instantly the RV is manually pulled open. Letting go of the RV makes them go straight back on without pedal activation. This suggest a condition that is causing the servo to have differential pressure when it shouldn't have. It might be the RV activation piston in the MC. I have had it apart before, slathered it with red brake grease and all has been well for a while, but then it returns. I went looking for other faults, but I only discovered the RV trick at the weekend, so I will turn my attention back to the RV piston.

Submitted by bonnettoboot@e… on Mon, 10/07/2013 - 08:50

There is another issue, poorly made calliper seals, there are aftermarket seals which are softer than the originals, as a result they drag in the calliper when they get hot.

Submitted by lbc.resto@veri… on Mon, 10/07/2013 - 08:44

There is a long history of discussion on this very topic, including a currently active one, on JagLovers. Lots of discussion on vacuum, hydraulic seal stiction and the composition of new vs. original style brake fluid.

I look forward to finding a resolution so that my car is not a PITA to drive on a hot day.