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Pushing in brake pistons during pad renewal,


stefank

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Hi all,

with some other makes of cars (i.e. Jaguar) there are problems with ABS (antilock) units due to dirty fluid beeing pushed up the lines during piston compression while renewing brake pads. The contaminated fluid affects some valves in the units, which results in uneven brake distribution under light braking. This is not too uncommon with the so called XJ40 type (1988 - 1994). While with a properly maintained vehicle the fluid should be changed at least every second year, this should be no problem, but reality is different...

One solution is to open the bleeder screws at each caliper while pushing / turning back the pistons, this will let the fluid in the calipers purge out, no brake fluid is pushed upstream. This is how I do it. Am I over-coutious?

Do you push back the calipers this way or simply without opening the bleeder?

What do you think?

Best

Stefan

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I always open the bleeders when pressing the pistons. And I also do a fresh fluid flush at all four calipers whenever the plumbing has been opened for any reason.

Jim

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I usually press in the pistons, then flush the system

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For brake pad replacement, the front pads can be pressed in. The pistons in the rear calipers must be screwed in.

If you're just flushing the brake fluid, you can remove the fluid from the master cylinder, wipe it clean and add new fluid. Then bleed all four calipers.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Hi all,

thanks for your replies. It's always interesting to share opinions.

When I bought a 94 XJ40 Jaguar some years ago, it had the problem that under light braking it would pull to one side. Braking harder it would pull straight. Usually symptoms like this are caliper-related, but removal and overhaul of both front calipers didn't cure the situation. Then I did some investigation and found out about this problem. There are hydraulic valves in the Bosch ABS unit which are VERY sensitive for dirt / contamination, and they were affected by dirty fluid pushed inside. This may also have to do with materials used in the system, i.e. different metals reacting with each other or the like, which may qualify this as a problem of a certain make/model, I don't know.

I rhen read that flushing the system with fresh fluid and working the antilock (i.e. braking hard on wet or gravel surfaces) may free up the valves. I tried that, it improved the situation a little bit but not completeley.

So I want to avoid that happening on another car especially on my nice Cadillac :D

Thanks again for your thoughts

Stefan

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Hi all,

thanks for your replies. It's always interesting to share opinions.

When I bought a 94 XJ40 Jaguar some years ago, it had the problem that under light braking it would pull to one side. Braking harder it would pull straight. Usually symptoms like this are caliper-related, but removal and overhaul of both front calipers didn't cure the situation. Then I did some investigation and found out about this problem. There are hydraulic valves in the Bosch ABS unit which are VERY sensitive for dirt / contamination, and they were affected by dirty fluid pushed inside. This may also have to do with materials used in the system, i.e. different metals reacting with each other or the like, which may qualify this as a problem of a certain make/model, I don't know.

I rhen read that flushing the system with fresh fluid and working the antilock (i.e. braking hard on wet or gravel surfaces) may free up the valves. I tried that, it improved the situation a little bit but not completeley.

So I want to avoid that happening on another car especially on my nice Cadillac :D

Thanks again for your thoughts

Stefan

Stefan,

The ABS on my car is BOSH as well. Two solenoids in the hydraulic modulator are responsible for the front brakes, and one solenoid works for both rear ones. For some reason one of rear brakes did not get fluid from the modulator. I could not pass NJ state inspection because I did not had left rear brakes at all. The modulator was about $1,600 at the time so I decided to fix it myself somehow to pass the inspection. I just spliced the the brake line coming out of the modulator so that the both rear brakes would get pressure. Sure they got half of what they were supposed to get but at least the pressure was even and I could pass the inspection.

Working ABS on a gravel road could be a good idea, but I never tried that.

The saddest thing in life is wasted talent

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Stefan,

The ABS on my car is BOSH as well.

Yes, the correct procedure depends a lot on who manufactures the braking system. Bosch systems (The Bosch III system on '92 and earlier Allantes for example) are particularly sensitive to any contaminate in the brake fluid... On these cars you MUST open the bleed screws before/as you press in the piston. If you don't you'll be buying an accumulator ($$$$$) about 6 months later...

On cars not equipped with the accumulator the procedure of opening the bleeder screw to flush the old fluid while changing the pads is still a good idea.. But technically not required.. It just turns a one man job into a two person project... (bonding time with your spouse... It is Valentines day after all)

IF you decide to do this... take extra care manageing the old fluid...

Brake Fluid will eat the paint off of just about anything...

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I had a fine fox in front, I had three more in the back

ZZTOP, I'm Bad I'm Nationwide

Greg

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Adallak,

cute idea...didn't they notice that during inspection? If the would have noticed it, would your car have passed?

Stefan

Stefan,

By the time I "fixed" the problem I moved to Pennsylvania which has a very friendly state inspection. Not only are Pennpeople nice (compared to those in NJ and NY :lol: but also very smart. They believe that if your car can reach the shop on its own, it's good enough! :lol:

The brake line modification was not that difficult. The main prblem was to find a "T" with right threads (both metric and English!). Cutting and flaring the brake lines right on the car made me a little bit nervous, but everything worked out well. I am pretty sure my fronts now do some 90% of braking and the rears take care of the rest (next to nothing).

The saddest thing in life is wasted talent

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Interesting read!

Over here, if they would notice that brake modification during the state inspection, they would take your stamps off the licence plates, which means you are not allowed to drive it any more...you have to call a flatbed to the inspection site and have it transported to a place where the car is repaired, and then bring it back for re-inspection after repair. Of course you can dump it, if the repair makes no sense any more.

They even sent you back if just your parking brake is different side-to-side by more than a certain percentage.

Stefan

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Interesting read!

Over here, if they would notice that brake modification during the state inspection, they would take your stamps off the licence plates, which means you are not allowed to drive it any more...you have to call a flatbed to the inspection site and have it transported to a place where the car is repaired, and then bring it back for re-inspection after repair. Of course you can dump it, if the repair makes no sense any more.

They even sent you back if just your parking brake is different side-to-side by more than a certain percentage.

Stefan

OMG! Funny thing is that half of population in PA is of German descent. :D

The saddest thing in life is wasted talent

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OMG! Funny thing is that half of population in PA is of German descent.

Well, maybe now you know why.

Never underestimate the amount of a persons greed.

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