XJ6 & XJ12 Series I, II & III 1968-1992

Series 3 Brake fluid change

 
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Old 02-06-2019, 01:02 AM
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Default Series 3 Brake fluid change

I am getting some brake pedal fade, particulalry when very hot and pumping the brake firms it back up again temporarily. I took it to a non jag specialist to have the fluid flushed and replaced, but they were too scared to do it in case it blows out the master cylinder etc.

how likely is this. He confirmed the fluid was quite contaminated which was my assumption, I assume there is water in the fluid which is evaporating when it’s hot and causing the soft pedal.

is this a common result of flushing the fluid?
 
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Old 02-06-2019, 07:01 AM
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When I did mine last summer, I used the "vacuum" method applying vacuum from each caliper in turn until the fluid ran clean. Almost a one person job, but nicer if you have a helper to keep the master topped up (and to hold your beer). Using this techique there is no need to pump the master cylinder and so you avoid the dreaded pontential piston seal damage. Took me about 5 minutes per wheel to bleed, not counting the time to jack and remove the wheels.
 
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Old 02-06-2019, 07:21 AM
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Originally Posted by AnD3rew View Post
but they were too scared to do it in case it blows out the master cylinder etc.

how likely is this.
Cowards!

There IS some truth to what they're saying, though

If the pedal is stroked to full travel during the process the master cylinder piston will travel to areas of the bore that might be corroded. This can damage elderly seals.

But, every decent mechanic is aware of this possibility and doesn't put the pedal right down to the floor.

OTOH, there's a case for disregarding that age-old method. Any master cylinder with corroded bores and fragile seals that can't tolerate the flushing process is due for replacement. If a master cylinder is gonna blow out I'd rather find out while flushing the fluid....as opposed to while driving.

Cheers
DD


 
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Old 02-06-2019, 05:22 PM
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What are your rear calipers like, (or maybe the front ones) ? Ever been inspected/replaced/stripped&rebuilt ?

Many years ago in the late 90s I had a 1980 XJ6 and had symptoms similar to yours, (occasional loss of pedal pressure). This culminated in an "incident" (brown stuff in one's pants type), when descending a steep hill on our way to the south of England for a holiday when all brake pressure was lost. Pumping restored some pressure, but on pulling into a garage/filling station that happened to come up, white smoke was pouring out of the back of the car underside. Inspection on a ramp showed a seized caliper piston had caused the caliper to heat up and the brake fluid to boil. The seal was toast, basically ! The mechanic eased off the piston. Despite this, I am an old soldier, so now aware of the problem, we carried on the rest of the 200 miles to our holiday destination, but with a large can of brake fluid to top up. And came back the 250 miles as well a week later !!!

New calipers cured the problem. Had to have new diff seals too.
 

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Old 02-08-2019, 11:42 PM
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Originally Posted by Doug View Post
Cowards!

There IS some truth to what they're saying, though

If the pedal is stroked to full travel during the process the master cylinder piston will travel to areas of the bore that might be corroded. This can damage elderly seals.

But, every decent mechanic is aware of this possibility and doesn't put the pedal right down to the floor.

OTOH, there's a case for disregarding that age-old method. Any master cylinder with corroded bores and fragile seals that can't tolerate the flushing process is due for replacement. If a master cylinder is gonna blow out I'd rather find out while flushing the fluid....as opposed to while driving.

Cheers
DD
yes I was thinking this as well, if its going to blow out Id rather it happened in the workshop than on the road.


the vacuum method does sound attractive, what do you use to generate the vacuum?
 
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Old 02-09-2019, 07:01 AM
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Picked up a $30 Vacuum pump/brake bleeding kit on Amazon. There are lots of choices out there.
 
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Old 02-10-2019, 08:51 AM
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I've had lots of luck bleeding brakes on several different cars using the mityvac method. One man job and very straightforward.
 
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Old 02-10-2019, 09:48 AM
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Red face

I'm with Doug. I did learn something. Lighten up on the foot when bleeding.
But, for sure a failure during the process portened one in a less safe place.

Lucky, I guess. I've bled many on many critters on the "pump, hold , crack, tighten. At times into a jar, and others on to the mat.

I do have a neat little HF sourced Vac Pump that will do that and more...

Soft pedal usually is indicative of air in the system. It compressed. Water not so much. Steam, yeah, I suppose.

Carl
 
 
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