David ā¦
Once again, did the vacuum boost system ever work properly after you did the modification or was the problem there right away?
Before you disconnected the master brake cylinder did you do the 2 booster checks I listed?
Iāve never tested the brake booster with the engine running and the master brake cylinder disconnected. Did you feel any difference on the pedal with the engine running vs off? Seems like there would be no resistance either way even if the booster was bad because itās not push against anything.
Sorry, but there is no way that booster is rebuilt with rusted studs / original paint and no markings of the canister opened. Hate to call the guy out, butā¦
I would be willing to bet the booster is simply just bad.
The actual rebuilt units are about $150.00.
EDIT - scratch this reman unit, your early master wonāt work with it.
I would suggest just requesting a replacement booster.
jeff,
i agree on the observation about the booster iām also a bit perplexed why people try doing work they arenāt familiar with or have a basic insight toā¦going back to a previous comment>>
David_Martin
well I have a check valve which is good, but the red thing has me stumped, is that also a check valve?
ā¦well that statement tells me if you donāt know what the āred thingā is then itās time to put down the tools and step away from the car, i donāt think weāre getting the full story hereā¦iām all for people āhaving a tryā & iām all for helping where we can but unfortunately iāll have to call it the way it looks, weāre getting a bit of a story with not quite the real info by someone who shouldnāt be working on parts of a car that peoples lives depend onā¦
yes I did the tests you suggested, the brakes donāt pump up at all, the pedal only goes about one third travel and is solid from the get go, there is no.pump up.
I take offence at your statement ,walk away from the car. I am very mechanically inclined and put out as much info that I can . However I find it easier to ask a dumb question to those that know rather than risk potential damage to somethimg I am uncertain about. And most of the time brakes are very easy.
Since the brake pedal is hard but bleeds normally I am thinking about a stuck caliper, the car has been sitting in sw Florida for a while I am going to check them first.
David ā¦
Just sitting here thinking about this. Unlike most other cars the XJ40 only has one very large piston in each caliper so having one stuck (especially one of the larger front ones) could definitely effect braking. Brake drag if a piston is stuck in the extended position or differential braking if a piston wonāt extend.
However wouldnāt the pressure required on the pedal (assuming the booster is working correctly) be the same to extend the good pistons, just the brake pedal travel would be different?
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Iām glad you took offence 'cause that means you paid attention, so now you might answer questions way back such as, did you take the vacuum hose off at the booster, you know āthat red thingyā and check for vacuum while engine running also what part of the intake manifold did you take the vacuum fromā¦iām curious of what part do you find brakes easy?
OK, circling back on this: Because it sounds like the master cylinder is āfrozen upā and the issue started after the above was performed, could something have happened when the seals were replaced that is now causing a problem? You may to remove and disassemble the master cylinder to see if there is an internal issue. The other possibility - quite remote, I would think - is that more than one caliper suddenly has a seized piston.
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If the pedal is bleeding normally, i.e. youāre getting fluid out of each caliper, and pushing out air, then you wonāt have a stuck piston. A hard pedal is one of two things (generally), either a failed booster, or a frozen master, but there again, if the system is bleeding, then the master isnāt frozen.
EDIT - check your soft brake lines, and replace them if original - as they age, they effectively swell shut with pedal application (like sucking a thick milkshake through a tiny straw).
I read the webpage / know of them for their V8 conversions, but 400 kits sold for 88-89 XJ40ās worldwide? Thatās interesting.
I do the conversion using X300 or XK / XJ8 bits to include the later more efficient master cylinder. The X300 et al bits are drying up, but the XK and XJ stuff is plentiful and very, very inexpensive.
Just for reference.
Jeff, I do not understand this statement. With the bleeder screw opened brake fluid (and air) could be pumped through the the caliper whether or not a piston was seized, could it not? Or did you mean the pistons within the master cylinder? If you meant the latter then I would agree.
Actually the former, however, my bleeding MO, when I have a helper, is to spin the wheel and have said ābleederā smash the brakes to see if that wheel locks up.
Some calipers can bypass around the piston feeds, others canāt.
that is my thought, when the bleed screw is open the pedal goes easily to the florr , only when closed does the pedal stop, my thought is something stuck or blocked.
yes I have plenty of vacuum at the check valve and red thingy,I also posted a pick of the vacuum hose attach point, and it it a simple hydraulic pressure system.
the seals I replaced are the seals between the reservoir tank and the master cylinder, nothing in the master cylinder.
David ā¦
Your problem isnāt that difficult to troubleshoot despite the 37 posts so far. But sometimes it gets hard when you donāt have a faced tho face dialogue.
Did your braking system ever work normally after your vacuum booster modification ??
Yes___ or N0 ___
CHECKING THE BOOSTER. You said you have plenty of vacuum going into the booster. This needs to be checked with a vacuum guage. A finger test wonāt hack it ā¦
-
Exactly how many inches of vacuum do you have at idle ?
_____ number of inches of vacuum. -
With the engine off pump the brake pedal several times until it gets very firm (which will be about half way to the floor) and hold it there for about 10 seconds. If should remain hard and not keep going down. This tells you itās not leaking. Did this work ? ā¦
Yes __ or No___ -
Now while still holding the brake pedal down start the engine. The pedal should immediately drop further and the pedal pressure should return to normal. This tells you the booster diaphragm is not ruptured. Did this work ? ā¦
Yes ___ or No___
MASTER CYLINDER TEST. When you apply the brakes until pedal stops and you continue to hold pressure on it does it slowly continue to drop ? This would mean fluid is internally leaking past the seals. Did it pass this test?
yes __ or No___
CALIPER TEST. Jack up the front of the car and spin the two front wheels. They should both spin freely. Start the engine and have a helper apply the brakes. Both wheels should be locked up. Now do the same thing with the rear wheels. This means the pistons are not frozen. If a wheel will not turn it means the piston is seized in the extended position or the master cylinder will not release pressure to that wheel. If a wheel will not brake it means the piston is frozen in the release position or it is not receiving pressurized fluid. Did it pass this test ?
Yes ___ or No ___
Please complete this quiz using a no.2 pencil (now Iāve dated myself) and donāt run in the halls.
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You kind of hit the nail on the head, brake pedal is hard from the start,I canāt pump it as it is already hard. Maybe I should re bleed?
Before you replaced those seals were the brakes working normally ? ie without the hard pedal ? If so, the first thing I would do is to have another look at those seals to confirm they are identical to the old ones. Maybe you have inadvertently blocked off a return port or vent hole ?