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Old 05-26-2003, 05:15   #1 (permalink)
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confused Brake pedal feel

I've got a TE Cortina that is extensively modified. I've upgraded the brakes with XY front discs with HZ alloy girlock calipers, an ED diff has been fitted so I got the standard rear discs as a bonus and I've fitted a 1" master cylinder from an XB. The only part of the braking system left unchanged is the booster. This setup works well but its got a very spongy pedal.
I was thinking the booster could be the problem as it makes a squelching noise when I push on the pedal. I'm unfamiliar with what goes on inside a booster so if any of you guys reckon the booster is the problem - or whatever you think it might be - I'm all ears.
Thanks.
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Old 05-26-2003, 05:54   #2 (permalink)
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A leaking master cylinder will result in brake fluid in the booster which will eventually stuff it. Check the rod connected to the brake pedal for signs of dampness (read leaking fluid).

Maybe your XB master cylinder and is letting air in the system and needs rekitting
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Old 05-26-2003, 14:26   #3 (permalink)
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Try this: Stand on the brake pedal hard, then start the engine. The pedal should drop as the booster comes online. It may drop about two inches. Was the master you used from a disc brake XB? If it is a proper dual circuit master, the crack valve setting may be wrong for your application. The caliper combination you have should work, are you absolutely sure the entire system is bled properly? A dodgy master can trickle air into the rear circuit via the main seal, making it impossible to bleed correctly.
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Old 05-26-2003, 15:41   #4 (permalink)
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The master cylinder is brand new so it shouldn't be leaking, and it is for a disc brake XB. I'll try pressing the brake and starting the car tonight to see if the pedal drops.
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Old 05-27-2003, 02:46   #5 (permalink)
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Is it for a 4 wheel disk brak XB Dreders?

I agree with WBT56, the proprtioning valve might have the wrong crack pressure for your setup, your master clinder may also not be correct for the HZ calipers, try looking up the MC size for a disk braked HZ and comparing it to the one you have.
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Old 05-27-2003, 04:08   #6 (permalink)
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HQ-WB use 64mm front pistons, 1" master and 48mm rear pistons. You have 42mm rear pistons, it will definately work, it will also work with 38mm (Commodore/skyline) rears. I have run all of these combos on different vehicles with no problems. Starting to sound like air in system. Tip for bleeding the rears- use a different colour fluid and bleed it till the new colour comes through.
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Old 05-27-2003, 05:10   #7 (permalink)
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Disc brake in an X.B was 9" and the diff you have is from E.D / B.W is there any difference in piston sizes ??? All flexable brake fittings in good nick ???
I had this problem once, came good when pads bedded in properly must have been slightly off parellel to rotor's ???
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Old 05-27-2003, 14:48   #8 (permalink)
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Quote:
Originally posted by ebxr8240
Disc brake in an X.B was 9" and the diff you have is from E.D / B.W is there any difference in piston sizes ???
9" disc brakes run 48mm pistons, same as HQ-WB.
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Old 05-27-2003, 16:43   #9 (permalink)
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Thanks for your all your info on piston sizes WBT56.
I'm starting to think there's still air in the system too. I'm picking up some line lockers and I'll have another go at bleeding it on Saturday morning. I've measured disc runout on all rotors and its less than 0.003". The angle of the master cylinder could be a problem as it tilts up at the front and their may be a bubble stuck in there.
If I fabricate a new bracket to make the master cylinder level, that will change the angle of the input shaft into the booster slightly. Would that be OK?
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Old 05-28-2003, 02:50   #10 (permalink)
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Quote:
Originally posted by Dreders
If I fabricate a new bracket to make the master cylinder level, that will change the angle of the input shaft into the booster slightly. Would that be OK?
You can't change the angular relationship between the booster and master, as I believe the push rod is solid, and you will load up the MC piston sideways. The pedal to booster pushrod has a knuckle to absorb movement, you may be able to do something there. Shouldn't be an issue,however, as many cars are uphill on the MC, if you are worried about it could you attempt to bleed the brakes with the car pointing downhill?
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