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Discussion Starter #1
Hi Everyone - I have a MK4 with the Whitby power brake kit and SN95 pedal box, FF supplied front brake calipers/rotors, 8.8 with discs (cobra GT). All pads, rotors and calipers are brand new. After I bled the system using a vacuum pump (starting from passenger rear) I had a very firm brake pedal-which I assumed was good? However once the car is at operating temp my brake pedal gets a little firmer and the brakes grab on all 4 corners. Anyone have any ideas as to the problem? Thought of an adjustable booster pushrod but it seems that when disconnected the pushrod is already at its max distance towards driver? Could I have a faulty master cylinder?

Anyways, as always any insight is greatly appreciated.
 

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Mine did that with the same set up (other than the comment about being up on temperature)

Needed to add another spacer between the footbox and booster (i assume an adjustable pushrod would have fixed it.)

Brakes would be fine initially but each press of the pedal would make them drag more. Had to bleed them a tiny bit to relieve pressure on the caliper to unlock them. Mark Daugherty knew exactly what the problem was and how to fix it when he helped me wrap some stuff up.

Greg
 

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Discussion Starter #3
I may be incorrect when I say it gets worse with temp, could actually be increasing the drag with every activation of the brake pedal. The spacer between the brake booster and footbox sounds like an idea but may be really tough to do with the body on. Will definitely look at that though. With the additional spacer did you end up with any interference between the brake pedal and the crossbar?

How thick of a spacer did you end up going with?

Thanks for the info...
 

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You have to have a spacer between the footbox and the booster. I didn’t use the Whitby kit but I believe their booster is the same one I sourced elsewhere. They recommend a 3/8 spacer, I believe but, mine is a little thicker. I made it out of 1/2 inch aluminium plate because that was the length of the spacers I removed from the front of the sn95 pedal box when modifying it to fit the mk4. Brakes work great.

You also have to adjust the pushrod that comes out of the front of the booster so that it allows the master cylinder plunger to just fully retract when the brakes are released.

Here’s a picture. You can see the spacer behind the clutch cable between the booster and footbox.

HTH

Norm
526455F0-A649-4BCF-B4FB-3D68EB485758.png
 

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Discussion Starter #6
Thanks Jeff, Norm and frd2. You guys nailed it again! I neglected to install the spacer between the mc and the booster and the acorn nut at the end of the push rod needed to be turned in considerably. Corrections made and brakes are working very well now. Thanks guys! - John

Also a shout out of thanks to Whitby. I sent them an email this morning via their website and they responded in a couple of hours and stated the same thing, Booster to MC spacer and push rod acorn nut adjustment!.
 
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