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Join Date: Aug 2002
Location: Kalamazoo, MI
Posts: 136
Question Master Cylinder Question

Hey Folks,

Got a quick 914 related question... I have a 914 17mm master cylinder in a Bug with front VW Ghia discs and rear CB Performance Roto-Hub discs.

The stopping power is great with this setup and the 914 M/C really makes a nice pedal feel.

I have one problem, the rear brakes keep hanging up, sometime pretty badly. When they are hung up, there is almost no play in the brake pedal, it has pressure from the top stroke.

When the brakes unhang, the pedal returns to normal (about 1-2" of freeplay).

Is there a residual valve in 914 M/C's? I don't have the porportioning valve installed, the brakes are very balanced as-is.

Any thoughts or suggestions would be appreciated.

Thanks,
Tom Perso
1963 VW Bug
1971 IRS Chassis, 2270cc T4 Power, 4-wheel discs, the list goes on
http://www.qtm.net/~persoj
Old 08-16-2002, 03:02 AM
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Join Date: Aug 1999
Location: Downingtown, PA, USA
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If your rear brakes are hanging up, the rear brake pistons are not retracting. That means when you press the pedal again, you don't have to displace the fluid to move them with the master cylinder stroke. Less stroke of the master cylinder, less pedal travel.
Harvey
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Old 08-16-2002, 03:51 AM
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does your cb setup have the same adjustment feature (venting clearance) as the stock 914's?

kevin

Last edited by Kevin Powers; 08-16-2002 at 04:09 AM..
Old 08-16-2002, 04:05 AM
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Location: chula vista ca usa
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You did not mention what you do or how you get the rear brakes to free up? If you just have to wait till they cool off, then you might want to check the pads to see if they are binding or welding to the rotor from the metal inside the pad material. I had this happen on the front calipers of an Audi once and the calipers had very sharp edges on the metal backing and when hot would dig into the alloy calipers and jam, at times the car couldn't move! To fix it, I file all the metal edges round and make sure each pad is nice and loose in it's slot. I also put some anti-seize or hi-temp grease on the edges of the metal and the piston contact area to make sure they will not stick. The stock 914 m/c does not have any built in residual valve. Good luck.
Old 08-16-2002, 07:41 AM
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Wow, thanks for the replies.

I've had the brakes hang up 3 times, here is what I have done.

1) Drove with the hung up until I could pull off somewhere safe, but they unstuck before I found a place to pull off.

2) The rest of the times, I pulled off and banged on the brake pads, calipers, and wheels until the car started rolling away (no e-brake on and it was in neutral).

They seem to hang up after pressing the brake pedal which is what lead me to ask about the residual valve.

I think I need to look at how the calipers are sitting compared to the rotor and see how the brake pads work.

These calipers are "W-body" calieprs, they are from early 90's Grand Prixs, Luminas, Cutlass Supremes, and Regals. From a GM know-it-all I know, he says those calipers absolutly suck for reliability, he says the freeze up all the time. I'm not sure if that is my problem or not....

But, both calipers hang up, so I doubt they broke at the same time.

Again, thanks for the help and any more advice would be appreciated.

Hopefully I'll be stopping back here to discuss my new 914 purchase (I just gotta get some room for cars.. )

Later,
Tom Perso
Old 08-17-2002, 06:20 AM
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