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Old 3rd July 2010, 11:37 PM   #1
BigB98
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Two Brake Questions - Dragging pads and brake lights come on with hard push

Well, today I did ~100 miles to and from the historics at Pacific Raceways...even got out on the track for parade laps. But two issues with the brakes. The rear pads are dragging (I think they are the ones). Second, the brake lights come on only after a hard depress of the pedal.

Simple fixes, right? Someone care to explain to a dummy like me?
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Old 4th July 2010, 01:24 AM   #2
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Sounds like one or perhaps both of the pushrods from the balance bar has not had the locknut done up & the pushrod has lengthened ( vibration etc ), taking up all or most of the freeboard, which in turn will mean that the pedal travel will now be reduced ( pedal higher) & you probably dont have enough travel to allow the stop light swith to operate. This is one of the pushrods going into the master cyls each side of the balance bar..
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Old 4th July 2010, 09:41 AM   #3
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Jac is more than likely right, do you have a adj. brake bias?
I have somewhat the same problem, but just thought it was the hyd brake light switch needing more hyd pressure to "light" than an oem electrical switch which "lights" with only moving the pedal some.
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Old 4th July 2010, 10:11 AM   #4
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

How is the brake light switch mounted? Does it need to be adjusted closed to the pedal?

Regarding the brake pad dragging issue - you are not sure if it is the front ot the rears? If they are dragging this should be evident by some real heat being generated which should make determining if it is front or rear pretty easy.
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Old 4th July 2010, 10:33 AM   #5
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

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Originally Posted by 2124 View Post
How is the brake light switch mounted? Does it need to be adjusted closed to the pedal?

I believe Brents and mine are the same switch. A hyd switch plumbed into the front brake hyd line.
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Old 4th July 2010, 03:41 PM   #6
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Other possibility is the clevis locknut on the balance bar has come loose & bias is now toward the rears which,( If the switch is hydraulic & installed in front line ) would explain the 'late' light activation.
Best find out whatever it is, bias to the rear & a panic stop usually means spin city!!
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Old 5th July 2010, 09:23 AM   #7
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Switch is usually installed in front circuit.

Which master size are you using for which circuit. Recommanded is 7/8" for front and 1" for rear. Than start with a 50/50 balancebar adjustment. may be the draging has also to do with the residual pressure valves and theire function.

TOM
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Old 15th July 2010, 11:25 PM   #8
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Tom, the culprit was the residual pressure valve. Fixed.
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Old 16th July 2010, 09:16 AM   #9
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Was the residual valve installed backwards?
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Old 16th July 2010, 09:31 AM   #10
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Why are you running a residual pressure valve on a disc brake system?
If pad knock back is the issue that is usually handled with springs in the piston bores
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Old 16th July 2010, 10:58 AM   #11
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Residual pressure valve was not backwards....but obviously had a little too much pressure and kept the pads tight enough against the rotor that as they heated up, the drag was pretty significant.

Dave, I don't know how to answer your question....It came with the RCR car and residual pressure valves in the 2lb variety are advertised for disc brakes. That said, I'm currently not running them as Dean Lampe had indicated in a thread somewhere to not use them so I'm not at this point. No brake dragging.
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Old 16th July 2010, 11:21 AM   #12
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

As quoted by Wilwood...and the RCR cars have a floor mounted pedal box.

A residual pressure valve is used when a master cylinder is mounted equal to
or below the horizontal plane of the calipers or drum brake wheel cylinders.
This valve prevents fluid flow-back to the master cylinder reservoir which can
cause excessive brake travel or “pumping” of the pedal to engage brakes.
Install the valve as close as possible to the master cylinder and position the
end marked “M.C.” toward the master cylinder and the end marked “OUT”
toward the brakes. Ports in the valve are 1/8-27 NPT threads and will accept
standard inverted flare tube nut adapters.
A 2 lb. valve is designed for disc brakes and a 10 lb. valve for drum brakes.
If the vehicle has a single outlet master cylinder and a disc/disc system, only
one 2 lb. valve is required. If the vehicle has a single outlet master cylinder
and a disc/drum system, a 2 lb. valve is required in the disc brake line and a
10 lb. valve in the drum brake line (after the tee fitting). Balance bar systems

require the appropriate valve just outside the master cylinder.
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Old 16th July 2010, 12:30 PM   #13
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Quote:
Originally Posted by RacerDave View Post
Why are you running a residual pressure valve on a disc brake system?
If pad knock back is the issue that is usually handled with springs in the piston bores
I'm running them and they seem to work just fine.

With respect to springs in the bore for knock back - is that hard to get the right spring tension? Seems that it'd be difficult to get it setup properly without causing too much drag, and, setup properly to account for race use and variations in heat on tracks.
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Old 16th July 2010, 03:23 PM   #14
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

You could always make it a bit more like the original MKIV's and fit an overhung pedal setup.
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Old 16th July 2010, 03:52 PM   #15
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Fran I understand your position.

Ron is correct knock back springs can be tricky 4lbs seem to work with AP's in most situations.
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Old 16th July 2010, 04:18 PM   #16
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Quote:
Originally Posted by jac mac View Post
You could always make it a bit more like the original MKIV's and fit an overhung pedal setup.

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Old 16th July 2010, 04:45 PM   #17
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

Jac,
thats what the "other" guys do for their 400k price tag...

Although Jay has done it I think ...right?
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Last edited by gt40fran; 16th July 2010 at 04:52 PM.
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Old 16th July 2010, 05:53 PM   #18
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

right.....
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Old 16th July 2010, 05:57 PM   #19
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Re: Two Brake Questions - Dragging pads and brake lights come on with hard push

You are SO special....my ride ...
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