[Jay]

Someone upstairs decided it's pick on Jay week... anyway. Been trying to finish up my Aerospace 4 wheel disc conversion and I've run into some trouble.

Basically here's the situation, the rear discs are locking up and staying locked off or on the pedal. The front discs are doing absolutely nothing. I have bled the system to death, including bench bleeding of the master cylinder. I've narrowed it down to several potential problems.

1.) The Wilwood master cylinder I am using does not have the best directions. All the instructions say besides the usual warning BS is that the MC is balanced 69% Front and 31% Rear ... now it does not say which line is the front or the rear and the reservoirs for each are the same size. I am running (as mounted on the car) the front line to the front system and the rear line to the rear system. http://www.wilwood.com/products/master_cylinders/tandem/tendemdwg.gif

2.) I ditched the original distribution block. I ran the rear output of the MC directly to the rear line and the front output goes through a T fitting to the front brakes.

3.) Maybe I need some type of residual pressure valve somewhere?

4.) Maybe I need a vacation.

On top of this I've had to ditch the ECI mechanical parking brake setup... that will be my next item on eBay 'cause I've got enough $300 paperweights.

If anyone has suggestions please fire away.

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1967 351W Convertible
2000 Mustang GT
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[VictorII]

Sounds like two problems. First the rears lock and stay locked becuase a check valve might not be operating correctly so that when pressure is applied it cannot be released when you let up on the pedal. Second you need an adjustable proportioning valve. As I understand it, you want less rear braking because more braking is necessary for the front and you want slower acting in the rrear so they don't lock up.

 

[abn]

Wow, I can't see why the brakes would lock on without pressure on the pedal unless the pushrod was actually hanging up in the M/C bore. Did you adjust the rear caliper alignment to the rotor with either shim stock or supplied precision washers? Perhaps the pistons are getting cocked and sticking in the bores, or maybe the pads are hanging up on their retaining mechanism. I really don't know what to tell you without being present. I believe the rear port is for the front brakes but I could be very wrong.

<P ID="edit"><FONT SIZE=-1>Edited by abn on 03/17/01 00:00 AM (server time).</FONT></P>

 

[Jay]

That's the confusion here...

I don't have a check valve in the system and the MC is proportioned internally (69%F and 31%R). It's gotta be something else...

[email protected]
1967 351W Convertible
2000 Mustang GT
Please bring back last post to top!

 

[VictorII]

Sounds like the internal prop. valve isn't working correctly. Everything I've read says to go with an adjustable external valve. I still think the rear circuit is acting like a line lock like the race crowd uses to burn their rear tires in. Have you contacted the manufacturers of the parts to get their insight?

 

[roadracer]

I had the same problem and it turned out to be the brake booster pushrod was just slightly too long (Power Brakes, thousandths of an inch). It was with a stock master cylinder though). Make sure you know the correct protrusion distance if using a brake booster and adjust the pushrod lenght carefully.

http://home.netcom.com/~jonescha/Photos/DCP_0355_178x109.jpg
"If you're under control you're not going fast enough"
Parnelli Jones
http://home.netcom.com/~jonescha/Frm_Cars.htm

 

[Jay]

I was careful about that. Actually I have an adjustable push rod. I have it set so there is a little play before it hits the brake pedal stop.

[email protected]
1967 351W Convertible
2000 Mustang GT
Please bring back last post to top!

 

[Guest]

Generally the front of a master is the rear circuit and the rear is the front circuit. You should adjust the push rod to have zero contact between the push rod and the master cylinder piston. A residual pressure valve would make matters worse it holds pressure in the line in which it is installed.
I gotta go with ABN on this one. Sounds like the pushrod is keeping the piston from returning to its rest position

Greg B