If the calipers have enough use to need rebuilding, I would suggest popping the pistons out and inspecting the bores. I had a set of Wilwoods once that were wearing pads badly (wearing fast, lots of taper, and unevenly left/right) and excessive wear in the bores was the cause.
codrus (Forum Supporter) said:If the calipers have enough use to need rebuilding, I would suggest popping the pistons out and inspecting the bores. I had a set of Wilwoods once that were wearing pads badly (wearing fast, lots of taper, and unevenly left/right) and excessive wear in the bores was the cause.
any time you see a damaged piston boot, that caliper should be fully disassembled for inspection of piston and bore. anything that gets past the damaged boot can cause the piston to not slide properly in either or both "apply" and "retract" directions, leading to reduced braking, or pad dragging, etc. honestly, i'd put new calipers on the car and rebuild the existing calipers for spares.
You guys are bumming me out. 
What's more, we just had major wind yesterday that blew down dead trees and broke fences. This is seriously shrinking my race car budget.
A seal kit is what, five bucks?
They are fairly easy to rebuild, especially if tou have access to compressed air to blow the new boot over the piston.
Pop it apart, clean out any gunk, new seal, new boot, heavy application of lube, pop the piston back in and you're done.
In reply to Pete. (l33t FS) :
Yep. Parts are ordered. I also binge-watched a bunch of caliper rebuilding videos just in case there might be some insights into best techniques for installing the dust boots. What is this technique of using air to blow the new boot over the piston? Haven't seen that described yet.
In reply to jimgood :
You install the seal, install the boot and its retainer clip/ring/whatever it has, push the piston up against the boot, apply air pressure to the fluid port. It will blow the boot out and over the backside of the piston, and then you just push the piston down into place.
Sure beats wiggling the piston this way and that trying to get the boot over it. I went for years with no dust boots on my calipers because I gave up trying, before someone told me about the air pressure method.
In reply to Pete. (l33t FS) :
Sweet. I'm going to give that a try. I purposely ordered extra dust boots in case I screw a couple up trying to wrestle them on. Thanks!
You guys got me to thinking about measuring brake system pressure, which I had heretofore never given any thought. I did a lot of searching this morning. First of all, pressure gauges are cheap; like between $10 and $20. Most of the racing supply places sell all kinds of kits that screw into the caliper bleed screw and range in price from $70 - $100 for one gauge and the adapter for the calipers. So you're paying a lot for a fitting. But then I saw this one on Speedway that I guess you would plumb from a "T" off your master cylinders:
https://www.speedwaymotors.com/Speedway-Mini-Brake-Pressure-Gauge,3136.html
That seems reasonable for the money compared to other offerings. I might look into this in the near future. It would be nice to be able to see the pressure difference front to rear when adjusting the bias. Or when spinning off the track.
Brake pressure gauges are pretty useless on track, you don't have time to look at them. I could maybe see it being useful for troubleshooting a system that's getting weirdo pressures due to obstructions in flex lines, but...
On the other hand, brake pressure senders as inputs to data logging systems are super useful. That's a lot more investment though.
Keith, you were right. My front and rear masters are different sizes. The rear master is marked 1.00. The front master is marked .88. I tried to take a cell phone pic but it's a tight space and at an angle so I confirmed by doing an etching with paper and a dirty finger. So I assume that means the front is a 7/8 (.875" rounded up to .88).
EDIT: This begs another question. If you have dual masters and a cockpit adjustable balance bar, why use different size masters?
jimgood said:EDIT: This begs another question. If you have dual masters and a cockpit adjustable balance bar, why use different size masters?
because it lets you get closer to ideal balance curve over a larger set of operating condition.
In reply to AngryCorvair (Forum Supporter) :
I thought it was more practical than that: you could get your brake balance bar more centered, which prevents weird geometrical issues.
Regarding pressure gauges, I have one that threads into a bleeder port, it is a diagnostic tool. I have only heard of the in-dash gauges used for drag racing, to ensure that a linelock had enough pressure on it before doing a burnout or staging. In drag racing, the only times you have the brakes applied are the only times you can pay attention to a gauge and vice-versa 
In reply to AngryCorvair (Forum Supporter) :
That makes sense.
In reply to Pete. (l33t FS) :
Yes. Those are the first ones that came up in my search. I just thought with this one being basically the same price, it might be the ticket. Those gauges that screw into the bleeder port are overpriced and I'm not sure which type of bleed screw I have. I haven't checked that yet but I think they might be different front and rear.
Just to wrap this up, I rebuilt the calipers, installed new pads and vacuum bled the system. The pedal feels good.
Had some hiccups with the Mityvac. Should have read the instructions first. I think there was a lot of air getting in around the bleeder hose so it was really hard to tell when to stop. At one point I just removed the bleeder entirely just to see if there was fluid to the top of the hole in the caliper. There was. So that made a mess. Next time I do this I'm going to get one of those fuel hose clamps and put it around the end of the bleeder hose to see if it makes a difference. Not one of the adapters that comes with the Mityvac fit the bleeder tightly enough. I had even put grease on the threads of the bleeder.
I'll check for leaks in the morning.
A couple of thoughts:(1) an adapter can be made from a bleeder and a pipe coupler to allow the use of a pressure gauge at the caliper. Braze the side hole in the bleeder closed then drill it straight through. Then braze the bleeder to the pipe coupler that matches your gauge thread size. Make sure your gauge is capable of reading at least 1000 psi. (2) I have had great luck at removing air from difficult brake (and clutch) systems by pushing the fluid backwards from the calipers (slave cylinder) to the master cylinder by using a 60cc or larger syringe.
You'll need to log in to post.
