need help diagnosing brake issue

[Al Wilson]

I had a similar problem on Strange rear disc brake conversion I did once. These were two piston calipers with a bleed valve on the top and bottom of the calipers. What I had to do was take the caliper off (with brake line still attached), turn it upside down and bleed the other end that was on the bottom. Problem solved.

[GallopinGhost]

On the caliper alignment, I have centered the caliper bracket to the rotor using shims, so they should be centered and parallel pretty good.


The pressure gauge that's on the front of the dash is mounted in a tee. the gauge is on the bottom and I have a bleeder screw at the top.


The calipers have bleeder screws top and bottom. I did try flipping them over and bleeding them, never saw a difference.


The issue has been going on since day 1, which was before the pressure switch and pressure gauge. I have flipped the lines between the front and back ports on the MC to get better holding power on the starting lines, didn't see much difference. Once pumped up, I can get 1000 psi on the gauge.

[dragracerray]

Originally Posted by Al Wilson

I had a similar problem on Strange rear disc brake conversion I did once. These were two piston calipers with a bleed valve on the top and bottom of the calipers. What I had to do was take the caliper off (with brake line still attached), turn it upside down and bleed the other end that was on the bottom. Problem solved.

Brian I also had problems bleeding Strange brakes. I use a dual caliper brake on the rear. One of the calipers is horizontal which means the bleeders are horizontal and part of the hydraulic part of the inside of the caliper is above the bleeder. I use braided line to each caliper so what I had to do is disconnect the caliper from the caliper bracket so the bleeders point straight up and straight down to bleed them(tywrap them in place for bleeding). Solved my problem on the first attempt. Here is my earlier CR post with pictures. Ray

https://classracer.com/classforum/sh...ad.php?t=67964

[GallopinGhost]

Eman, yes you are correct on what I have done. Checking with the lines plugged sounds like a good step. If it's determined I need more volume in the MC, how is that spec listed ? I have an adjustable push rod on the MC, maybe if I can get a longer throw that might help. Check valves also seem like it's worth a try.



The thing that bugs me is after a few pumps of the pedal, all is good.


Also my calipers are more or less vertical front and back.


Anyone have a good example of these check valves ? where do they go, MC ports ? any issue with using them front and back.


I appreciate all the suggestions.

[Monte Howard]

Have you checked your pedal ratio?

[Bobby Fazio]

Had a similar issue with my sons fox body mustang with all Strange parts. Come to find out the pedal ratio was the problem. Change to aftermarket pedal and rod assembly to change the ratio. The problem was the pedal was not pushing the rod into the cylinder 100%. Thus trapping air. After that i put the pressure guage on each caliper to verify and adjust the strange proportioning valve to the desired front to rear split. Only other issue i have seen with others is not getting all the air out of the line lock, you may have to activate a few times when bleeding. Hope this helps.

[FireSale]

I had trouble with Strange masters on my 3400lb Mustang. They are 1.125 bore and that is a bit big for manual brakes. I have a pair of step bore masters now. An early Monza with an .875 bore is in it now and I have one from a 85' S 10 that is .945 bore. Both give me 300psi with a light foot and 1000 with effort. I'm 74. Step bore or quick takeup masters are hard to bleed. It is important to not rush this step with any master. Wait 30 seconds between presses to be sure the cylinders are recharged, I use a stopwatch.

[Eman]

Originally Posted by GallopinGhost

Eman, yes you are correct on what I have done. Checking with the lines plugged sounds like a good step. If it's determined I need more volume in the MC, how is that spec listed ? I have an adjustable push rod on the MC, maybe if I can get a longer throw that might help. Check valves also seem like it's worth a try.



The thing that bugs me is after a few pumps of the pedal, all is good.





.

I'd say the reason the pedal gets better when you pump it is the pads move out towards the rotor with the first pump so they have less to travel on the next pump. People tried springs to push the pads back and eliminate any drag from the pads rubbing the calipers. What happened was the first pump went almost to the floor. Just like when you do a disc brake job and push the piston back. You have to pump the pedal to move the pistons back out.
Someone mentioned pedal ratio which is important, usually 6:1 or better. You also have to be sure that the pedal can push the MC all of the way to bottom. You them have to be careful when you adjust the pushrod as sometimes you can cause brake drag especially when the brakes get hot.

[GallopinGhost]

Pedal ratio is 7:1


Ok, I have a game plan.



1) going to check out MC pushrod travel and see if I'm getting a complete stroke.


2) Since I've been swapping lines on the MC, I will thoroughly bleed the brakes again, then as mentioned, remove the lines at the caliper and cap them. Not sure what I will cap them with, but a short flare plug would be great as not to add a lot of air.


3) If the light bulb doesn't turn on at that point, I'll add a couple of check valves to the MC. I see they're only $20 a piece, a cheap test.


So I do have springs on all the calipers, and yeah it makes since that it could be part of the problem. But as I've mentioned this issue started at day 1, the springs hadn't been on for very long.


Ok, thanks again for the help. I'll update as I move along. gonna take a while........

[Painter]

Two possibilities-
1- You have to bleed the gauge.
2- If you have moved the attachment point for the brake too far and created too much angle where the push rod enters the mc it will **** the piston and cause this problem.