brake rant

Alright. I have 4 wheel GM disk brakes. I have a 1" bore master cylinder. I have 2# residual valves both front and back. I have marginal brakes made worse with big tires. The master cylinder is new, so was the one I replaced. I replaced the residual valves. I changed out the semi metallic pads for organic. I have speed bleeders all 4 corners. I bled the brakes today again for the 100th time. There is no air in the system. there is no up flow into the master cylinder as the brakes are applied. there are no leaks anywhere in the lines.

the brakes REQUIRE at least 1 pump to get a high brake pedal. They will not lock up at any time. This may be because of the tire size but the preliminary pump has nothing to do with that.

My assessment is that the stock 1970ish master for manual brakes with a 1" bore does not move enough volume of fluid to push the caliper piston. It might be fine with disk front and drum rear, but not both. The 2# pressure valve is garbage and does almost nothing. The reason I replaced the first set was that when i took it apart the cup and spring were broken and not able to seal.

I am not apposed to going with 11" drums in the rear and a new 1 1/4 bore master to fix this BS. I have tried everything else, but I cannot make this system work satisfactorily as it is.

One winning solution was the Nicopp. I bought a roll to fix a slightly leaking line. My Ridgid brake inverted flare tool tends to make offset flares. The good thing about the nicopp vs steel is the line is soft enough to conform to the brass fittings and make a better seal.

Would a 1 1/4 bore master cylinder and 11 brakes in the rear help solve this issue and has anyone else had this amount of BS? I do realize I am asking for a lot with 35" tires.

 

I had a similar problem when I did some brake work last summer. My neighbor was helping me bleed them.....it felt like there was air in the system but after bleeding pure fluid with no bubbles for a long time we realized there had to be another problem... It was a combination of a bad proportioning valve and a bad caliper. the caliper had a tiny leak and that was enough to suck air and keep it from holding pressure. I used to have 35's on my jeep with manual brakes....it sucked. I since have switched to a YJ booster....one of the best mods I have done.

 

A 1" Bore MC should be fine to move the volume assuming this is a later dual reservoir MC............do you still have the floor mounted Master Cylinder?
I doubt you have a volume issue...........Going up in bore size would decrease the braking force..............Have you checked your pedal ratio?.......................Is this strictly a manual system only with no Booster? And is the pedal soft or hard?

 

Thanks for the replies guys. you're giving me what I need.

I still have the floor mounted master. I copied herms mounting bracket system to install dual master from a 1970 cj5. Purely manual. I reused the cj2a parts, the pushrod and the brake lever. No proportioning valve and nothing jammed in the outlets for the master either. I drove it all over the place today and the pedal got higher and harder with no appreciable increase of effective braking. In addition to that, the brake light switch is now intermittently functional. It does not seem to be directly related to pedal pressure either. In my experience this has been related to air in the master cylinder. I did bleed the entire system with zero air and a pint bled from all 4 corners after that. I had trouble with the switch before not closing under pressure, got a low pressure one from summit and it worked for a couple months and now I'm back to switch issues.

I have no idea what a bad caliper can do symptom wise. I have 4,so that could be it... I would love a brake booster, but i really don't think thats an option because i don't have any more room there with the bell housing. Maybe i do.. I really like the retro floor pedals but i might have to go swinging with a firewall mounted brake booster.

Maybe the frame mounted master is just stupid.. I been fighting these brakes for quite some time.

 

I would visually inspect each caliper/disc pad set to make sure the pads are 100% true to the rotor.
I have seen a couple systems where owners couldn't get the firm pedal.
The pads were mounted correctly, but the mounting bracket wasn't aligned properly.
So the pads weren't true to the rotor; they were angled ever so slightly.
The first push of the pedal aligned the pads; the second push stopped the Jeep.

 

Also realize the pads have to seat or "wear" in to be effective.
Maybe drive a little more riding the brakes.

 

I will check that. I actually have one rotor where that might be happening. The other 3 seem to be fine.

I am doing a little research on hydrooost.....

 

Yeah, I had that issue with my Silverado. The last set of pads took a bit to bed in. I have been trying to do hard stops all day in my jeep on purpose. I don't wanna glaze them though. It DOES stop, I'm just going to have one GIANT leg. whats going to happen is my brake leg is going to get enormous, and that in turn is going to make my gas pedal get smashed harder and it becomes a terrible cycle terrible i tell you.

 

A couple of things I did not see mentioned.
1. Are you using organic brake pads, makes a huge difference with non power M/C. (pg 3 of the thread below)
2. Are the brake lines hooked up correctly. I had mine backwards and could not get pressure. (pg 5 of thread below)
Thread: http://www.earlycj5.net/forums/showthread.php?26819-D27-Disc-brake-swap-on-my-71

 

I have the brake lines run as you and McRuff state is correct, back port goes to front brakes and front port goes to back. I ran it the other way a while back. Change it after I read your thread about this. Didn't make a whole lot of difference for me.

I just ordered and installed organic pads today. i do realize it might take a minute for them to bed in.

 

changed out that brake light switch with one from auto zone. This is the third switch that has failed in less than 6 months. garbage.

My brake pedal last night was high and firm, insert joke here. This morning it went to the floor, but did become firm with some pumping, insert joke here. In my experience this signifies that the cups inside the Master cylinder are not sealing fully and allowing bypass of the fluid. That would denote a faulty master in my experience. this master is "new" and the second "new" one I have had in this jeep in 6 months.

WTF is my problem? how can I be screwing this up? are these parts really of this low of quality?

 

I have had lots of junk parts from the FLAPS in the last couple of years, as have the mechs at work. 2 bad, new, alternators, bad brake rotors, bad pads, etc., etc. I would not be a bit surprised by 2 bad M/Cs.

IMO, and it isn't based on anything, swinging pedals and a modern M/C would be the way to go. Just seems to me that. a "modern" 4 wheel disc set up deserves, and maybe one could even say needs, the support of a modern m/c. I know many have made it work with the old parts and they have had success. Not trying to argue that point. Just my way of thinking, which is usually backwards anyway.

NAPA is more expensive sometimes, but, I've found better luck with their higher grade parts. Sometimes.

 

Sounds like master cylinder. going to 1 1/4" bore mc will make it harder to stop, not easier. All it would do is move more fluid and reduce pressure at the calipers. Check and make sure your mc bracket is not flexing also. Also check the pushrod and make sure it is adjusted with a small amount of freeplay. I ran 4 wheel 1/2 ton GM discs for years with the stock under floor single reservoir mc and could lock them up at will. I've since installed the R&P dual conversion (easy to do and mc needed replaced anyway as did some lines) and brakes are even better.

 

I also had a leak at the "block" on the frame that routes the front and rear. I ended up replacing the line going in for the fronts.

 

Howard, I purposely did go get a master from a different supplier. That doesn't mean they didnt originate from the place though.

Nick, my bracket does flex slightly. Not enough to cause any galling though with the pushrod or piston. I did adjust it to have a little bit, 1/4 inch or so, free play. If you don't do this the brakes will eventually get hot and lock up. I have experienced that. I have a 1970ish master with the dual reservoirs and I feel I should be able to easily lock these up. I have no proportioning valve so i should at least be able to lock the rears up, but nada.

every part of my brake system is brand new including distribution block.

Jpflat2a told me to look to my caliper mounting plates to see if they are causing the calipers to not apply the pads tot eh disk evenly. What I saw today is the backing plates and calipers moving slightly as pressure is applied from the master to push out the caliper piston. It looks like every other brake system I have looked at. Nothing out of the ordinary or wrong looking. I could chalk it up to a bad master, but i already did that.

I could be doing something idiotic too.

By the way, you guys are awesome for trying to help me and I fully appreciate it.

 

I bought a 68 vette manual master cylinder today without the GM brake code J56. I guess that is some sort of performance upgrade. The corvettes ,I gather, had disk rears during this era with manual brakes and power as option. The issue I see is that the outlets are going to face my frame. I am either going to need to source some 1/2-20 banjo bolts or get creative with my brake line routing.

I could solve this issue with hanging pedals and a vacuum booster from an 88 cherokee, but then I also need to redo my clutch routing. I am running the 71 or whatever cable system I got NOS. I really like the through the floor deal, but I gotta have some modernity with the brake system.

By the way, the raybestos master for the 68 vette ran me 29.79. if it doesn't work I will not have expended a lot of cash. Cheap.

 

Your really resisting............Disc brakes take about 1200 PSI a Drum system about 800-900 PSI............pedal ratio comes into play for mechanical force & advantage as does piston size and the size of your legs! The booster helps that lack of pedal force..........I could go on , but you get the picture.

 

Sounds like the cure is just to ski moguls hard for a few years------

 

I am using the stock clutch placement with a AA chain along with Booster from a Cherokee.

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