Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| Re: [GMCnet] Disc brake project still in failure mode [message #282199 is a reply to message #282148] |
Wed, 15 July 2015 18:14   |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
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Neil Fonville wrote on Wed, 15 July 2015 04:23I have not lengthen the push rod at this point. I feel the .010 gap when
beginning to push the pedal. I guess I'm clueless on the braking system
because I don't understand how .010 gap can lead to 2/3 of the pedal
stroke before braking action occurs? Or the pedal being soft?
I'm very frustrated at this point and must find some on hands help. I
spent about 20 hours installing the kit. 60 trying to bleed it and get the
MC replaced. Can't be this hard.
Neil
I really am sorry this is so tough. (But then my coach has been on stands for three weeks, so I can understand being frustrated.)
I have no real skill in this area, but am going to try. If nothing else, when the smart guys correct me, perhaps an answer for you will appear.
When I did my disc brakes I had to differentiate between brakes that stop and brakes that feel soft. We fussed and fussed over what I thought was a "soft pedal". Most of this was in the shop and not on the road. My brakes still feel softer than when I had drums. But, and this is where you are having trouble that I did not have, when I finally test drove I found out that the coach stood on its nose before the brakes began to feel as firm as they did before." Once the disk brakes are working these things stop and I mean stop. I was going off an off ramp, down hill when a fellow in front did something silly and I had to make a more or less panic stop from about 50. I thought I was in the Accord. I was pushing 1/3 as hard as when I had the other setup and the coach just squatted. I don't have reaction arms, but I guess am just lucky. No skidding tires, just squatted.
Mine are not Manny brakes, but I mention this just in case. JimK mentioned getting the bleeder pointing up like they are in front. This was a big hassle for me at first. I mounted my rear calipers on the top, because they looked so good there... like the front. But that meant the bleeder was no near the top but at an angle. Perhaps the Manny system has the bleeder at the top but if not, air is hiding up in the part of the piston that is above the bleeder.
The Huby pressure bleeder should shove air out (if the bleeder is at 12 O'Clock) but I mention that the bleeders on the calipers (Caddy, I think) I have leak air. We tried to use a vacuum bleeder at the caliper and we kept sucking air. Only pressure at the MC was able to help us.
I didn't hook up my parking brake right away and did fine. As I understand mine, the adjuster is only necessary because you are trying to set the brakes with a lever. Disc brakes "auto adjust" in that the piston never returns all the way, but follows the rotor as the pads wear. Nice, but sometimes even in our modern cars we can get a light telling us to add brake fluid. That is a sign that the pads have let the pistons travel a ways. Time to look at more than adding fluid.
On the run-out issue, I would think that if that were the problem you could "pump" the brakes at stand still, which you have done ad-nausium, and make up the difference. But if you then drive and the pedal goes low again, that, to me, would me the run-out is opening the calipers to wide. As I said, I don't know beans about run-out.
I tried to read all the posts. Do you have the "sensitized" booster and bigger MC? I assume so, but I think both are needed because we are pushing more fluid.
Last, I know it seems odd that just a little play would make a difference but that rod is critical. Randy Van Winkle went to the moon and back in a goat's mouth trying to trouble shoot that thing and once he got the right combination he has brakes. Two things could be happening.
One, already mentioned by others, is that the rod is too short and the pedal goes too far before it hits pay dirt. In the measuring of that distance, is the spring on the pedal itself pulling it up as far as it should? If not the gap, if any, is perhaps misleading.
The second is that if the rod is too long, the MC doesn't go to rest and let the piston get more fluid. There must be that tiny bit of play. If the pedal spring is not letting the tiny gap happen the MC can just be pushing the same fluid back and never adding any to make up the difference and to raise the pedal. You can't see in the top of that sucker but ususally you can see a little disturbance as the piston hole opens to let more fluid in. With drum brakes the spring made the MC have a little "spout" of fluid make a bump on the fluid surface.
I really hope you don't give up. We all feel like it sometimes, especially when we want to go and can't. Hate missing opportunities because the coach is dead.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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