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Disk brake swap done, test drove......hmm?? *PROBLEM SOLVED*

78Suburban

78Suburban

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I put new calipers at all 4 corners of the burb. I've just driven it on two short runs (1/4 mile or less).......I made it stop alot. The front rotors are getting dang hot, the rears are maybe getting barely warm.. It feels like I can kinda lock up only the front, the pedal is a bit spongey. It also kinda maybe feels like the front calipers are sticking closed after I let off??

Who's got their money on it being a bad master cylinder? Who thinks I just need to bleed the piss out of the brakes AGAIN..? I'm stumped...

EDIT: my brake light is also on.
 
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did you give the guide bolts a good coat of lub? you might want to make sure that the calipers are not sticking so you don't warp a front rotor
 
1979jimmy350 said:
did you give the guide bolts a good coat of lub? you might want to make sure that the calipers are not sticking so you don't warp a front rotor
Click to expand...

So I need to lube all the caliper bolts? Will any kind of grease work?
 
1st rule of spongy brakes after a disc swap. Bleed the hell out of them. Just when you think you are done, do it again.
 
Brake light on is a dead giveaway that there is air in the lines, the master is bad, or there's a leak in a line somewhere. (given the light is working as it should)

Can you bleed them and get it to shut off, at least for a bit? I'm not sure it's ever been explained on here, but apparently you can "reset" the proportioning valve IF it sticks when bled. It is supposed to reset itself with fluid pressure, but apparently pushing a pin in on the end of the proportioning valve will do this as well.

Make sure your light is working correctly as well, assuming it wasn't doing this before, it probably is, but make sure the wire is ok, not shorted, that it doesn't have something to do with the e-brake pedal which also triggers the light.
 
dyeager535 said:
Brake light on is a dead giveaway that there is air in the lines, the master is bad, or there's a leak in a line somewhere. (given the light is working as it should)
Click to expand...

The easiest way to tell if the MC is bad is too have someone watch the caliper when you bleed the brakes. If you pump it up and it bleeds back (backs off the rotor) with your foot still on the pedal, the MC is bleeding back into itself.
 
shane74 said:
The easiest way to tell if the MC is bad is too have someone watch the caliper when you bleed the brakes. If you pump it up and it bleeds back (backs off the rotor) with your foot still on the pedal, the MC is bleeding back into itself.
Click to expand...

Are you talking about having all the bleeder screws shut and doing this test, or are you supposed to be bleeding one at while you get somebody to look at the caliper?

Maybe I should try to bleed the brakes some more and then try to hold the pedal down and get a buddy to watch the caliper pads??

Is having lube/ grease on the caliper bolts very important and if so what kind should I use?
 
just a quick thought but when i tubbed my corvette i went from 4 wheel disc to drums in the back. Kinda the opposite of what were doing on these rigs.....anyway i had to change out the proportioning valve for drums in the back.

would we need to swap our valves out for discs in the back? kinda like putting a corvette valve on the M/C.
 
Yup, either need to add an adjustable or change out the p-valve althogether...

But he has some other issues going on.... All good suggestions so far...

His backs should be working overtime now with drum pressure feeding em.... Got an air issue I'd bet...
 
I've got a buddy coming over in 30 minutes.. he's been volunteered as my official pedal pumper for the evening............I'm thinking there are two possibilities.........

1. I don't have all the air out of my rear lines

2. the old drums were so filled with mud that when the pressure of the rear lines tried to go the the wheel cylinder, it couldn't go anywhere, and blew out the MC seals for the rear portion of the MC. In which case I would need to rebuild my Master Cylinder....
 
78Suburban said:
Are you talking about having all the bleeder screws shut and doing this test, or are you supposed to be bleeding one at while you get somebody to look at the caliper?

Maybe I should try to bleed the brakes some more and then try to hold the pedal down and get a buddy to watch the caliper pads??

Is having lube/ grease on the caliper bolts very important and if so what kind should I use?
Click to expand...

Yes, all the bleeder screws should be shut and the lines pumped up and under pressure. You may have to watch it for a few minutes, but if the calipers back off at all, you still have air in the system, or your MC is bad.
 
problem solved!!!!!!!

shane74 said:
1st rule of spongy brakes after a disc swap. Bleed the hell out of them. Just when you think you are done, do it again.
Click to expand...

Ding ding, we have a winnner! Just a few minutes of bleeding the rears and the light is off, the pedal is firm, and the rears lock up!!!!!! I love locking those brakes and sliding around.. It works excellently! I got alot of air bubbles out... appearantly I just hadn't bled those long burb lines enough :bow:
 
Yep, those burbs have some pretty long lines on them. Glad you got it worked out.
 
shane74 said:
Glad you got it fixed :) Takes fer dang ever doesn't it?!
Click to expand...
Not when you use one of those bleeder bottles that Mity-Vac's come with, and hook it to manifold vacuum! Need to remove the bleed screws first though, smear some brake assembly lube in the threads and then screw it back in.
 
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