Braking problems

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furz4

furz4

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I recently replaced the rear end in my dart with a 8 3/4 with all new brakes on rear. I found I had a bad master cylinder so I replaced that and the booster. I did not buy the pre assembled set up as I changed the master first then determined the booster was bad. I installed the reman booster, did not adjust the push rod as I figured that was probably set at the re-builder. Have new front calipers and pads also. I bench bled the master and have bled the lines several times and am not getting out any air. My pedal seems a bit low but I seem to have excessive pedal travel if I need to preform a quick stop and it seems to take quite a bit of effort. I know I can set the rears tighter to raise the pedal but I am wondering if I didn't screw up by not checking the push rod adjustment. I have done lots of brakes over the years and never had anything like this from just changing components.
 
Well yes.

You should have checked it. Fine adjustment it is, but needs to be confirmed. Thighting up the rears May help but at what cost?

What are your full braking system components?
 
Its a standard front disc rear drum car. Rears are 11" as I built the rear end with proper width to account for the wider onset at the axle flange in order to use resplined big bolt axles. Uses same size wheel cylinders as the 10". Fronts are standard disc, master is 15/16" unit.
 
Year?

A bodies can be all over the place in specific components used.
 
Okay. I am wondering about residual pressure valves but think newer wheel cylinders take care of the need for them.
 
furz4 said:
I recently replaced the rear end in my dart with a 8 3/4 with all new brakes on rear. I found I had a bad master cylinder so I replaced that and the booster. I did not buy the pre assembled set up as I changed the master first then determined the booster was bad. I installed the reman booster, did not adjust the push rod as I figured that was probably set at the re-builder. Have new front calipers and pads also. I bench bled the master and have bled the lines several times and am not getting out any air. My pedal seems a bit low but I seem to have excessive pedal travel if I need to preform a quick stop and it seems to take quite a bit of effort. I know I can set the rears tighter to raise the pedal but I am wondering if I didn't screw up by not checking the push rod adjustment. I have done lots of brakes over the years and never had anything like this from just changing components.
Click to expand...
Friend had kind of same problem,We were really scratching our heads. The problem ended up being the front calipers were on wrong causing the bleed screw not to be up at the very top witch caused us from not getting all the air out of the caliper. They can be installed wrong front to back of rotor.If I remember correctly the caliper should be mounted back of rotor not in front if this makes since. Good luck
 
As to the pushrod length;
If it is too long, your booster will activate very early in the pedal travel making it hard to modulate the braking.
If the M/C was properly bench-bled, and just swapped over after the rest of the system is functioning properly then everything else works normally, for a while. But the too long pushrod will not allow the piston to park properly. Two things are gonna happen; 1) the brakes may not/will not fully release, and 2) over time, as the pads and shoes wear, the pedal will drop continually lower, for lack of compensating fluid entering the system.
But if you try to bleed a system with a too long pushrod, that does not compensate, almost immediately you will know that something is wrong because, after the first pump, no more fluid comes out when your helper pumps the brakes.
If the rod is way too long, you could break the control valve on a panic-stop, rendering the booster garbage.
If the rod is too short, the first portion of the pedal travel will be taking up the slack, and it will take excessive pedal travel to get the braking done. Brake boost may come on too early

It is easy to prove the C-port is working; just shine a light down into the reservoir, at the C-port, while a helper very slowly steps on the pedal. You should see the fluid roiling as the fluid backs up into the reservoir. Close the lid and clamp it before your helper allows the pedal to return, as sometimes if you have air in the system, it can push the fluid back rather violently creating a geyser that can hit the underside of the hood,and then drip down everywhere; and you know,
most brake-fluids eat paint.

Ok I think I got that right

 
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Thanks for the replies. The calipers are mounted with bleeders at the top as original. I am suspecting the rod length is too short as really good braking does occur at almost end of travel. Also I noticed when you start the car with you foot on the pedal you can feel it drop it's defiantly a lot more then 1/4 inch. I will attempt to measure and get it set to .020. Not sure if that is done with vacuum applied or not will have to find the procedure. If anyone knows a good procedure for this I would appreciate it.
 
Looks like measuring is pretty straight forward my only question is does booster need vacuum applied to get the measurement at the booster end
 
No , it does not need to be running. Adjust the pushrod to eliminate as much of the free travel as you can. But not to the point it pushes the MC piston in when you bolt it up.
 
@furyus2
That is usually the case..... because with a booster you have your leg power assisted to help push that big brute. But this also makes it very easy to over-brake, and IMO, modulation becomes more difficult. Personally,I much prefer the feel of a 15/16 with a booster.
However, having a smaller bore does require more stroke to move the same amount of fluid out. If for some reason your pads retract too far off the discs, or your system has an unusual amount of "flex" in it, then you can run out of pedal travel before adequate clamping is achieved. I have not experienced this with Mopar parts. I have heard it has happened using certain Chevy parts on your Mopar.
And yes the 15/16 mc requires a bit more travel, to achieve that modulation.
 
I lengthened the rod today and have got satisfactory braking now. I will get an exact setting on the gap tomorrow. Thanks for all the input.
 
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