OneRotor

iTrader: (3)

So I've been dealing with mediocre braking performance for a while, and have given up on the search for why and am going to ask the experts here.

Brake setup:

1982 front spindles from a GS (4x110 bolt pattern)
Front pads are some generic (a small part of the problem IMO) parts-store "low dust" brake pads.
Braided Stainless replaced front soft lines

Rear axle is a GSL from a 1982 EUDM model (4x110 solid discs)
Rear pads are Hawk HPS
Factory rubber soft lines

I've been through 3 different brake master cylinders since I bought the car.

Here is the history of my suspension and brakes:

When I bought the car, I swapped out my front suspension from my '82, as it had RB springs and Illumina struts, but unknown pads, and put in my rear RB springs and Tokico HP shocks. The car would easily lock the belts and throw you forward with a hard stab of the brake pedal. I took the car to school, and while out driving one afternoon/evening, I melted the brake pads out of the front of the car. I did not just wear them out, as I had chunks of melted brake pad material stuck to the inside of my front rims post-cooldown.

I replaced the pads with the generic low-dust pads that are in it now, and properly bedded the pads with 6 moderate 30-0 stops, then 8 hard 60-0 stops, with a 15 minute cool down period afterward. This is when I started to notice the decrease in braking performance.

I then proceeded to break the rear axle. I replaced my '85 big bearing rear axle with the small bearing rear axle from my '82, with fresh shoes for the drums. The wheel bearings went on that axle last summer, and I acquired the EUDM axle with discs and a LSD.

I wore out the rear pads and replaced them about 150 miles ago with the HPS pads.

Here are the braking characteristics before melting the front pads out of the car:

Lots of pedal feel
hard brake pedal
easy to modulate brakes
low heat range on the pads
strong braking performance
running 185/70R13 BFG all season radials that were more than likely dry-rotted (no clue on age...)

Braking characteristics post-melting of pads:

Lots of pedal travel (2x what it was before)
Very little brake feel
low heat range for pads
weak braking performance
I was running the same 185/70R13 tires until last week when I upgraded to 205/50R15 Potenza RE11's (very sticky).

The braking performance is still lackluster post-tire-and-rear-pad swap. Soft pedal. Very little feel, pedal requires a lot of pressure for mediocre braking performance.

Here is what I think happened, but I would like second opinions:

When I melted the pads out of the car, pad material was deposited onto the rotors, which has caused a decrease in friction between the pads and the rotors. Is this a logical assumption, and if so, would a simple sanding of the discs get rid of the deposits, or should I just toss on two new front rotors?

Kentetsu

What about the booster and vacuum source? That was my first thought.

My second thought is, if things got hot enough to melt the brake pads (never heard of that), then maybe you boiled the fluid too. So maybe a full flush is in order.

And I would think it could be dangerous to run generic pads on the front with Hawks on the back. You really don't want your rear brakes to out perform your front brakes.



.

OneRotor

iTrader: (3)

I've bled my brakes enough over the past year or so to get all of the old fluid out. I was bleeding my brakes once a week for a full summer in the UP, as I would boil brake fluid that often from hard runs through the Keewenaw.

Maybe I should do a full bleed with some DOT4 fluid, just to up the boiling point of the system.

And with regard to it being dangerous to run rear hawks and generics in the front, I will be addressing that in June, after I get the new tires/mounting off of my credit card.

My vacuum line for my booster is in good shape. Will a dying booster give you a soft pedal?

Kentetsu

How about the check valve in the vacuum line? But then, without vacuum the pedal would get hard. Maybe its just plain worn out calipers?

OneRotor

iTrader: (3)

I have about 20k miles on rebuilt front calipers.

theNeanderthol

iTrader: (1)

My dying brake booster gave it a hard pedal feel. Had to push very hard to brake at the same rate as a good booster. Pedal felt stiff and unresponsive.

dj55b

iTrader: (2)

If the rotor has been scored , performance will be hindered no matter what you do. But really sounds more like an improper brake bleed to me. How do you normally bleed the brakes?

thunkrd

iTrader: (1)

i had to replace my master, coz it wasn't bleeding correctly... did you bleed the master?

OneRotor

iTrader: (3)

Rotors are not scored.

Bleeding procedure:

Passenger Rear
Drivers Rear
Passenger Front
Drivers Front

I make sure that I go through 1/2 of a reservoir, refill, and go through another 1/2 reservoir.

I put a rubber hose over the bleeder, and submerge the other end into a quart of brake fluid.

Pump fast so I can get the little bubbles past the changes in direction in the lines.

How do you bleed the master?

dj55b

iTrader: (2)

Bench bleeding is really not required unless its a new master, pumping fast isn't usually a good idea from my experience as it creates more smaller bubbles. The way I do mine is with two people , one in the car pumping, and the other at the bleeder. With the bleeder closed, I pump moderately making sure I go fully to the bottom, each time. I do this about 10 times, and then as im pressing down on the last time I tell them to open it till it goes to the floor, I do this a couple time then move to the next one. Once you've been around all four then turn on the cwr to get the booster going and help push more, pump it a few more times, shut it off, and then do one last bleed all around.

Slightly Warped

iTrader: (4)

Did you machine the rotors after melting the old pads? If the brakes got that hot, the rotors are most likely glazed. If the rotors are true and not scored, you may be able to get away with a cut as small as .005 inches on each side. This gives a slightly rougher surface to help wear the pads in. I personally machine my rotors every time I change pads.

Have you looked at the joint between the master cylinder and booster for evidence of a leak? The master on my SE project was leaking so badly that it ate the paint off of the lower side of the booster and the frame rails below it. If the master is leaking around the internal seals, it bleeds pressure off and your good pedal feel goes away.

Rotospeed

iTrader: (8)

sounds like a bleeding issue. and if your boiling you brake fluid you need to change it to dot4 or dot5. and get some one to help you with the bleading just to be shure that its not sucking air back in ( if your trying to do it your self).

OneRotor

iTrader: (3)

If I didn't bench bleed the master, should the air have worked its way out by now?

I'm thinking that I am going to do a full system flush with some DOT4 fluid this Sunday, as my old fluid isn't very clear (brown tinge...water contamination??)

So what you're saying is:

pump 10 or so times, then open bleeder with person holding a lot of pressure on the pedal, forcing all the pressure out into my quart of fluid that I'm bleeding into.

Rinse-repeat through a full reservoir.

Go on to next bleeder.

Do the same as above.

Turn on car

pump brake pedal a bunch of times

turn off car

Re-bleed @ each corner

And I should be good (no more air in the system)?

I have put on two different master cylinders since I bought the car (original + 2 rebuilt = 3 total). No evidence of leak.

I did not machine the rotors after melting the pads. I will do that when I get a set of front HPS pads.

I'm probably going to do a full flush w/ DOT 4 this weekend.

Slightly Warped

iTrader: (4)

When you bleed brakes with 2 people, have the person in the car pump the pedal 10 or 15 full strokes and not real fast. You are not trying to whip the air and fluid together, you are trying to get the air out of the system. Once the person in the car has done this, he should let you know that it is OK to open the bleeder valve. Open the valve and the person in the car should follow the pedal to the floor and hold it there until you close the valve. He should not use a lot of pressure to do this. Just enough pressure to push it to the floor. Repeat this until you see no bubbles coming out of the hose submerged in the brake fluid. Check the fluid in the master cylinder every 4 or 5 cycles so you don not run out of fluid and suck more air into the system. Then you have to start all over.

The order is as you have been told.

Pass rear
Driver rear
Pass front
Driver front

Slightly Warped

iTrader: (4)

Also, I usually will go back the next day and do another quick bleed. This will get any remaining air from small bubbles that were still in the lines out. After driving and letting the car sit overnight, the small bubbles come together into a larger one and rise to near the bleeder valve. The remaining air in the system is then removed and if there are no leaking seals anywhere, you should have a good pedal feel.

Kentetsu

Hmm, I think we have found the problem. By simply pumping the pedal quickly you really aren't accomplishing anything, even though you do have the end of the hose submerged in brake fluid. Basically, you're just moving the air bubbles back and forth, rather than forcing them out.

That will work if you have speed bleeders though.

Each time you depress the pedal to force fluid out, you have to close the bleeder before you release the pedal. Then, once you have done that, open the bleeder and press the pedal again. Then close the bleeder before releasing the pedal. Repeat until you are sick of it.

This is why (without speed bleeders) you need two people to do this. Although there are some "one man bleeder" kits you can get at the parts store, I've never been very happy with their results.

Also, place a chunk of a 2x4 or something under the brake pedal before you bleed. This limits the movement of the piston in the MC to what it would actually see in real world use. Otherwise, the piston will go past the normally worn area and can tear up the seals.

If I were in your shoes, I'd just go with the speed bleeders. They make life so much simpler.

Slightly Warped

iTrader: (4)

Good advice on the 2x4 Kentetsu. I never thought of this but it makes sense. I can see how the area beyond the normal seal travel may have corrosion that could damage the seals.

dj55b

iTrader: (2)

Bench bleeding is really not required unless its a new master, pumping fast isn't usually a good idea from my experience as it creates more smaller bubbles. The way I do mine is with two people , one in the car pumping, and the other at the bleeder. With the bleeder closed, I pump moderately making sure I go fully to the bottom, each time. I do this about 10 times, and then as im pressing down on the last time I tell them to open it till it goes to the floor, I do this a couple time then move to the next one. Once you've been around all four then turn on the cwr to get the booster going and help push more, pump it a few more times, shut it off, and then do one last bleed all around.

OneRotor

iTrader: (3)

?? Was this copy-paste on purpose, or is there a glitch with the server?

dj55b

iTrader: (2)

That what happens when you type on a smart phone and go back in the browser a few hours later. My apologies.

OneRotor

iTrader: (3)

no worries.