Let's talk about brakes

[Helirich]

I have up graded to vented discs. I've read where some other members have gone to bigger wheels so they can install bigger discs. That's interesting, but all these upgrades help in stopping brake fade. I'm not having that problem. My problem is not stopping the wheels/tires from turning. My problem is stopping the car.

Twice in the last week, I was driving along at maybe 45-50 mph and a side street I was looking for came up unexpectedly. I laid on the brakes and skidded. One of the times I got slow enough to turn in. (It was not pretty, but I made it) The other time, I had to give up and pass the street and come back. Both times I can say I would have easily made those turns in my 30 year old Bronco without cherp from the tires. (It has small brakes and big tires and doesn't stop very good)

I know the D has a rear weight bias, but is this something I just have to live with? Obviously, my front brakes are working. (Because they skid) Do you think my back brakes are doing nothing? Do you guys notice a major differnce compared to other cars?

I'm thinking about jacking up the rear and running the car to see how much the rear brakes stop the spinning wheels. Not sure if this is a good test. Is there any other test I could do?

[Michael]

Do you still have the old tires on the car?

[Mark D]

I have up graded to vented discs. I've read where some other members have gone to bigger wheels so they can install bigger discs. That's interesting, but all these upgrades help in stopping brake fade. I'm not having that problem. My problem is not stopping the wheels/tires from turning. My problem is stopping the car.

Twice in the last week, I was driving along at maybe 45-50 mph and a side street I was looking for came up unexpectedly. I laid on the brakes and skidded. One of the times I got slow enough to turn in. (It was not pretty, but I made it) The other time, I had to give up and pass the street and come back. Both times I can say I would have easily made those turns in my 30 year old Bronco without cherp from the tires. (It has small brakes and big tires and doesn't stop very good)

I know the D has a rear weight bias, but is this something I just have to live with? Obviously, my front brakes are working. (Because they skid) Do you think my back brakes are doing nothing? Do you guys notice a major differnce compared to other cars?

I'm thinking about jacking up the rear and running the car to see how much the rear brakes stop the spinning wheels. Not sure if this is a good test. Is there any other test I could do?

Are you running the original brake master cylinder or a crossover/replacement? The original is proportioned 32 front/68 rear. If you're using a crossover brake master that is 50/50 from a Saab or whatever they come from you'll have changed the braking balance to favor the front of the car more and that could introduce lock up.

DMCH and a few other vendors sell master cylinders with the correct proportioning. Might be worth looking into if you're not sure of what's installed on yours. The originals have "Girling" cast into them, and the DMCH reproductions say "DMC"

[Helirich]

Do you still have the old tires on the car?

Brand new Hankochs. Filled as per the Guru's recommendations.

Are you running the original brake master cylinder or a crossover/replacement? The original is proportioned 32 front/68 rear. If you're using a crossover brake master that is 50/50 from a Saab or whatever they come from you'll have changed the braking balance to favor the front of the car more and that could introduce lock up.

DMCH and a few other vendors sell master cylinders with the correct proportioning. Might be worth looking into if you're not sure of what's installed on yours. The originals have "Girling" cast into them, and the DMCH reproductions say "DMC"

Don't know what I have for master. This sounds like a possible reason for my trouble. My master fill cap is very high. It barely fits under the rubber cover. Makes me think it might not be stock. Is there a good way to tell what I have?

[Rich]

We've talked about brake bias elsewhere.

See this thread.

The stock setup is fine as long as it's working.

'The stock setup' means OE tire sizes at both ends and the original MC. The referenced thread includes a photo of the OE Girling unit.

[Helirich]

We've talked about brake bias elsewhere.

See this thread.

The stock setup is fine as long as it's working.

'The stock setup' means OE tire sizes at both ends and the original MC. The referenced thread includes a photo of the OE Girling unit.

Thankyou, that thread was great. I be checking mine for the orange or black band.

[Helirich]

Yea, it turns out I have a black band with 50/50 on it. I ordered a new one and I will update this thread after installation and testing. I hope this is the answer.

[Mark D]

Hopefully swapping back to the 32/68 will reduce front lock up make the braking feel better balanced. I'm not surprised to hear your car had a 50/50 biased master cylinder since for quite a while there was no other choice. I think DMCH started making the reproductions to the original specs sometime in the mid 2000s.

[Josh]

I see that the 50/50 is sold from some vendors, I dont see how it is an upgrade of any sort. Since DMC is making the proper reproduction this should be the only way to go in my opinion. You have larger brakes in the back (very uncommon) and only 1/3 of the weight over the smaller front wheels. no need to split the brakes half and half. Even with the DMC reproduction master I can get my front wheels to lock up if I stomp on it.

[Rich]

....I know the D has a rear weight bias, but is this something I just have to live with? Obviously, my front brakes are working. (Because they skid) Do you think my back brakes are doing nothing? Do you guys notice a major differnce compared to other cars?

I'm thinking about jacking up the rear and running the car to see how much the rear brakes stop the spinning wheels. Not sure if this is a good test. Is there any other test I could do?

Back to your initial questions:
A. Is it likely your rear brakes are 'doing nothing'?
No. You can check to see if the calipers/pistons are free just by looking/feeling - you've probably already done this; also by trying to turn the axle with the foot brake both on and off. Check both sides. With solid hydraulics and freely-moving pads/pistons the rears will work.
B. Is there any other test you can do to make sure they aren't 'doing nothing'?
Yes. You can try a post-braking rotor temperature check back there. Run through 2-3 very hard stops in a row from 40-60mph to a lower speed or even stopping, ending the last braking run in a safe, roomy parking area. Try to brake each time just as soon as you quickly get the car back up to your selected speed. Immediately park safely, engine off. Quickly use an IR thermometer aimed at the lower inside of each rear wheel rotor, making sure to get the IR gun within a foot or so of the shiny rotor. Both rotors should be hot, proving they are doing something.

Will Test (B) prove the rears are doing as much as they should do? No. I know of no quantifiable brake performance test short of a split-side roller dyno for that.

For grins you could try this test now/soon and then repeat it after you install the OE MC. Keep all else (weather, route, speeds, braking times etc.) ~the same if you can. See if the rears get hotter under the same conditions with the OE MC or not.