A new brake bleeding thread ... what did I do now?

[pmckechnie]

Bodhi
Sometimes when you have new rotors and pads they will have a tendency to get hotter than normal when new. That will go away after they brake in. There are a couple of test to try. Jack up the wheel you suspect. Spin it. Get in the car and depress the peddle firmly. Go back to the wheel and spin it again. If it was the same both times and not to hard to spin then everything is AOK. If the wheel is hard to spin, loosen the bleeder and re tighten. then try to spin again. If it is easer this time, then you do have a problem. Press the peddle again, but this time loosen the brake line at the master cylinder that goes to that end of the car. Spin again. If it spins easily, then there may be a problem with the master cyl. You can also try at the anti lock unit. I think you get the idea. You are looking for something holding pressure on the caliper.
Have a SALT sandwich, get the BP up a little and have a GREAT DAY.
Paul

[whunter]

Originally Posted by Carpenterman

I built my own pressure bleeder and the instructions said to not go over 14psi. I didn't want to have to crawl out from under the car so many times so I figured 20psi would give me a longer interval, plus maybe drive the old fluid out with a little more force taking more crud with it.

While under the car I noticed fluid dripping out near the engine bay and I found that the rubber grommets that fit the reservoir to the master cylinder cannot take that kind of pressure without leaking.

Lesson learned.

Brake bleeder - power bleeder Homemade
Brake bleeder - power bleeder Homemade

The critical factor is keeping the bleeder fluid level full enough that only pure fluid reaches the pickup.
The bleeder fluid maintains the reservoir fluid level, preventing air entering system.
Most systems bleed just fine at 2 - 5 PSI.
Some systems I have connected to and popped the reservoir off the master cylinder at 3 PSI, the mount grommets where junk.

[BodhiBenz1987]

Originally Posted by pmckechnie

Bodhi
Sometimes when you have new rotors and pads they will have a tendency to get hotter than normal when new. That will go away after they brake in. There are a couple of test to try. Jack up the wheel you suspect. Spin it. Get in the car and depress the peddle firmly. Go back to the wheel and spin it again. If it was the same both times and not to hard to spin then everything is AOK. If the wheel is hard to spin, loosen the bleeder and re tighten. then try to spin again. If it is easer this time, then you do have a problem. Press the peddle again, but this time loosen the brake line at the master cylinder that goes to that end of the car. Spin again. If it spins easily, then there may be a problem with the master cyl. You can also try at the anti lock unit. I think you get the idea. You are looking for something holding pressure on the caliper.
Have a SALT sandwich, get the BP up a little and have a GREAT DAY.
Paul

Thanks Paul. I had been starting to drive myself crazy second-guessing whether or not the brakes actually still have a problem. I just stayed away from the car for a day to "recalibrate" my perspective and fiddled with it more today. I don't think the brakes are really dragging very much ... for comparison I checked the wheels on my Jeep, and they actually drag a LOT more than the 300D's. Not that that proves anything, since the Jeep could need brakework too (have not noticed any problems). I wish I had a better perspective of what normal drag feels like vs. bad drag. They certainly don't drag like the wheel did when the caliper seized! I did try cracking the lines on the MC and it didn't change the feel of any of the wheels. When I just pump the brakes a few times and go to spin each each wheel, there's a light resistance at first but once it's in motion it goes back to the way it felt prior to pumping the pedal. I drove the car a bit today and didn't think the brakes got horrendously hot ... again, it's really hard for me to judge what's too hot and what's normal hot. I did notice that when I get the car to about 30 and just let it coast on flat road, it keeps rolling easily for quite a while. I took it out on the highway, and the only thing I noticed abnormal was a slight steering wheel vibration at 80 mph (prior to the brake job I had vibrations at 50, 60,70, etc.). Also, no smells ... maybe I got a bit of stray grease on the rotor on that first test drive.

So ... I have the doner MC and ordered the seal that goes between it and the booster ... but I'm torn as to whether I need to replace it, or if I'm just making a big to-do about totally normal behavior.

[BodhiBenz1987]

Originally Posted by whunter

Brake bleeder - power bleeder Homemade
Brake bleeder - power bleeder Homemade

The critical factor is keeping the bleeder fluid level full enough that only pure fluid reaches the pickup.
The bleeder fluid maintains the reservoir fluid level, preventing air entering system.
Most systems bleed just fine at 2 - 5 PSI.
Some systems I have connected to and popped the reservoir off the master cylinder at 3 PSI, the mount grommets where junk.

For some reason I thought in an ABS-equipped vehicle you needed higher PSI?

[whunter]

Originally Posted by BodhiBenz1987

For some reason I thought in an ABS-equipped vehicle you needed higher PSI?

There are some out there.
Rule of thumb:
Use 2-5 psi, if it fails you can raise the pressure by increments of five, up to 20 psi.

FYI:
Some of the newer vehicles require a diagnostic tool to bleed the brakes by cycling the ABS and reset the system.


Brake:
--------------------------------------------------------------
Some Facts About Brake Hoses:
#1. The average life of a brake hose is six years.
#2. Brake hoses deteriorate from the inside as well as the outside.
#3. Moisture is absorbed into brake fluid systems through brake hoses.
#4. Contaminants in brake fluid act abrasively on the inner wall of brake hoses.
#5. The brake hose reinforcing fabric deteriorates through expansion and moisture.
#6. High operating temperatures contribute to the deterioration of hoses.
#7. Brake hoses swell with age and restrict flow.
#8. Generally all brake hoses on a vehicle deteriorate at the same rate, So all hoses should be replaced if one is found to be faulty!

Brake hose failure mode:

#A. Rupture (burst hose) = age, exercise (too many miles) or impact are the typical cause.

*B. Partial internal collapse = the inner ply becomes damaged/detached acting as a partial restriction and/or one way valve.

#C. Full internal Blockage = the inner ply becomes damaged/detached acting as a plug = brake pedal still feels good but there is no brake application.

Brake:

[Carpenterman]

Thanks for the info on bleeder pressure, Whunter. My grommets were new and they still leaked at 20psi.

Regarding brake drag, after experiencing (and repairing) a seized rear caliper, I always check the brake drag while coming to a stop. I release the brakes at the very last moment of travel to see how the car moves those last few inches. Easy to see if it stops abruptly/tightly or free. Also on a very slight incline, the car should roll upon brake release.

[BodhiBenz1987]

So I've put about 300 miles on since the brake job. Everything works great, and I can't detect any drag when riding on the highway, accelerating, or when I jack up and spin the wheel including after firmly depressing pedal and letting off). But they still get blazing hot, especially on the front, after stop and go traffic. Too hot to hold a hand on for more than a second or two, and though it doesn't have a burning smell per se, it smells kind of toasty. They don't seem to get this way after highway drive and cruising to a stop. My dad test drove it and says stop obsessing and just drive it ... I guess he's right. I do have two fire extinguishers on board after all.

[Wodnek]

One thing I have done to make the pressure bleeding go easier is use the ATE super Blue. When I do them again in 18 months i will use the ATE amber. The color change is a great visual indicater.

[Yak]

Originally Posted by BodhiBenz1987

So I've put about 300 miles on since the brake job. Everything works great, and I can't detect any drag when riding on the highway, accelerating, or when I jack up and spin the wheel including after firmly depressing pedal and letting off). But they still get blazing hot, especially on the front, after stop and go traffic. Too hot to hold a hand on for more than a second or two, and though it doesn't have a burning smell per se, it smells kind of toasty. They don't seem to get this way after highway drive and cruising to a stop. My dad test drove it and says stop obsessing and just drive it ... I guess he's right. I do have two fire extinguishers on board after all.

Darn. I was hoping you'd have some sort of result. I've got more/less the same thing: rebuilt my calipers, replaced the lines, repacked the bearings (with gauge), no drag on spinning, reasonable MPG = inexplicably hot front wheels.

I was about ready to re-re-build my calipers and see if the "whiskers" on the gasket that the FSM says is responsible for retracting the pads are working or installed correctly.

[vstech]

stop and go is very harsh on the front breaks. lots of friction heating them up, and very little airflow cooling them off. it's the nature of the beast. to see if the heat is a problem, with a cold car, drive 100 feet, stop normally, then drive another 100 feet, and check the temps. if still cold to the touch, you are fine, if they are very warm, investigate the caliper release system again.

[BodhiBenz1987]

Originally Posted by vstech

stop and go is very harsh on the front breaks. lots of friction heating them up, and very little airflow cooling them off. it's the nature of the beast. to see if the heat is a problem, with a cold car, drive 100 feet, stop normally, then drive another 100 feet, and check the temps. if still cold to the touch, you are fine, if they are very warm, investigate the caliper release system again.

Even so hot you can barely touch them? I don't feel like my Jeep or 240D gets as hot, although certainly wheel design may have to do with that (240 has hubbies and the Jeep has different material wheels and bigger holes in them). I'll give the 100-ft test a try. After a short bit of driving (i.e., I drive to the grocery store) they don't get very hot. But usually when I drive around a lot, or drive to work and hit a lot of lights, it gets ferociously hot.
I can't really compare whether it's gotten hotter than before the brake issues and repairs, because before I knew of brake issues, I didn't obsessively feel my wheels.

[pmckechnie]

Bodhi,
If it will make you feel any better, I just drove about 10 miles with 1/2 city type driving and 1/2 slow highway (45 mph). I just went back out and the front wheels were so hot I couldn't hold my hand on them for very long. The ambiant temp is about 96 deg here and I was driving my 500SEL.
In the morning we are making a 400 mile trip to the Outer Banks for the week, and I am not at all concerned about the brakes. Relax and enjoy that FINE car.
Paul