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240 Inconsistent brake pedal feel

240-FAN

New member
Joined
Aug 15, 2018
Brake MC was replaced with a Autozone unit in 2012 right after I purchased my '91 244. It was in a parking because I didn't know anything about working on cars then and I was a broke a$$ poor student. Needless to say.....air in the line.

Last year, why doing the rear shocks, I replaced the rear calipers, rotors and pads. And manually bled the system (I depress the brake and my buddy would open the bleeder valve). Followed the procedure in the Hayne's manual.

But I have been suffering from inconsistent brake pedal feel. 6/10 times I have solid feel. The remaining 4/10 times it feels mushier/longer travel than normal.

I had to take apart the rear driver's side caliper and re-do it because the back side piston seemed to be stuck causing that pad to drag. I now have consistent brake rotor temperature across the sides (based on 12-15 miles of testing).

Any pointers of where I should start?
 
A warped rotor or bad wheel bearing can push the pistons into the caliper causing a longer stroke on the pedal to push them back out.
 
Interesting. I don’t think it’s rotors because there’s no shudder associated with the usual feel when Rotors are warped. For the bearings, wouldn’t they make a sound or a roar?
 
Back to a hotter rear driver’s side rotor. After a drive, I measured about 125C on the driver’s side rear rotor and about 107C on the passenger side rear rotor.
The car also seems to be pulling on to the left/driver’s side
 
It’s the hottest around the area of the rotor that sits around the hub. Is that normal?
This is my first attempt at diagnosing brake systems....
 
You didn't mention whether you replaced the rubber flax lines in your brake system. Which means they are due for replacement. They internally swell and can give inconsistent brake pedal feel and since they are swollen internally where you can't see. The fluid doesn't travel back properly after braking. This makes constant residual pressure causing higher temps as well.
 
Hottest around the hub may mean the wheel bearing is dry. Jack up the car and if they feel chunky and not smooth to rotate. then a worn bearing is causing the higher temp. You can back off the brake pads to let the rotor rotate easier to feel the bearing. Don't forget to reseat your brake pads.
 
As far as I know, those brake lines are all original to the car (both front and back).

I took both the rear wheels off. The drivers side definitely feels grungier although the other side didn’t feel all that much better.
Can the bearings be re-greased?

If re-greasing doesn’t work, I can look into replacing the flex brake lines perhaps?
 
Yes the bearings can be re-greased, AKA re-packing, you’ll find some info in the Haynes manual. When you have the bearings out for re-greasing, you can inspect the bearings and races for scoring and pitting. Since they are grungy as you discovered they likely need replacing as well as the axle seals regardless if you re-grease or replace. If they’ve never been replaced, probably best to do so. Typically a hydraulic press is required to replace the bearings.
 
Plan on replacing both rear bearings if one is compromised. You can't actually repack the rears because you would have to do it with the bearing installed on the axle. Plus you can't replace the outer seal without the bearing removed.
 
Ouch! Looks like replacing wheel bearings is outside of my scope of skills. Given how much it will cost me, is there a sure fire way to diagnose the wheel bearing? The car has no shimmy or shake or growling or whining or anything of that sort.

The only thing I can say is, when put the brakes back on that side, it seemed to run fine till I repeatedly applied the brakes and it went back to running hotter and pulling to the left/driver's side. Any possibility that the caliper I installed is defective?

I also took the other side off to see how it felt. They feel the same. When I say grungy, I mean that you can hear it make some noise against the parking brake shoes....
An odd thought as I type this: could the rotor be off slightly causing the the inside of the rotor to constantly rub against the parking brake shoe? Is there any way to adjust the parking brake shoe when I take the rotor off?

Now that I have had that side brakes off twice after the brake job, I am starting to get a little more convinced that there's something wrong with the brakes rather than the bearings.
Another point, the brake lines going into the rear calipers are solid lines, not the rubber hoses...
 
The parking brake adjustment is on the handle inside the car. It could be that one side of the two brake cables is tighter causing some rubbing inside the rotor. Take off the back ashtray and rear plastic cover on the cneter console. You and also remove the center console and have better access. Then check where the two brake cables attach to the parking brake handle. You can loosen or tighten the nuts on the ends of the cables or the center puller that pulls the cables has a bolt for adjusting both cables at once.

The rear axle has two flex lines coming from two pressure regulators on the body and then just to the left of the center diff housing they are connected to the metal lines going to the calipers. That is the lines that fail. You can also have problems with the pressure regulators. But that isn't as common as flex line failure.
 
Ah, gotcha.
This is the spot where it is the hottest and then the temp falls off pretty rapidly:

KAdF5c4.jpg


As you can see, its right where the rotors horizontal portion becomes vertical (the one going perpendicular to the door of the car is the horizontal and the vertical is the area where the brake pads make contact if that makes sense) is the hottest
 
Well with slightly compromised parts like one line being a little more restricted than the other or a slight difference in pressure from the regulators. You could have a bit hotter side.

I would suggest at least making sure all the brake fluid is fresh and probably replace the flex lines if they are that old. If things are working fine after that. I wouldn't worry about a temp difference.

Do you know another person with a 240 with good brakes? Then you can compare temps to another car.
 
Makes sense. I had gotten fresh brake fluid when I did all the work originally last year.
I’m hoping to have some time next week to take it apart again and check out the brake flex lines.

Another thought, could it be that pads are dragging on the two “slider” pins that run across the caliper? Perhaps, take it off and grease it good with some brake grease/lube and give it a go?
 
Well, more than 25 year old brake flex lines that don't let the fluid return cause brake pad dragging like you suspect. Even if the pins are greased as they should.
 
Inconsistent brake feel can also be caused by a worn out (collapsing) vacuum line between the intake and the power brake booster. It will intermittently collapse and open up again. Inspect the hose and see if there is a weak section - pinching around gently on the line can turn it up pretty quickly.
 
Any possibility that the check valve is failing partially?
Also, I let the car idle for a bit and then repeatedly pressed the brake.
Consistent pedal feel?!?!? Wtf....

I did replace my rear calipers during the original brake job. Any possibility that there’s some air in the lines?
 
Interestingly, if I’m hitting the brakes with the car in “P”, the pedal feel is solid.
It’s only when I’m coasting to a stop and I hit the brakes, is there longer travel.

Also, after that if I step off and back on, it’s back to normal travel.
 
Check the brake booster vacuum hose as recommended above. Higher rpms will cause higher vacuum and could be enough to collapse a soggy vacuum hose. When you’re in park, it’s enough vacuum to assist with braking but not enough to collapse the vacuum hose.
 
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