Brake pedal feel/ABS module questions

traingeek2000

New Member
Authorized Seller
Joined
Aug 8, 2018
Messages
24
With the virus scare, campus is moving to online classes and I'm getting sent home. On the bright side, this means much more time to work on my '91.

When I first bought the car, I had issues with the brakes dragging, which I didn't realize soon enough into my first drive and I got stranded. Car got towed to my mechanic, he replaced all four calipers with remanufactured units. Still had issues with brakes dragging, so then he replaced the master cylinder. No more dragging, but the pedal feel sucks. I asked him about this and he told me that when they were adjusting the new master cylinder, they couldn't get good pedal feel without the brakes dragging, even after bleeding the brakes several times. Currently, there's about 2 inches of travel in the pedal before I feel any real stopping power. I checked the brake booster actuator rod and it's only ~3mm from the pedal itself, so I wrote that off as a potential cause.

I do have an anti-lock warning light on that I haven't run codes for nor addressed. I was planning to live with it, assuming it was because I currently have no working speedometer, but I realize I don't know if it needs input from the speedo cable and the speed sensors in the knuckles or just the knuckle sensors. I have also read that the ABS module in our cars can get gummed up and prevent good braking. While looking into the brake dragging issue I also read it could be from a vacuum leak at the brake booster, but I have yet to check for vacuum leaks.

The ABS delete kits out there are tempting, but I admit I am a novice driver and will be driving this car mostly on the street, and would prefer to keep the system. I also don't know how to diagnose such an issue beyond brake bleeding. Eventually I will be upgrading to the Mercedes BBK, but I would like to have a working brake system before then.

How can I determine the root cause of this pedal feel issue? Out of what I've heard, what is most likely to be the cause? Should I bother with keeping ABS?
 

A70nut

Active Member
Authorized Seller
Joined
Sep 21, 2018
Messages
183
Location
Lexington, Ky
I would definitely pull abs codes to see what that issue is. Lots of time with dragging calipers though it can be caused by the brake hoses by the knuckles being collapsed inside, allowing pressure to go to the caliper because it has so much force, but not having enough to overcome the collapsed line and return to the master, causing pressure to stay in the calipers and make them drag. But I would pull abs codes first.
 

traingeek2000

New Member
Authorized Seller
Joined
Aug 8, 2018
Messages
24
When my mechanic replace the calipers, he also replaced the rubber hoses going to them. Is it likely that the hardlines in the body themselves would have a similar issue?
 

Asterix

Lurker of Power
Authorized Seller
Joined
Mar 31, 2005
Messages
514
Location
Vienna, VA
I've played with mine in the past for quite some time but have learned to live with the loose pedal. The first stop of the day can be worrisome.

The booster input rod has adjustment as well, but I've not been able to move it. There's an important measurement there to get right. The TSRM explains how.
 

Piratetip

Far From Maddening Crowds
Staff member
Super Moderator
Authorized Seller
Joined
Dec 30, 2005
Messages
1,993
Location
MKE, WI
After replacing my master cylinder and all calipers/softlines, I have very little freeplay before engagement.
Once properly adjusted it feels pretty close to how new vehicles are these days.

If anyone has issues still, there is likely something wrong / not adjusted correctly.
 

andrew_mx83

Member
Authorized Seller
Joined
Mar 22, 2008
Messages
151
Location
Melbourne
Shouldn't the booster push rod have more like 0.5mm of clearance? If its adjusted wrong it will give the symptoms you're describing. I'd check the spec in the tsrm and adjust if necessary.
 
  • Like
Reactions: A70nut

traingeek2000

New Member
Authorized Seller
Joined
Aug 8, 2018
Messages
24
Me again! Back home and I ran a code 33 for rear wheel speed sensor. I'm assuming since there's no rear left/right sensor, it runs off the speedometer signal from the transmission speedo cable. Since my speedometer is non-functional, is it reasonable to assume this is the issue?

I have yet to test for vacuum leaks or test the brake booster.
 

A70nut

Active Member
Authorized Seller
Joined
Sep 21, 2018
Messages
183
Location
Lexington, Ky
Me again! Back home and I ran a code 33 for rear wheel speed sensor. I'm assuming since there's no rear left/right sensor, it runs off the speedometer signal from the transmission speedo cable. Since my speedometer is non-functional, is it reasonable to assume this is the issue?

I have yet to test for vacuum leaks or test the brake booster.
I thought they were two different entities but I could be wrong. Maybe the rear speed sensor is unplugged?
 

Asterix

Lurker of Power
Authorized Seller
Joined
Mar 31, 2005
Messages
514
Location
Vienna, VA
The rear speed sensor is in the transmission, and is separate from the speedometer.
 

traingeek2000

New Member
Authorized Seller
Joined
Aug 8, 2018
Messages
24
So, even if I do get the rear speed sensor connected, the soft pedal would be a separate issue I'd have to resolve?

I did a simple test on the brake booster by pumping the brakes with the car off, turning it on, and feeling the boosted brake pedal sink. The pedal sank ~1/4" when I turned the car on, and from what I understand this means the booster is working properly. Anything else I can check? Or are there other tests I should run to diagnose my brake booster?
 

JustAnotherVictim

Well-Known Member
Authorized Seller
Contributor
Joined
Mar 30, 2005
Messages
4,820
Location
Somewhere...
Your problem is most likely connected to master cylinder or booster. Air or leak in the hydraulic system or air leak in the vacuum system.
If you can find a booster rebuilder in your area I would definitely have them take a look, it's not much work to remove it and it's one more thing you can totally eliminate as a possibility.
 
  • Like
Reactions: traingeek2000

A70nut

Active Member
Authorized Seller
Joined
Sep 21, 2018
Messages
183
Location
Lexington, Ky
You could always have someone pump the brakes and watch the rubber lines to make sure they aren't ballooning under pressure.