Can bad front ABS sensors prevent the front calipers from compressing the brakes as much as they should?

[Blesna]

I know the question has an obvious answer, at a certain point in the braking cycle. But I'm wondering if the bad sensors were suppressing them more than I knew.
I'm asking because, in the process of replacing bad front ABS sensors, I noticed that the rotors looked as though the pads were not coming in complete contact, and the pads had hardly any wear on them. I replaced all front pads/rotors/calipers about 4 1/2 years ago (about 30k miles), but they have surprisingly less wear than I thought they would (only weathering on the rotors).

I've definitely been experiencing the brake pedal fade at slow speeds, esp. just prior to stopping, but I've never really felt like the brakes were doing a great job in general. Now I'm wondering if the ABS was engaging more than I thought?

 

[MrMarty51]

Welcome to the forum Blesna.
I believe that the rear brakes do less than a desirable job.
I wonder if that’d be whatsa matter with Your truck.

 

[Will L.]

The feeling of brake fade can be the sad rear drums as mentioned.
I learned another common one is people buying “long lasting” pads and shoes. They last longer because it is harder materials which causes poorer performance and easier overheating.
Thinking of a tire for comparison is my best example. Really soft compound rubber will give amazing traction but wear out quickly. Hard rubber lasts for more miles but you can spin them easier especially in water. Now imagine the tire was concrete- it would never wear out but you would have zero traction because it is so hard. Same thing applies to the brakes. Better stopping pads/shoes will simply wear out faster- so never get the long life pads/shoes.

Another common error is installing new pads/ shoes /rotors/ drums and not burnishing (aka bedding) them. Hmmwv/hummer braking is so poor by design this will effect the results by 40%. Pickups do better obviously- but still critical imo.
I cant find the GM process, but here is the generic one from Summitt:

How do I break-in new pads and rotors?

help.summitracing.com

you must do this WHEN NEW. If you didn’t- you can obviously try to scuff the pads/rotors but don’t expect big changes. Just know to do them when you change out the parts- and yes I have had to throw away parts with under 1,000 miles on them to restore people’s braking in dealerships and regular shops. Kinda sucks but is what it is.

High dollar rotors that are worth salvaging- having them chryo treated will correct the lack of burnishing. But do burnish when you get them back from 300 below or wherever you use. Obviously don’t waste the money on poor quality ones.

 

[Will L.]

It is important to verify brakes are properly bleed, brake fluid isn’t contaminated- i live where we have the lowest humidity in the country and my fluid gets replaced on 5 year intervals longest. People in really wet areas should cut that to 3. Your brake fluid absorbs humidity like a sponge.

Proper shoe adjustment is critical as as proper sliding pins and keeping them lubed.

 

[Rockabillyrat]

If its a GM truck they can be tough to get all the air out without a scanner to preform the special bleed procedure. Also a pressure bleeder is a big help for these. The best solution for someone at home is to panic stop in gravel to activate the ABS. This will work out the trapped air. Then simply rebleed the system by having some one pump the brakes and opening the bleeders. Of course this only works if your ABS functions.

 

[Big Ray]

It is important to verify brakes are properly bleed, brake fluid isn’t contaminated- i live where we have the lowest humidity in the country and my fluid gets replaced on 5 year intervals longest. People in really wet areas should cut that to 3. Your brake fluid absorbs humidity like a sponge.

Proper shoe adjustment is critical as as proper sliding pins and keeping them lubed.

This^^^^

My 90 has rear antilock. The light kept coming [n in my dash, but the brakes worked fine.
I'd unplug the box up by the master cylinder and drive it for a while, then plug it back in.
Drive fine for a while, then the light would come back on.
Pulled the drums, checkered adjustment, everything was fine.
Finally left it unplugged. Never noticed a bit of difference.
3/4 ton suburban with hydroboost.
Retina detaching brake performance.

 

[Blesna]

Thanks to all of you. I really appreciate your comments, and the time you spent responding.

@MrMarty51 - thanks for the advice about the rears; that hadn't entered my mind at all.

@Will L - thanks for putting so much thought into your replies. The analogy was great and I appreciate the bedding/burn-in details (I did NOT do that) and will definitely be bookmarking that. I did bleed them during the first replacement, but I might go through it again to make sure I didn't miss any air.

@Rockabillyrat - thanks for the info on bleeding, I did not know that these are especially hard without a scanner or additional tools (outside of having someone pump, hold, bleed, release, repeat..). I don't have that level of scanner, but your comment about triggering ABS is very interesting so I might try that as well.

@Big Ray - thanks for reinforcing the fact that the pads/shoes need proper lubing. And your, "Retina detaching brake performance." comment, LOL!

I did put new pads and rotors on the back at the same time (OE parts all the way around, replacing the original ones which held up for ~150k; I believe the OE replacement pads said they were semi-metallic). But I'll pull the rear wheels and have a look at those too. I'm just concerned that the front ones don't seem to be engaging fully, so perhaps I should look at bleeding as well. And yes, I'm definitely in a wet area, near Seattle.

Just to avoid wasting time, I did to ahead and buy new rotors and pads for the fronts, as much as it pains me to think of throwing the current ones So I may put those on and do the burn-in that @Will L recommended. Whether I replace them with new (again) or not, I will definitely make sure the slide pins are lubed again and the metal guides that the pads slide on. I'm even thinking of lightly sanding the glaze on the pads if I reuse them..

Thank you all again!

 

[Big T]

Thanks to all of you. I really appreciate your comments, and the time you spent responding.

@MrMarty51 - thanks for the advice about the rears; that hadn't entered my mind at all.

@Will L - thanks for putting so much thought into your replies. The analogy was great and I appreciate the bedding/burn-in details (I did NOT do that) and will definitely be bookmarking that. I did bleed them during the first replacement, but I might go through it again to make sure I didn't miss any air.

@Rockabillyrat - thanks for the info on bleeding, I did not know that these are especially hard without a scanner or additional tools (outside of having someone pump, hold, bleed, release, repeat..). I don't have that level of scanner, but your comment about triggering ABS is very interesting so I might try that as well.

@Big Ray - thanks for reinforcing the fact that the pads/shoes need proper lubing. And your, "Retina detaching brake performance." comment, LOL!

I did put new pads and rotors on the back at the same time (OE parts all the way around, replacing the original ones which held up for ~150k; I believe the OE replacement pads said they were semi-metallic). But I'll pull the rear wheels and have a look at those too. I'm just concerned that the front ones don't seem to be engaging fully, so perhaps I should look at bleeding as well. And yes, I'm definitely in a wet area, near Seattle.

Just to avoid wasting time, I did to ahead and buy new rotors and pads for the fronts, as much as it pains me to think of throwing the current ones So I may put those on and do the burn-in that @Will L recommended. Whether I replace them with new (again) or not, I will definitely make sure the slide pins are lubed again and the metal guides that the pads slide on. I'm even thinking of lightly sanding the glaze on the pads if I reuse them..

Thank you all again!

Need to make sure the rears are adjusted, because the auto parking brake adjusters (stopping in reverse) do not always work, or may work unequally. When they are not adjusted to close tolerance, you will lose a lot of pedal height.

 

[Blesna]

@Big T - thanks very much for the advice. I don't like my pedal height either so I will definitely look at those.

Just a quick update... I ended up inspecting the front calipers a bit more. It turns out the top caliper slide bolts on both sides looked like they had overheated at some point (see attached). So I looked inside the caliper brackets as well, and sure enough the top slide holes on both sides were also distorted. I ran a small angled pick through the tops and it was very rough; the bottom holes were smooth as glass. I'm assuming this was causing drag and preventing the calipers from sliding correctly.

So I replaced both caliper brackets (decided to use Cardone 14-1125 and 14-1126 reman), and all 4 bolts and rubber sleeves (tops were also a bear to get out), along with plenty of high temp grease. And they work great now. So thanks again to @Will L. for making me reconsider inspection of the sliding pins! And no more faulty ABS engagement either.