'99 OBS CC SWB Brake Issue

[SCOTI]

Finished up a brake rebuild on my '99 OBS truck:
*Rotors
*Calipers
*Pads
*Wheel bearings/seals
*Hoses
*Master Cylinder
*Rear wheel cylinders
*Rear shoes
*Drums

Well there still seems to be some post work diag effort needed. I bled all 4 corners per usual. Did 3-rounds after purging all initial air from the lines first. Bench bled the new master within the last week & kept fluid in it until install.

Sprayed everything down connection wise w/some brake clean so I would have dry surfaces when leak checking. Took a couple laps around the neighborhood. Stopped as expected. Re-checked for leaks & found 1 area where there was moisture (driver side front hard-line to hose connection). I re-cleaned that spot because i couldn't tell if it was some remaining fluid I didn't soak up or an actual leak. Master cylinder volume looked good.

Did a couple more laps w/o issue. No visible leaks/moisture from seeping brake fluid upon re-inspection. I stopped & had some dinner @ my local pub. Was driving over to my GF's house & when I slowed to turn onto her street the truck shuddered. That's definitely new. My mind immediately went to 'ABS' shudder as the default issue. I parked @ her house, grabbed a flashlight & inspected all line connections & bleeders. Everything was still dry/clean. The fluid is still full (same level).

I guess tomorrow @ lunch I'll pull the wheels off & check braking surfaces for moisture or fluid. No dash board ABS warning either for what that's worth.

Thoughts? Look-outs?

[pwdcougar]

Did you feel the shudder through the pedal?

[SCOTI]

Yes. I feel it in the pedal but I can feel it through the steering as well. Heck.... I could see it in the dash (shaking).

The front end was all rebuilt this time last year w/zero issues so the front end steering wise is solid. I pulled the calipers & rotors off after work today for a quick re-inspection. The rotors felt slightly tight on a 'spin test' so I decided to back off 1-tooth on the castle nut. I hit them w/the temp gun after a short drive (5-miles city/suburb traffic) but temps were pretty even.

After the wheel bearing adjustment, the shudder was still present. It's not constant either. I hit the brakes @ the end of the street & everything felt fine. Next stop, it shudders. I tried altering (modulating?) pedal pressure & I suppose I could say it changes if I'm more aggressive on the pedal.

I compared the reluctor wheel on the old rotors w/the new ones & they look the same. Another thing I wondered was if the sensor(s) could have been impacted when I sprayed the dust shield & spindle down w/brake cleaner. There also was basically no rear brakes before this service (based on tear-down autopsy). With the pass side adjuster maxxed out & the shoe material worn into the rivets + the driver side adjuster frozen & the wheel cylinder seal ripped/worn on one side there was basically nothing there.

There is definitely rear braking now. I adjusted both sides until there was slight drag of the shoes on the drums. They were still turnable but w/slight drag.

IDK @ this point what to think.

[Snarl95]

Check to see if rear drums are out of round.

[SCOTI]

They're brand new units so I wouldn't think so. Anything is possible w/new items though....

[Snarl95]

Originally Posted by SCOTI

They're brand new units so I wouldn't think so. Anything is possible w/new items though....

I had a set that was "new" that I'm guessing had been stored standing up and were so out of round when you hit the brakes the whole car shook.

[SCOTI]

Originally Posted by Snarl95

I had a set that was "new" that I'm guessing had been stored standing up and were so out of round when you hit the brakes the whole car shook.

You didn't notice vibration just driving?

I still have the old drums in the shop. I suppose I could throw them back on this afternoon to see if there's any difference.

[SCOTI]

Originally Posted by Snarl95

I had a set that was "new" that I'm guessing had been stored standing up and were so out of round when you hit the brakes the whole car shook.

Originally Posted by SCOTI

You didn't notice vibration just driving?

I still have the old drums in the shop. I suppose I could throw them back on this afternoon to see if there's any difference.

@Snarl95... Brother, I want to extend a 'Thank You Sir' to you.

I yanked the new drums off & popped the old units on. Other than blowing off the brake dust I didn't make any other changes. Drove it around my shop-complex neighborhood & normal pedal. It's a little lower vs w/the fresh drums but since I didn't adjust for the wear on them I expected that possibility. I did 3x laps around the neighborhood varying my speeds & no brake shudder on any of the 'stops'.

I'm going to run the 'new' drums over to my buddy @ a dealership tomorrow AM & see if we can rig them up on the balancer or lathe for a visual. I'll follow-up after.

Sometimes its you guys out there on this great forum/site taking the time to assist & help us see the obvious things we might miss right in front of us. Discussion, bouncing ideas back & forth, + learning from others experiences are one of the GREATEST benefits of these forums.

Again, I do appreciate the feedback from you & @pwdcougar.

[lolife99]

Glad you got it figured out.
This forum is lucky to have you, SCOTI,… You have helped MANY on here with all your knowledge.
Still one of the best forums on the internet.

[SCOTI]

Originally Posted by lolife99

Glad you got it figured out.
This forum is lucky to have you, SCOTI,… You have helped MANY on here with all your knowledge.
Still one of the best forums on the internet.

TY sir.... Ten-fold back @ you for all you've helped!

[Snarl95]

Just glad I could be of assistance.

[SCOTI]

Originally Posted by Snarl95

Just glad I could be of assistance.

Definitely were simply by sharing your story.

I popped in to visit my buddy @ the dealership Wednesday after work. We discussed possible scenarios & decided to just keep driving until Saturday & see if anything changed. If nothing changed, we would look into the ABS stuff.

I mentioned I could always swap the previous rotors or drums back on since I still had them but even he felt 'what are the odds?'. He knows I'm slightly 'particular' about how things are done so even he figured it could very well be one of the sensors failed w/the thorough 'brake clean' job.

You mentioned having experienced an issue w/drums so I figured it would be easy enough to do them 1st. If there was no difference, I was going to swap them back around & then do the same w/the rotors. The rotors would have taken more effort because the inner seal had failed making the drums the easier option.

[Boog]

Well, that's not surprising. I once bought a new pair of drums for my Blazer and experienced a pedal pulsing when stopping. I removed the drums and took them back to the store to have them check them and sure enough they were out of round. Brand new too. They trued them up and I reinstalled them and all was good. I had a "mechanic" tell me "oh I always have all new rotors and drums turned before I put them on". I said a brand new part is supposed to be finished right and ready to install. The store manager told me new rotors and drums and such were just dropped in a crate or bin after machining process and stored that way until packaging. Some warping happens. So they don't automatically turn them for you. You have to ask them to do so and pay for the turning of course on top of the cost of the parts. Totally ridiculous.

[special-K]

It's truly a great thing to have these forums to learn unseen issues from the experiences of others. Glad you got it!

I just want to add, because you had suspected maybe the dust affecting the sensors. It's been my experience, though limited, that the slightest contamination effecting a sensor will light that dash right up. We all know there could be a rare chance of issue between sensor and indicator light but, basically, that light will let you know the slightest issue. You were digging for clues and anti-lock is where my mind went. Dang faulty parts. I never would have thought a cast part sitting on it's side could distort.

[SCOTI]

Originally Posted by special-K

It's truly a great thing to have these forums to learn unseen issues from the experiences of others. Glad you got it!

I just want to add, because you had suspected maybe the dust affecting the sensors. It's been my experience, though limited, that the slightest contamination effecting a sensor will light that dash right up. We all know there could be a rare chance of issue between sensor and indicator light but, basically, that light will let you know the slightest issue. You were digging for clues and anti-lock is where my mind went. Dang faulty parts. I never would have thought a cast part sitting on it's side could distort.

Yes sir.... My brain went straight to my overzealousness w/my clean-up effort spraying things down w/brake cleaner. Getting things 'like new' is a fault of mine. It's bit me in the arse more than once.

I was defaulting to the "oops I did it again" logic. That being said.... Those sensors are clean 😁

[SCOTI]

Put the drums on a brake lathe this AM & they were definitely not true.

On the first quick pass, it was crazy how much material it took off @ several spots. Three passes on each drum cleaned them up. I got back to the shop & swapped them back on.

No more pedal pulsation or vehicle shake.

[Palf70Step]

Glad you got it figured out

[special-K]

Originally Posted by SCOTI

Yes sir.... My brain went straight to my overzealousness w/my clean-up effort spraying things down w/brake cleaner. Getting things 'like new' is a fault of mine. It's bit me in the arse more than once.

I was defaulting to the "oops I did it again" logic. That being said.... Those sensors are clean 😁

On my first, actually my second, rotor replacement... I'll stop here and tell about my first. On my first rotor replacement I (nor my very skilled mechanic buddy) never could get those four sunken bolts to break loose from the knuckle. Broke three impact sockets before giving up and going to the junkyard for a knuckle-out assembly.

Ok, so on my second rotor replacement on this Suburban, with antilock brakes, I was told I'd be lucky if the sensors weren't seized up. Well they weren't, came out super easy. So I used anti-seize when installing, being the thorough guy I am, and got some on the sensor. So light was on and no anti-lock. I learnt something thar!

[speedygonzales]

Nice job but.......

I didn't see where you did (at least you didn't mention) an automatic brake bleed.

It is suggested in the 400's that every time you bleed the brakes, you do an automatic bleed. This process for me made all the difference in the world for brake feel/ strength/ grab.

So?

[Just call me Sean]

He said he bled the brakes.

[SCOTI]

Originally Posted by speedygonzales

Nice job but.......

I didn't see where you did (at least you didn't mention) an automatic brake bleed.

It is suggested in the 400's that every time you bleed the brakes, you do an automatic bleed. This process for me made all the difference in the world for brake feel/ strength/ grab.

So?

Originally Posted by Just call me Sean

He said he bled the brakes.

As @JustcallmeSean stated, the brake system had to be bled since both calipers, front hoses, & rear wheel cylinders were replaced.

I started flushing @ the farthest position & bled until the air was purged & fluid looked new. Once the fresh fluid was coming out, I purged @ each other corner until I got more fluid vs. air. Then 3x rounds @ each corner until no air.

Not sure what an "automatic bleed" is??

[speedygonzales]

Originally Posted by Just call me Sean

He said he bled the brakes.

I'm sorry do I seem to be an idiot? Or perhaps you missed the word "automatic".

Originally Posted by SCOTI

As @JustcallmeSean stated, the brake system had to be bled since both calipers, front hoses, & rear wheel cylinders were replaced.

I started flushing @ the farthest position & bled until the air was purged & fluid looked new. Once the freshh fluid was coing out, I purged @ each other corner until I got more fluid vs. air. Then 3x rounds @ each corner until no air.

Not sure what an "automatic bleed" is??

For both of you, an Automatic brake bleed is where a "capable" scanner takes over the bleeding process and shuttles the antilock valves while the occupant has his foot on the brake pedal. You will feel the pedal go down a little and stop. Then go down a little further and stop. And go nearly all the way down and then come back up. This is all done by the scanner.

A dealer obviously would be able to do this for you. A highly knowledgeable independent shop also. Since I have my own Solus, I do my own. I had bled my own brakes the normal way for years. Then I finally looked deeper into the 4 books of the shop manual and found the automatic bleed process and have never had a better pedal feel since.

So from page 5-249 in the 98 GM shop manual:

Do a standard 4 wheel bleed procedure
Press the brake pedal firmly and run the scan tool automated Bleed Procedure once.
Bleed all 4 wheels using the standard process again.

I don't understand the influence this process has on the brake pedal firmness and grab but it does. If you aren't doing it, you're leaving a lot of good on the table.

Good luck

[SCOTI]

Originally Posted by speedygonzales

I'm sorry do I seem to be an idiot? Or perhaps you missed the word "automatic".



For both of you, an Automatic brake bleed is where a "capable" scanner takes over the bleeding process and shuttles the antilock valves while the occupant has his foot on the brake pedal. You will feel the pedal go down a little and stop. Then go down a little further and stop. And go nearly all the way down and then come back up. This is all done by the scanner.

A dealer obviously would be able to do this for you. A highly knowledgeable independent shop also. Since I have my own Solus, I do my own. I had bled my own brakes the normal way for years. Then I finally looked deeper into the 4 books of the shop manual and found the automatic bleed process and have never had a better pedal feel since.

So from page 5-249 in the 98 GM shop manual:

Do a standard 4 wheel bleed procedure
Press the brake pedal firmly and run the scan tool automated Bleed Procedure once.
Bleed all 4 wheels using the standard process again.

I don't understand the influence this process has on the brake pedal firmness and grab but it does. If you aren't doing it, you're leaving a lot of good on the table.

Good luck

First I've ever heard of this & I have 2 long-time buddies that have been employed @ dealerships most of their careers. I mentioned visiting the one @ the Ford dealership he works at (it's within walking distance from where we both live as well). When he wasn't @ Ford, he worked for higher end independent shops so he's familiar w/GM products.

I'll hit my buddy up that's the GM lifer & see what he knows (or can find out).

Thanks for the follow-up & explanation of the 'term'.

[Just call me Sean]

Originally Posted by speedygonzales

I'm sorry do I seem to be an idiot? Or perhaps you missed the word "automatic".

Yes, no.

[speedygonzales]

Originally Posted by Just call me Sean

Yes, no.

So let me get this straight you think I'm an idiot and you didn't miss the term the automatic bleed"?

So what is an automatic bleed?