Abs brake bleed

[JS45]

I’ve got a 97k1500 i was loosing brake fluid saw the left rear wheel cylinder was leaking changed that looked at the right rear when putting it back together for reference and the right one was leaking so replaced that one as well.

What’s the procedure for bleeding the abs? I’ve seen a video on it but I couldn’t get any fluid to come out. Do you do it before you bleed all 4 corners or after or both? Either way I never got fluid to come out of it.

Brakes feel maybe a bit better but the pedal feel is more spongy so it looks like I read maybe the drum pads need pushed out more so they come in contact with the drum sooner? Is there a place to adjust them through the backing plate so you don’t have to take the drum off?

How do these brakes self adjust? Parking brake use or braking under reverse or normal braking? It has the newer style drums that are differnt than the drum rebuild sticky thread. My old 84 had drums like those.


I am also getting a sound of air from the brake booster area when pressing the brake. Is this normal I’ve never heard it but I have also never paid attention for it. Thanks for the help.

 

[Schurkey]

I’ve got a 97k1500... ...What’s the procedure for bleeding the abs?

Page 2 of the attached .pdf. You'll need a scan tool and a gallon of fluid. You'll also need a pressure bleeder or a helper. If you use the pressure-bleeder method, you're also supposed to have a "Special Tool" to hold the metering valve pin.

drum pads

"Shoes"

need TO BE pushed out more so they come in contact with the drum sooner?

FIFY.

Probably. The hateful leading/trailing shoe rear brakes are infamous for being way out of adjustment.

Is there a place to adjust them through the backing plate so you don’t have to take the drum off?

Probably not. Some backing plates may have a knock-out for that, but it's a pain to punch it out of the backing plate; there may not be a knock-out; and even if there is, it's easier to just pull the drum.

How do these brakes self adjust? Parking brake use or braking under reverse or normal braking?

If it's the usual 254mm (10 inch) rear drums, you've got the crappy leading/trailing shoe brakes, they adjust the first time you step on the brake pedal AFTER using the park brake. You may have to do that twenty or thirty times to get them back in adjustment, (easier to pull the drum and do it by hand, so you can verify that the adjuster isn't seized, and all the parts are still in place) and then you need to use the park brake frequently to keep them adjusted.

I am also getting a sound of air from the brake booster area when pressing the brake. Is this normal

Depending on what, exactly, you're hearing--No.

The booster should make a fairly quiet "squoosh" as you step on the pedal, while the pedal moves. If it's loud, there's something wrong. If it continues after the pedal stops moving (holding pressure with your foot) there's something wrong.

 

[JS45]

thanks for the reply. first thing I will do is pull the drums and adjust the shoes out until they drag the drum a slightly. I can do the bleeding again too as I didn't drain a pint from each just enough to get a steady flow of fluid. I think the shoes not being in adjustment is the main issue as I adjusted them in so the drum would slide on easily. The adjuster moves freely.

I think the squoosh sound you describe is what I am hearing so I dont think I have an issue with the booster.

Its kind of crazy you have to have a tech1 tool to bleed the system properly. I don't have one of those. Has anyone done it how this guy shows in below video?

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[Schurkey]

I tried like in the video, and got nowhere. I never got fluid to bleed out of the lil' push-button under the rubber cover. Remember, that video CANNOT work for '88--'99 because GM used FOUR DIFFERENT ABS units in the C/K pickups in that time frame--Cast-iron RWAL, aluminum RWAL, EBC4, and finally EBC310 starting on the C/K in '95. The ABS in the video appears to be the EBC310 like I have...but like I said, it wasn't working for me.

My Snap-On MTG2500 with 6.x software, and my S-O Solus Pro with 8.2 software wouldn't do an ABS bleed of my '97 K2500. However, they'll do an ABS bleed on SWMBO's 2003 Trailblazer. Go figure.

I got a Solus Pro with 14.2 software, and THAT will do an ABS bleed on the '97. I don't know when that feature was added to the Snap-On software, except that 8.2 doesn't and 14.2 does. They could have added it later in '08 or anytime between then and the second-quarter-of-2014 software update.

[Edit] Found out on another thread that a Solus Pro with "2010" software (10.x) will do the ABS bleed. So it would have been added to the software after 8.2, but at or before whatever version of 10.x he had.[/Edit]

 

[Zerio29]

I'm in the same boat as shurkey here, I've never got the procedure in the video to work, no matter how many times I tried.

Usually you only have to bleed the ABS module if you change the M/C or the lines "upstream" of the ABS unit - and then most people end up deleting it and opting for a prop valve setup instead. My guess is that your shoe adjustment is to blame.

 

[Pinger]

Shurkey's boat will be sinking soon with us all climbing aboard...
What did improve mine - without having a scan tool - was pushing the ABS into activation (by driving it onto a slippy surface and slamming the brakes on) then bleeding at the wheel. I only did this for the front wheels (individually) though.
It improved the pedal and further improvement came by itself (presumably with air finding its own way to the MC).
This was after fitting a new (bench bled) MC and all flexible hoses.

 

[Zerio29]

Shurkey's boat will be sinking soon with us all climbing aboard...
What did improve mine - without having a scan tool - was pushing the ABS into activation (by driving it onto a slippy surface and slamming the brakes on) then bleeding at the wheel. I only did this for the front wheels (individually) though.
It improved the pedal and further improvement came by itself (presumably with air finding its own way to the MC).
This was after fitting a new (bench bled) MC and all flexible hoses.

Haha yup. This isn't exactly a new issue is it.

I did actually do that in a gravel parking lot to bleed the ABS with some improvement for sure, but I just didn't do it for long enough to make a difference. I guess i got fed up with beating up my truck so hard in the lot. Would have been a lot better if I had done it in the winter.

 

[Schurkey]

Stopping on gravel or ice is probably fine...if you can be sure to activate ALL THREE CHANNELS in the ABS unit.

Activating one or two still allows the non-activated channel(s) to retain air.

The scan tool cycles the ABS unit multiple times--four or six. You probably want to slam the brakes on gravel multiple times.

And, of course, you still have to bleed at the wheels to get the air out of the system, not just out of the ABS unit.

 

[Zerio29]

Stopping on gravel or ice is probably fine...if you can be sure to activate ALL THREE CHANNELS in the ABS unit.

Activating one or two still allows the non-activated channel(s) to retain air.

The scan tool cycles the ABS unit multiple times--four or six. You probably want to slam the brakes on gravel multiple times.

And, of course, you still have to bleed at the wheels to get the air out of the system, not just out of the ABS unit.

Ahh of course, you definitely need to bleed the wheels after activating the abs module. all it does is free up the air potentially trapped in the solenoids and sends them downstream a little bit. And yea certainly the scan tool is miles better - no arguments there lol. Pretty much if there's no other option. The only place in town that had a scan tool at the time told me I was crazy for thinking that a brake bleed needed a scan tool and wouldn't even touch it, so I had no other option at the time.

That is a good point though, because if you only manage to bleed one or two of the channels, it would have all kinds of other issues.

 

[94ChevyZ71]

My brakes have been awful for about 2 years now. I changed the booster, master cylinder and even swapped the abs module to a spare that I had. I don’t know a lot about this abs stuff (besides it’s junk) but I believe I have a hydraulic unit because there is only 2 lines that come out of the MC and go to the abs unit. Could my abs module be bad? My parking brake light stays on all the time and I replaced the switch for it but it never turned off. Also the abs light on my dash has never came on. Thanks for the help!