lunghd

2000 Chevrolet Express 3500 1-ton / 8-lug
(Single rear wheel - NOT a dually or box truck)
Hydroboost


I've been having an issue with my brakes being 'weak' since having the rears redone at a garage. The pedal goes down but doesn't go to the floor & brakes just act like they don't want to stop. Casual braking you aren't really sure if anything is wrong... but if you panic stop the darned thing doesn't want to stop. Pedal is semi-firm but doesn't feel right... doesn't sink/fade when braking hard.

In order that things were done:

1. 2014: Rear drums replaced. The drums still look new - literally no wear due to next item (#2).
2. Spring 2017: New ACDelco Pro Master cylinder (The rear wheels weren't getting much pressure. Basically I had front brakes only.)
3. Summer 2017: Rear brakes started grabbing intermittently like there was an axle or wheel cyl leak.
4. Had a garage replace rear shoes, wheel cylinders & hardware kits. (Shoes were not worn down.)
5. Brakes operate worse than with the old pads & wheel cylinders. Had garage re-bleed & re-adjust brakes. No change.
6. Jamming on brakes on gravel road cycles ABS system.
7. Jamming on brakes on pavement cycles "BPS / butt pucker system". The brakes engage... but just don't want to stop properly. (My seat now has a permanent crease. Panic stops are not fun.)

I pulled the drums. NO resistance whatsoever to removal, the shoes were not touching the shoes & show light 'glazing'.
It took 20 clicks on the driver side star adjuster and 26 clicks on the passenger side to have the shoes drag enough to 'feel' moderate resistance. From my view - the idiot at the garage did NOT adjust the brake shoes correctly ... first OR second try.

After adjusting the stars I took it out to test & did a few 'panic stops'.

1. First or second time I did this; the pedal went down 2/3 (not to floor) then 'kicked back' up.
2. Made several forward 'panic stops' & pedal and after that weird one where the pedal 'kicked back' braking seems somewhat better. (Subjective: it still doesn't 'feel right'.)
3. Did several reverse 'panic stops' & ABS cycles when doing this in reverse but likely because of tar on pavement + so much weight at rear of van allows front tires to slide some. ABS cycles ok on gravel.
4. 5 mile round trip & pedal + braking seems better.

Driver side appears to be 'too tight' - could smell brakes from that side so need to back that one off a bit.


My questions are:

1. How much drag should new shoes have on the drum to start with? There was zero drag when I pulled the first drum. Shouldn't the brake shoes drag just enough to feel light resistance when moving the drum or wheels by hand (when new)? It took 20-freaking-clicks on the driver side and 26 clicks on the passenger side star adjuster to get the brakes dragging enough to introduce any resistance to turning the drums by hand.
2. For the self-adjusters: how many cycles of 'backing up & hitting brakes' should it take for the darn things to adjust? (I've had the van back a month after giving up on the garage to get it right.)
3. Does anyone know the proper bore size rear wheel cylinder for my van (details at top of post)? There were (3) different rear wheel cylinders for this year Express van... now I'm worried that the garage threw a dart to pick which one they put on. The counter guy told me that there was only one listed when he ordered them at the garage. (For all I know GM just labeled the same part with three numbers and boosted the price. Parts diagrams show wheel cylinders for: dual-rear wheel/box vans, short wheel base/light duty & long wheel base/heavy duty (3/4 or 1 ton?) vans. Dunno internal bore sizes.)

lunghd

Swapped out the garage's rear wheel cylinders with another set plus a rear brake hose. Still just doesn't have rear brakes worth a damn.

Just this past week I was driving in a wet, paved parking lot at under 10 mph & turned while braking. The front brakes 'locked up' (the ABS did cycle) and the van kept pushing itself along.

Is there a way to bypass the ABS system so I can rule it out as the cause (without going to a dealership)? I'd rather rule out parts than use a 'parts shotgun' to replace everything.

StanVan

If something is wrong with the ABS, it should be throwing a code. My thought when I just read your first post(sorry I missed it in July) was, were the lines bled properly? But now my question would be, has the system been flushed? If not, it's due.

canucklehead

When adjusting the rear drums, you want just a little drag. When you spin the tire it should rub rub rub as it spins but not rub the whole time it spins.....if that makes sense.
If your emergency brake will stop the van from moving forward with a little gas, but they dont drag then you are fine.
Also if the emerg brakes work, but the hydraulic does not, then its a problem in the brake system......There is a combination valve after the mater cylinder, is that ok? Could there be contamination in the lines? could the brakes be binding up on the backing plate?

lunghd

Total flush about 2 years ago & bled 3x in past 6 months. One bleed was using ABS tool to bypass ABS motor.

My code reader doesn't show anything on the ABS system... but from what I understand most of that system isn't accessible (can't turn off/on etc... dunno if generic reader will even show an ABS code??)

Fluid is dirtier than it should be in 8 month old master cylinder but cap wasn't properly sealed after earlier bleed at garage when rear drums were serviced. Another fun thing they overlooked doing right.

Thanks!

Yep, know what you mean about drag. After they replaced the shoes & rear wheel cylinders (and after screaming like a banshee trying to make an emergency stop...) I adjusted the drag & it was like 20 clicks just to get the rear shoes to even rub (garage mechanic was a total idiot & then repeated same mistake when I took it back again). Don't think there is any binding going on - wheels turn freely when on jackstands & no noises when applying brakes. It does apply the rear brakes... just not enough to do much more than give you time for a short prayer.

I also replaced the garage installed rear wheel cylinders plus rear brake hose & readjusted the drag a second time. (There are three different rear wheel cylinders for these depending on dually, 1-ton or 1/2 ton...)

Replaced master cylinder late last year so I'm thinking prop valve too. That's next, I suppose. Thanks!

joelsplace

A good parts house should be able to tell which wheel cylinders are needed based on the brake code on the option sticker for the vehicle. They changed based on GVWR and size of the shoes.
Are the leading and trailing shoes in the correct location? Leading (primary) shoe should have less (in length not thickness) material. Some aftermarket shoes are not sold with leading and trailing shoes and need to have the leading shoe material shortened or just buy some that are made correctly. Maybe this ace mechanic put them on backwards or put both primary shoes on one side. The primary shoe makes the brakes self energizing so they take much less effort for the same stopping power. You can tune the brakes by changing the length of the primary shoe material.
I've also had some new shoes that just didn't work and had to be replaced. They were a charcoal grey and had a sort of crumbly appearance. Different new shoes made a world of difference.
The self adjusters should make one click of adjustment every time you back up until they take up the slack.
Does your van have a proportioning valve? I'm not sure. Some just have a valve that turns on the light. If it does you may be able to remove the guts to disable it and see if that is the problem. I've done that on older GM cars before.

dberladyn

Just out of curiosity, do you have left hand rear doors?

If you do, check the brake line visible in the driver's side rear wheel well, just ahead of the tire. Pay attention to the filler spout and where it may be rubbing on the brake line. There is a recall with a design problem in this area. On mine, the brake line sprung a leak right in that spot and I was constantly losing fluid with no rear brakes.