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shdesigns
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ARRIS SB6121

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shdesigns

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95 Suburban LS Brake oddness.

Neighbor had be come look at a brake problem. Pedal goes to the floor.

She said she has had the calipers and rotors replaced. Would have told her it was not the problem.

She picked up a booster and master cylinder of pullapart as she was convinced that was the problem.

Sounded like air in the system or bad master cyl to me. I vacuum bled about 3 oz out of the rear and 2 from the left front. I did not want to snap off the bleeder on the RF so left it. Did not have any fluid with me to do more.

Odd was when I cracked the rear bleed screw I could hear it sucking a lot of air. The vaccum bleeder pulled it out and then a bunch of fluid. Front seemed the same.

Swapped master cylinder and not much difference. When you run it, pedal goes near to the floor then you hear/feel the ABS pulsing. After turning off the car, it was gushing fluid back into the reservoir. 2nd pump the brakes will work.

THe only thing that would make sense to me is a huge bubble in the ABS unit.

I may try bleeding a lot of fluid through it tomorrow.

I was wondering if there was any special procedure for bleeding the ABS unit itself. It seems like the ABS box is storing up the fluid rather than letting the brakes work. My feeling is air or the ABS box is bad.

Any ideas?

Edit: found forum post that copied the bleed procedure Had the line:
"This procedure may use more than a pint of fluid per wheel"

Then mentions a scan tool automated bleed precedure.

bmilone2
join:2001-01-26
Mays Landing, NJ

bmilone2

Member

I had a Dodge Caravan that had the same issue a number of years ago after the replacement of the fliud reservoir. The system was re-bleed of air and worked fine but problem came back a very short time after re-bleed. Found more air in system. Come to find out that the ABS control system is very difficult to get all the air out of due to the way the internal passages are made.

It took several days consisting of multiple bleedings (forget how many total, but alot) and finally resolved the issue.

mattmag

join:2000-04-09
NW Illinois

mattmag to shdesigns

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There is an automated ABS Module bleed procedure, but it does require the use of a scan-tool with advanced controls. It is possible that you can accomplish the same with a pressure bleeder, or maybe even the old-fashioned way, but I can't promise it will work. The automated procedure cycles the control solenoids/valves in order to pass air out of the system.

shdesigns
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I did find forum posts that say you need to use a scan tool that can send the automatic ABS bleed command.

The ABS reservoirs and pump are closed off from the system unless you tell the control unit to open them up. No amount of bleeding by itself will fix the problem.

mattmag

join:2000-04-09
NW Illinois

mattmag



Ya, that's what I was saying.

guhuna
5149.5
Premium Member
join:2001-03-31
Benicia, CA

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For what its worth I was working on a 03 GMC that had air inside the ABS unit. After multiple flushes the ABS unit still had air in it, and where I was I couldn't get my hands on a scan-tool that would put it into the automated cycle mode. So I took it down a dirt road that had nothing around and got up to about 30 and just romped on the brakes about 10 times. After the 5th time I heard a funny sound come from the ABS unit. After that I came home and flushed the system twice and lo and behold the brake peddle to the floor went away.
Its worth a shot if you don't have the scan-tool.

shdesigns
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shdesigns

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I told her to take it somewhere with the proper scan tool.

Now she calls me, said she had someone replace the ABS unit. Now says it must be the brake booster (pedal still goes to the floor.)

Probably the same guy that screwed it up when he replaced the master cyl and did not bleed it first (and them vacuum bleed to prevent air from getting into the ABS/proportioning unit.)

I give up. She won't listen. 2 master cyl's and brake boosters, all from upullit and still believes the problem is with the booster.

mattmag

join:2000-04-09
NW Illinois

mattmag



OMG...... I feel for you. Dealing with parts-changers instead of educated technicians is a real challenge.

shdesigns
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shdesigns

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Oh, now I her she has the brake booster replaced and "that fixed it".

Yeah, they charged labor to replace a working booster then did the bleed procedure.

gillespie
Premium Member
join:2001-11-28
USA

gillespie

Premium Member

When a booster goes bad, the pedal doesn't go to the floor. Instead you get an extremely hard pedal because there's a rubber diaphragm that is causing a vacuum leak.
Sounds like you have your hands full with this one. I'd say piss on her and let her spend her money foolishly from now on.

shdesigns
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shdesigns

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Thought I'd finish up this thread. Owner stopped by for me to check on an oil leak. Rear seal, I don't want to pull tranny and pan to do it.

She did tell me the final fix for the brakes. Apparently she had a cracked caliper. Under braking, it was flexing. I had looked them over but did not see anything odd.

Have seen frozen calipers, stuck pistons, missing pads, bad seals, worn guides but never a cracked caliper.
HarryH3
Premium Member
join:2005-02-21

HarryH3

Premium Member

If you dare get involved, take a really close look at the oil leak. I thought that the rear main was leaking on our 94 Sub, but on closer inspection I found that the oil was actually coming from the oil filter adapter. On 4WD models they installed an adapter that mounts the filter horizontally to make room for the front driveshaft. (I've never looked under a 2WD model to see if it also has that adapter) A new O-ring kit for the adapter is around $10. Ours hasn't leaked a drop since the new O-rings.

shdesigns
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shdesigns

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It is 2WD and the filter is vertical.

The filter was my first suspect as was the drain plug. There was only oil on the bottom of the filter. I wiped it all clean. Then I saw the oil was dripping out of the bell housing weep hole.

My Jeep had a right angle adapter with similar problems. New O-rings helped but it still had a slow leak. The fix was to get a remote oil filter adapter. No leaks and the filter is behind the bumper