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Old 01-29-2010, 05:54 AM
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How to bleed anti-lock brakes?

I have a 91 chevy pickup and since I got it last year, it had a leaking rear brake cylinder (drums) and the pedal was pretty squishy. I put new calipers and rear brake cylinders on it since they were very cheap and looked old. I'm not sure if the rear reservoir ever went dry on it. The old brake fluid was very black and had dirt or something in it. I soaked up a lot of the dirty brake fluid with papertowels and poured new stuff in on top thinking that then I'll bleed the brakes and flush the rest of the old junk out that way.

I bleed the brakes and the rears shoot fluid out pretty good using the old pump, pump, hold method. I went to the front and fluid came out but not with as much force as the rears. I think nothing of it but then the pedal ends up being worse than before! I adjust the rear brakes some more and have it back to close to how it was before but it's still a squishy pedal and I hate it. I tried bleeding them twice since and it did not get any better.

I posted over on www.fullsizechevy.com and they were saying that I need a scan too to activate the rear antilock and get the air out. I don't have one nor do I have access to one and I would hate to have to take it to a garage to have them bleed the brakes.

it definitely only has rear antilock and not front which seems wierd since I was getting alot of fluid shooting out the rears but not much out the front. It also 'feels' like the rears are grabbing good but the fronts don't.

Anyone have experience with these trucks? Is there any other way to activate the rear anti lock other than with a garage's scan tool? Maybe by like jumpering something somewhere?

I'm really at the end of my rope here.... I hate driving an unsafe vehicle.

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Old 01-29-2010, 08:12 AM
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Pump pump pump hold is not a good plan, it tends to aerate the fluid. It's better to crack the bleeder, push the pedal, close the bleeder, release the pedal. If I'm changing a master, sometimes I will push the pedal, wait a few seconds for the air to travel back up though the lines, crack them loose at the master, then tighten them back up. This helps keep you from pushing any air bubbles there at the master all the way through the system.
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Old 01-29-2010, 08:14 AM
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Everybody experiences what your experiencing with antilock brakes and it's normal. Antilock brakes are supposed to be squeeshy. You should be able to even push the peddle all the way to the floor. That means your antilock system is working fine.
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Old 01-29-2010, 11:40 AM
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Quote:
Originally Posted by cjperotti
Everybody experiences what your experiencing with antilock brakes and it's normal. Antilock brakes are supposed to be squeeshy. You should be able to even push the peddle all the way to the floor. That means your antilock system is working fine.
This cannot be right. the pedal on any other vehicle I ever drove with antilock brakes was firm just like non anti lock.
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Old 01-29-2010, 11:52 AM
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Quote:
Originally Posted by cjperotti
Everybody experiences what your experiencing with antilock brakes and it's normal. Antilock brakes are supposed to be squeeshy. You should be able to even push the peddle all the way to the floor. That means your antilock system is working fine.
I'm afraid that's not normal, and not OK. 4WAL or RABS should feel just like non-ABS brakes, except when it's "active".

Is it 4 wheel ABS or RABS? You might be surprised how often you can just gravity bleed the whole system, one bleeder at a time. I think if I were in your shoes, that's exactly what I would do, start at the one farthest from the master, bleed until you've got clean fluid coming out, then move to the next one.
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Old 01-29-2010, 01:19 PM
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Just rear RWAL
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Old 01-29-2010, 01:59 PM
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I'd gravity bleed the whole system till you've got clean fluid coming out all 4 corners and see what you've got then.
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Old 01-29-2010, 03:22 PM
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Quote:
Originally Posted by Rickracer
I'd gravity bleed the whole system till you've got clean fluid coming out all 4 corners and see what you've got then.
X2, Just remember to keep the M/C full at all times.


Cole
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Old 01-29-2010, 03:26 PM
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I had a similar situation with my 91 GMC, bled and bled but couldn't get a good pedal. Finally I disconnected the electrical connector to the anti-lock computer and let it reset itself. Plugged it back up and everything was good.
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Old 02-07-2010, 06:09 PM
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you know what they say about opinions.. they are like armpits.. everybody has them. and they all stink..lol anyway

when it comes to bleeding brakes, I prefer to put a clear hose on the bleeder.. run it down into a container with just a little bit of brake fluid in the bottom, submerging the end of the hose.. then simply pump the pedal until clean fluid comes out. .making sure i dont' run the m/c dry.
btw.. start out at the wheel furthest from the m/c and work your way closest.

don't need any fancy equipment beyond that
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Old 02-07-2010, 09:47 PM
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As far as I know. As long as you didn't break any lines open from the master cylinder to the ABS modulator or around the ABS unit. You should be ok with normal brake bleeding procedure. Since you had this problem for a year it sounds like you have gotten air into your ABS modulator and that you need might not need the ABS scan tool to help you with this. If you have DELCO ABS-VI ABS system. Witch some vehicles came out with in 91. Open the front bleeder screw at the modulator. There should be two of them, So make sure you open the front one. Then bleed the ABS modulator. Tighten the front screw up, then bleed the right front brake first. Then the left front brake. Check to see if you have a firm pedal. If you do then drive the vehicle around the block. Or above 3 mph until the controller resets the system. Once this has happened, you can stop the vehicle and bleed the rear brakes. Have Fun..
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Old 02-15-2010, 09:14 AM
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You will NEVER bleed most anti lock brakes without a power bleeder. Some GM systems require activating the ABS system during bleeding as well. A buddy of mine has a very busy repair shop and was gracious enough to lend me his bleeder, and the printout of how to do the '02 Silverado ABS system in my '51 Pontiac wagon or I'd have never gotten it done.

I used the ABS from a '94 Caddy, complete, in my '48 Pontiac 'vert, and was (against all odds) able to simply gravity bleed the system. It shouldn't have worked, but it did. The ABS in that car has saved my neck, and the car, 3 times now. Somebody was looking out for me with that adaptation...

Brian
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Old 02-15-2010, 09:59 AM
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I made myself a power bleeder but never knew what pressure to use, did your friends system state a pressure setting?

TIA!

Russ
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Old 02-15-2010, 11:08 AM
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I have to agree with the power or pressure bleeder. I ran into the same problem with the ABS on the Dodge truck. I also solved the soft pedal on my streetrod with pressure bleeding. I made one out of a simple garden sprayer. Works great.

I can also add another controversy regarding pushing the caliper pistons back with a clamp or pry bar. Apparently this can cause ABS problems as well as seal problems in modern brakes. The approved way that was given to me is to release the fluid out of the bleeders as you retract the pistons. This prevents pushing contaminated fluid back into the MC as well as protecting any check valves in the system from over pressure. Not my rule but instruction from the Dodge guys. I've done this and had no problems. I'm sure issue can be taken but after 240k on my dually the MC fluid is still pretty clear and the brakes are very hard and strong even pulling the heavy trailer.
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Old 02-15-2010, 12:36 PM
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Quote:
Originally Posted by cjperotti
Everybody experiences what your experiencing with antilock brakes and it's normal. Antilock brakes are supposed to be squeeshy. You should be able to even push the peddle all the way to the floor. That means your antilock system is working fine.
That sounds like bad info here. I agree with others saying that a brake pedal to the floor is not normal.

As for the bleeding, try Speedbleeders if by yourself. (Sorry if this is the same as Power Bleeders)
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