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auxiliary P/B booster pump HELP

slt5.3z71
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slt5.3z71 Enthusiast

slt5.3z71

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I have a 2004 SLT 4x4 with bad brakes. I had the brake lines replaced 4 years ago when they rusted out and started leaking.

Brakes now go all the way to the floor and stop the truck although slowly. Just paid $700 for new front calipers, rotors, pads and lines. Bled with scan tool. This did not improve the brakes. Mechanic said the auxiliary P/B booster pump is bad. When plugged into the harness it runs continually with vacuum and pressure at the nipples. This part is unavailable. Part #

89058946. Do I now junk the truck due to an part that is not obtainable?

Has anyone else had experience in solving this problem? Is there a solution?

IMG_0946.jpg

IMG_0947.jpg

slt5.3z71 Enthusiast

slt5.3z71

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Thanks for the links. I just talked to GMC shop. They advised to bring the truck in. Their thinking it is not a problem with the booster pump as it runs and creates vacuum. They are thinking that I may still need  lines bled manually first at rear wheels then front then at the abs block. Also to check master cylinder. I guess I will try this before trading it in for a ugh Mopar.

richard wysong Senior Enthusiast

richard wysong

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booster will not cause your problem, most likely bad master cylinder. a bad booster would cause the pedal to be hard to depress enough to stop the truck but not affect pedal travel

slt5.3z71 Enthusiast

slt5.3z71

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5 minutes ago, richard wysong said:

booster will not cause your problem, most likely bad master cylinder. a bad booster would cause the pedal to be hard to depress enough to stop the truck but not affect pedal travel

Thanks. Getting that checked at GMC shop next week. I can hold the brake all the way down give it a little throttle and the truck will start moving with the brakes pushed! Looks as though I may have spent $$$ on new calipers, rotors, pads, and brake hoses that weren't needed. Live and maybe learn.

dna9656 Enthusiast

dna9656

Posted
Posted (edited)

Yeah the calipers, pads and such aren't your problem; a master cylinder issue is my educated guess. GM publishes trouble shooting checklists for all systems....

Edited by dna9656
slt5.3z71 Enthusiast

slt5.3z71

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Thanks. So to the dealership next week to spend more money all on a truck that is to be traded in. just didn't like the idea of passing the truck off with a known safety issue even if the dealer will probably send it to auction.

richard wysong Senior Enthusiast

richard wysong

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can you pump the pedal and have it come up and stay there with your foot on it?if so theres still air in the system somewhere. if it still creeps to the floor its either the master cylinder or you have a leak somewhere

slt5.3z71 Enthusiast

slt5.3z71

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51 minutes ago, richard wysong said:

can you pump the pedal and have it come up and stay there with your foot on it?if so theres still air in the system somewhere. if it still creeps to the floor its either the master cylinder or you have a leak somewhere

OK. So most likely the master cylinder. It will not stay pumped up and their are no discernible leaks. I now remember that not long after I got the truck I did have a brake fluid leak and all the brake lines were replaced. This was about 4 years ago. The mechanic said there was one item he was not able to replace because it was too rusted. The brake line kit parts were supplied by GMC at their cost. It was after this happened that all the trouble started. I questioned that tech about the weak spongy brakes after the repair and he said that is just the way they are with abs. Recently had a cam and dyno tune installed. The tune increased my idle speed slightly and now it seems really hesitant to stop and to hold at a stop.  I guess I could have the most recent repair shop that replaced the calipers, rotors, pads and hoses to do a master cylinder as he has wasted $800 of my $ maybe he will give me a break! That or just go on to the dealership?

richard wysong Senior Enthusiast

richard wysong

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lots of shops just looking to make the fast easy $doing half ass brake jobs, the mark up on brake parts here north of Boston is %100. they didnt take the time to properly diagnose your problem OR when they did the job they pushed crap back into the abs & master. the properway to compress calipers is 2 clamp off the brake hoses and open the bleeders as the calipers are the lowest parts in the system so all the debris ends up  in them. VERY few techs do this tho. its a shame you have to go to the dealer and cant find a competant independant.. the shop that did the brake job was foolish to release the truck like it is, you could easily have crashed and hurt yourself or someone else opening them up to a lawsuit. its 1 thing if your truck doesnt start but a whole different thing if it doesnt stop

slt5.3z71 Enthusiast

slt5.3z71

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This is the same shop that removed the aux. booster motor, said it was faulty and hooked the brakes back up with the vac line into the booster instead of through the aux booster motor. I had to ask for the aux motor back. When I plug in the motor it runs and pulls vacuum. Now I need to remount it along with bleeding or master cylinder. 

slt5.3z71 Enthusiast

slt5.3z71

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Mechanic said the auxiliary P/B booster pump is bad. When plugged into the harness it runs continually with vacuum and pressure at the nipples.

Is this correct operation for this part??

  • 2 years later...

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