slt5.3z71

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??

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.

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?

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.

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.

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.

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?

Thanks for your reply Cameron. On another note it seems to me that this is a dying forum. Looking for another GMC/Chevy forum with more active participation.

I have my 2004 GMC 5.3 scheduled 10/05/20 for a cam swap and beehive springs. Also adding aftermarket intake and filter, water pump and thermostat. After the engine work my builder will put a tune in it. It has a 3.73 rear end and 265/70R17 tires. I wanted more torque and my engine builder advises me that I do not need to alter the stock exhaust. No cat delete or even cat back system advised. The new camshaft grind is 112+2 lsa, .523/.524 Lift. 218/227. What do you think?