Intermittent stiff brake pedal - vacuum pump going bad?

[pickupman]

Recently I have began to notice that the brake pedal seems a stiff every once in a while. Today I saw the brake light illuminate briefly. It seems like this symptom could be either a issue with the booster or the vacuum pump, I suspect the vacuum pump because I replaced the booster about a year ago because the old one was hissing pretty bad.

I don't currently have a vacuum gauge, so I can't test the vacuum yet, but I will be buying one. Mainly I just want to know if this sounds like a vacuum pump issue or not.

To give a little background, about 3 years ago I got my brakes done at Pep Boys. Bad bad bad bad idea. Anyways, I've never been too happy with the performance of my brakes in general. When they originally did the brake job, the parking brake was out of adjustment after they finished, so I brought it back and they gave me some BS about how it was going to cost extra to fix it. After putting up a fuss, they eventually adjusted it, and it worked for awhile. Currently it doesn't hold.

If it's just a vacuum pump, I change that out pretty quick. I live in an apartment complex, so I can't really get away with doing a whole brake job. I am not 100% confident about the job Pep Boys did, so I want to at least address any vacuum issues and then if anything further is needed I can find somewhere to take the truck for any other brake work.

 

[franklin2]

Check all the rubber vacuum lines, especially the one that leaves the pump. I know on mine the rubber line goes over and rests against the inner fender on the pass side and the vibration of the engine causes the line to rub back and forth on the inner fender. Check it all the way and around the firewall, put your hand around it looking for cracks.

If you have a good brake pedal the first time you hit the brakes, and then it gets hard after that, it sounds like you are running out of vacuum, and a leak could cause that as well as a weak vacuum pump. How low is your brake pedal? If it's really low, it can also cause problems. I ask that because you said your parking brake doesn't work right. If your rear shoes are out of adjustment, your parking brake will be low and your brake pedal will be low also.

 

[pickupman]

If you have a good brake pedal the first time you hit the brakes, and then it gets hard after that, it sounds like you are running out of vacuum, and a leak could cause that as well as a weak vacuum pump. How low is your brake pedal? If it's really low, it can also cause problems. I ask that because you said your parking brake doesn't work right. If your rear shoes are out of adjustment, your parking brake will be low and your brake pedal will be low also.

I do have a good brake pedal the first time I hit the brakes, if I hit them several times repeatedly I get a stiffer pedal, and the pedal actually doesn't go very low after doing so, it moves much less than normal.

 

[pickupman]

Well I went to Harbor Freight and got a vacuum gauge. I connected it directly to the line coming from the pump and from a cold start it was reading ~15in-Hg at idle and once it warmed up it was up to ~23in-Hg at idle. Revving the engine up would make it go up to 26in-Hg almost immediately. At idle it might be a little low, but according to my shop manual, it's within spec.

I wasn't able to tee the gauge in to the rest of the system because I don't have the right size tees yet to do that.

 

[vegas39]

Well I went to Harbor Freight and got a vacuum gauge. I connected it directly to the line coming from the pump and from a cold start it was reading ~15in-Hg at idle and once it warmed up it was up to ~23in-Hg at idle. Revving the engine up would make it go up to 26in-Hg almost immediately. At idle it might be a little low, but according to my shop manual, it's within spec.

I wasn't able to tee the gauge in to the rest of the system because I don't have the right size tees yet to do that.

If you find you have no leaks, than the booster may be suspect and be careful when you buy one, I went through several before getting one that worked properly.

 

[vegas39]

I do have a good brake pedal the first time I hit the brakes, if I hit them several times repeatedly I get a stiffer pedal, and the pedal actually doesn't go very low after doing so, it moves much less than normal.

My newer truck with the original booster acts the same way but I think repeated pushing several times in a row and having the pedal go stiff, is pretty common on these things.

 

[79jasper]

My newer truck with the original booster acts the same way but I think repeated pushing several times in a row and having the pedal go stiff, is pretty common on these things.

Shouldn't be normal. Not when everything is correct.
Maybe look into the zero loss booster?

Sent from my SM-G900R4 using Tapatalk

 

[mu2bdriver]

Well I went to Harbor Freight and got a vacuum gauge. I connected it directly to the line coming from the pump and from a cold start it was reading ~15in-Hg at idle and once it warmed up it was up to ~23in-Hg at idle. Revving the engine up would make it go up to 26in-Hg almost immediately. At idle it might be a little low, but according to my shop manual, it's within spec.

23" is at the lower end of acceptability. I would get a hard brake pedal about 10-15% of the time, usually in city traffic, and usually immediately after coming off the accelerator and going to apply the brake. When I tested it with a vacuum gauge and gave it gas it would spike up to the upper 20s and then when I backed off the accelerator to idle it would occasionally drop all the way down to ~12". I don't know how many brake pumps you should be good for before getting a hard pedal but I would say at some point you're just going to run out of vacuum.