Brake Problem, Vacuum Booster?
 

Hey Guys, sorry it's been a while.

Left work Thursday and all of a sudden my brake pedal stiffed up and the car didn't brake properly. The pedal traveled about 3/4" and I was able to get another 1/4" out of it but it doesn't stop and quicker.

Leaning towards either vacuum loss or bad booster. Friday my partner helped me bleed the brakes and check the calipers. Doesn't seem like the issue is there as all rotated and locked up fine. When I opened the valve to bleed, the pedal traveled to floor like it should. So that kinda rules out master cylinder, calipers, etc.

Looked up the booster and it says it's a 6.5 to 1 ratio so I believe that's the culprit, but not sure if vacuum loss or booster itself. Is there an easy way to test for vacuum loss before I look at replacing the booster, or just get a 20' leg to stomp on the pedal. Might be a little tight as I don't think there is that much leg room:).

I was going to check for vacuum at the booster but was'nt sure how to disconnect the fitting going into the booster and don't want to break it. Does anyone know if it's just a press fit and all I need to do is wiggle it out, or do you have to rotate and pull? Or is there a proper way of testing?

While I am sure that there have been vacuum booster failures they are rare and vacuum line leaks much more common.

Engine off, press pedl as hard as you can 4-5 times. While pressing pedal firmly, start the engine. If the pedal movers closer to the floor the booster is working. If not, check the vacuum supply. Yes, the fitting is just barbed and pulled out with a little wiggling and twisting. You might also try spraying a little WD40 or similar between the fitting and the grommet to aid removal. Just be sure to remove all traces of the oil from the grommet before reassmbling, otherwise the grommet will eventually disintegrate.

Got it fixed, thanks for the help guys. Did the bosster test Beav mentioned and the pedal barely moved on startup.

I checked the vacuum at the booster and was only reading 7hg.
Checked my parteners Yukon and he had about 25. I also checked the for vacuum on the driver's side valve cover connector and only had about 15hg.

Turned out the short vacuum hose from the pass side of the valve body that connects to the booster line melted in a spot. That protective cover opened up and it must have been touching something hot. Just wrapped it in elec tape and resewed the boot and got a reading of 21hg. Pedal travels just fine now and I can lock-em up if needed.

On a second note, Friday morning after it failed I also had a check engine light and got a P171 and P174 code for engine to lean. Would also get a Engine Fault and Poor Vehicle Performance message on the main display. The Engine Fault only happedened when at idle and not every time. Once I accelerated it went away. I cleaned the MAF and replaced the Filter to no avail, the message still came up. After the fix today I still have the check engine but no Engine Fault on the way home. I hope that the vacuum was also the cause of this. I know it takes a little bit for the check engine to reset. I'll let you know if it clears.

Thanks again for the help guys.

Also check the accordion section of the MAFS to Throttle Body duct. High failure rate due to heat above the exhaust manifold.

Check Engine light is gone too.
It's all good. It's nice to know a vacuum leak will also cause
a P171, P174 code to trip.

Thanks again for the help

. . . and thanks for the follow-up information on the resolution!