The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Too much travel before brake booster kicks in?

JLeather · 03-15-2014, 04:45 PM

Ok, poked at the truck some more today. I have a suspicion that my "new" (rebuilt) m/c might be bad. With the truck not running when I step on the pedal it firms up, but if I keep pressing on it the pedal creeps towards the floor. Also, I noticed that when I do that do it (i.e. force it to keep moving after it firms up) when I release the pedal a ton of bubbles appear in the rear section of the m/c. I did this probably 25 times and every time I got a ton of bubbles, but the level of fluid never went down so it's not leaking. Where could all this air be coming from? This seems similar to the issue I had with the previous m/c. Not leaking, but somehow creating air. I'm going to vacuum-bleed the truck and make certain there's no air in the lines, and also re-do the bench bleeding on the m/c and after that if I'm still getting all these bubbles in the reservoir like this it must be the m/c. Has anyone else seen this before?

I checked the booster with a vaccum gauge and it pumped down and held vacuum without loss for a good 10 or 15 minutes, so that doesn't seem to be my issue.

Just to clarify, I have not replaced my proportioning valve because I was able to get fluid at all 4 wheels with the new m/c. Any way that could be allowing air into the system?

03-15-2014, 04:45 PM	#18
JLeather Registered User Join Date: Jan 2012 Location: Ijamsville Posts: 12	Re: Too much travel before brake booster kicks in? Ok, poked at the truck some more today. I have a suspicion that my "new" (rebuilt) m/c might be bad. With the truck not running when I step on the pedal it firms up, but if I keep pressing on it the pedal creeps towards the floor. Also, I noticed that when I do that do it (i.e. force it to keep moving after it firms up) when I release the pedal a ton of bubbles appear in the rear section of the m/c. I did this probably 25 times and every time I got a ton of bubbles, but the level of fluid never went down so it's not leaking. Where could all this air be coming from? This seems similar to the issue I had with the previous m/c. Not leaking, but somehow creating air. I'm going to vacuum-bleed the truck and make certain there's no air in the lines, and also re-do the bench bleeding on the m/c and after that if I'm still getting all these bubbles in the reservoir like this it must be the m/c. Has anyone else seen this before? I checked the booster with a vaccum gauge and it pumped down and held vacuum without loss for a good 10 or 15 minutes, so that doesn't seem to be my issue. Just to clarify, I have not replaced my proportioning valve because I was able to get fluid at all 4 wheels with the new m/c. Any way that could be allowing air into the system?