Rpms rise when brake pedal depressed

twilightcall · 06-13-2003, 05:41 AM

I noticed that when I depress my brake pedal on my 83' that the rpms rise about 150 or so. When I let them go it goes up too. Is this a sigin of a bad booster or slightly leaking booster?

PKRWUD · 06-13-2003, 12:23 PM

No, that's somewhat normal. How hard is it to push the brake pedal?

twilightcall · 06-13-2003, 12:58 PM

It really doesn't take much effort to push the pedal down. I removed the vacuum line to the booster and tried it, it was much harder. I just still have the 2-3 inches of free play at the top and when I get to braking it is ok. I was just thinking maybe a small tear in the diaphram could cause this. When the vacuum line to the booster is unplugged you have to almost stand on the brakes.

PKRWUD · 06-14-2003, 02:16 AM

Yeah, if you had even the tiniest vacuum leak at the booster, the pedal would become harder. It is the vacuum that makes the booster work, giving you "power" brakes. Anything that would reduce that vacuum, such as a tear in the booster diaphram, or a radical camshaft, will cause the booster to operate less than optimal, makeing you, the driver, have to work harder to get the same braking results. In other words, as the vacuum goes, the pedal becomes harder.

Did you get the light fixed?

You know, you may just need a longer pushrod from the booster to the master.

twilightcall · 06-14-2003, 06:55 AM

Yes, the new proportion valve took the light out. I am not sure about the rod. I thought it would be best to not mess with the adjustment. It could be off though. How would I check? Thanks for the help.

PKRWUD · 06-14-2003, 12:52 PM

I'm glad the new valve worked. Adjusting the rod is kinda complicated because you need a special gauge to do it, but you can do it without. Unbolt the master from the booster, but DO NOT LOOSEN THE FLUID LINES, and pull it far enough away from the booster so you can adjust the rod. Hold the rod with a pair of pliers, and use a wrench to back the adjuster nut out a couple turns. Bolt the master back on, start the engine, and check the brakes. If they are better, but the pedal still isn't quite right, then adjust it further until you get it right. Make sure the brakes aren't dragging, though!

Drop me a line this time and tell me what happens.

Take care,
~Chris

06-13-2003, 05:41 AM	#1
twilightcall Registered Member Join Date: May 2003 Posts: 86	Rpms rise when brake pedal depressed I noticed that when I depress my brake pedal on my 83' that the rpms rise about 150 or so. When I let them go it goes up too. Is this a sigin of a bad booster or slightly leaking booster?

06-13-2003, 12:23 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	No, that's somewhat normal. How hard is it to push the brake pedal? __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

06-14-2003, 02:16 AM	#4
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Yeah, if you had even the tiniest vacuum leak at the booster, the pedal would become harder. It is the vacuum that makes the booster work, giving you "power" brakes. Anything that would reduce that vacuum, such as a tear in the booster diaphram, or a radical camshaft, will cause the booster to operate less than optimal, makeing you, the driver, have to work harder to get the same braking results. In other words, as the vacuum goes, the pedal becomes harder. Did you get the light fixed? You know, you may just need a longer pushrod from the booster to the master. __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

06-14-2003, 12:52 PM	#6
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I'm glad the new valve worked. Adjusting the rod is kinda complicated because you need a special gauge to do it, but you can do it without. Unbolt the master from the booster, but DO NOT LOOSEN THE FLUID LINES, and pull it far enough away from the booster so you can adjust the rod. Hold the rod with a pair of pliers, and use a wrench to back the adjuster nut out a couple turns. Bolt the master back on, start the engine, and check the brakes. If they are better, but the pedal still isn't quite right, then adjust it further until you get it right. Make sure the brakes aren't dragging, though! Drop me a line this time and tell me what happens. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

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06-13-2003, 12:58 PM	#3
twilightcall Registered Member Join Date: May 2003 Posts: 86	It really doesn't take much effort to push the pedal down. I removed the vacuum line to the booster and tried it, it was much harder. I just still have the 2-3 inches of free play at the top and when I get to braking it is ok. I was just thinking maybe a small tear in the diaphram could cause this. When the vacuum line to the booster is unplugged you have to almost stand on the brakes.

06-14-2003, 06:55 AM	#5
twilightcall Registered Member Join Date: May 2003 Posts: 86	Yes, the new proportion valve took the light out. I am not sure about the rod. I thought it would be best to not mess with the adjustment. It could be off though. How would I check? Thanks for the help.