69 red fastback 20 Report post Posted October 16, 2014 Gotcha, thanks again Quote Share this post Link to post Share on other sites
bartzzimpson 18 Report post Posted October 19, 2014 I fixed my similar problem with a dual diaphragm master cylinder from Scott Drake. I tried just about everything else first. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 Ok, I bled the brakes again and when I drove it to test them out I noticed when I was sitting at a stop sign that my idle was higher and as soon as I let off the brakes the idle drops back down.Is this a bad brake booster or is it something else that I'm missing? Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 23, 2014 So your saying that as your sitting with the brakes applied that the motor idles up and when your off the brakes the motor idles down? As you sit and hold the brakes or use them in traffic the Vac is consumed and your pedal will get softer especially if your running a sizeable camshaft. I cant say if I notice an RPM increase or change when I apply my brakes but I am not gonna say this is not the case. How old is the booster? if it were pretty old I would swap it out as well as the check valve where the vac hose hooks to and when you do that you can also check the push rod adjustment to be sure its correct. There is a procedure to check a booster but generally I have found that when they are bad you get a rock hard pedal all the time, but a tiny leak might cause what your describing. HOWEVER i can see how it would cause an idle increase as the vac is charging up the booster which is basically a controlled vac leak then its still being consumed while you have foot on the pedal.....tough one to call lol I have never had this problem. Dont feel bad bud, we drove to CTC and I have driven my car to work a few days and 2 nights ago I saw I had a rear wheel Cyl leak, a header gasket leak and both outer tie rod ends had busted boots from dry rot. Quote Share this post Link to post Share on other sites
barnett468 418 Report post Posted October 23, 2014 Ok, I bled the brakes again and when I drove it to test them out I noticed when I was sitting at a stop sign that my idle was higher and as soon as I let off the brakes the idle drops back down.Is this a bad brake booster or is it something else that I'm missing?;possibly, i would test the booster with a vacuum gauge with pedal up and depressed. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 Yeah the pedal gets real hard and the idle goes up about 3-4 hundred rpm's to make up for it. It's a rebuit booster, so maybe I need a new one, yeah I've been going through fixing things on mine since I've got it on the road, so I feel your pain. Thanks for the info. I forgot to ask, can't I hook a vacume pump up to the booster to see if it holds vacume to tell if it's bad, or am I wrong in thinking that? Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 23, 2014 Not sure on hooking up the vac pump but if your pedal is getting hard like that then its a bad booster....it should get softer really as the vac is the canister is consumed. Change that bad boy out and you should be good to go. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 Sounds like a good idea, any ideas on where to get a new one, I don't think I want anymore rebuilt ones Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 23, 2014 I bought my booster from Oreilly auto parts...good quality and good warranty Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 I'll give them a try, Thanks for all of the advice Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 23, 2014 Anytime Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 23, 2014 Anytime Quote Share this post Link to post Share on other sites
stangme428 33 Report post Posted October 23, 2014 I bought my booster from Oreilly auto parts...good quality and good warranty after my unit from advance auto failed i went to Oreilly auto parts also... works great! Quote Share this post Link to post Share on other sites
stangme428 33 Report post Posted October 23, 2014 I bought my booster from Oreilly auto parts...good quality and good warranty after my unit from advance auto failed i went to Oreilly auto parts also... works great! Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 Thanks, I think I'll give Oreilly a shot Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 23, 2014 Thanks, I think I'll give Oreilly a shot Quote Share this post Link to post Share on other sites
stangme428 33 Report post Posted October 27, 2014 well.... just because i posted a reply to your question.... my master cylinder is on the way out... pedal is returning very very slow then not at all... i can stop but... the last time this happened i replaced the brake booster and master cylinder with a unit from O'reilly... now im ordering a NEW not refurbished master cylinder from NAPA NMC M1929. i started a thread discussion ... Master Cylinder Woes... Quote Share this post Link to post Share on other sites
stangme428 33 Report post Posted October 27, 2014 well.... just because i posted a reply to your question.... my master cylinder is on the way out... pedal is returning very very slow then not at all... i can stop but... the last time this happened i replaced the brake booster and master cylinder with a unit from O'reilly... now im ordering a NEW not refurbished master cylinder from NAPA NMC M1929. i started a thread discussion ... Master Cylinder Woes... Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted October 27, 2014 Ok, I bled the brakes again and when I drove it to test them out I noticed when I was sitting at a stop sign that my idle was higher and as soon as I let off the brakes the idle drops back down.Is this a bad brake booster or is it something else that I'm missing? The idle speed shouldn't change when applying the brakes. Sounds like your rebuilt brake booster is bad and has a vacuum leak when you apply the brakes. There may be a small additional issue unrelated to your brakes. That is your idle air fuel mixture may be a little too rich since the idle speed increases 300 to 400 RPM when additional air from a leaking brake booster is introduced into the engine. Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted October 27, 2014 Ok, I bled the brakes again and when I drove it to test them out I noticed when I was sitting at a stop sign that my idle was higher and as soon as I let off the brakes the idle drops back down.Is this a bad brake booster or is it something else that I'm missing? The idle speed shouldn't change when applying the brakes. Sounds like your rebuilt brake booster is bad and has a vacuum leak when you apply the brakes. There may be a small additional issue unrelated to your brakes. That is your idle air fuel mixture may be a little too rich since the idle speed increases 300 to 400 RPM when additional air from a leaking brake booster is introduced into the engine. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 27, 2014 1969_Mach 1 Thanks I'll check it out Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 27, 2014 1969_Mach 1 Thanks I'll check it out Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 28, 2014 Any updates? Quote Share this post Link to post Share on other sites
MikeStang 247 Report post Posted October 28, 2014 Any updates? Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted October 28, 2014 I've got one ordered from Oreilly, as soon as I get it and get it put on I'll let you know how it turns out Quote Share this post Link to post Share on other sites
