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Old 09-26-2012, 07:41 PM
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brake booster

I have a 57,3100 chev pickup with a CPP firewall mount P/B kit. After two different boosters, from them,problem still remains. Brake pedal will not return last 1/4"-1/2" or so. Brakes bind. With vacuum disconnected,driving vehicle, brake pedal returns completely and firmly. Everything is new,no binding anywhere, pedal has return spring,etc. Booster pin is adjusted with a gauge. All the usual areas to check/confirm have been done. Brake system works great otherwise. I am convinced it's a cheap overseas booster that's the problem. CPP believes otherwise. I get, "there's nothing about a booster that could cause this". Well, then why does the pedal return VERY good with out vacuum applied, while idling/driving vehicle? Am I missing something here?

Talked to a booster rebuild shop, and they said definitely a booster issue.Maybe they said that in order to sell me a booster, but I'll give them the benefit of the doubt for now. Any thoughts?

Was looking at MBM brake boosters. USA made? Got to get this bullcrap resolved.

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Old 09-26-2012, 08:56 PM
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Sounds like the booster to me. Maybe try an actual gm unit? Sometimes oe parts are the best choice. (not oe for your truck, i mean off a standard car like a nova or chevelle)
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Old 09-27-2012, 08:05 PM
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Quote:
Originally Posted by vetteman View Post
I have a 57,3100 chev pickup with a CPP firewall mount P/B kit. After two different boosters, from them,problem still remains. Brake pedal will not return last 1/4"-1/2" or so. Brakes bind. With vacuum disconnected,driving vehicle, brake pedal returns completely and firmly. Everything is new,no binding anywhere, pedal has return spring,etc. Booster pin is adjusted with a gauge. All the usual areas to check/confirm have been done. Brake system works great otherwise. I am convinced it's a cheap overseas booster that's the problem. CPP believes otherwise. I get, "there's nothing about a booster that could cause this". Well, then why does the pedal return VERY good with out vacuum applied, while idling/driving vehicle? Am I missing something here?

Talked to a booster rebuild shop, and they said definitely a booster issue.Maybe they said that in order to sell me a booster, but I'll give them the benefit of the doubt for now. Any thoughts?

Was looking at MBM brake boosters. USA made? Got to get this bullcrap resolved.
For them to say there's nothing within the booster that could cause this is ludicrous.

There's a valve that seals the side of the booster nearest the pedal so there's vacuum on BOTH sides of the diaphragm when the brake pedal is not applied. This valve opens when the brake pedal is depressed, which allows atmospheric pressure to enter the pedal side of the booster, allowing the vacuum on the master cylinder side to help apply pressure to the MC.

If this valve isn't sealing the pedal side when the brake pedal isn't depressed, the vacuum on the MC side of the diaphragm will pull the pedal downward.

Here's an interactive representation of a vacuum operated power brake booster.

Last edited by cobalt327; 09-27-2012 at 08:22 PM.
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Old 09-27-2012, 09:54 PM
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What I would do is contact CPP via email directing your email to the owner, senior manager and manager of customer service and again explain your problem. Then explain how your problem and how its being handled by their company is currently being discussed on Hotrodders.com. Explain that the collective concensus is that there is a problem with their unit and perhaps the other members of this site might take their business elsewhere where their concerns are addressed better. Point out that after service is what brings customers back and word of mouth brings new customers in or keeps them away. Then explain that you probably talked to the wrong person the first time and ask who would be able to resolve this issue because you know they want to keep you as a happy returning customer. You might also point out that Hotrodders.com is the largest and busiest automotive website in the world.
Never hurts to try. BB
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Old 09-28-2012, 05:10 PM
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Thanks much for the very much appreciated replies everyone.
I just had a gut feeling that the booster is causing this. I feel more convinced now.
However, they did send me a different booster a few weeks ago,hesistantly, and it has the same issue. Now I guess you could assume that since both boosters have the same issue, that the problem lies elsewhere. OR, both boosters are at fault, as well as maybe countless others.
Everything they sell has a lifetime warranty,and I will not talk harshly about any vendor but aggravate me enough and I will. When an overseas made product is faulty, the vendor won't tell you this. So it's hard to get customer satisfaction being that,that's the way it is. I feel that in all actuality, they should keep sending me these cheap overseas disposable boosters until I get a good one.
Oops, starting to rant. I guess I was thinking of the advice they gave me, which was to relocate the pedal to booster push rod, on the pedal.Try drilling a different hole on the pedal. Maybe I need to change the angle of the pushrod. WHAT???? I bought a PREENGINEERED FULLY ASSEMBLED BRAKE ASSEMBLY KIT.
I am under the assumption MBM boosters are USA made. I will probably just eliminate the source altogether and hopefully get lucky with MBM. Whatcha think?
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Old 09-28-2012, 06:53 PM
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Quote:
Originally Posted by vetteman View Post
Thanks much for the very much appreciated replies everyone.
I just had a gut feeling that the booster is causing this. I feel more convinced now.
However, they did send me a different booster a few weeks ago,hesistantly, and it has the same issue. Now I guess you could assume that since both boosters have the same issue, that the problem lies elsewhere. OR, both boosters are at fault, as well as maybe countless others.
Everything they sell has a lifetime warranty,and I will not talk harshly about any vendor but aggravate me enough and I will. When an overseas made product is faulty, the vendor won't tell you this. So it's hard to get customer satisfaction being that,that's the way it is. I feel that in all actuality, they should keep sending me these cheap overseas disposable boosters until I get a good one.
Oops, starting to rant. I guess I was thinking of the advice they gave me, which was to relocate the pedal to booster push rod, on the pedal.Try drilling a different hole on the pedal. Maybe I need to change the angle of the pushrod. WHAT???? I bought a PREENGINEERED FULLY ASSEMBLED BRAKE ASSEMBLY KIT.
I am under the assumption MBM boosters are USA made. I will probably just eliminate the source altogether and hopefully get lucky with MBM. Whatcha think?
You did verify the pedal is returning fully and that the pushrod is adjusted/sized so that it's not bearing down at all on the pushrod seat?
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Old 09-28-2012, 07:35 PM
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Quote:
Originally Posted by cobalt327 View Post
You did verify the pedal is returning fully and that the pushrod is adjusted/sized so that it's not bearing down at all on the pushrod seat?
Yup. Pedal has free play,when it's fully returned. Double and triple checked booster to M/C bore pushrod clearance, with a gauge. 1/6"-1/32" clearance.
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Old 09-28-2012, 07:40 PM
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Quote:
Originally Posted by vetteman View Post
Yup. Pedal has free play,when it's fully returned. Double and triple checked booster to M/C bore pushrod clearance, with a gauge. 1/6"-1/32" clearance.


Too bad it can't be something easy...
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Old 09-29-2012, 05:17 AM
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Quote:
Originally Posted by cobalt327 View Post


Too bad it can't be something easy...
Do you feel it's a booster problem when,as I mentioned, that the pedal fully returns when driving the vehicle with vac line unhooked from booster?
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Old 09-29-2012, 10:21 AM
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Did you ever check the petal to booster length? Just for grins shorten it a little bit and see what happens.
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Old 09-29-2012, 07:03 PM
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Originally Posted by boothboy View Post
Did you ever check the petal to booster length? Just for grins shorten it a little bit and see what happens.
Yes.

It's adjustable, and shortening/lengthening it doesn't help at all.
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Old 09-30-2012, 06:12 AM
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Quote:
Originally Posted by vetteman View Post
Do you feel it's a booster problem when,as I mentioned, that the pedal fully returns when driving the vehicle with vac line unhooked from booster?
Yes, I believe it's a prob w/the booster. The valve I mentioned has a seat that has to hold vacuum, even a broken/weak internal valve spring has the potential to be the problem, but the booster would need to come apart to confirm this- something that's outside the ability of most guys, besides the poit that you shouldn't need to fix a problem not of your making.

Given the info you've provided and the checks you've made, if it's not the booster, I'm at a loss.

It shouldn't cause the problem, but have you checked the vacuum check valve between the engine and the booster?
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Old 09-30-2012, 07:53 AM
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Quote:
Originally Posted by cobalt327 View Post
Yes, I believe it's a prob w/the booster. The valve I mentioned has a seat that has to hold vacuum, even a broken/weak internal valve spring has the potential to be the problem, but the booster would need to come apart to confirm this- something that's outside the ability of most guys, besides the poit that you shouldn't need to fix a problem not of your making.

Given the info you've provided and the checks you've made, if it's not the booster, I'm at a loss.

It shouldn't cause the problem, but have you checked the vacuum check valve between the engine and the booster?
Yeah, I checked the valve. All is good.
If no useful help from CPP, I guess I will have to take a gamble and try a different booster from another source. If all else fails, hydroboost it.
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Old 09-30-2012, 09:30 AM
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Install a second return spring. With the engine running depress the brake petal and release. If petal returns fully try a few more times. If that fixes the problem that's good. If not and the petal dose'nt return without touching the petal shut the engine down and have someone pull the check valve from the booster. If the petal returns to the proper position you've got a bad booster, if not you've got a possible restriction in the brake system. It might be the fluid is not returning compleatly to the master cvlinder. Something to try.
BB
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Old 04-29-2013, 11:00 AM
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I hope by now, your brake problem is resolved. Try going to MBM website, it may help you to trouble-shoot problem. They are very helpful on the phone...1-800-231-4125, talk to sales. Good luck!
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