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Username Post: MBM brake booster Issues        (Topic#345642)
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
06-25-17 07:55 PM - Post#2697503    

In a previous post I wrote that my brake pedal would not fully return every once in a while. Decided I had a bad brake booster. Had the rear end off the ground the other day and found there was a little bit more drag on the wheels than I wanted from the rear brakes being adjusted a bit too tight. Gave each adjuster three clicks in. Rear wheels spins freely now.

Now My Issue: Brake Pedal now does not return most of the time.

My Questions. Do the return springs in the rear brakes lose tension over time. By adjusting the rear brakes IN is there less tension on the return springs. Could there be any connection between the amount of spring tension on the return springs and the brake pedal not returning? Thanks



 

YOUNG57 
Contributor
Posts: 966

Loc: Tennessee
Reg: 12-06-10
06-25-17 08:53 PM - Post#2697506    
    In response to carolinakid

"Could there be any connection between the amount of spring tension on the return springs and the brake pedal not returning?"

NO, the pedal has its own return spring. And your booster must be holding it down. You need to replace the booster before you have no brakes or it locks them up.



 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
06-26-17 12:22 PM - Post#2697576    
    In response to YOUNG57

Finally got to talk to MBM tech. They said I have

1. A bad Booster

2. Not enough vacuum - I have 20 inches

3. Line too close to heat source - Not that I can
see
4. Booster clevis rod binding due to incorrect location on pedal

They ask what hole in the brake pedal I was using. I told them the original hole that was for manual brakes. They said to drill another hole 1 inch below the original and attach the clevis to that hole.

Original directions that came with kit instructed you to drill a hole 1 inch below the original ONLY if you had an angled booster. Directions are from east coast chevy.

Directions also stated you could drill an OPTIONAL hole 1/2 inch hole below the original IF you wanted a higher pedal

The original hole in brake pedal seem to me to be halfway between upper and lower most travel of booster clevis

The Bottom Line: Due to conflicting info: What have other done in regard to position of booster clevis on the brake pedal? Thanks



 
Rick_L 
Honored Member
Posts: 27207
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
06-26-17 04:32 PM - Post#2697601    
    In response to carolinakid

The advice you got about drilling a new hole for the brake clevis is correct. You should use the original hole if you have a flat mount booster. You should use a hole 1" down if you have an angled bracket for the booster.

Now to the details. Drilling that hole 1" down from the original assumes that the booster bracket makes the pushrod "want" to be there without forcing it up or down. If the clevis does not line up with the hole, they screwed up the bracket angle. If you have to force the pushrod up or down, that's going to side load it and that's not good.

There is NO way that 20" of vacuum (or any amount higher or lower) is going to affect pedal return. All the vacuum does is affect how much boost. There are no other excuses that would affect this except pushrod alignment.

The other effect of re-drilling the clevis pin location in the brake pedal arm is that it changes the pedal ratio. This affects the brake pedal leverage and pedal stroke. Moving the hole 1" down means you have 4:1 pedal ratio rather than the stock 6:1. This means the pedal travel will be 2/3 of stock and the force required is 1.5 times what it would be in the stock location. What it's doing is killing some of your boost so that you can have a shorter pedal. This is what the OEMs do, so it replicates that "feel".

There were a lot of offshore manufactured boosters made the last few years that have pedal return problems. And almost every seller on the market was (is) affected. I'm not real confident that they have truly fixed the problem. I don't see as many complaints on these forums so maybe they've made progress. I'm sure that inventory moves slowly from some vendors. Probably a bigger deal is customers buying stuff and not using it right away, or not piling up miles once installed.



 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
06-26-17 05:52 PM - Post#2697613    
    In response to Rick_L

I have a flat/level mount booster. The manual brake original hole seemed to line up with the booster clevis pretty good to me. However I have drilled the optional hole 1/2 inch down from original and will see if this solves my problem. I have also ordered another booster just in case it doesn't.

I have googled this problem and there are a lot of folks that are having the same problem.



Edited by carolinakid on 06-26-17 05:55 PM. Reason for edit: No reason given.

 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
06-27-17 06:21 PM - Post#2697764    
    In response to carolinakid

Removed pedal spring and attached booster clevis to new hole approximately 1/2 inch down from original manual hole.

WOW what a difference, Pedal stroke has been cut in half and pedal doesn't stick anymore.

Booster rod must have been binding when it was in original hole.

Now have a new spare booster and brakes that work great. Doesn't get much better than that!!!!



 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
07-27-17 10:12 AM - Post#2701656    
    In response to carolinakid

Update. Moving booster clevis down on pedal 1/2 inch DID NOT solve my problem of pedal sticking. Pedal sticking returned. Replaced Booster! Did noticed that after removing rubber boot on rear of old booster the ring that holds the two foam and one cotton packing washers was cockeyed causing cotton washer hole to be misaligned on clevis threaded rod. Hole in cotton washer was elongated. Don't know if this could of cause enough of a binding condition with the threaded rod to cause pedal sticking but it probably didn't help.



 
swbatt 
West Coast Show Support
Posts: 3980
swbatt
Reg: 03-25-01
07-27-17 08:47 PM - Post#2701773    
    In response to carolinakid

So Kid, did the pedal quit sticking?
I have same problem. Got under dash and looked at it, when not running it seems to work better. After I fiddled with it it worked about a day and started to stick again. Mine looks like the alignment may be off some, but not rubbing or touching anywhere. I need to measure the second hole, will look again this weekend. Thanks for getting this topic going again.



"Which do I prefer? Chess or sex? It depends on the position." - Spassky


 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
08-02-17 06:18 AM - Post#2702446    
    In response to swbatt

With new booster brakes work GREAT!!!. Pedal is not sticking. Call me crazy but with new booster the braking quality seems to have improved over the old booster which makes me believe there was a internal problem with the old booster.

Swbatt, Pull rubber boot forward on rear of booster and check to see if ring holding felt/cotton washer is in straight and level with rear edge of booster



Edited by carolinakid on 08-02-17 06:25 AM. Reason for edit: No reason given.

 
swbatt 
West Coast Show Support
Posts: 3980
swbatt
Reg: 03-25-01
08-03-17 02:16 PM - Post#2702685    
    In response to carolinakid

Ok, off work for a week. Will try it. Thanks for the reply.


"Which do I prefer? Chess or sex? It depends on the position." - Spassky


 
1956chevy 
Contributor
Posts: 304
1956chevy
Loc: Orlando, FL .
Reg: 05-11-01
08-05-17 02:46 PM - Post#2702953    
    In response to carolinakid

CK, thank you for bringing this up. I have had this problem ever since I installed my brake booster in 2012! I got in the habit of pulling the pedal back up with my foot each time I pull away from a stop.

When I installed my system I read all the conflicting info. I went ahead and drilled a new hole 1" below the original hole. Then I ended up getting a flat mount booster, so I used the original hole. The pushrod didn't seem to be binding, and certainly would have had I used the new hole I drilled.

I don't have very much brake pedal. Have been thinking about getting an angled bracket. However, I will also get a new booster since the pedal sticks a lot. It is worse once the car has been running for awhile.

Here is my current set up.







I just HATE to remove the brake lines and have that nasty mess all over!

Glad you figured it out. Thanks for sharing and the motivation.

Keith Marang
Webmaster
Central Oklahoma Classic Chevy Club
www.55-57chevys.com


 
carolinakid 
"6th Year" Silver Supporting Member
Posts: 912
carolinakid
Loc: Sanford NC
Reg: 08-27-03
08-06-17 09:56 AM - Post#2703029    
    In response to 1956chevy

When I removed my brake lines from master there wasn't a lot of leakage. I did one at a time and have threaded plastic plugs that fit both opening in master. Cap the line themselves with soft plastic caps. Didn't even have to rebleed the system. I did put a thick towel under master just in case though. Nice Car car by the way. Good Luck



 
4dr 57 
"9th Year" Silver Supporting Member
Posts: 4449
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
08-12-17 08:01 AM - Post#2703856    
    In response to carolinakid

  • carolinakid Said:
Finally got to talk to MBM tech. They said I have

1. A bad Booster

2. Not enough vacuum - I have 20 inches

3. Line too close to heat source - Not that I can
see
4. Booster clevis rod binding due to incorrect location on pedal

They ask what hole in the brake pedal I was using. I told them the original hole that was for manual brakes. They said to drill another hole 1 inch below the original and attach the clevis to that hole.

Original directions that came with kit instructed you to drill a hole 1 inch below the original ONLY if you had an angled booster. Directions are from east coast chevy.

Directions also stated you could drill an OPTIONAL hole 1/2 inch hole below the original IF you wanted a higher pedal

The original hole in brake pedal seem to me to be halfway between upper and lower most travel of booster clevis

The Bottom Line: Due to conflicting info: What have other done in regard to position of booster clevis on the brake pedal? Thanks





Why anyone would do something like drill a second hole in their brake pedal, other than having a BBC engine and are stuck with no room for the booster, & beside the fact that, "that's the way we have always done it" (on SBC's) points to a pedal ratio problem that could be resolved with a ratio bracket from PJ's, however this will not solve excessive pedal travel.

Drilling a second hole is not recommended by engineers, just sales personal. If one has a level mount system, drilling/using a lower hole will break off the rear plastic parts of the booster and cause "awkward" pedal rod application to the booster.

In one of your other posts you mentioned a lot of fluid loss when you disconnected the brake line. This would indicate that the booster pin to master cylinder clearance is off and needs to be set up properly.

This can take some finessing as the recommended .020-.030 clearance will disappear just by tightening up the master cylinder, and your preload condition on the master cylinder won't be solved.








 

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