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Author Topic: "over-boost" from new booster?  (Read 1768 times)

Ken

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"over-boost" from new booster?
« on: June 18, 2008, 02:15:08 PM »

Can a new/reman booster provide an over-boost condition, where the front brakes are REALLY sensitive to brake pedal input??

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'67 300 2 door "Fast top" with factory A/C, 1973 disc power brakes,Firm Feel Stage 1 power steering, Auto-pilot, up for sale!

Steve

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"over-boost" from new booster?
« Reply #1 on: June 18, 2008, 02:59:35 PM »

That would be more a distribution valve not shifting the load to the rears.
 
You'll have to describe that better.
 
Let me refine that 2nd sentance.
 
POLARACO2008-06-18 20:54:47
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Steve

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"over-boost" from new booster?
« Reply #2 on: June 18, 2008, 03:18:56 PM »

The other thing that just occured to me. . .Are you sure the master is front disc, rear drum?
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Ken

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"over-boost" from new booster?
« Reply #3 on: June 18, 2008, 04:20:37 PM »

Steve, yes, the master is for a '73 disc/drum C-body.  It's the one I got with the '73- up booster that didn't fit.

All I can say is, when doing a very short forward and backward brake test, the fronts came on VERY quickly while the rears seem fine.  The pedal felt a touch low, maybe 1/4" of take-up before the stopping occurred, but when it did it was NOW! *Admittedly, this was an improvement of magnitude, which I thought was great, but still I don't want to go through my brandy-new windshield on my first stop light!*

Ed seems to think the booster is "over-boosting" (his words) and cited a past example where a defective booster in a B-body he worked on was cured when the replacement booster was installed.  He noticed the sound of a vacuum leak from under the dash and seemed to think it was indicative of a faulty booster, while I am not so sure, as I heard the same leak before the swap ever took place (the last time I started the engine and let it idle I heard the same leak, and the car never left Park) and I think it could be the A/C switch having a leak/broken fitting.

How's that for info, better than Mobby?


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'67 300 2 door "Fast top" with factory A/C, 1973 disc power brakes,Firm Feel Stage 1 power steering, Auto-pilot, up for sale!

Arlen Vander Hoff

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"over-boost" from new booster?
« Reply #4 on: June 18, 2008, 06:28:17 PM »

I had pretty much the same thoughts as our fearless leader Moe.
Are you sure you got a disc/drum master cylinder?? Did you get it from "parts monkeys" or some place that knows what they are giving out???
I know another guy that had the same problem and he ended up going with a 74-75 master just to get it right. His brakes are fine now.
Also take a peek at that prop valve and see what position its in. (just for fun)
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Ken

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"over-boost" from new booster?
« Reply #5 on: June 18, 2008, 06:45:50 PM »

Ard, I don't think the MC is incorrect as it is for a disc/drum setup since it has the larger primary reservoir and smaller secondary reservoir.  I know enough about cars to know that at least (hey, I BETTER, after earning 3 AA degrees in auto tech!).

It COULD be a valving problem, or it could be too much length in the booster pushrod, since all the booster does is add force to the movement of the rod itself via force acting on the inner diaphragm.

I did forget one thing I did check, there are two checks one can do to a booster, and one is to pump the brake pedal with the engine off, with the ideal outcome being the pedal becomes firmer and firmer, which it did.  Then, one starts the car and the application of a pressure differential via the engine one should feel the pedal drop a little, which would indicate the diaphragm is not leaking, and I didn't do that.

The only other check I could do is disconnect the hose that provides the vacuum to the booster, and listen for either a change in the volume/disappearance of the vacuum leak I can hear inside.  If there is no change, then there is a leak elsewhere and the booster is not the problem, and it could be a problem in the hydraulic side of the brake system.

What says you Kahoona??  You're the one with the 4 year college degree! or ?



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Ken

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"over-boost" from new booster?
« Reply #6 on: June 18, 2008, 07:03:38 PM »


Just to add some fuel to the fire, the Online Imperial Club had this little nugget in their brakes section, listed under a 1968 vehicle:
My problem is the front brakes
      don't release-I don't know what the rear brakes are doing but definitely
      the fronts won't release. Today I parked the car in my driveway which has
      a substantial slant to it. I put the car in NEUTRAL and I could not budge
      it. I put it back in PARK, separated the master cylinder from the booster
      and put the car in NEUTRAL and it started to roll down the incline unassisted.
      I put it back in PARK, reconnected the master to the booster and put it
      in NEUTRAL one more time-it would not move! So, is there a push rod adjustment
      somewhere or am I looking at this illogically?

Replies:
From Larry:
Yes there is an adjustment
        to solve the problem you described. On most cars the rod from the brake
        pedal to the booster (it goes through the firewall) is adjustable. Some
        cars also have an adjustable rod between the booster & master cylinder.
        There should be a little free play when the pedal is all the way up. If
        these adjustments don't work, you may have some mismatched parts. I have
        seen the wrong master cylinder mounted to a correct booster and the wrong
        rod at the pedal.
HA!!!  It's either an adjustment or mismatched rod, hopefully the former and not the latter!  I'll tell Ed tomorrow.


Moesy2008-06-19 00:05:02
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'67 300 2 door "Fast top" with factory A/C, 1973 disc power brakes,Firm Feel Stage 1 power steering, Auto-pilot, up for sale!

Ken

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"over-boost" from new booster?
« Reply #7 on: June 19, 2008, 09:48:54 AM »


Well shoot...It IS the booster  Time to call Rock Auto.  The only thing it seems to be is the spring in the front of the forward diaphragm is weak, allowing the primary piston in the MC to be pulled forward a little, causing a drag/grabby brake situation, since the tech adjusted the rod between  the booster and MC to correct length.

I hate to think Rock Auto got a bunch of rebuilt units from A-1 Cardone that were not up to par.

On the good side of things, with the 1411 Edelbrock carb on the engine, I can now have the dual snorkle airclearner installed! I think it looks "EVIL"  


Moesy2008-06-19 14:54:43
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'67 300 2 door "Fast top" with factory A/C, 1973 disc power brakes,Firm Feel Stage 1 power steering, Auto-pilot, up for sale!

Steve

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"over-boost" from new booster?
« Reply #8 on: June 19, 2008, 12:39:07 PM »

Brian just had the brake dragging problem.  His was the adjustment of the rod.
I called that one
 
You say the pedal grabs about 1/4" of travel.  That's good.  Means the rear brakes are adjusted and there's no air in the lines.  As the rear brakes wear down alittle, that travel will increase.
 
The Rod doesn't make sense.  The fronts and the rears are going to be activated at the same time regardless.  The plunger on the master is fixed.  If anything, they would activate late or be locked up as described.  All that adjustment does is set the pedal travel to the master.
 
I don't know the internals of a booster off the top of my head.  I'd have to see how a master can over boost.  But if Rock will give you another one, you have nothing to loose.  I never heard of over boosting before.  If memory serves me correctly, there is a valve in the booster.
 
The old Bellows Boosters were sensitive.  But the boosters were huge!  I remember a 56 New Yorker that was very hard to deal with at slow speeds.
 
Let me know more.  You learn every day.
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Brian

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"over-boost" from new booster?
« Reply #9 on: June 19, 2008, 08:12:18 PM »

Well I still have the brake drag problem...gave the rod a small clockwise turn and went to the car club meeting last night and the brakes started to heat up on the hwy...
 
Had to take the slow...long way home last night so the brakes wouldn't heat up too much.
 
SO I gave the pushrod another adjustment this evening and will take the car out again this weekend and see if it's any better.
 
It seems to be the rear drums that are loading up, the fronts don't seem that hot so I'm wondering if the old prop. valve I used from the 71 300 is toast??
 
 
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Brian

02 Chrysler Concorde Lxi
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68 Chrysler Station Wagon 440/auto
48 Desoto 2dr Sedan flat 6/3spd manual

Paul

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"over-boost" from new booster?
« Reply #10 on: June 20, 2008, 06:36:25 PM »

  I don't want to get too deep into this, since I don't know all the facts, but I will attempt to give you some of my past experience from a long time ago, when disk brakes were first being introduced.  I can tell you that some of the early dual brake master cylinders had a restrictor built into them, and the later ones were built without the restrictors on some cars.  I also know that if you must match the master cylinder properly to the proportioning valve.  If your car calls for a master cylinder with the restrictor, and it doesn't have it, then too much fluid pressure will be allowed to go to the calipers.   Unfortunately, today, when you buy rebuilt parts, you have no idea exactly what you are getting.   The casting numbers might be right for your car, but the actual innards of the unit might have been produced for another application that is different than your application.  It is for  this exact reason that I always prefer to rebuild what I have, then  to purchase a rebuild that I know nothing about.  When I am faced with not having a choice but to take  the unknown rebuilt part, I never turn in my old core.  I see this as my salvation if the replacement part turns out not to be any good.
If you adjust the booster push rod, and it is causing the brakes to get hot, then you are adjusting it in the wrong direction. 
My final thought is how old was the container of brake fluid that you used.  If it were sitting on the shelf and had been previously opened, it could have absorbed moisture.  When your brakes get hot, and the moisture in the fluid starts to boil as a result, it can also give  you the brake drag that you are experiencing.  Brake problems are very difficult to diagnosis, unless you can actually lay your hands on the car and physically check each component for correct application, installation, etc.  Junk........
PS......... I don't know if this applies to the proportioning valve that you are using, but some of them required that you "release" them prior to bleeding the brakes.  Some had a button on top that you either pulled up, or pushed down to release.  Some of them also had a sliding internal switch that would turn on a brake warning light on the dash if one side of the system failed.  This also needs to be re centered for the valve to work properly. 
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Brian

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"over-boost" from new booster?
« Reply #11 on: June 20, 2008, 08:13:24 PM »

Junk.....Good info Thanks!!
 
My prop. valve that I used from the 71 300 is a little rough around the edges and the reset/release button you make refrence too is not functioning.  I think I will install a new one just to be safe.
 
The brake fluid I'm using is new...a few months at best and stored in a dry garage and sealed tight....actually had to buy a new jug last week since I have gone through a gallon of fluid so far on the wagon....
 
 
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Brian

02 Chrysler Concorde Lxi
84 Dodge Crewcab, Cummins/5speed
68 Chrysler Station Wagon 440/auto
48 Desoto 2dr Sedan flat 6/3spd manual

Paul

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"over-boost" from new booster?
« Reply #12 on: June 21, 2008, 05:37:02 AM »

Quote from: thrashingcows
Junk.....Good info Thanks!!
 
My prop. valve that I used from the 71 300 is a little rough around the edges and the reset/release button you make reference too is not functioning.  I think I will install a new one just to be safe.
 
The brake fluid I'm using is new...a few months at best and stored in a dry garage and sealed tight....actually had to buy a new jug last week since I have gone through a gallon of fluid so far on the wagon....
 
 
Why so much fluid?  I have seen where master cylinders will leak fluid into the brake booster, and the engine vacuum will suck it in and burn it.  Makes for a very interesting upper cylinder lubricant, and a mystery where the brake fluid was going...
If you give me the master cylinder application, I can check some of the old parts books to see what the part number is for the old application, and if it has an  updated part number, that will be a good clue that the old one is different.   One size fits all is very popular today.... Junk...
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Paul

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"over-boost" from new booster?
« Reply #13 on: June 21, 2008, 05:48:33 PM »

Sometimes a thought comes to me at the strangest time.  Today, I was looking at some cars at a car show, and I thought back about this thread.  That is when it came to me that you might just have the proportioning valve installed backward.  Usually they are stamped with a "R" at the port that the rear line goes to.  If you put it on backward, that will definitely give you the "over boost" condition that you are referring to.  Check this before you do any thing else.  Sometimes, it is the simplest things that get reversed, and reek havoc with your mind and car.
 
I also looked up the part numbers for the disk brake option for a 1967, which I believe your car is, based on your signature line.  The Wagner part number for 1967 is 64874.  The 1071 is a 75818.  I have no idea how they differ, but that might be one of the problems also.  The caliper numbers are also different.  I would suggest that you use the master cylinder that matches the year of the caliper use, so the system is properly balanced.  Calipers and master cylinders are designed to work in tandem, and you shouldn't mix different year parts in the system. 
 
Junk2008-06-21 22:58:48
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Arlen Vander Hoff

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"over-boost" from new booster?
« Reply #14 on: June 21, 2008, 06:14:32 PM »

Moesy's car is using the 73 set up so the master and prop valve should be for a 73 not the 67 Budd set up. 
 
ardog2008-06-21 23:16:25
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