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6/05/2013 7:40 PM  #1


Power brake problems

I just finished installing the MS power brake set up on my 66 coupe front disc rear drum. My brake pedal is about 3/4" lower than the clutch pedal and when I apply the brakes I have quite a bit of travel. The brakes work well but the pedal seems low to me. Also after being parked for a while when I went to move the car the rear brakes are locked up.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
 

6/05/2013 9:26 PM  #2


Re: Power brake problems

Is this a new master cylinder and front/rear brake buildup? 
What MC are you using? 
What front brakes do you have? 
Did you get the booster from me or somewhere else? 
Did the MC come from me? 
Have the rear drum brakes been properly adjusted? 
If the booster did not come from me, did you adjust the output shaft to fit the MC you are using? 
Did you modify the pedal assembly and pedal yourself or did I do it?

I always have more questions than answers, but if you can answer all those, I will be alot closer to helping you with a solution.

The power brake pedal does sit lower than the old manual brake pedal.  It is that way by design.  Once you get everything dialed in, the pedal travel requirement will be alot less, so there is no reason for the pedal to sit up as high as the old manual pedal did.  All power brake Mustangs, at least through 70, were that way from the factory.  The PB pedals always sit about 1" lower.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

6/06/2013 10:48 AM  #3


Re: Power brake problems

Steve, this was originally an MS gt2008 manuel disc/drum conversion that work fine except for the pedal effort. I got the Cardone reman booster from Auto Zone Pt # 54-74000 and the MC from Advance new pt#20350053 (67 Mustang).
I did the pin relocation myself and I'm pretty confident it is correct.
Right now the brake pedal is 2" lower than the clutch but it was a little lower to begin with so I'm ok with that. I have about 2" of travel before I get brakes. The brakes work well, not overly sensitive. So the amount of travel is what I would like to correct if possible.
I checked the measurement of the booster shaft and it seemed right. I did turn it to adjust it but it did not change or I didn't do it right.
I had previously adjusted the rear drums so I know they're right.
Could the locked rears be caused by prop valve adjustment?


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

6/07/2013 7:50 AM  #4


Re: Power brake problems

Location of the brake pedal pin is very important.  Since the pedal ratio is 4:1, if you are 1/8" off in pin location, the pedal will sit 1/2" lower than intended.  Same for the position of the flanges at the front of the pedal support.  Normally they get repositioned about 1/16" closer to the pedal than the stock location.  Other than that, there is nothing that will cause the pedal to sit lower in its static position.  By design, you want it about 3/4" to 1" lower than it was with manual brakes.

How long is "parked for a while" ?

To adjust the booster output shaft, you must hold the outside of the booster shaft with some vise-grips while turning the hex bolt head at the end of the shaft.  There are two different boosters supplied under the 54-74000 part number.  Only one of them has an adjustable shaft.  Years ago when I first started selling those boosters, they were all adjusted perfectly when I received them.  Now, they are all adjusted about 1/8" too short for some reason.  So, multiply that 1/8" by your pedal ratio and that is the amount the pedal will move down before it does anything.  So, if the pedal is sitting 1/2" lower than stock in static position, then has to move another 1/2" before the booster output shaft touches the master cylinder piston, you will have a pedal that is quite a bit lower than stock when the brakes are fully applied.  I am not saying that is the problem with yours, just giving an example of potential for problems if everything is not done a certain way.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

6/07/2013 9:23 AM  #5


Re: Power brake problems

Thanks Steve. I'm pretty certain that the problem is the booster pin adjustment. I'll try it and see. I can live wih the static position  its that long travel when applying the breaks that can be alarming if yer not ready for it.
It only sat for about an hour whenI tried to move and the rears were locked. However its been in the garage for months prior to that so first step is to pull th drums and clean every thing up. 
Thanks for the help.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

6/07/2013 6:47 PM  #6


Re: Power brake problems

Pulled the mc and as suspected the booster is not adjustable. I took mearements and it appears to me that the shaft to mc clearance is good. Like I said I've got good brakes so I guess a little pedal travel is something I'll just have to get used to.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

6/08/2013 1:06 PM  #7


Re: Power brake problems

You should have immediate braking.   I would keep looking until you find the problem!


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

6/08/2013 8:06 PM  #8


Re: Power brake problems

I'm out of ideas. Everything points to the booster pin mc clearence but my mearsurements say its ok. I may just replace the booster when I can with one of yours. Not gonna happen for a while though so I'm gonna drive it as is.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

6/08/2013 8:11 PM  #9


Re: Power brake problems

Make sure you have the correct pedal. I had the same trouble. Fought it until I found out I had the wrong brake pedal. Check MS;s pedal page for the correct pin setting.


67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
 

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