Brake Pedal Height Issues

[HawkRod]

I converted my 1970 Road Runner from manual drum brakes to power front disk. While everything hooked up per the FSM, my brake pedal height is too low. It doesn't even contact the brake pedal switch so the brake lights are constantly on.

Does anyone know if there were different sizes for the Bendix linkage, especially the rod (shown with the red arrow below)? It seems if I make this longer that it will fix my problem, but I don't want to start hacking into the brake system until I understand the issue.

Here is the overall problem with the brake pedal.


This picture is upside down, but this shows how the brake rod doesn't even contact the brake pedal switch.


Here is my Bendix style booster. It almost seems that the rod shown with the red arrow is too short? Or could it be the push rod from the booster? Or maybe were there different mounting holes in the brake pedals? :icon_scratch:


Here is another picture from the FSM on the mounting of this booster. Mine seems to be mounted exactly like this.


Appreciate any help or measurements anyone can offer.

Thanks,

Hawk

 

[mopar12372]

http://www.manciniracing.com/brakcylpuspa.html

you need on of these

 

[HawkRod]

http://www.manciniracing.com/brakcylpuspa.html

you need one of these

To replace the push rod on the master cylinder? And I am fine with doing that, I guess what baffles me is that to the best of my knowledge, I have used all stock parts. I could see if I was adapting an aftermarket brake system, but if these parts are all stock brake parts, why the &%$#! doesn't it fit?

 

[DoctorDiff]

The pedal sits low on all OEM Mopar power brake cars. The reproduction Bendix booster assemblies share the same characteristic.

 

[69roadr]

i had same problem when replacing my master cylinder (using original push rod). brake pedal sat too low and brake lights were on. pressed a hard rubber boot over the round white plastic part of the brake switch, and works well. just a quick fix

 

[Cranky]

The pedal sits low on all OEM Mopar power brake cars. The reproduction Bendix booster assemblies share the same characteristic.

I agree that PB systems did have a lower pedal from the factory but don't recall ever seeing a factory car with one as low as the one posted in the pic.....

 

[eldubb440]

Hawk....... back in the 80's, i found what i thought was a brake booster for my gtx in a big car, similar to an imperial i think....... it looked exactly the same......... but i found the rod coming out of the back side was the wrong length, and i cut/welded it to the proper length.......... i cant remember exactly, but it appears i had to shorten the rod........ a shorter rod will raise the pedal ( i think?)........... here is a pic of that booster with the welded end on the rod. and a booster i have on the shelf......... holding a tape measure to the back of the booster it measures 3 1/4 maybe 3 3/8 to the center of the bolt hole............. check your rod for length





- - - Updated - - -

after looking at the diagram, maybe i made it longer? ...... either way, it was wrong and i made to to the length of my original booster...........1986 was a long time ago

 

[Cranky]

Was thinking the same thing....but I would make the pedal rod longer....that is if you have the proper tools etc to do it with and don't want to spend the extra money on a new one. Biggest problem I've had over the years with stuff like that is that the new part will either be the same or too long or somehow not right so I usually just modify what I have and be done with it in the same day.

 

[kiwigtx]

I cannot measure my car right now, but I can say that my brake pedal is low. The clutch pedals are always high...and it does look odd when both are at rest. The brake light switch can be adjusted if that helps at all. :icon_thumright:

 

[HawkRod]

Thanks guys for all the replies. I decided to lengthen the brake rod (the one in my earlier post with the red arrow).

Here's what I did. I first cut the old one in half, and then I cut a bolt to the size that would make the overall rod the right length.


Damn picture got rotated again... When I was ready to assemble it, I put it in a vise to hold the ends in the same plane, and then I tack welded the two seams. I then fully welded the piece outside of the jig.


Here is the finished piece after I welded and then ground down some of the weld. I elected to leave some of the raised weld on there to give it extra strength just in case my weld didn't penetrate so good (I am pretty sure it did). No one will see it anyway, and it won't get in the way, so why not leave it?


Here is the finished pedal assembly. The brake pedal is just a tiny bit lower than the clutch, but is at a height that seems closer to where it was originally


Here is a reference picture of my original setup. They are pretty close now, so we will try this out and see how it works...


THANK YOU again for all of your responses and help! :headbang:

 

[1st Mopar RR]

I am having similar issue, my power brake linage you have pictured is hitting my brake pedal and not allowing the return to hit switch, it has nothing to do with my power brake rod. its same as you,. I have all stock parts and do not know if there are two diff pedals? power and manual??? anyone know?? appreciate any help.

 

[HawkRod]

I am not aware that there are two different pedals - I think they are all the same. The fix I came up with was quite easy and the car has been driving great with the pedal that way.

I would suggest you try the same thing, but if you do find out anything, please post here so we can all learn!

Thanks

 

[grtflred]

Thanks guys for all the replies. I decided to lengthen the brake rod (the one in my earlier post with the red arrow).

Here's what I did. I first cut the old one in half, and then I cut a bolt to the size that would make the overall rod the right length.
View attachment 259791

Damn picture got rotated again... When I was ready to assemble it, I put it in a vise to hold the ends in the same plane, and then I tack welded the two seams. I then fully welded the piece outside of the jig.
View attachment 259792

Here is the finished piece after I welded and then ground down some of the weld. I elected to leave some of the raised weld on there to give it extra strength just in case my weld didn't penetrate so good (I am pretty sure it did). No one will see it anyway, and it won't get in the way, so why not leave it?
View attachment 259793

Here is the finished pedal assembly. The brake pedal is just a tiny bit lower than the clutch, but is at a height that seems closer to where it was originally
View attachment 259794

Here is a reference picture of my original setup. They are pretty close now, so we will try this out and see how it works...
View attachment 259795

THANK YOU again for all of your responses and help! :headbang:

View attachment 259791 View attachment 259792 View attachment 259793 View attachment 259794 View attachment 259795

Hi do you have the exact length of the bolt that you welded into the middle. I have the same problem. Thanks

 

[HawkRod]

Hi do you have the exact length of the bolt that you welded into the middle. I have the same problem. Thanks

Sorry, I am afraid I didn't record the exact length. I did just go out and measure it on the car, but since the welds are there, it was tough to measure. I measured the added piece to be about 7/16" long. Again, this is an ESTIMATE. I suggest you cut one to that length, and then tape it up with electricians tape and mock it up to adjust the height to where you want it. Once it sits right, then weld it up!

Good Luck!

 

[BS23]

Sorry, I am afraid I didn't record the exact length. I did just go out and measure it on the car, but since the welds are there, it was tough to measure. I measured the added piece to be about 7/16" long. Again, this is an ESTIMATE. I suggest you cut one to that length, and then tape it up with electricians tape and mock it up to adjust the height to where you want it. Once it sits right, then weld it up!

Good Luck!

Gentlemen

I'm sure a lot went into bringing these bendix style boosters to the market and I do appreciate the effort of all involved in supporting our hobby.

I see that some of the dealers that sell the boosters have weighed in. The information on your site regarding this problem is outstanding! The PB-8536-2

booster conversion kit by MBM is for both B & E body applications and I too have a brake pedal height issue. I am well aware that Mopars in general with

power brakes, came with their brake pedal normally lower by an inch or so compared to the clutch pedal from the factory.I removed the original OEM Midland

Ross pancake style booster and linkage from my car, (do to low vacuum stroker engine and testimony that the bendix will operate with as low as 10 in vac) but

the brake pedal had sat much higher with the OEM compared to the PB-8536-2 booster and linkage.I believe MBM wanted the height of the brake pedal the same as

the gas pedal or just reduced the brake pedal height to reduce the stroke to only what is needed to operate the booster. Either way, the manual trans cars

with clutch and brake pedal assemblies now have a major difference between the two pedal heights in addition of not being able to adjust the OEM brake light

switch assembly to the MBM linkage. I have reached out to MBM Mark Campbell, MBM operations manager and to his credit called me back. He was aware of the

situation and recommended using a different brake light switch to compensate for the new linkage. I suggested he make a longer brake pedal push rod, like

hsorman suggested, so that the pedal would sit more like the OEM set up in Manuel trans cars and be within adjustment range of the OEM brake light switch. He

said he look into it but I haven't heard back.I have searched out a precision machine shop capable of extending and correctly welding the pushrod protecting

its integrity. I’m sure it’s going to add a Ben Franklin to this project when MBM should be providing a linkage compatible to the OEM setup. There is also a

safety factor concerning the strength and integrity of modifying a brake pedal linkage that concerns me. I hope this will get the attention of the MBM

dealers to address the issue with MBM.

 

[Car Nut]

I thought I heard somewhere that a pushrod from a "C" body would fix the height problem.

 

[BS23]

I thought I heard somewhere that a pushrod from a "C" body would fix the height problem.

If so, MBM didn't suggest it. Would be interest to know if that linkage pushrod measures up to the length needed.

Thanks

 

[Fran Blacker]

Brake light switch I bought on ebay has a lot of adjustment. Had to make a new bracket for my application.

 

[BS23]

Brake light switch I bought on ebay has a lot of adjustment. Had to make a new bracket for my application.View attachment 392405

Right on Fran, that is the quick fix MBM recommended. Are you driving a manual trans car? If not it doesn't really matter how low the brake pedal sits. The manual trans cars with both clutch and brake pedals look like hell with this kit and are not even close to the original OEM setup and brake pedal height one would expect. Not being able to adjust the brake light switch with the OEM bracket and original switch is just one aspect that really isn't the bigger issue here. Finding other pushrods from "C" bodies or otherwise are not going to properly match up with the MBM (bellcrank) linkage either. We all know owning 40 year old + cars sometimes require fabrication and modification, but MBM should be more forth coming. They didn't give me any good reason why the pedal height couldn't match the OEM power brake pedal height or why they wouldn't supply a longer push rod linkage for manual trans applications. Although the guys on this board seem more than capable of figuring out a fix and making the proper weld and modification to the push rod, not done right can be a major safety concern. While the cost of these units range from anywhere around $366.00 to $649.00, it would be responsible of MBM to either address the issue knowing that people are making modifications or explain why it's necessary for the brake pedal height to remain as sold with their kits.
I appreciate the time you took to post a photo of the switch and your work around solution!

.

 

[HawkRod]

I have searched out a precision machine shop capable of extending and correctly welding the pushrod protecting its integrity. .... There is also a safety factor concerning the strength and integrity of modifying a brake pedal linkage that concerns me.

For what it is worth, I have put 6000 miles on my car with that revised rod with absolutely no issues. I am not sure that there is anything "precision" about the rod though. Trust me, I am big on safety stuff. I would like to be around many more years, so I want stuff right, especially things that can make the car unsafe. The big deal with that rod is that you don't want it to break (as opposed to brake!) under pressure. So as long as the weld can withstand the maximum couple of hundred pounds of pressure that you leg can exert, then you are fine. Any competent welder should be able to weld that up very easily and that rod will guaranteed not break. The much more flimsy factory metal assembly that holds the entire pedal assembly would break before that rod did.

So the bottom line is: I wouldn't fret too much about it. Cut it and get it welded. It's not that big a deal as long as the welds penetrate. Then you have a brake pedal that sits and works like it is supposed to.

Good luck whatever you decide.

Hawk