Single Diaphram Booster Question on a slabbie with column shifter?

[mr. fix it]

Hi guys, I'm asking this question about my 66 Polara Slabbie before actually trying this for myself.

I know that in the past for the 73 disc brake conversions to which I have done most of is this other than replacing the booster.
I replaced every nut & bolt otherwise including upgrading to the 72 2 1/2" rear brakes
Currently I have a 67 drum booster single diaphragm setup.
It's worked ok for the past 1 1/2.

I had the M/C give me some trouble so I replaced it under warranty, bled it and then installed and bled again at the M/C then the distribution block.

I now have a good solid pedal again.
Too good though as the pedal is now to hard for my liking.

I did adjust the booster pushrod out since the replacement M/C piston had a deeper pushrod hole than the original Cordone rebuilt unit.

The brakes work but I have to exert some pretty good effort to bring the car to a complete stop.

With the old M/C I had added a 10psi residual valve to the rear brake circuit since I had to pump the pedal to get a decent pedal. I local performance shop suggested this after I found out that the M/C drum circuit should have a residual valve(which it didn't) even adding a 2nd valve wouldn't hurt if one existed already.

So fast forward to yesterday.I got the new M/C and checked right away for a residual valve & again the replacement did not have one so I left the AM one in place.

I checked the pushrod length and it was really short compared to what the hole in the new M/C needed so I adjusted outwards leaving 1/8" difference.

I did take notice when bleeding the brakes that the proportioning valve on the frame now pushes forward slightly(front circuit) when applying the brakes but the safety light doesn't come on.
I don't think this would cause a hard pedal with 1/8" travel but can't tell for sure since there is limited info out on the web.

I've been googling for an hour plus trying to come up with an answer without having to create this thread.

Is it time for me to bite the bullet and get the dual diaphragm booster or will the 73 single booster work even though it will likely come close to interfering with the column shifter.

Previously, the dual drum booster felt decent but a little effort was needed to apply the brakes safely) not too much but not super easy like new car braking...

Will the single booster work for "drive' position or totally interfere?
I did see an E-body booster suggested on another thread but has anyone confirmed it will work?

Suggestions are appreciated.
Thanks, Tom

 

[traintech55]

Hi Tom, I can tell you from experience, with the 72, 73 single booster, your column shifter will hit when you try to go lower than "Drive". I went thru this when I converted my 66 300 to disc brakes. I bit the bullet and got the "Dual Booster" and everything works great. Good luck.

 

[mr. fix it]

Hi Tom, I can tell you from experience, with the 72, 73 single booster, your column shifter will hit when you try to go lower than "Drive". I went thru this when I converted my 66 300 to disc brakes. I bit the bullet and got the "Dual Booster" and everything works great. Good luck.

Thanks so it will work unless I drop it into 2nd or 1st from your response.
The main reason asking is that I have a single booster and if it will work as a test to eliminate the hard pedal issue then I will go for the dual booster
I’m tight on fun money these days and can’t afford to throw parts at something until it works approach.

 

[Davea Lux]

Hi Tom, I can tell you from experience, with the 72, 73 single booster, your column shifter will hit when you try to go lower than "Drive". I went thru this when I converted my 66 300 to disc brakes. I bit the bullet and got the "Dual Booster" and everything works great. Good luck.

The other issue with the larger diameter single booster for '72-'73 is that on some 440 applications, it will not clear the valve cover, so check your dimensions first. If the warning valve is cycling part way, are you sure the brakes are properly bled? It only takes one bubble to sometimes cause a "hard" pedal on a dual circuit MC. I would try re-bleeding the front brakes first. The E-Body booster is a smaller diameter dual diaphragm unit and it does not have the same mounting bolt pattern.

Dave

 

[mr. fix it]

The other issue with the larger diameter single booster for '72-'73 is that on some 440 applications, it will not clear the valve cover, so check your dimensions first. If the warning valve is cycling part way, are you sure the brakes are properly bled? It only takes one bubble to sometimes cause a "hard" pedal on a dual circuit MC. I would try re-bleeding the front brakes first. The E-Body booster is a smaller diameter dual diaphragm unit and it does not have the same mounting bolt pattern.

Dave

Thanks Dave I’m running a Poly 318
I will do some more measurements to make sure that the valve cover doesn’t touch
I do plan on re-bleeding the brakes tomorrow to see if this helps.
Reflecting on this, I remember having fun with the brakes when I did the conversion

 

[traintech55]

Thanks so it will work unless I drop it into 2nd or 1st from your response.
The main reason asking is that I have a single booster and if it will work as a test to eliminate the hard pedal issue then I will go for the dual booster
I’m tight on fun money these days and can’t afford to throw parts at something until it works approach.

If you are only using it for a test, then I will say it should work. When I converted mine the engine and trans were out. You might still have a hard pedal with the newer booster.

 

[mr. fix it]

If you are only using it for a test, then I will say it should work. When I converted mine the engine and trans were out. You might still have a hard pedal with the newer booster.

I have issues with mobility so I'm always looking for the best & easiest solution.
My car buddy is coming by later today to do the grunt work such as jacking the car up onto stands again then crawling around helping to bleed the system.
I'm re-reading the FSM to make sure we are following the right bleed sequence as well.

 

[mr. fix it]

I admit I only bled the M/C lines leading out of the M/C after bench bleeding & then down to the proportioning valve.

I will now follow this method as instructed in the FSM for the 1973 Chrysler Newport.

 

[mr. fix it]

Update:
I rebled the brakes & also removed a 10PSI residual valve I had add last year to help pump the rear brakes up during braking.

It is still a very firm pedal & the distribution valve is still pushing forward slightly under normal brake application.

I suspect a defective M/C plus the single diaphragm booster I am running is not up to the job even though it worked fine with the old M/C.

I'll post updates as I progress.

 

[saylor]

hang on -

its the .dia of the M/C piston = how much pressure

put your money back up and lets work this out. or send it to me when your brakes work

 

[saylor]

the residual valve(s) should be built into the bottom inside of the M/C, or inside the holes where the lines connect - if you see some little divots or pilot hole lookin things, i think those are them

 

[saylor]

i know you guys will argue this because we argued about it 5 years ago but ill say it again the booster only BOOSTS your pedal effort. a single booster is fine.

why do they call it a booster. same reason we park in a driveway i guess.

try not to die -

- saylor

 

[mr. fix it]

i know you guys will argue this because we argued about it 5 years ago but ill say it again the booster only BOOSTS your pedal effort. a single booster is fine.

why do they call it a booster. same reason we park in a driveway i guess.

try not to die -

- saylor

I have run the drum booster for 1 1/2 years now and I have felt good about it with not concerned about pedal effort involved but lately i found that the pedal was traveling further than before
I had the brakes checked over and found a slight leak
Tightened the fittings and no more leaks
I found that the front inner brake pads were rattling quite a lot so we secured the pads
Adjusted the brakes in the rear but no change in pedal position

Since the pedal was dropping after a good drive but better when the car sat for a few days I suspect it was the M/C
It has warranty so why not take advantage of that right?

Now the pedal is doing well but the harder pedal effort is needed
I did go for a drive this evening and had to use both feet which makes me think that it’s a defective M/C or the booster is now having to work more than designed to do

Suggestions are welcome on what to focus on next.

 

[Davea Lux]

I have run the drum booster for 1 1/2 years now and I have felt good about it with not concerned about pedal effort involved but lately i found that the pedal was traveling further than before
I had the brakes checked over and found a slight leak
Tightened the fittings and no more leaks
I found that the front inner brake pads were rattling quite a lot so we secured the pads
Adjusted the brakes in the rear but no change in pedal position

Since the pedal was dropping after a good drive but better when the car sat for a few days I suspect it was the M/C
It has warranty so why not take advantage of that right?

Now the pedal is doing well but the harder pedal effort is needed
I did go for a drive this evening and had to use both feet which makes me think that it’s a defective M/C or the booster is now having to work more than designed to do

Suggestions are welcome on what to focus on next.

Might also be that your booster is failing. Start the car and let it run for 30 seconds or so and shut the car off. Do you hear any hissing with the car off? The booster should hold vacuum for a short while after the engine has been turned off, if the pedal is "dead" as soon as the engine stops, the diaphragm may be leaking or the check valve is failing. If the check valve is failing, it will usually make a hissing noise also. The other thing these older mopars sometimes do is to collapse the lining inside of the hose to the booster, when the liner collapses, the booster is starved for vacuum and fails to work properly. Might also want to check the port fitting for the hose where it screws into the manifold, these fittings sometimes get plugged with carbon.

Dave

 

[mr. fix it]

Might also be that your booster is failing. Start the car and let it run for 30 seconds or so and shut the car off. Do you hear any hissing with the car off? The booster should hold vacuum for a short while after the engine has been turned off, if the pedal is "dead" as soon as the engine stops, the diaphragm may be leaking or the check valve is failing. If the check valve is failing, it will usually make a hissing noise also. The other thing these older mopars sometimes do is to collapse the lining inside of the hose to the booster, when the liner collapses, the booster is starved for vacuum and fails to work properly. Might also want to check the port fitting for the hose where it screws into the manifold, these fittings sometimes get plugged with carbon.

Dave

The booster is only 3 years old along with the vacuum line but all suggested items worthy of investigation

 

[twostick]

Any chance the new M/C has a larger piston than the old one? A larger piston will instantly firm up the pedal and reduce brake pressure which is why you now have to stand on it more to get it to stop.

Kevin

 

[mr. fix it]

Any chance the new M/C has a larger piston than the old one? A larger piston will instantly firm up the pedal and reduce brake pressure which is why you now have to stand on it more to get it to stop.

Kevin

Anything is possible Kevin.

The only way to find out would be to dismantle both M/C's
I had to return the original one to get the current one.

 

[mr. fix it]

The booster is only 3 years old along with the vacuum line but all suggested items worthy of investigation

Ok
I was able to test the booster and it is holding 20” vacuum for 5 minutes
Each press of the pedal drops it 5”
I got 4 presses of the pedal

After that pressing the pedal resulted in a 1” pressure until I released the pedal
I am yet to do a manual test of the valve but I think it’s going to pass the test
Vacuum line is good and not collapsing under 20” vacuum

Every thing is leading up to a defective replacement M/C since I don’t see a positive back flow of fluid in the disc chamber compared to the drum chamber

 

[rkrochen]

I would agree it’s something to do with the new MC. If it worked prior to this and the only change you made was the MC chances are that’s what it is.

 

[mr. fix it]

I have to recheck the push-rod distance & the check valve yet.
If this doesn't cure it then it is the #1 suspect...

And I have to check the engine vacuum as well.