Dual Diaphragm booster for 1964 Chrysler (smaller firewall bolt pattern)

Brakes, Suspension, Rims and Tires

  1. xander18

    xander18 New Member

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    Hey all

    I did the Scarebird conversion on my 1964 Chrysler a few years back but I've never been able to get a dual diaphragm booster in there for the pedal feel that I want. I've ordered 2 or 3 but nothing fits right. My early car (and all pre 65, I assume) has a skinnier and more rectangular bolt pattern for the firewall and most of the late boosters don't fit. I think there should be a later Imperial that works, maybe a Bendix unit. Can anyone help me with the right part number to order for the car or am I too deep into the weeds over here?
     
  2. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Contact www.boosterdeweyexchange.com. They keep most of the data for these boosters handy. They might also be able to locate a compatible core that they could rebuild for you. The correct booster is a '66 Bendix Dual diaphragm unit, if memory serves me correctly, '66 is the only year that used this booster on a C-Body with the narrow bolt pattern. This booster is a hard one to find and the core might cost you as much as the rebuild. The A and B body boosters from this time frame will not fit your application. This is a tough one because disc brakes were not that common and many were standard, not power assisted, so good luck.

    Dave
     
  3. xander18

    xander18 New Member

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    Dave,

    Awesome! Just the info I was looking for. I think I have boosters around here for '67s and '69s, just didn't quite go old enough. I'll take a quick look around for that Bendix one but yeah probably gonna have to go right to Dewey for it.

    Thanks!
     
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  4. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    65 - 68 Bendix dual diaphragm uses the same bolt pattern, so that info may not be entirely correct.

    I believe the narrow bolt pattern Bendix dual diaphragm ended in 64...
     
  5. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Another good reason to check with Booster Dewey to find out what works. You may be right because I am working from memory here and my head can't find all the trivia any more!

    Dave
     
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  6. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Agreed - check with Dewey. I would source a 64 Chrysler (not Imp as the rod length will likely be different) Bendix booster core and have him rebuild it.

    You also need to check that master has the right bore - if the master bore is too big the pedal feel will suck.

    @Davea Lux - not trying to contradict your post - your info is always spot on... I'm just pretty sure the boosters don't swap between 64 and 65-up even though they may look identical.

    The other option is to redrill the 64's support plate and firewall to accept the 65-68 booster bolt pattern since I think you said you already have one. As well, all 67 and up dual res 4 bolt masters will bolt right up, giving you many more suitable choices in an appropriate master for the size and weight of your car.
     
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  7. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    I wonder if a guy could swap the '65 support plate and pedal? Not one I ever tried on those two years, but a lot of the later ones interchanged.

    Dave
     
  8. xander18

    xander18 New Member

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    I gave Dewey a ring (friendly guy!) and while he didn't have part numbers on hand he said that two boosters fit. The rare and desirable Bendix unit that people swap into B-bodies and the mid 70s Midland unit (74-78 big Chryslers). So that narrows the search a bit but not a lot, I still can't find a list of years and models. But it sounds like all of the mid 60s Bendix units used the smaller bolt pattern so any Bendix I find will work. The Midland one should be easier to find. But Mopar swapped pedal rods around so much that I'll probably be sending one to him to put the correct rod in anyway. I'm going to scour some yards and see what I can find for rebuildable cores.

    I considered redrilling the firewall but without using the later pedal assembly the booster wouldn't bolt to that support plate. So that just becomes an ordeal to swap the support plate and redrill the holes. I think I would be more inclined to try disassembling a booster, drill the new pattern, weld in bolts, and reseal everything. Not like I care much about originality and at least that doesn't require contorting myself up under the dash as much.
     
  9. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Smart plan. Keep us posted.
     
  10. savoy64

    savoy64 New Member

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    if your car had an original single diaphragm it can be rebuilt-------my brother was fixing a travco motor home that did not have a source for new or rebuilt---napa said they had one size fits all rebuild kit for the boosters----the mechanic that used the kit said it was surprisingly simple to rebuild-------and the dual set up is just a bunch of fluff-----you get plenty of boost out of the single-----that is what i am running on my 69.....
     
  11. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Whether or not one chooses to use a single diaphragm DRUM brake booster in a disc system, know this: The drum brake booster DOES NOT provide enough boost to fully energize the disc system in the event of a panic stop. Yes it will bolt up. Yes it will work in 90% of braking situations. Yes, it might never let you down in normal braking. But then ask yourself WHY over all the years did Chrysler choose to have a different booster for disc systems? Why? Because it is needed to fully take advantage of the disc brake system's capabilities.

    It might make the difference of 15 or 20 feet in a panic stop - enough to prevent you from killing the little kid who rode his bike out in front of your car, or the granny who pulls out in front of you...

    To say nothing of the field day lawyers will have if after you kill or maim someone they have a qualified mechanic investigate why your car didn't stop soon enough and discover you actually chose to put the WRONG booster on your system... and believe me, in this litigational age, when an old car is involved in a fatality, they check it from stem to stern.

    Don't mess around with brakes. There's a drum booster for drum brakes. There's a disc booster for disc brakes. Don't mix the two systems.
     
  12. twostick

    twostick Senior Member

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    Just for the record, my 66 New Yorker had a disc booster off a 69 300. If I had to guess I'd say the booster had the same bolt pattern on the firewall side as a 4 bolt master.

    I would think if you have to redrill the firewall to fit the later booster, as long as the rod is centered the same as the 64 was, the stock pedal should work. Assuming the rod length etc is compatible.

    Kevin
     
  13. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    @twostick - yes, the 69 and part 70 boosters interchanged as well, I was just trying to simplify things.
     
  14. mr. fix it

    mr. fix it Old Man with a Hat

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    You beat me to the response Ross.
    I was going to suggest a re-drill and possible replacement of the re-enforcing plate...
     
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  15. savoy64

    savoy64 New Member

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    just for the record---i run manual 4 wheel disc brakes on my 64-----plenty of stopping power, great pedal feel without the danger of accidental lockup----if you are severely crippled or let your 90 year mom drive the car then look for the dual setup-------otherwise i stand by my "bunch of fluff statement....if you lock your brakes up your efficient stopping distance goes out the window--------in a panic stop you want to hear a sound like paper tearing----that is the peak of all that is good.....
     
    Last edited: Jun 29, 2019
  16. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    A well balanced manual system can be excellent, and yes, effeciency (and control) goes out the window on lockup. However, I believe one needs to be able to get to lockup to maximize general braking power, but with the attendant understanding that one needs to avoid lockup if possible. (FWIW, test show that in certain situations lockup is the most efficient, but that's another discussion).

    Chrysler never offered C body manual disc systems back in the day as far as I know, and with the booster and master combinations out there, it's fact that using a drum booster in place of a disc booster in an otherwise factory power disc system results in a disc system that will likely not be able to be locked up at all, therefore reducing maximum braking capability. This is where the concerns I spoke of above enter the picture.

    Granted, a better balanced system can be achieved with parts today, and with that, possibly using a drum booster may suffice, but generally those doing the conversion to discs tend to use a year appropriate disc master and a similar drum booster (since the disc booster can be a challenge to source), which puts the conversion squarely into the danger zone described above.

    Ultimately it's one's call... personally, I'd rather have too much braking capability than not enough... and the parts exist to ensure that capability is in place by using the correct factory engineered parts.
     
  17. savoy64

    savoy64 New Member

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    and surprisingly modern dodge ram trucks are running with a single diaphram----must be some other secret gidget inside that helps the 6500 pound trucks get stopped---oh they do all have rear antilock and some have front antilock----there is something to be said about mopar engineers--their police drum brakes were out performing the early disc competitors---that shouldnt have happened according to science----and those same engineers will cheap out to reduce costs----my favorite 64 brakes are the 11.75 rotors covered with stock calipers---maybe you guys have read the mopar muscle article about putting viper brakes on a roadrunner that already had the 11.75 installed---as an experiment they put the viper stuff on one side and took it for a drive--drove 30 mph hit the brakes--it stopped straight----drove 30 again--stomped on the brakes --stopped straight---upped it to 60 mph hit the brakes--stopped straight----back up to 60--stomped on the brakes----stopped straight----moral of the story--if you make 10 panic stops in a row your viper brakes cool faster......and they look cool too........
     
  18. twostick

    twostick Senior Member

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    Easy explanation. The diaphragm was bigger. Bigger diaphragm, bigger boost.

    Kevin
     
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  19. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    It is mostly a question of surface area, the larger the surface area, the more boost potential. Initially, with disc brakes the space for a booster was limited, hence the dual diaphragm units. Large surface area in a relatively small unit. The dual units were however somewhat more expensive and more complicated to produce. Starting in mid '71 Chrysler moved to a larger single diaphragm unit that stopped almost as well. The dual units remained an option for vehicles with the trailer tow option and certain high performance police options until '73. The later booster units were larger and more efficient so that the dual units were no longer necessary.

    Dave
     
  20. savoy64

    savoy64 New Member

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    couldnt sleep last night---kept having that recurring nightmare of someone locking up their brakes and sliding sideways in front of me-------i would wake up reverting to muscle memory training of steering around the barge with my tuned 4 wheel manual brakes properly applied---then i would remember those old nascar drivers didnt have power (lock-em-up) brakes and i would fall back asleep.....