Dr Diff power brakes; need new booster?

[Billccm]

Considering a disc brake conversion for my 1967 Coronet. This car has power drum factory brakes. I have a email into Dr Diff (Cass) asking about brake boosters as I have read you need 'dual bias' (whatever that means) Brake Boosters with the disc conversion. I'll see what Dr Diff says, but wanted to ask the experts here before I pull the trigger.

Really happy with the Dr Diff kit on my Road Runner, but that was a straightforward manual conversion. Want to make certain what I'm getting into here. I may also try the easy route with Scarebird, but they are unresponsive to my emails (see my other post).

Appreciate any feedback!

 

[Billccm]

FAST reply from Dr Diff! I need this booster:
Bendix Style Dual Diaphragm Booster for Mopars

 

[Mackman]

Hope it works out for you. I did the same conversion on my 67 Coronet. Please post your progress.

 

[Billccm]

Hope it works out for you. I did the same conversion on my 67 Coronet. Please post your progress.

Still researching between Dr Diff, Scarebird, and the MuscleCarBrakes in a Box (drums). I'd like to just go with manual disc, but I am gun shy on linkage and stiffening plate changes. I like simple plug and play kind of stuff.

 

[gtx6970]

I'm converting a 1966 power drum brake car to power disc.
Using this kit.
So far...it's a piece of cake install.
I'll update you later in the week how it stops. Pedal height etc etc

1966-70 B Body Charger Power Disc Brake Kit OE Style Booster & Master Cylinder | eBay

 

[Billccm]

Thanks, Bill. I'd appreciate your feedback and help when I finally buy the kit

 

[1MYTGTX]

Last year I had issues with Dr. Diffs Bendix boosters. These were the ones he was selling stating that they didn't need any modification to the firewall (enlarging hole) like the MBM booster needed. Im not sure if he is still selling these.....I would inquire

I tried 2 of these....both of them with severe defects. While they both bolted right up to the plate & firewall with no mods needed, both of them had what seemed to be internal leaks at times.
Lightly stepping on the brake and creeping either forward or back would cause a misfire in my engine (vacuum leak) Both did this. However if applying full pressure it did not do this and they would also hold vacuum at rest....

The major problem was actually upon brake apply. Coming to a stop (say a red light) the pedal would be firm-ish then all of a sudden would have "extra" power assist and damn near put you through the windshield. Trying to adjust the booster to master pushrod either too long, too short, exactly right etc would not cure the problem with BOTH of the ones he sent. Even swapped master cylinders to no avail. Granted my car already had power brakes and did not do this. Only reason for the swap was to get the "correct" disc booster to replace the power drum booster I had installed from a previous owner

Finally I gave up and had him send me one of the MBM brakes ones, enlarged the firewall hole and all was right with the world....ZERO problems.

I can say Cass was ACES through the whole process....sent me the boosters on his own dime and offered help with zero complaints.

Also I am now quite proficient in booster swapping....I can swap them in and out in under an hour now

 

[Mackman]

I also had a dual diaphragm booster from Dr. Diff that leaked vacuum at the crimp. He replaced the booster, but it took me a while to diagnose , and the install isn’t that much fun.

 

[Billccm]

Personally I would like to convert to manual disc. I know pedal height and geometry changes and don't want to go there, either. I've heard from several sources that the Chinesium boosters from everyone are problem prone and just add another point of failure.

I'm still contemplating what to do next. Thanks for the replies I value the opinions.

 

[Sinitro]

I mounted 73 A Body Spindles/disks on my 70 RR used a Dakota master cylinder, no booster required..

Just my $0.02...

 

[68 Sport Satellite]

Last year I had issues with Dr. Diffs Bendix boosters. These were the ones he was selling stating that they didn't need any modification to the firewall (enlarging hole) like the MBM booster needed. Im not sure if he is still selling these.....I would inquire

I tried 2 of these....both of them with severe defects. While they both bolted right up to the plate & firewall with no mods needed, both of them had what seemed to be internal leaks at times.
Lightly stepping on the brake and creeping either forward or back would cause a misfire in my engine (vacuum leak) Both did this. However if applying full pressure it did not do this and they would also hold vacuum at rest....

The major problem was actually upon brake apply. Coming to a stop (say a red light) the pedal would be firm-ish then all of a sudden would have "extra" power assist and damn near put you through the windshield. Trying to adjust the booster to master pushrod either too long, too short, exactly right etc would not cure the problem with BOTH of the ones he sent. Even swapped master cylinders to no avail. Granted my car already had power brakes and did not do this. Only reason for the swap was to get the "correct" disc booster to replace the power drum booster I had installed from a previous owner

Finally I gave up and had him send me one of the MBM brakes ones, enlarged the firewall hole and all was right with the world....ZERO problems.

I can say Cass was ACES through the whole process....sent me the boosters on his own dime and offered help with zero complaints.

Also I am now quite proficient in booster swapping....I can swap them in and out in under an hour now

thanks for sharing these details. I recently had a Dr Diff Bendix style dual diaphragm booster installed. The touchy brake thing sounds a lot like what you describe. I haven't noticed any engine related vacuum issues - yet.
Can you please share what you mean by one of the MBM boosters? Looking on Google, I see that MBM is a brand and they also make Bendix style boosters. Do you have a link and what is different about it vs the first Bendix from Dr Diff? You said you had to enlarge the firewall hole? Thanks.

 

[1MYTGTX]

thanks for sharing these details. I recently had a Dr Diff Bendix style dual diaphragm booster installed. The touchy brake thing sounds a lot like what you describe. I haven't noticed any engine related vacuum issues - yet.
Can you please share what you mean by one of the MBM boosters? Looking on Google, I see that MBM is a brand and they also make Bendix style boosters. Do you have a link and what is different about it vs the first Bendix from Dr Diff? You said you had to enlarge the firewall hole? Thanks.

That is correct. Those boosters have a larger diameter casing that requires enlarging the firewall hole to fit it. You also need to use the corresponding reproduction firewall plate or enlarge the factory one. No link as they are the manufacturer and Cass was able to have one drop shipped directly from them.

 

[68 Sport Satellite]

That is correct. Those boosters have a larger diameter casing that requires enlarging the firewall hole to fit it. You also need to use the corresponding reproduction firewall plate or enlarge the factory one. No link as they are the manufacturer and Cass was able to have one drop shipped directly from them.

Thanks. I don't see these on the Dr Diff website. Is this something that Cass just did on the side to help you out?
I see that MDM makes several different types. Is the MDM one you got a Bendix style or some other design? Thanks. I'd like to get the same one as you to try out.

 

[1MYTGTX]

Those might be the only ones he is selling now. His original booster listing used to tout that no firewall modification is necessary. It was cheaper too. I paid $245 for his booster last year....he has them for $300 now so I'm assuming they are not the same ones..... His site listing do not say that either way. I would call him and ask the manufacturer of the boosters he's selling now.
This is the one I got. Bendix disc brake style
PB8536-1 - 1966-1969 B Body Mopar Bendix Style Booster

 

[1MYTGTX]

Further looking on his site he now lists that you have to enlarge the hole.....so Im assuming hes not selling the defective ones he had originally anymore and these are the MBM ones.

Again I'd call to confirm...

 

[68 Sport Satellite]

Further looking on his site he now lists that you have to enlarge the hole.....so Im assuming hes not selling the defective ones he had originally anymore and these are the MBM ones.

Again I'd call to confirm...

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thanks a bunch. With this MDM Bendix style booster, does the brake pedal feel touchy with SUPER light effort? Mine does. I bought this Bendix style Dual diaphragm booster from Dr Diff about 4 months ago. I adjusted the push-rod gap to .020" using one of those special H-shaped tools and a feeler gauge and it's better, but still VERY light and a bit touchy compared to what I was expecting with a 1-1/8 Raybestos blue disc/drum Master Cylinder. If someone didn't tell me, I'd likely think I had a smaller bore 7/8" MC. The old booster I had in my car before was one of the gold colored dual diaphragm from Master Power Brakes. Not touchy at all, about the firmness I would expect with a 1-1/8" bore MC, but a little mushy even after numerous air bleeds. Both boosters stop the car just fine and could lock up the brakes and skid - I'd say the newer one from Dr Diff has greater stopping power overall. In the end, it's the pedal feel and modulation that I'm looking to fine tune.

 

[1MYTGTX]

Not touchy at all. Smooth and linear