power drum/drum to power disc/drum question

[keenkeener]

I own a '68 charger that someone converted from power drum/drum to power disc/drum. It still has the power drum booster, but I changed the MC to a disc version. I'm not sure what kind of conversion was done, but it looks like mostly new stock style parts. New lines, MC, calipers, rotors, etc, but it looks like the proportioning valve or distribution block (not sure what the difference is or if I have both) is old. Bled and adjusted the push rod out of the booster.

Just took the car for a test drive and the brakes work, but do not stop the car extremely quickly. I was able to lock the wheels up if I got on it really hard. I wanted to see if maybe the booster wasn't working well, so i disconnected the vacuum line and I had to practically stand on the thing to get it to stop.

My question is, does it sound like its because of the wrong booster? Maybe because of the old proportioning valve? Maybe something else with the parts that were put on the car before I purchased it? Or maybe because I am just used to newer cars brakes and I don't know what an old car should brake like?

[Mopar Nut]

Pictures?

Your booster should look like this.

[Dino]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

[MSRacing89]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

[68charger440]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

I'm confused..  What are you saying is incorrect?  Is it his statement that the stock dist block should not be left in place, any you are saying it is OK to leave it in place?

[keenkeener]

Thanks for the help guys.

Mopar nut- I have the drum power booster, not the one in your picture.

I am beginning to think that I may have the wrong MC/booster combo. The one that I have is made for a disc car, with the bendix booster. My MC is the cardone 10-1475 (not sure what size bore). That might make sense that the mc that I have requires the stronger bendix booster.

The distribution block appears to be stock. I will try and take a pic.

Is there another mc that would work better with this booster or should I swap the booster?

[keenkeener]

The distribution block:


The retrofit calipers:


Gratuitous grill shot:

[Dino]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

How can you run a disc/drum setup without prop and metering valves?  Are you saying when you swap the front drums for discs you only need to replace the MC?

[68charger440]

 

[68charger440]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

How can you run a disc/drum setup without prop and metering valves?  Are you saying when you swap the front drums for discs you only need to replace the MC?

I converted my drum/drum to disk/drum a few years back in my 1968 using the disk setup from a 73 Dart.  I left my original block in place and have not noticed any problems, but I have also read that I should have used the proportioning valve from the Dart.  So I am following this thread to find out if I am OK or not.  Mine does not have a power booster though.

[keenkeener]

What MC did you use?

[68charger440]

What MC did you use?

My original non power mc.

[MSRacing89]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

How can you run a disc/drum setup without prop and metering valves?  Are you saying when you swap the front drums for discs you only need to replace the MC?

I was stating you can leave the drum/ drum valve in there if you so chose. Simply add an aftermarket brake bias if you feel the need. For normal driving you will most likely never need one, but again your choice.

Definetly have to change the master to at least a disc drum.  (78 Cordoba) works great. 

[MSRacing89]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

I'm confused..  What are you saying is incorrect?  Is it his statement that the stock dist block should not be left in place, any you are saying it is OK to leave it in place?

Yes. Him stating that the drum/drum block can't stay is incorrect. No reason to replace it.

[Dino]

I just spoke to someone else who says he swapped to discs up front and didn't change or add anything to the stock distribution block.  That would make this swap a whole lot easier, I have a brand new disc/drum master and a front kit ready to go.  It was the swap to a combo valve that kept me from doing this job because there's so little room to reach these things.

[keenkeener]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

How can you run a disc/drum setup without prop and metering valves?  Are you saying when you swap the front drums for discs you only need to replace the MC?

I was stating you can leave the drum/ drum valve in there if you so chose. Simply add an aftermarket brake bias if you feel the need. For normal driving you will most likely never need one, but again your choice.

Definetly have to change the master to at least a disc drum.  (78 Cordoba) works great. 

Thanks for the info MSRacing89.

I am looking at the 78 Cordoba MC and it says that the bore is 1 1/32". Earlier you wrote that I might need to get a bore that is 15/16" or 1". I understand the relationship between force and bore size. What MC do you suggest I use?

I currently have the A-1 CARDONE Part # 101475 MC in the car. I am not sure what bore size this is. It is my understanding that this is the MC for a 68 originally equipped with Disc brakes.

[MSRacing89]

Although not the same as a disc booster, a drum booster should theoretically work and stop the car properly even though the pedal feel may not be ideal.  Sounds like they may have left the stock distribution block in place which is a big no no.  Got any pics of it?

This is an incorrect statement. The mopar drum/drum block has no proportioning built into it, so it is fine to run with that setup. You most likely have too big of a bore on the MC. They probably sold you an 1.125" bore, when you really need a 15/16" or 1".

How can you run a disc/drum setup without prop and metering valves?  Are you saying when you swap the front drums for discs you only need to replace the MC?

I was stating you can leave the drum/ drum valve in there if you so chose. Simply add an aftermarket brake bias if you feel the need. For normal driving you will most likely never need one, but again your choice.

Definetly have to change the master to at least a disc drum.  (78 Cordoba) works great.  

Thanks for the info MSRacing89.

I am looking at the 78 Cordoba MC and it says that the bore is 1 1/32". Earlier you wrote that I might need to get a bore that is 15/16" or 1". I understand the relationship between force and bore size. What MC do you suggest I use?

I currently have the A-1 CARDONE Part # 101475 MC in the car. I am not sure what bore size this is. It is my understanding that this is the MC for a 68 originally equipped with Disc brakes.

A-1 CARDONE Part # 101475---This is an 1 1/8" bore.  Let me take a step back and recommend this number A-1 Cardone: 13-1627 MC (76 Volare disc/drum) 1 1/32".   There is a newer o-ring style also ('85 5th Ave disc/ drum) 1 1/32",  BENDIX Part # 11822.  It will require a 4-hole to 2-hole adapter, but it is much lighter and seals better.  

There is nothing wrong with the 78 Cordoba model either, you would just want to verify it is for a Disc/ drum application.  Just about 100% it is, as I do not think they offered 4-wheel disc in 78!

[keenkeener]

Awesome info.

Do you think there would be that much difference in feel or performance from a 1 1/8" bore to a 1 1/32" bore?

[MSRacing89]

Awesome info.

Do you think there would be that much difference in feel or performance from a 1 1/8" bore to a 1 1/32" bore?

I think for the mild power combo you are running the you will get a better feel with the smaller bore.  I run an 1 1/8", but I back it up with Hydroboost and Brembo calipers. 

[keenkeener]

I ordered the dual diaphragm Bendix style booster from Pirate Jack. Just waiting to get it in the mail. I will let you all know how it goes once I install it.

Thank you for all of the great help. 

[krigel]

I am going through the same thing. Put in a disc conversion up front on my 68. I left the distribution block in place, but added an adjustable valve towards the back of the car. I didn't want to run the Chevy style booster that came in the kit, so I tried it with a disc booster I got from a wrecker (the diaphragm was shot, so the pedal wouldn't bounce back) but the pressure feel was great (essentially manual brakes). I put the stock drum booster back in, and now it takes all kinds of leg power to stop the car. Instead of spending 400 on a new booster, I might just go manual discs. Thoughts?

[keenkeener]

I struck out with Pirate Jack. It is going to take 90 days for them to get boosters in and I am simply not willing to wait that long.

Good news is that I rummaged through the attic and found an original bendix b-body booster and MC. We have been hoarding some parts for a few years. I am just going to have these rebuilt.

[Mopar Nut]

I struck out with Pirate Jack. It is going to take 90 days for them to get boosters in and I am simply not willing to wait that long.

Good news is that I rummaged through the attic and found an original bendix b-body booster and MC. We have been hoarding some parts for a few years. I am just going to have these rebuilt.

Booster Dewey does a fantastic job rebuilding or selling boosters outright.

[krigel]

Is there a massive difference in brake performance between the single and dual diaphragm booster? Anyone with first hand experience? I've got a local brake shop telling me it's not worth the price difference

[keenkeener]

It all depends on the bore of the MC is what I am finding out. If you have a large bore MC that came on the originally equipped disc charger in 68, then it requires much more pushing power. If you have a smaller bore MC as equipped on a drum car with or without power or later year disc cars, then it does not require as much pushing power.

Does that make sense?