Disc Brake Master Swap & P valve Question

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MoparBrit

HillingdonDart
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Okay, got all the disc brake stuff off of the '73 Dart yesterday. Going to clean it up, rebuild it and prepare to put it on the '71 Dart.

Thought I'm having and have a question about is this:

'71 Dart has manual disc brakes on it now. Swapping to get larger bolt pattern to match rear swap I did.

'73 Dart is a power disc brake car.

Instead of swapping the power disc brake assembly off the '73 as a whole onto the '71 (going to be wife's car so considering power brakes for her) will the existing '71 Manual Disc brake master cylinder work as is?

'71's existing brakes are the 4 piston older small bolt pattern ones of course.

How about the valving? As it was a disc drum car to start with can I leave it alone or do I need to swap the '73 Dart stuff over?

Thanks for any help. I looked through a search (perhaps did not use the right terms), but did not really find any definite answer to this issue. Most everything I find is on going from drum to disc.

Cheers
 
i just put bbp disc brakes on my car (68 dart)

my car is originally manual brakes, is still manual brakes.

I did not add a proprotioning valve and my car stops just fine, i have awesome pedal response.

dunno if any of that helps.

my sister in laws 70 dart swinger is set up the same way, someone else upgraded and did not add the p-valve, so I did not. since it has no braking issues
 
Thanks for the reply.

So did you just swap on a disc brake master cylinder and that was it (assuming you had drums to start?)?

I guess I should fill in more just to be sure on my car. Swapped an 8.25 rear in that has the 10" drums on the back instead of the 9's that the car came with. Front disc are already on the car, but are the older type.

Just want to be sure it is safe and no problem with rear lock / control loss upon a semi panic type stop on the highway or the like. Amazing the number of people who pull across the median on the highway to turn around and then pull right in front of traffic going 75 plus and do about 20 while they suss out who's calling them on the cell phone!

Thanks for your help.

Cheers
 
I went from 9" drums all the way around to the 73+ 11" A-body disks on the front and 10x2.5" drums on the back. I used the proportioning valve from the 73 and swapped it in place of the distribution block that was on the car.

Whether other folks have gotten away with it or not I would plan to use a proportioning valve on the rear's. Drum brakes are self energizing and will lock up with a lot less pressure than disks will.

BTW, you never mentioned that you were swapping the upper control arms and spindles. You will need to do that to use the 73 brake rotor and caliper.
 
Thanks for the post. Yes, swapping upper arms, spindles etc. Actually, just took the whole suspension off the '73, going to rebuild it and then bolt everything on to the '71. That way I know what I've got if I need parts later on.

The '73 has its proportioning valve on it so I can use that. I just wondered, as the '71 is a disc drum car already, if I needed to make the swap. It is the disc already that throws me a bit and gets me wondering. Manual master cylinder is for the existing disc drum set so wonder if it has the same proportioning valve that will work with the updated discs and drums?

Hope I'm making sense.

If I can use the existing master cylinder and valving (is something different on the '71 disc drum cars as far as system there?) then that will save me some work. If not then I'll have to get into seeing what it entails to bolt on the '73 master with booster onto the '71 with the '73's proportioning valve.

Thanks for all the help.

Cheers
 
MoparBrit said:
Thanks for the post. Yes, swapping upper arms, spindles etc. Actually, just took the whole suspension off the '73, going to rebuild it and then bolt everything on to the '71. That way I know what I've got if I need parts later on.

The '73 has its proportioning valve on it so I can use that. I just wondered, as the '71 is a disc drum car already, if I needed to make the swap. It is the disc already that throws me a bit and gets me wondering. Manual master cylinder is for the existing disc drum set so wonder if it has the same proportioning valve that will work with the updated discs and drums?

Hope I'm making sense.

If I can use the existing master cylinder and valving (is something different on the '71 disc drum cars as far as system there?) then that will save me some work. If not then I'll have to get into seeing what it entails to bolt on the '73 master with booster onto the '71 with the '73's proportioning valve.

Thanks for all the help.

Cheers
Click to expand...


Let me see if I can help clear up a couple things.

First of all any disc brake master cylinder from 1967-1978 will work.
A disc brake m/c has one big pod and one small pod.

So yes your disc master will work fine.

In 1979 a new aluminum m/c was introduced,but was mounted with two studs instead of four.Using this m/c is possible,but will require an adapter bracket from Mopar Performance.This m/c is a favorite of many,lightweight with great performance.

Avoid rebuilts! There is no single item which,when rebuilt,has such a poor reliability record as master cylinders.

On the valving:
Going from 9" brakes to 10" brakes you should not have lock up problems.If you were to go from 10" to 9",then you could.

On a side note:
If your rear brakes locked up a old trick would be to install rear wheel cylinders of a smaller diameter.Many Chrysler cars of the late 1960's and early 1970's used a 15/16" rear wheel cylinder.Using a 7/8" wheel cylinder would help balance brake proportioning.

I say run it how it is.

If you dont like the performance of the back brakes then install the 73 proportioning valve,or install a adjustable proportioning valve for the rears.You should be fine!!!!!!!

John
 
Johnny Dart said:
Avoid rebuilts! There is no single item which,when rebuilt,has such a poor reliability record as master cylinders.
Click to expand...

FWIW, I have been working on my own cars, worked my way through HS & College and for a few years after college in the father inlaws garage for over 30 years. I have never replaced a master cylinder with anything but a rebuilt and have only had one failure, if you can call it a failure.

The one failure was recently when I did the swap to disk brakes. The casting for the MC had a void along the surface where the cap seals that did not clean up during the machining resulting in fluid leaking past the cap. As with any rebuilts I buy it came with a lifetime warranty and I just brought it back for another.
 
Avoid rebuilts! There is no single item which,when rebuilt,has such a poor reliability record as master cylinders.



I believe the pro's at Mopar Action know of what they speak.
 
Thanks for all the clarification. As you can tell, bit thick this end sometimes. Nice to have a board like this one where people are quick to help!

Looks like time to get going on it then. Already rebuilt the top arms. Take the rotors to get them turned today and once I've got the bottom arms rebuilt it will be full steam ahead on doing the swap.

Thanks again!

Cheers
 
Considering the number of out right mistakes I see in every issue of Mopar Action and Mopar Muscle I wouldn't put much stock in statements like that from them.

I know my 30+ years working on cars, rebuilt MC's have never been an issue and do not support a statement like that.

I know when I go to the parts store and have the choice between new and rebuilt, I will take a rebuilt everytime just because they come with a much better warranty.
 
I have never had good luck with rebuilt master cylinders. Sure if it leaks they will give you a new one. I guess if replacing master cylinders yearly is your idea of fun, go for it. But will they repaint your inner fender or replace your fluid soaked carpet. Nope. Never had a new one give me a problem (they all wear eventually, 5 years is reasonable life).

Here's a question you should ask your insurance man. Does your liability policy distinguish between new or rebuilt parts? Will it cover you if YOU as the owner replace brake parts? How good is the warranty on either part? I am pretty sure the parts store rebuilt has a disclaimer saying something like "we assume no liability or responsibility for damage to persons or property resulting from the installation of this part on a motor vehicle used on public or private roadways". The new part may have such a disclaimer as well. Something to think about.
 
Well other than the one I mentioned that leaked past the cap gasket I have never had one of the rebuilts I have used leak. Can't say for sure about the ones I installed as a mechanic but never replaced one from a customer coming back. In any case a MC should be a life of the vehicle part and in the vast majority of the cases they are. I certainly wouldn't consider 5 years to be acceptable.

Of all the rebuilt parts you can purchase a MC is the least complicated to rebuild. I started working on cars back in the day when one leaked or plugged up you went to the parts store and got a rebuild kit. Honed the bore, replaced the seals and you were back in business. I still have the brake hone in one of my tool boxes. The controversy back then was did you charge the customer the extra money for a rebuilt to save time or spend the extra time to do it yourself and charge the customer less.

I don't understand what the insurance company has to do with making repairs on your car. Even new cars are serviced under warranty with rebuilt parts. MC's don't fail catastrophically, you know when they going before your brakes fail to work so there is no liability issue there.

I have never seen any parts warranty that was anything other than coverage of the part since they have no control over the installation. The only parts an labor warranties are issued by the organization installing the parts where they have some level of control over the installation.

FWIW, being that brake work is one of the least complicated repair activities you can perform on a vehicle this work will typically be given to the less experienced techs in a garage if you take it some where to be worked on. I know when I started working part time in service stations in high school I got oil changes, tire changes and brake jobs. Wasn't until I had proven myself that I was given more complicate work that required diagnostics.
 
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