Master cylinder bore size

[Tirekickertoo]

Hello all, On my 70 Challenger I am changing the front drum brakes to 1973? Challenger "Kelsey-Haynes" single piston pin style disc brakes. The car originally had manual brakes and I would like to keep it that way. To do this swap I will also need to change the master cylinder. In an old article from Mopar Action, Richard Ehrenberg explains that with a smaller master cylinder diameter (bore), the less brake pedal pressure is required to stop. These cars typically had a 1 1/8 master cylinder bore. Is anyone using a smaller bore master cylinder. I want a direct fit disc brake front drum brake rear master cylinder without any modifications. Please reply with manufactures names, part numbers, and where to buy.

I'd appreciate the help.

Thank you,
Tirekickertoo

 

[Daves69]

I use the '74 Dart MC on my '69. Manual disc front / drum rear.
similar..............
More Information for RAYBESTOS MC36412

 

[Tirekickertoo]

I use the '74 Dart MC on my '69. Manual disc front / drum rear.
similar..............
More Information for RAYBESTOS MC36412

Thanks Daves69 for the reply and MC info. Question for you; How does your brake pedal feel when stopping for a light at 65mph? Do you have to stand on the brake pedal and hope for the best, or have you seen an improvement with the master cylinder you are now using?

Thanks,
Tirekickertoo

 

[Daves69]

Certainly not as responsive as power disc. I'll tell you they are stiff compared to my old standard drum fronts but it stops quicker.

 

[Tirekickertoo]

Certainly not as responsive as power disc. I'll tell you they are stiff compared to my old standard drum fronts but it stops quicker.

Thanks Daves69, I'll give it a try. In the future I may try power disc when I hunt down all the components to make that work. I believe power disc needs a completely different master cylinder to run that system. I've also read guys having issues with not enough vacuum (depending on their engine build) to make the brake booster work. What can you tell me?

Thank you,
Tirekickertoo

 

[bc3j]

I use a 1" bore from master power brakes with the '78 Córdoba rotors. My system is manual and it works good. Pedal ratio is important with a manual system. Also have a 15/16" MC to try. Don't have that one installed yet. Master Cylinder (Mopar Style, 1" bore, LH ports, Deep Piston Hole) - p/n: MC11571P/M

 

[Tirekickertoo]

I use a 1" bore from master power brakes with the '78 Córdoba rotors. My system is manual and it works good. Pedal ratio is important with a manual system. Also have a 15/16" MC to try. Don't have that one installed yet. Master Cylinder (Mopar Style, 1" bore, LH ports, Deep Piston Hole) - p/n: MC11571P/M

Thanks bc3j, Was this MC a direct fit? About how much brake pedal travel do you have? In his Mopar Action article, Ehrenberg said the smaller the MC bore the more travel you would have. Just curious how close your brake pedal comes to the floor boards!

Thank you,
Tirekickertoo

 

[Daves69]

If you get to the point your build won't provide enough vacuum for power brakes, I think an electric pump might be the fix.

 

[Tirekickertoo]

If you get to the point your build won't provide enough vacuum for power brakes, I think an electric pump might be the fix.

Daves69, You're right. I've also read guys using what I think is called a "Hydrovac". You tap into your power steering pump and use the (oil) hydraulics to assist a special type of brake booster. These units were designed for heavy equipment applications. I haven't read that much about it yet.

Thank you,
Tirekickertoo

 

[bc3j]

Thanks bc3j, Was this MC a direct fit? About how much brake pedal travel do you have? In his Mopar Action article, Ehrenberg said the smaller the MC bore the more travel you would have. Just curious how close your brake pedal comes to the floor boards!

Thank you,
Tirekickertoo

The car is an auto. My brake pedal is stock and is 7" off the floor. Currently with the 1" bore & my travel is 3". I'm going to experiment with the 15/16" bore for more line pressure. A software program I have indicates a 13% increase in line pressure. Right Stuff, the 15/16" MC, told me to expect an additional 1 to 1 1/2" travel. The car is in storage now and I'll install the 15/16" cylinder when I get it back. Of all things, got 4" of snow last night. Go figure.

My MC was a direct bolt up. It has a deep end to accept a manual brake pushrod. It was an easy install. FWIW my stock brake pedal is 6.5:1 pedal ratio.

I also used the Ehrenberg article as a model.

 

[Tirekickertoo]

The car is an auto. My brake pedal is stock and is 7" off the floor. Currently with the 1" bore & my travel is 3". I'm going to experiment with the 15/16" bore for more line pressure. A software program I have indicates a 13% increase in line pressure. Right Stuff, the 15/16" MC, told me to expect an additional 1 to 1 1/2" travel. The car is in storage now and I'll install the 15/16" cylinder when I get it back. Of all things, got 4" of snow last night. Go figure.

My MC was a direct bolt up. It has a deep end to accept a manual brake pushrod. It was an easy install. FWIW my stock brake pedal is 6.5:1 pedal ratio.

I also used the Ehrenberg article as a model.

Thanks bc3j, My car is also an automatic. After getting quality feedback from you and other E body enthusiast's (not to mention reading similar threads from A and B body forums), I want to try the 15/16" bore MC and 7/8" cylinders for my rear drum brakes. I will also install a manual adjusting proportioning valve for the rear brakes. The 3" brake pedal travel you are experiencing, I would assume it is from the smaller bore size MC we've been talking about. Just wondering if your brake pedal pin that connects to the MC is the correct length? Other forums have mentioned adjustable pins in this situation. Your setup is most likely correct. Just thought I'd ask.

Thank you,
Tirekickertoo

 

[bc3j]

Thanks bc3j, My car is also an automatic. After getting quality feedback from you and other E body enthusiast's (not to mention reading similar threads from A and B body forums), I want to try the 15/16" bore MC and 7/8" cylinders for my rear drum brakes. I will also install a manual adjusting proportioning valve for the rear brakes. The 3" brake pedal travel you are experiencing, I would assume it is from the smaller bore size MC we've been talking about. Just wondering if your brake pedal pin that connects to the MC is the correct length? Other forums have mentioned adjustable pins in this situation. Your setup is most likely correct. Just thought I'd ask.

Thank you,
Tirekickertoo

My pushrod is stock. I like the 3" travel as it gives me excellent feedback as I brake. My rear wheel cylinders are 13/16" from a 90s Dakota. I do not use a proportioning valve and have the stock tee and use the smaller wheel cylinders for proportioning. I do not experience rear wheel lock up. The pedal travel and brake "feel" is pretty much a personal thing.

I have an adjustable pin and will probably install it just to lower the height of the pedal to get it closer to the accelerator pedal level. The travel should remain the same.

 

[Tirekickertoo]

My pushrod is stock. I like the 3" travel as it gives me excellent feedback as I brake. My rear wheel cylinders are 13/16" from a 90s Dakota. I do not use a proportioning valve and have the stock tee and use the smaller wheel cylinders for proportioning. I do not experience rear wheel lock up. The pedal travel and brake "feel" is pretty much a personal thing.

I have an adjustable pin and will probably install it just to lower the height of the pedal to get it closer to the accelerator pedal level. The travel should remain the same.

Thanks bc3j, "Someday" when spring arrives, I will install the parts and do a test drive. I see your point about the brake pedal travel and feel being a personal thing. I'm sure there will be more changes and/or modifications for me to make. Can you share part numbers and vendors for the 13/16" wheel cylinders and adjustable pushrod? Wheel cylinders are cheap from RockAuto!

Thank you,
Tirekickertoo

 

[bc3j]

Summit Racing is local for me so I do local pickup. The adjustable pushrod is from Summit and is #P4510640. There are other vendors that carry adjustable pushrods. The wheel cylinders are from RockAuto for a '90 Dakota with 10" rear brakes, Dorman WC37696. The bolts holding the cylinder to the backing plate are different threads than the stock ones. I just went to a local hardware store with the cylinder a got ones the same length as stock, but I believe they were metric. Don't remember what I bought, sorry. They will bolt right up, but need the right bolts.

 

[Tirekickertoo]

Summit Racing is local for me so I do local pickup. The adjustable pushrod is from Summit and is #P4510640. There are other vendors that carry adjustable pushrods. The wheel cylinders are from RockAuto for a '90 Dakota with 10" rear brakes, Dorman WC37696. The bolts holding the cylinder to the backing plate are different threads than the stock ones. I just went to a local hardware store with the cylinder a got ones the same length as stock, but I believe they were metric. Don't remember what I bought, sorry. They will bolt right up, but need the right bolts.

Thanks for all the information and part numbers bc3j. Waiting for the weather to warm up and all the salt washed off the roads so I can get to work!

Tirekickertoo

 

[js29]

What part of upstate New York are you in? I am in northern Oneida county.

 

[Tirekickertoo]

What part of upstate New York are you in? I am in northern Oneida county.

Hi js29, I'm near Rochester, NY. This June check out Mopar Madness at Longbranch Park Syracuse, NY. An all Mopar show Sunday June 26 2016. Great show to attend.

 

[js29]

Wanted to go last year, it got rained out.

 

[Tirekickertoo]

Wanted to go last year, it got rained out.

It's a great show (weather permitting). I went the year before last and it was a perfect day. Saw Plymouth and Dodge models I thought I'd never see in person.

 

[bc3j]

The 15/16" MC is installed. Surprisingly, almost no additional pedal travel. So far, I'm happy with the results. Side note, the DBMC15 MC from Right Stuff has no residual pressure valve for the rear wheels. No issues using the modern wheels cylinders with the expanders.