Help with sizing brake Master Cylinder

[SavageBurro]

Hey all,

Very sorry if there has already been recommendations on this. I did some searching and found some good suggestions but am wondering if someone has tried a proven recipe. Looking to see if someone can recommend a specific master cylinder.

(good article I found: https://classicbroncos.com/forums/threads/1-ton-axle-master-cylinder-advice.236900/)

What I have and am going to: Have: Standard size 8" bronco vac booster w 1" bore mc designed for bronco front disc/bronco drum rear; Going to: 2006 F250 d60 dual piston stock calipers/disc front. Rear 14 bolt w Lugnut4x4 rear disc conversion using standard front gm 12.5 rotors and 76-78 Eldorado ebrake calipers.

For fear of not wanting to rob from my ps flow for my ram assist - I do not want to go hydroboost at this time. (maybe some day in future because hb is awesome).

So... if there is a recommendation for a specific master cylinder that someone has that would be appreciated. Also, not sure if the 8" booster is going to be an issue. Pretty sure my mc is not going to pump enough volume.

thnx!

 

[Apogee]

You are correct that your Ø1" bore MC will not push enough fluid to actuate the brakes properly, as you're increasing the effective caliper piston areas significantly with the new brakes. The 2006 Ford F250 front calipers have 8.76 sq inches of effective piston area, a 35% increase over the factory Ford single-piston calipers with Ø2.88 pistons, and the rear 76-78 Eldorado calipers have Ø2.50" pistons with 4.91 sq inches of effective piston area, slightly smaller than the F250's 5.60 sq inches, but close enough that you could size your master cylinder accordingly.

If we look at the factory F250 system for guidance, they came with either a dual-Ø10.89" vacuum booster or hydroboost paired with either Ø1.313" or Ø1.500" bore master cylinders respectively. You're running a booster that has 46% less diaphragm area, but also a rig that's hopefully lighter weight as well (F250 is 5500 to 6500 lb depending on configuration). I would probably start with a Ø1.250" master cylinder (F250 2WD Camper Special) that have been mentioned on here a time or two before and see how it goes. FWIW, each 1/16" if bore size equates to about a 10% difference in terms of volume versus output pressure, with smaller bores pushing less fluid at a higher pressure and large bores the opposite.

If the pedal still has a higher effort than you prefer, you could decrease the bore size accordingly so long as you don't have any pedal travel issues, increase the brake pad CoF or possibly upgrade to a dual-9" booster for added gain/boost.

Tobin

 

[SavageBurro]

You are correct that your Ø1" bore MC will not push enough fluid to actuate the brakes properly, as you're increasing the effective caliper piston areas significantly with the new brakes. The 2006 Ford F250 front calipers have 8.76 sq inches of effective piston area, a 35% increase over the factory Ford single-piston calipers with Ø2.88 pistons, and the rear 76-78 Eldorado calipers have Ø2.50" pistons with 4.91 sq inches of effective piston area, slightly smaller than the F250's 5.60 sq inches, but close enough that you could size your master cylinder accordingly.

If we look at the factory F250 system for guidance, they came with either a dual-Ø10.89" vacuum booster or hydroboost paired with either Ø1.313" or Ø1.500" bore master cylinders respectively. You're running a booster that has 46% less diaphragm area, but also a rig that's hopefully lighter weight as well (F250 is 5500 to 6500 lb depending on configuration). I would probably start with a Ø1.250" master cylinder (F250 2WD Camper Special) that have been mentioned on here a time or two before and see how it goes. FWIW, each 1/16" if bore size equates to about a 10% difference in terms of volume versus output pressure, with smaller bores pushing less fluid at a higher pressure and large bores the opposite.

If the pedal still has a higher effort than you prefer, you could decrease the bore size accordingly so long as you don't have any pedal travel issues, increase the brake pad CoF or possibly upgrade to a dual-9" booster for added gain/boost.

Tobin

Thank you. Very helpful! Since I'm going to spending money on upgraded booster anyway...I decided it's time to also make the hydroboost work. Plan to send to vanco to have it hiflowed....to hopefully help ram assist steering. My hb unit came from 2013 ram 2500 that has extra tall mc reservoir...so plan is to either locate low profile reservoir that fits the 2013 ram mc.... or find mc w low profile res that will bolt to the hb... since that connection is angled...I might end up having to add an adapter to rotate.

Thx again.

 

[SavageBurro]

Pic of 2013 ram hydroboost

 

[toddz69]

I think you'll have the best luck with ditching that angled mount and making/purchasing a 90 deg adapter between the booster and the master cylinder of your choice, and the proper length pushrod between the booster and the master. That's what many of us have done with great results - it allows you easier access to all the ports on the booster, the accumulator clears the valve covers/intake (if you have EFI), and opens up a lot of options for a master cylinder. I doubt the one in the pic (along with that hose bracket) will fit under the Bronco hood.

I don't know how it will work with the caliper bores/volumes you have on your rig, but I recently switched to a 1.25" Dodge master cylinder ('98 Ram 1500 is the application) and I love the pedal feel/height with it. I ran a 1.125" bore Dodge master cylinder for 20+ years before that.

Todd Z.

 

[SavageBurro]

I think you'll have the best luck with ditching that angled mount and making/purchasing a 90 deg adapter between the booster and the master cylinder of your choice, and the proper length pushrod between the booster and the master. That's what many of us have done with great results - it allows you easier access to all the ports on the booster, the accumulator clears the valve covers/intake (if you have EFI), and opens up a lot of options for a master cylinder. I doubt the one in the pic (along with that hose bracket) will fit under the Bronco hood.

I don't know how it will work with the caliper bores/volumes you have on your rig, but I recently switched to a 1.25" Dodge master cylinder ('98 Ram 1500 is the application) and I love the pedal feel/height with it. I ran a 1.125" bore Dodge master cylinder for 20+ years before that.

Todd Z.

Thanks again Todd!

100% that will not fit as is...reservoir too tall and hard lines w bracket holding those lines are way too tall. Thx for suggestion on dodge mc. The one on the hb is 1.313 bore. Trying to find a low profile reservoir for it w not much luck...just to try it.

Last hb setup I put together used a 78 camaro disc disc mc.. it worked awesome w 96 f250 brakes fr rr.

The booster and mc in bronco rt now is mounted to angled bracket kit from toms. I haven't looked yet to see if I can make that work.

 

[Apogee]

Everything above the bore is low pressure, so you could fabricate/machine a reservoir solution similar to many of the current Wilwood and Tilton remote reservoir options...depending on the diameters, they may even have something that would work. If/when you remove the reservoir from the master cylinder, post up the tube diameters where the slip into the MC for reference.

 

[SavageBurro]

Everything above the bore is low pressure, so you could fabricate/machine a reservoir solution similar to many of the current Wilwood and Tilton remote reservoir options...depending on the diameters, they may even have something that would work. If/when you remove the reservoir from the master cylinder, post up the tube diameters where the slip into the MC for reference.

Thanks for the great tip!! I did not know about those.

 

[79INA69]

Thanks for the great tip!! I did not know about those.

FWIW, I currently have a compromise combo working safely. I have a dual 9" booster from a c5 corvette (rock auto) and a master cylinder with a 1.063 bore from a doge application with screw on caps (looks just like the black plastic Strange units). Front is 2 piston 8 lug D44 calipers (possibly same as old D60) and the RS 77 eldo calipers that have 2.49 single piston. I have the angled 45 bracket currently. I put a pressure guage at each wheel and only had 4-500psi on medium apply and spiking only to 900psi with a 1.25" bore master. Originally had a 1.125 on there with the 1/2 ton brakes. Went one step smaller with the aluminum body master and now have 8-900- on medium apply and spikes to 1200psi. 1500psi spike would be ideal, but it feels safe to drive now. The angled bracket drops the leverage ratio down to 4:1 range. Bronco brakes are tricky for sure, which is why HB is so popular. I just see all these Tj and Jk builds with one tons and stock booster/master which is a 9-10 dual booster with a 1"master

 

[SavageBurro]

Everything above the bore is low pressure, so you could fabricate/machine a reservoir solution similar to many of the current Wilwood and Tilton remote reservoir options...depending on the diameters, they may even have something that would work. If/when you remove the reservoir from the master cylinder, post up the tube diameters where the slip into the MC for reference.

Finally pulled things apart. Tube diameters are 14 mm

 

[Yeller]

I know I’m late to the discussion. I’m running the 9” c5 booster and 1-1/4” bore master for an 85 K30 GM truck. I’d love to find a plastic resevior master but have yet to find one that is short enough, needs to be less than 4-1/4” from the center of the bore to the top of the reservoir. However the truck stops spectacularly. You will not want anything smaller than 1-1/4” bore. With hydroboost the dodge unit you have will probably be just about perfect, want a little less pedal pressure you could always drop down to 1-1/4”.

 

[SavageBurro]

I know I’m late to the discussion. I’m running the 9” c5 booster and 1-1/4” bore master for an 85 K30 GM truck. I’d love to find a plastic resevior master but have yet to find one that is short enough, needs to be less than 4-1/4” from the center of the bore to the top of the reservoir. However the truck stops spectacularly. You will not want anything smaller than 1-1/4” bore. With hydroboost the dodge unit you have will probably be just about perfect, want a little less pedal pressure you could always drop down to 1-1/4”.

Thx Yeller! I've been half ass interweb searching for a low profile compatible reservoir to go on that 2013 ram mc but haven't found one yet. Might try the remote res. Having a bit of a hard time confirming what will fit w those as well.

If I go to different mc...I'm not sure what adapter is needed between booster and mc. Nothing is obviously compatible.

Maybe all the above are reasons I haven't seen much for folks swapping to mopar brake parts.

 

[Yeller]

I have both here, if I can get a chance and then remember I’ll measure, I bet they are the same. See if I can confirm.

 

[toddz69]

I know I’m late to the discussion. I’m running the 9” c5 booster and 1-1/4” bore master for an 85 K30 GM truck. I’d love to find a plastic resevior master but have yet to find one that is short enough, needs to be less than 4-1/4” from the center of the bore to the top of the reservoir. However the truck stops spectacularly. You will not want anything smaller than 1-1/4” bore. With hydroboost the dodge unit you have will probably be just about perfect, want a little less pedal pressure you could always drop down to 1-1/4”.

I thought I might have a winner for you in the height department but I checked mine last night and it's over 5" tall in the dimension you're looking at.

Todd Z.

 

[Yeller]

I thought I might have a winner for you in the height department but I checked mine last night and it's over 5" tall in the dimension you're looking at.

Todd Z.

Thanks Todd. Brian measured his for me yesterday. At the moment my cover isn't leaking, but I'm afraid to open the lid, it might. I need to replace my front brake hoses and will have to crawl down that hole sooner or later. If I didn't have 10# of stuff in a 2# box it would be easy LOL. Nowhere to move the master to other than under the dash...... no heater so there is some room under there only other option is to go to a 3-1/2" spring and redo the framework for the coil mount and chassis support. can't lower the spring mount on the axle housing, the spring is over the top of the king pin. besides I like the roll center this provides

as low as the top of this master is, it still rubs the hood some, there is dimple in the hood from the bail on the lid.

 

[sprdv1]

Hey all,

Very sorry if there has already been recommendations on this. I did some searching and found some good suggestions but am wondering if someone has tried a proven recipe. Looking to see if someone can recommend a specific master cylinder.

No need to worry about all that.. Anytime in doubt that's why this site is the best. Ask and ye shall receive all the wisdom

 

[sprdv1]

Thanks Todd. Brian measured his for me yesterday. At the moment my cover isn't leaking, but I'm afraid to open the lid, it might. I need to replace my front brake hoses and will have to crawl down that hole sooner or later. If I didn't have 10# of stuff in a 2# box it would be easy LOL. Nowhere to move the master to other than under the dash...... no heater so there is some room under there only other option is to go to a 3-1/2" spring and redo the framework for the coil mount and chassis support. can't lower the spring mount on the axle housing, the spring is over the top of the king pin. besides I like the roll center this provides

as low as the top of this master is, it still rubs the hood some, there is dimple in the hood from the bail on the lid.

View attachment 900089

Gives a great example though

 

[nvrstuk]

I've just been reading and not writing but I will add in case it helps.

1.25" bore min for that setup but pedal pressure "feel" will be your determining factor I think for comfort.

Like Steve was saying, mc height is critical in some builds. I am now running a Chev, alum bodied, plastic lid 1.25" bore with D60 J6 pistons in the front and a 14 bolt rear with JD6 pistons also. I swapped because of the leaky cap and rust from the 1.3"dia mc which worked excellent and great pedal feel. And kudo's to Steve 6 yrs ago it fixed all my volume issues back then. Only way to keep the cap from leaking was to run radiator clamps around it. 2 new caps, 3 new gaskets... radiator clamps fixed it LOL

 

[SavageBurro]

Again - awesome info. thx guys!

Brian, do you recall which ' Chev, alum bodied, plastic lid 1.25" bore' mc you are using?

Spent my lunch hour at junkyard today for couple reasons:

1. to get a driveshaft. (sorry, off topic) I 'think' a front ds from 2014 Ram 3500 w 6.7 diesel and auto trans should work w my atlas tcase w 1410 flange and gm 14 bolt rear w 1350 yoke. The ram ds has 1410 flange on dbl cardon (tcase) end w correct male/female parts... and the other end has a flange w 1350. Once I remove the flange on axle end- it should be correct length and connect w the 14 bolt rear w the 1350 yoke. might have to shorten it an inch or two. Will see. If it works, I'll get another one and have it shortened for the front ds.

And back to on-topic reason 2 for the jy trip: See if they have a reservoir that will fit the 2013 ram mc hydroboost setup. They did not. But... I picked up a 'spare 2007 F350 hydroboost and mc while I was there. . It uses a 1 1/2" bore mc and there appear to be lots of options for shorter mc reservoir for it. Since the super duty trucks have dual piston brakes front and rear and I only have dual piston in front w single piston in rear.... that 1 1/2 bore might be a tad on large side.

Unfortunately, I already sent my ram hb unit to vanco to get it hi-flowed to help w steering ram.

 

[nvrstuk]

Slow but here ya go!

Chev 3500, 1995