15/16" or 1 1/32" bore master cylinder?

[Gpuller]

Going to order a front disc brake kit from Doc Diff for a '70 Charger.
Car is going to be manual brake, front disc, rear drum.
When it comes to size of master cylinder what is everybody running on a manual system? I'm thinking 15/16" bore.
Any input from anyone running similar setups would be appreciated.

Thanks!

 

[lewtot184]

i've found a 15/16" works a little better than 1 1/32".

 

[Cranky]

A smaller bore MC usually puts up more PSI for the same pedal (foot) pressure but at the expense of more pedal movement.

 

[Kern Dog]

The smaller bore results in a better feel in my opinion. Dr Diff is pretty helpful with advice though. I've had the guy talk my ear off though, having me wonder if it was a slow day at the office for him!

 

[Cranky]

The smaller bore results in a better feel in my opinion. Dr Diff is pretty helpful with advice though. I've had the guy talk my ear off though, having me wonder if it was a slow day at the office for him!

Or either he has people doing the bulk of the work now a days.....?

 

[Kern Dog]

Maybe....I've had a few guys like him chat my ear off... I must get lucky or something. Dwayne Porter was another one. Very sharp cylinder head guy in Vermont. I called for advice, expecting a quick response. He went into some great detail about a number of options and in the end, didn't try to sell me anything. I was very impressed. Some guys at Mancini racing also took more time to help and explain things. I've dealt with so many busy vendors that it just amazes me when someone shows actual interest and takes time to help.

 

[Cranky]

Man, been years since I talked to Dwayne. IIRC, I think I bought a set of heads from him. The brain is getting cloudy lol. Wes at Mancini (iirc, that's his name), if he's still there was the guy to talk to. Depending on how busy he was, he might seem kinda abrupt but he knows his stuff. 20+ years ago I had a list of people that were good to talk to and also the ones that weren't. Jegs and Summit were hit or miss but the majority of the time it was a miss lol. Don't know how they are now since I do not do much work anymore and haven't ordered parts from them in years...

 

[BigYellaStella]

Jegs tech guys are top notch if you ask me! Lol but I may be unfairly biased.

 

[Rick Carson]

I talked to the guys at GPS Brakes at the show on the weekend, they said deffently run the 15/16 master with manual brakes,if not you better have legs like a bull.

 

[Jeremiah]

My experience with both OEM slider calipers and Wilwood Dynalite calipers was that the 15/16 gives much more brake peddle modulation which equates to a brake pedal with some effective travel where the 1 1/32" gives the pedal a much more firm pedal with less movement. I'd go 15/16" unless you are running really skinny front tires (i.e. 4" wide wheel).

 

[Gpuller]

Thanks for the replies!
I did call and talk to Doc Diff but he was a little hurried. He told me he was trying to make his shipping deadline for the day. He asked if I could call back in an hour.
I understand, gotta get orders out when you have to.
He explained a little about both MC's, said the 15/16's would give more of a power brake feel. Guess that's what I'm after but just wanted to hear what everyone else thought or had experience with. I'll order the 15/16" MC.
Thanks again!

 

[Cranky]

Thanks for the replies!
I did call and talk to Doc Diff but he was a little hurried. He told me he was trying to make his shipping deadline for the day. He asked if I could call back in an hour.
I understand, gotta get orders out when you have to.
He explained a little about both MC's, said the 15/16's would give more of a power brake feel. Guess that's what I'm after but just wanted to hear what everyone else thought or had experience with. I'll order the 15/16" MC.
Thanks again!

Power brakes of today are much better than they were in the 60's as far as being too touchy as the power steering was too. It took 'mom' a good while to figure out that being able to steer and brake using a pinky finger and pinky toe was a bit over the top so when Cass says the 15/16ths MC would give you more of a PB feel, he's not talking about how they were in the 60's lol. Geez, I hated that feel back then but....the PS in my 66 Belvedere did very well with a hand cuff steering wheel!

 

[furyus]

This has come up before, and it really depends on the size of the caliper bore. I had the standard 73 up A body stuff, with a 15/16 bore MC. Worked great like everyone says. But when i went to the larger rotors, and larger calipers, i couldn't get a pedal. I went to the 1 1/32 bore MC. I got my pedal back, went with EBC pads, and smaller rear wheel cylinders. Works great. Not a hard pedal. So, if you have the smaller bore calipers, 15/16 MC is fine, bu you should verify the bore size to be sure. It's all gotta match.

 

[71charger_fan]

I just ordered a Raybestos MC36412 from Amazon. Not sure what the bore size is. I saw the listing on Rockauto listed as front disc/rear drum, manual brakes. Rockauto had no stock, so I ordered from Amazon. I'm piecing together a front disc conversion for my '55 Plymouth wagon using Scarebird adapters, RamMan proportioning valve/distribution block, Chevy S-10 calipers, Ford Probe rotors, and Cadillac hoses.

 

[Cranky]

I just ordered a Raybestos MC36412 from Amazon. Not sure what the bore size is. I saw the listing on Rockauto listed as front disc/rear drum, manual brakes. Rockauto had no stock, so I ordered from Amazon. I'm piecing together a front disc conversion for my '55 Plymouth wagon using Scarebird adapters, RamMan proportioning valve/distribution block, Chevy S-10 calipers, Ford Probe rotors, and Cadillac hoses.

Not sure if all that will work ok together but it's a big package of parts!

 

[cudak888]

This has come up before, and it really depends on the size of the caliper bore. I had the standard 73 up A body stuff, with a 15/16 bore MC. Worked great like everyone says. But when i went to the larger rotors, and larger calipers, i couldn't get a pedal. I went to the 1 1/32 bore MC. I got my pedal back, went with EBC pads, and smaller rear wheel cylinders. Works great. Not a hard pedal. So, if you have the smaller bore calipers, 15/16 MC is fine, bu you should verify the bore size to be sure. It's all gotta match.

Sorry to bump this thread up after being dormant for about a month, but it looks like you've headed down the same path that I'm currently weeding my way through. Just did a conversion from 10" drums all around to 11.75" discs up front (with F/M/J style 2.75" piston calipers; not the earlier pin-slider type) and the Budd 11" brakes - and went for the 15/16" MC based on what most people seem to recommend here on the forum.

Today was the first time I could actually enjoy the car, and I can tell you right now: My brakes are sponge city. It stops, but will practically bottom out if you slam them on, and it feels impossible to lock them up.

That said, it looks like you found yourself in the same predicament - but I've yet to find the part number/model reference for both the master you ultimately chose and the smaller rear wheel cylinders.

Do tell if you get a chance (and if anyone feels as if this is a thread hijack, I have a build thread going here: http://www.forbbodiesonly.com/mopar...-refurb-and-big-fat-engine-swap.96118/page-10)

-Kurt

 

[Billccm]

I too went with Dr Diff's advice and ordered the 15/16 bore master cylinder. I'm almost half way through the conversion and a little concerned about what pedal feel I will get. I've read many people are very happy with the 15/16 bore with manual brakes, and I've been warned by many people that the 15/16 travel is too long. I guess we will see when I get this conversion completed.

Whatever I get, it will be an improvement over what I had with the very bad, almost dangerous manual drums.

I will also add that I did a Wilwood conversion back in 1993 on a 68 Charger, and I do remember some disappointment in that it was an improvement, but not as improved as I expected.

Please report back on your findings with your conversions.

 

[cudak888]

I too went with Dr Diff's advice and ordered the 15/16 bore master cylinder. I'm almost half way through the conversion and a little concerned about what pedal feel I will get. I've read many people are very happy with the 15/16 bore with manual brakes, and I've been warned by many people that the 15/16 travel is too long. I guess we will see when I get this conversion completed.

Whatever I get, it will be an improvement over what I had with the very bad, almost dangerous manual drums.

I will also add that I did a Wilwood conversion back in 1993 on a 68 Charger, and I do remember some disappointment in that it was an improvement, but not as improved as I expected.

Please report back on your findings with your conversions.

From the more specific searching I've been doing, the 15/16" is good enough if you're working with the older 2.6" pin style calipers in a manual disc/drum combo.

If you're running the FMJ 2.75's, general consensus seems to be that you'll get a Spongebob pedal.

And in the present state of my pedal, I'd take those 10" manual drums up front with the stock drum/drum master any day over the feeling I'm getting with 2.75 calipers hooked to a 15/16" master. Ran it with 10's for quite a while, and though the pedal feel did not match that of my '69 Valiant (which has 9" drums all around - and has superb pedal feel and response), it would brake well.

YMMV.

-Kurt

 

[Cranky]

Is the bleeder at the very top of the caliper/cylinder? Many times I've seen people with a custom installation or even had the calipers swapped to the wrong side. Even with a small MC bore, you should still be able to get a hard pedal even though you might end up with more travel. Spongy brakes is a clear sign of air getting in the system.....

 

[cudak888]

Is the bleeder at the very top of the caliper/cylinder? Many times I've seen people with a custom installation or even had the calipers swapped to the wrong side. Even with a small MC bore, you should still be able to get a hard pedal even though you might end up with more travel. Spongy brakes is a clear sign of air getting in the system.....

MC was bench bled, caliper bleeders are facing to the top rear, and the whole system has been bled with DOT3 from the rear right to the front left - and bled extensively.

Can say with certainty that there is no air in the system - went overkill on every bleeder to ensure no air was coming out.

It's spongy in the sense that there's no firmness to the brake application. It's not like there's a spring (air) bridging two independent tubes of hydraulic fluid.

It feels like I'm pushing fluid without issue, but not enough of it to fill the caliper piston bores.

-Kurt