4-wheel disc brake booster

[streetdemon]

I am in the process of converting my 1950 Plymouth coupe over to 4 wheel disc brakes. I have the Scarebird kit up front and a 8.8 with discs in the back.

 

I want to use the ECI master cylinder mount under the floor because it uses the factory pedals and mounts in the factory location. 

 

Who has used this bracket without power brakes with 4-wheel disc brakes and what master cylinder did you use?

 

Can you use a manual master cylinder with disc brakes or does it have to have a power booster.

 

Thanks,

Brad

[Doug&Deb]

I have a scarebird kit on my Coronet with the original mc. No problem so far.

[Sniper]

39 minutes ago, Doug&Deb said:

I have a scarebird kit on my Coronet with the original mc. No problem so far.

That's just front discs, right?

[Doug&Deb]

Yes. Quick easy fix for an out of round drum.

[Sniper]

I think the OP is going all wheel discs.

 

IIRC, ECI gives you the option of a disc/drum master or a disc/disc master.  Other than that I cannot help though ECI might have some ideas.

[streetdemon]

Eci said they don’t offer a disc/disc setup, only a disc/drum. Hmmm I wonder if I could get the bracket and rework it to make it fit a full disc brake master cylinder…It’s kind of a pricey experiment though!

[DJ194950]

Do some online searches as to what size of master cylinder bore to use depends on pedal ratios for power like (long stroke) vs  heavier pedal ( short stoke pedal)  required to stop. What residual valves needed etc.

 

Too  many possibilities for me to get into even if I had all the knowledge!  I do read a lot but_ _ It Is out there for you to research.

 

DJ

[Sniper]

1 hour ago, streetdemon said:

Eci said they don’t offer a disc/disc setup, only a disc/drum. Hmmm I wonder if I could get the bracket and rework it to make it fit a full disc brake master cylinder…It’s kind of a pricey experiment though!

 

Well, ECI says, on the website

 

"These dual master cylinder conversion brackets use the stock brake (and clutch) pedal and are a direct bolt in to the factory master cylinder bracket. They will accept the EC-445 and EC-446 master cylinders and come complete with a new master cylinder and attaching hardware.

 

If you look up the two master cylinders listed as available you will see EC-446 is listed as a four wheel disc master cylinder.  So I dunno what's going on here.  But that master is readily available, new, from any number of sources, for cheap too.

[Racer-X-]

I was going to suggest 1970 (ish) Corvette as a possible application with 4 wheel discs and manual brakes. The 1" bore master cylinder for manual brakes, and it may be enough for your setup, depending on the piston size of your calipers. The 1.25" bore version might be a better choice, but I'm less certain it will fit your bracketry.

 

The Corvettes with manual brakes had the 1" bore master cylinder and single 1-7/8" front pistons and single 1-3/8" rear pistons. If you use that, you'll have to be selective with calipers, especially at the rear. 

 

That's likely your issue with that master cylinder and the Ford 8.8" rear axle. I think the Ford Explorer rear calipers are around 1-7/8" piston diameter (possibly 48mm, as I think they are Metric), and will be a little too large for the Corvette manual Master cylinder. The Crown Victoria rear calipers are even bigger, around 2".   The smallest caliper you find for that axle is probably the 1994-2004 Rustang calipers. Those are 1.5" pistons, I think, and might work with the Corvette manual MC without running out of pedal travel on the rear circuit. 

 

Your front calipers with the Scarebird kit are about 2.5" pistons, and those are also a bit big for the Corvette manual MC.  I'm not sure how they are for the other MC (supposed to be for disc/drum brakes).

 

I'm not sure if the Corvette 1.25" master cylinder will fit that bracket you have, but if it does, that would be a better choice. That master cylinder in the Corvettes was used with 2 piston front on both ends of the car.  Two 1" pistons in the rear caliper and two 2" pistons  in the front caliper.  You should have no problems with that and the GM front calipers and the 1994-2004 Rustang rear calipers. 

 

Also, be sure to include a 2PSI residual pressure valve in both the front and rear lines with that master cylinder. You'll definitely need that.

[Sniper]

One thing you have to do with any rear caliper that uses the caliper itself as a parking brake, you must have a functional parking brake setup AND you must use it, that;s how the caliper adjusts for pad wear.

 

As for master cylinder bore sizing, the larger the bore the shorter the needed stroke but the more leg muscle you need.  The smaller the bore the longer the stroke needs to be but it's easier on the leg.  At some point your leg isn't strong enough.  When I converted my 6 Cuda to front discs I put a 1.125" bore master cylinder in there, manual setup, too big.  I ended up with a 15/16" one and that works real nice. 

 

Now Wilwood makes a bunch of disc/disc masters that fit where the Vette M/C would go and vary in bore sizing, but they are expensive for guessing.  Maybe a call to them can get you setup.

[vintage6t]

I bought a 1-1/8" bore manual/power master cylinder from Speedway. Part # 910-31440.  I plan to use this on my 50 Desoto 4 wheel disc conversion also with 8.8 disc rear. I'm going to use it with a power brake booster and custom made under floor bracket/original brake pedal. This is still in the fabrication stage so I can't tell you if it will work or not but looks good on paper!

[streetdemon]

Thanks for all the useful information. I have built many cars but this is is my first go at converting a car to 4wheel discs without a full kit or at least a list to go by.

 

It didn’t even cross my mind to check with Wilwood, I’ll have to check them out.

[Racer-X-]

When/if you call Wilwood for a recommendation, they'll need some information including:

• Piston diameter and piston count of front calipers
• Piston diameter and piston count of rear calipers
• Overall pedal ratio (this includes both the pedal linkage itself and any lever or bellcrank between the pedal connection and the master cylinder piston)
• Total stroke of the master cylinder piston from top of pedal travel to bottom of pedal travel.

If you have that information ready, they'll be able to help you out much more.

 

As @Sniper pointed out, too big a master cylinder bore and the pedal gets too hard to push and you can't get full braking (lockup) with your leg strength.

 

Too small of a master cylinder will result in running out of pedal travel before you get to full braking (lockup), although the pedal will be much easier to push.

[James_Douglas]

I did a 4 wheel disc on the '49 Desoto. I am using the stock mater cylinder with a remote fill. I also am using a midland-ross remote power brake booster mounted in the trunk next to the spare tire. (see my old threads).

 

I works almost too good!

 

You may want to try it without a power assist first to see how it feels.

 

One thing to note and it is important. The rear axle shafts are tapered. You MUST take the axle shaft and the hub you want to use and take it to a serious machine shop. Put the hub on the shaft and torque it down. Then have the shop turn the face of the hub so that it is perfectly perpendicular to the center line of the axle shaft. Like 0.001".

 

Then engrave the axle and hub as a matched set.

 

If you do not do the above, the disc when mounted to the hub will very likely be out and you will get pulsing. A couple of the makers of conversion kits do NOT make a rear conversion kit for these tapered axles as they told me that got too many call backs with pulsing issues.

 

If you do ask I said, it will be smooth as silk on application.

 

Best, James

[nonstop]

I have no experience with rear discs (converted to Bendix self adjusting style) but I used the ECI master cylinder mount with an adapter and brake booster. I was very happy with the quality of the kit.  I might have missed it, but I would recommend a Wilwood combination valve.  I have changed out too many leaking combination valves from other brands.