The Stovebolt Site Forums The Shop Area Driveline Master Cylinder swap advice

I will be swapping out the master cylinder on my stock '36 for a front disc conversion that I'll be doing soon. I'm planning to use a GM/Corvette style manual brake disc/drum master cylinder that I hope to adapt into my stock clutch/brake pedal assembly under the floor. I'm using GM D52 single piston calipers. The rear drums will be the stock Huck drums, but this will only be temporary until I install a yet-to-be-determined open drive rear when I do a 235/T5 swap. The new rear will almost certainly be drums as well.

Looking for advice on the following:

-1" or 1 1/8" bore size? (I'm figuring 1" for manual use)
-Do I need a proportioning valve with a disc/drum MC? (I'm assuming yes)
-Do I need a residual valve(s) on either/both front and/or rear?
-Any other advice welcome

Thanks!
Ron

On my truck with 100% factory brakes I used the dual master kit from Jim Carter truck parts. I don’t remember the bore size but i did not use a prop valve or residual valves. Zero issues. The brakes will lock all 4 wheels up at 70mph which is pretty impressive. Thats the master in stock location under floor.

I also just built a ‘41 ford 1 ton with stock master under floor with no residual valves. Zero issues. Brakes are nowhere near as good as the GMC but it has a firm high pedal with all oem sized bores. Its just a ford I guess hahaha.

Others with more experience may add more or even question my experience, but….you might gain something from this….
Per below my points are:
-mixing huck and anything in my view is questionable, the volume differences likely are too great to have a viable system.
-don’t go 1/2 in/part way, don’t accept “ok”, safety systems are either 100% right or not.

The longer story:
My 46 1/2 ton it came to me with huck front/new bendix rear brakes (had a new Currie rear end put behind a T5), pressured by a tired single zone master cylinder with reasonably good condition rubber flex lines.
It was not a good setup, period. Spongy pedal, long travel, needed a strong leg, etc… basically: just say no.

I installed new front huck brake cylinders, springs, FF shoes… nah, still not right… so…

Next I went with a 1” bore corvette style disk/disk mstr, sourced (thanks to stovebolt) and swapped out my front hucks for 54 bendix backing plates, new bendix front wheel cylinders, new springs, new drums (mounted on the 54 hubs and turned), new lug studs, and new tapered roller bearings(old bearings were scored).
Put residual pressure valves 1 front and 1 rear in lines as low and close to master as possible, plus an adjustable proportioning valve on the rear line. Front 2 flex and rear flex changed to DOT stainless braid/teflon lines (ie:no rubber).
What I have is (for me) a solid full bendix braking system, very solid reliable pedal, requires only moderate force, in tested panic stop the rears (prop valve adjusted) only starting to lock up. Pedal travel is right on, no pull on steering even in heavy braking test.
Then I added the front (anti) sway bar, helps a lot in turn/braking situations… but that’s another story…

Chuck

The Huck rear brakes were only going to be temporary until the swap. But as you mention, safety is safety, temporary or not. As it turns out, I'm pretty sure I can put the T5 in behind my stock 207 bellhousing. Need more measurements, but looks like the transmission bolt pattern on my 207 bell housing is the same as the bolt pattern on the 235 bell housing that I have. My T5 adaptor may work for both bell housings. I might just do the T5 and rear end swap right away, and do the 235 swap later. This way I'll also have more modern drums on the back.

I never understood any downsides of huck brakes besides availability. Mine with not much effort locks all 4 wheels up at any driving speed. Impressively good in my opinion.

I have no complaints with Huck Brakes at all. They work as well as any brakes on any of my other Bendix equipped vehicles. I come off exit ramps at 60 mph and don't have to worry if the truck will stop or pull one way or the other.

Looking at the design, you might think that they are superior to Bendix brakes in some ways in that they are attached to the backing plat at the top and the bottom - maybe keeping the shoes aligned with the drums better.

I have no issue with huck brakes either, I do however question mixing them with bendix on the rears…..much as I tried i did not get satisfactory performance on my 46.


Chuck

Yes. When it comes to brakes, the original designers usually know best. I don't make changes to stock brakes on any of my vehicles. I don't know enough to do it right.

There's a trick that round track racers use that might be worth considering. Use two master cylinders applied by one pedal, with a pivoting link connecting them. Front and rear brakes are totally separate- - - -they don't share any components, even metal and flex lines. If necessary, different diameter master cylinder bores can be used to apply wheel cylinders (or calipers) that displace different volumes.
Jerry