Master cylinder for c8a
 

Hello

Some years ago I had start the rebuilding of an HUP (coming from the museum in DIEPPE). I stoped the work because I was not enable to find a master cylinder. Recently one of my friend found a new master cylinder whose external sizes seem the same as the original part.

After the dismounting of the part ,I saw that the bore was 25 mm and not 1'1/4
so my question is about the efficience of such part. These one has been builded in ARGENTINA.

Thanks for any comments

The result will be long pedal travel (maybe too much, even when well adjusted) but good pressure.

Master cylinder
 

I have seen on of these G506 cylinders used but you need to delete
the original mounting bracket.

https://www.chevsofthe40s.com/detail...2dOcbBkI5LEy68

I can't find it right away bit there is at least one post (with photo) of a bracket made by Barry Churcher that fit between the original mount and a master cylinder similar to that mentioned by GJamo.
If you can find an original (even one that is pitted so that it is unusable) consider getting it sleeved with either stainless steel or brass. Many people have reported success (only a few report leakage between the sleeve and the original metal).


On edit, this http://www.mapleleafup.net/forums/sh...ghlight=master is not the thread I was thinking of but is another approach Barry has used...

If the external dimensions of the new master cylinder are ok, could you not get a machine shop to bore it out to 1-1/4 and install a rebuild kit?



At work, I made an adapter and installed a Ford master cylinder in place of the chev in a couple of instances.

Bonjour Serge,

As you noted the master cylinder you have has a smaller bore than the one normally fitted to the C8A. Thus, for the same amount of brake pedal pressure, a higher pressure will build up in the brake system. I think with a cylinder of 1" diameter you risk locking up the brakes when applying normal brake pedal pressure. I would say it would be better to fit a brake cylinder with the correct diameter of 1.25"

See the thread Replacement Chevrolet master cylinder for the thread Grant referred to.

Without measuring the cylinder, my concern about overboring the master cylinder would be the small passage vertically into the fluid reservoir. Most masters I've seen have a larger diameter dimple cast in the base of the fluid reservoir and then a smaller hole drilled into the cylinder. If the overbore extended the working cylinder into the larger part of the hole to the reservoir, would the larger hole risk damaging the rubber cup? You might also need to redo the clip-in cap at the pushrod end of the cylinder depending on how much material remains for it to seat against. I'm not saying it can't be done, just things to check....

Argentine master
 

Well i bought one of those Argentine master cylinders and put it on my C60L during restoration. Bled the brakes and everything worked fine or so I thought. Once the rest was put together and had the power booster on and actually used them, after a couple of brake applications the brakes went mushy. So bleed each wheel, remove drums to make sure no leaks etc. Damned if it wasnt the master cylinder. worst machining I've ever seen in a new part and dangerous the day it was put in a box.
The casting had a tapped and threaded hole near the base, it actually entered into the side wall of the cylinder. as you activated the brake the seal passed over this hole and cut off moon shaped slices off of the seal resulting in total loss of brake pressure. upon further inspection nothing was right about the machining, off centre. If you can't get the original resleeved try a later side mount with a fabricated bracket.

There are options in the wheel cylinders as well. I don't know what bore size is fitted to the truck, but aside from the 1 1/2" bore, there were also 1 3/8" bore wheel cylinders. I imagine the small bore master cylinder matches up with the small bore wheel cylinders in the small truck. I know the large trucks also had vacuum boosters which is another consideration.

Hanno, I believe you have the pressure thing the wrong way around.
Harry, may I suggest that if the master cyl. was bled carefully the cup should never travel that far down the bore. Not to offend, just that the m/cyl should be bled first off the vehicle, and then with short pedal strokes until the air is gone.
I believe this is a std practice these days, otherwise all the internals get hammered.
The seal that goes at the end of the bore, should be pushed down the hole straight until the end and then tipped over past the hole.

Serge is working on a C8A HUP, so the standard heavier CMP approach of "all wheel cylinders are Ford parts" doesn't apply, the rear brake set-up on the C8A is Chevrolet including the wheel cylinders. I'm quite sure Rob Clarke found suitable rear wheel cylinders "off the shelf" at one of the Chevrolet restoration parts sellers.

Master cylinder for c8a
 

Hello every one

First I thank you for all answers you wrote to help me for the resolution of the problem. The lack of these part was the reason why I had stop the work of restoration. With the new master cylindrer that I believed to be a good part I have restarted the job and even put off the cab from the frame.

Due to the small thickness of the pressure pipe, overboring the master cylinder would modify the small passage vertically into the fluid reservoir leading to a malfubction of the brake.

What ever the solution I have to change the bracket and build an other vertically bracket.
With these new bracket I could use a DODGE WC master cylinder (1' ¼) or the WAGNER MC9220 but these last seems to be no more available but I found Dorman M9220,

https://www.dormanproducts.com/p-29853-m9220.aspx

I have asked for availability

Wagner numbers for front and rear C8A cylinders. This master may be still available and is the same as the WW2 one except it has two transverse holes for mounting bolts instead of the correct two vertical studs. Short of finding or rebuilding the WW2 type this works by making a simple adapter out of angle iron.

At first glance, Summit Racing may have either the Raybestos or Dorman 9220 master cylinders https://www.summitracing.com/parts/AGB-MC9220 Dorman appears cheaper than Raybestos.

Of course Lynn, now corrected.

At least we established it is best to use the original size master and slave cylinders :thup: