VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 How to Replace master cylinder on 38 master deluxe

Ok, discovered cracked rear brake flex line and brake pedal needs to be pumped i order to work.
-I changed rear flex line, front looked good, relatively easy
-had my new master cylinder from chevsofthe40s
-how hard could changing a MC on a 38 master deluxe be?
-mostly everything came apart easily until I got to the pedal linkage!
1. Could not get far left pedal linkage off of shaft though it would almost clear shaft but not enough.
2. I decided to separate upper pedal linkage from lower portion still attached to MC
3. I tried to separate linkage but they would not budge until I removed bolts entirely to separate linkage ands shazzam they popped out.
4. Left lower linkage easily popped off of MC shaft assy.
5. Finally home stretch, so I thought, but now I do not know how to remove pin from shaft to separate lower right pedal linkage
a. Is pin solid and tapered?
b. is pin a roll pin spring loaded, doesn't look hollow?
c. Does pin remove from top to bottom or bottom to top?
d. Should pin be pressed out or should heat and ice be used?
Any advice would be greatly appreciated, I'm stuck and do I re-use pin
Thank you
Mike A

Have you looked in your 1938 Chevrolet Shop Manual?

The pin which holds the pedal shaft into the master cylinder needs to be driven out with a 5/32" pin punch. I just had a look at a spare 1939 master cylinder and pedal assembly, and the pin does seem to have a slight taper towards the bottom, you may need a solid steel backing block to stop the bouncing while driving the pin out. Driving the pin up would be the way out. I think off memory , that I replaced the pin with a piece of 3/16" steel rod , and peening over on both sides.

The spare master cylinder that I just looked at , has the pin rusted away in the center of the hollow pedal shaft.

I have the 1938 Chevrolet shop manual. What page/pages tell you how to remove and replace the master cylinder?

Jack,
Thank you for the advice. I was hopeful it would be that simple. I actually thought there might be a setscrew, but that might not have been common in 1938.
Mike A

Once the pin is removed , you should be able to remove the pivot shaft with a hammer and drift bar. You may find that your shaft is worn , and may need to be built up to remove all slop from the brake and clutch pedals. New bushes are available from the www.fillingstation.com

The pivot shaft is slight undersize to 3/4" , and not reproduced.

Thank you for help, I will continue this weekend, commute kills most of the day so projects have to wait for weekends, holidays or vacation. I will keep you posted.

Ok, picked up,punches to remove steel pin and I'm being optimistic assuming everything will go smooth and simply reassemble. What should I use as a replacement pin?
-are there any better options than steel pin or is that as good as it gets.
-I used to rebuild B737 engine starters and we used roll pins, but they did require a tool to compress them to install.
-I can't be the first person to have recently removed the master cylinder.
-any recommendations on a good extensive service manual for my 38?
Thank you
Mike A

There is no reason why you can't use a roll pin , they can be driven into a slightly undersize hole without a compressing tool. You will have to measure the size of the hole in the master cylinder top and bottom to make sure it is parallel or tapered .
I think off memory the hole was 3/16 in my 1939 master cylinder, but been a few years now.

In most cases modern roll pins are stronger than 193? solid pins so I see no problems in using 1 but as Jack warned check that the hole is NOT tapered.
Tony

Picked up some punches and knocked the pin out easily, however the shaft was a different story. I tried to drive the shaft out but it barely budged. I decided to take MC to an auto machine shop and have the shaft nicely pressed out of the old and nicely pressed into the new.
I will fight other battles.
-I am getting anxious.
-Buying a set of Town & Country horns from a friend in case brakes fail and I can warn people from far away.
Mike A

The job might have not been big, but the upside is I found an old school machine shop. The owner gent, Mike, I spoke to of Loyd's Engineering in Oakley was awesome. Mike said he rebuilt many 235's so I know were to go if I need any machine work.
-The shop removed shaft from old MC and installed on new along with installing a roll pin versus a solid pin.
-Next I will install and bleed system.
-I can't wait to get her on the road again.
Mike A

Still working on the Master cylinder, but making progress. I decided to clean and paint everything including hardware, linkage, chain, springs and finally pedal assys. The 38 is coming along. Paint is drying so I should be installing this Monday. I can't wait to get her back on the road.

Excellent Mike , always good to tackle those little extra jobs while you are working in that area.

Thank you Jack. I visited Perth and Freemantle in the mid 80s while stationed aboard the USS Midway. Nice places, nice folks.
Mike A

Loved San Francisco when I was there 4 years ago.

Mike,

There's a brake supplier that you may want to know about that is very close to you. It's Chuck's Brake and Wheel in Santa Rosa (Sonoma County). They've been there for decades and have stuff that would really surprise most people, like wheel cylinder cups so you don't have to buy a whole "Kit" to get the inexpensive parts you need to rebuild wheel cylinders.

They can also still get asbestos friction that has vastly better grip than the so called "organic" friction that has been required since about 1980.

They can also still arc-grind brake shoes, an extinct service in California due to environmental regulations.

Thank you for the tip, Santa Rosa is about 80 miles away. I will keep that in mind when ready.
Mike A

While we are on the subject of the brake MC....I just finished replacing the brake fluid in my '38 MD, tested it and found that the brake light switch is not working...

I went ahead and replaced it, wasn't hard to do, but was surprised that little fluid came out, as I expected a lot more to come out. Wondering if I have to start the bleeding process again?

It is nice that the new silicone fluid is purple, easy to see when you've gotten the old stuff out.

If you changed to silicone fluid from dot3 I would recommend flushing it with alcohol to get it clean and all the old fluid out. They don't mix or work together.

Don: The existing fluid in the system is silicone, albeit 20 years old. Saw some dirt come out while flushing.

To start with, I am not an auto mechanic, but do have common sense and don't have to be shown twice. I have an avionics background, but want to do the work on my 38 MD.
-Now that I have my MC installed whats next.
-I was going to fill MC and start bleeding.
-The previous owner did the brakes, but did not change MC.
Thanks for the patience and help.
Mike A

Mike,

Were the linings arc ground? You can tell by looking to see if the linings are making full contact with the drums.

Silicone brake fluid makes "microbubbles" when it's first poured in, yielding a soft pedal. That leads some to claim that it's coppressible. They probably slept through the physics class when we learned that liquids are not compressible.

If you post your email address I'll describe the method that works for me in getting a hard pedal with silicone brake fluid. No, I don't put a blue pill in the MC.

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I would appreciate a copy of your advice too, please. Can PM me.

I have the rear end raised on my '38, and the brake lines' highest point would be back there somewhere, hoping any air bubbles will migrate to it and then bleed them again.

Thanks-

Green427,

I can figure out anything on a car or other mechanical device but computers have always been a mystery to me. How do I send you a PM? Do I click Email Post?

I have Dot 5 brake fluid in both my restored '36 Chevy and my '32 Ford roadster street rod and both have a hard pedal. I'd be glad to send you a description of the bleeding method that worked out for me.