The Stovebolt Site Forums The Shop Area The HiPo Shop Opinions needed / Can I keep the original master cyl in my 38 ?

Before I go thru the trouble of finding a kit and rebuilding the original master cylinder on my 38 - 1/2 ton I want to run it past you guys.

Will this m/c do a decent job of running 4 newer drum brakes ?
I kind of want to keep some of the old systems on the truck like this master cylinder and battery under the floor. Though it will be a 12 volt system and automatic trans and probably newer ( 50's or 60's ) straight 6 motor.

Or am I just asking for trouble . . .

I feel that if you are thinking of rebuilding or replacing the master and don't plan on a completely original restoration from top to bottom then the smart thing to do is update to a dual circuit master cylinder.

While it may not be necessary it is a huge safety improvement. If you are questioning if it's a good idea to update take this test:
While driving around on a normal day think to yourself every 3 or 4 minutes, what would I do right now if I had no brakes the next time I stepped on the pedal? If you don't have a good answer every time then you need a dual circuit master cylinder.

Once you have made the dual circuit decision then think about a booster, if you have disc brakes a booster is a must.

Grigg

Not to be flippant here, and not to knock the dual master cylinder brake set-up - the answer to the question Grigg asks, in every case, is hit the emergency brake. That's why it' there. I know they call it a "parking brake" today but it is a mechanical system designed to bring the hurtling beast back to 0mph in a hurry.

Good point about the emergency brake, I was not considering that when I first posted. Mostly because last time I lost brakes was in a 10,000 lb truck without an emergency brake. I was getting off the interstate and was able to down shift and get stopped in a parking lot without incident, but not much fun...

I often tow things, the emergency brake is not as good as 4 wheel brakes, and could still leave you in a pickle.

Some emergency brakes are better than others too.
Think about the time required to realize what is happening and grab or press the emergency brake.

Also consider the other people out there. If you stomped on your brakes to avoid someone else being stupid your brakes could fail right then, and it's to late to think about the emergency brake...

I think that for most everyone there are still several times in a week that my "question" could not be answered with a good emergency brake.

I do think a single circuit brake system kept in good condition can be as reliable as a dual circuit system. On the other hand a dual circuit system will always be safer, you can't argue that.
Everyone must make there own decisions, but for a daily driver that is not bone stock I still say dual circuit is best.

Grigg

will the dual circuit master mount right where my old one is ?
and use the same linkage ?

I don't know about the 38. My guess is there is a kit available. Or a search on this site may show how others have done it.

Grigg

Here is a link to the page where I try to describe how I put a dual master cylinder into my 1940.

http://home.twcny.rr.com/schickling/1940Chevy/rebuild5.html

I also have a T-5 transmission so you don't need the special bell housing if you retain your original transmission.

Is this the same setup as the 38?

Safety trumps originality every time its tried!!!
I suggest dual system, booster and disc brakes. There are too many crazies out there now days.

There is a system that piggybacks a dual master to the output of the original master cylinder. It seems to have too many moving parts for my piece of mind, but a system like that is out there.

I know one of the parts carriers had a 2 chamber master for my 1940, but the catch was it would not accomodate a clutch, so an automatic transmission had to be used. The 38 and 40 should have a very similar brake and clutch setup with the brake and clutch pedals mounting to the transmission and bellhousing.

Would it not be possible to move the MC back to accommodate the clutch and lengthen the rod?

here is a bracket to mount the booster farther back.
http://www.abspowerbrake.com/4754chevytruck.html
Second picture up from the bottom.
You may or may not use a booster, but that's the idea of the bracket and push rod.
Should be simple enough, and you don't need the pedal assembly they offer, as you can use your old one.

There are kits available for your 38 master cylinder. If the pits won't hone out there are people that sleeve them with brass or stainless. Only two things influence how your master cylinder performs; the bore size in it versus the wheel cylinder bore size and the ratio of the brake lever itself. Your original MC will work fine with the brakes it was designed to actuate or with newer ones if the wheel cylinder bore size is the same size as the 38. If the wheel cylinder bore size is more than an 1/8" larger on the newer brakes then you will not have enough pedal stroke or if it's smaller there will be full pedal but it will be very hard and take too much pedal pressure. Unless one runs over some road debris or tears open the system in some other way then brake failure is 99% the fault of the owner. Inspection of the steel and rubber lines, noting and correcting any leak, and immediately investigating when the brakes feel different will make brake failure non existent. Having boosters and disc brakes on a vehicle with 600-16 bias ply tires is kind of like using a sledge hammer to drive in carpet tacks. If you go to a big engine and sticky tires then all of that is a necessity but not for a 38 that is still the way it left the factory with gearing that limits speed to about 50 mph.

ditto's on what Big Chevy 3600 said...

Safety trumps original, unless perhaps you are building a trailer queen.

Personally if you cant stop the vehicle without brakes you shouldnt be driving! That was one of the first things my dad taught me when I learned to drive. Plus real trucks have stick shifts and you can do darn near anything with a stick!

No problem upgrading though. I tend to prefer the originality and I seem to pay a heck of a lot more attention then the other drivers out there...

In 1967 chevy started using the dual master cylinder in the G-10 Vans being produced. Please note that the early series Chevy and GMC Vans were the old flat nose vans and that the M/C was located under the floor board with pedal extending through the floor board like in your '38. After owning and playing with old straight axle Chevies for the past 45 years, I would think that the 67- 69 Van M/C maybe worth looking into. The cylinder bore is 1" and the M/C can be ordered through Advance Auto Parts either new or rebuilt. Check the bore size on your '38 M/C for compatability. If mounting holes are close enough, your in. Re-route front and rear brake lines to the correct outlet on the new M/C and drive safer,longer. You may have to modify the brake rod attached to your pedal assembly. Strictly a Chevy Nut !!!!!!!