Brake master-cylinder dismount.

Well, it’s spring break.  I spent some quiet time at the office doing administrative necessaries, some time at home reading microfilm, and on the last day of the break I took a break and just said “time to work on the truck.”  So I did.


The job I chose was to remove the master brake cylinder, which is the mechanism that turns kinetic energy (leverage from pushing on the brake pedal) to the hydraulic pressure that powers the drum brakes in all four wheels.


Here is a period film demonstration on automotive hydraulics; toward the end it uses an identical Chevy brake cylinder as a power source.

Reminiscent interlude:  Once I decided to do something marginally interesting for a date.  This would have been in the summer of 1980, before I kept a diary, so I can’t check for specifics.  I got Blair Mumford to get a girl as well.  I drove Green home from Hilltop (Grandpa didn’t drive much, and never in Green those days, so getting it was merely a matter of telling Grandma I was taking it), put a porch love seat in the bed for extra seating, picked up a young woman who could well have become Mrs. Saunders, and took a double date up the canyon to cook a dutch oven dinner.  The brakes, which were always little light, were almost not there.  I had to really push hard, and well before a stop sign or corner, to slow down.  When Grandpa found out I’d taken three other people up AND DOWN the canyon he almost hatched kittens.  I had not known the truck was unregistered because it essentially had no brakes and could not pass a safety inspection. Yes, “I could have killed somebody.”  It must have made a difference because she tossed me over without a backward glance for someone else two years later.

Fast forward thirty-five years. Like I said earlier—Green has no brakes at all.  Looking at the present condition of the master cylinder, even before it came off, it is pretty clear why.  The seal cap on the front, through which the plunger runs, is split clear off (you’ll see it below). It would take merely a good tug to remove it. The cylinder has to be removed, cleaned, and rebuilt entirely.  Yes, I could buy a new one for about $130, but what is the fun in that?  Rebuild kits are about thirty bucks and this is a learning experience, isn’t it?

So, I started back in January by giving the mounting bolts a good soaking with WD-40 and let them sit. This afternoon I simply loosened the bolts, disconnected the brake line and off it came—bone dry.  Not a drop of brake fluid in the line anywhere.  That’s why there are no brakes. You can also see that one of the split washers really was split.

So here is the master cylinder, the mounting bolts and everything else that came off (front is the linkage fork). Obviously the cap–which should seal off the plunger at the front of the unit—will be replaced in being rebuilt.



It needed a good brushing to start with, which took off most of the dirt. It will still need to be actually cleaned. Started on the job by removing the triangular snap ring that kept the external plunger in place at the linkage end. The plunger engages the piston inside (which I neglected to photograph) and simply floats free between the brake linkage and piston, one end restrained in place by the spring clip and retaining washer-thing.


I don’t yet have the rebuild kit on hand, but since I started the blog talking about numbering, I might as well continue the tradition.  The end of the cylinder has “MODEL | 361-J” stamped around the end, as you can see.  The cap has the usual and expected industrial/corporate imperative to “USE G.M.C. BRAKE FLUID”.  Obviously nothing else will do.

The driver or left side has both the Delco name (GM’s parts manufacturer) and “MADE IN USA” cast into the side.  On the opposite side of the body is the part or component number:  5450830 R2 (maybe B2, I can’t tell clearly).  Below it is cast one important detail:  1 1/4″ DIA—or that the internal bore is one and a quarter inches.  That little detail is significant, because the tolerances inside are measured in thousandths of an inch, and there is a good chance, since the cap is in such lousy shape, that the sides of the cylinder will be rusted badly enough that they can’t be honed out without making the bore too large for the piston and caps; brake fluid should not pass around the caps or the braking action will be compromised. Below that, on what looks like a plate screwed onto the mold, is probably a casting-date code. There are two characters which can barely be made out, even in good light, which look like “1-6” or “7-6”. No clue how to read it.

I put the cylinder into a shop vice to remove the end cap but encountered two problems. First, that I don’t have a wrench large enough for the 1-9/16″ nut dimension (other than slip-joint pliers); second, that it is snugged down really, really well.  I cannot get enough leverage with pliers to budge it.  There also seems to be a babbit or lead washer or something between it and the housing.


Try as I might, I could not get into the cylinder itself, so I’ll save the rebuild for another post.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s