The Stovebolt Site Forums The Parking Lot Big Bolts GMC 630 ?'s

Well, come to find out after asking a bunch of questions about my 426ci engine, I noticed that the data plate in the glove compartment said it has a 503ci. The previous owner told me it was a 426, so I figured it may have been replaced. Looked on the top of the rear of the crankcase and sure enough, it's a 503. Seems to run pretty good but no brakes at all so I haven't had it out on the road yet.

The transmission is a 5553a-od and the rear axle ratio is 6.50. What am I looking at for a comfortable cruising speed with this combo? I was hoping not to have to change out the rear axle but may have to down the road.


Tyler

The 503 with a 5 speed overdrive with a 6.50 rear will run as fast as you will want to drive.

My 630, 503, same gears got between 6 and 9 mpg driving between Arkansas and CO at reasonable speeds-no working speedo.

I have since gotten a two speed, 4.33 gears, like that.


Ed

Thanks for the replies.

So Ed, you really didn't know how fast you were going? Would you guess 55 or 60?

Tyler

Tyler,

probably 50 ish, judging how long it took to get home.

Ed

Thanks Ed.


Tyler

Tyler,

See my post on brakes.

Ed

Tyler,

You might want to try Jerry's (HRL) method to clean out your pan of old oil, etc. Put
some clean oil in, not full, then add 3 or 4 quarts ofdiesel or kerosene. Run at a fast idle for a while to get it warm, do not drive or load the engine, flush everything out.

Ed

Thanks for the info, Ed.

Tyler

Tyler,
You haven't said if it runs or not, or if the brakes work? Since I have started to remove my rear brakes, here is what I have found.

I got new cups and end covers. Two cylinders per wheel. Both cylinders on each wheel only had one side working, other rusted or stuck with yellowish Al corrosion. Was able to clean everything up, replacing both cylinders now.

One shoe adjuster broken by me because would not adjust. Shoes might be zink, won't weld. Made steel bracket to repair. Needed gentle heat and large wrench to get adj. bolt loose and remove to remove solidified grease.

Was able to hone the cylinders to remove corrosion, White Post Res. In VA will reline for $125. Per.

Since both our trucks came from the rust belt, you might encounter similar conditions.

New bleeders to replace rusted ones are available from NAPA, PN Z4148, .437" x 20 threads, they also have the Cu washers, although they are thicker. Same bleeders work on front.

Was able to find Cu washers for the wheel cylinders, two sizes, NAPA PNs: 3877 for large ID one, 1243 for small ID one.


To loosen nuts holding cylinder to backing plate, had to use 4' cheater on breaker bar. Be prepared for rusted hardware.

For anyone reading this, these are FR-3 rear brakes on a '54 GMC 630, 6" by 16" brakes shoe PN FF3144. New shoes are nonexistent. These brakes also appear on others, Brockway for sure. They take a .375" Allen wrench to adjust.

Ed

Hi Ed

My truck runs, or did run until we started tearing into it some. Brakes don't work at all, only driving I have done with the truck is about 100 yards in reverse to get it up my driveway.

Radiator hoses are scary so they're getting replaced as are heater hoses, fuel pump, some fuel lines and getting rid of some unesesary plumbing. Will have it running again shortly but have to take a break for a while, going moose hunting for ten days or so and have to get a garage built before snow flies.

Got my master cyl. relined and a buddy is rebuilding it. Not looking foreward to the wheel cyl.s

Tyler

Great.

Ed

Got new Cu washers for brake fittings today, most economical to order 100, so I have plenty of spares. Got new wheel cylinders, not original for 630, but 1.7/8"
slaves that can modify to fit factory if factory ones are unusable. Will post results.

Ed

Thanks for the update, Ed.


Tyler

It turns out the wheel cylinders are mounted at a 45 degree angle, hard to get them bled that way, unless one tips their truck that much. No wonder I always had to pump them twice to get pedal. Backing plates are riveted on, 10 each side, more than I want to tackle.

Ed