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Well if you've been driving your truck around for awhile or taken it on the highway you've heard that famous whine of the 6 cylinder giving you all the speed it can muster and probably the sound of a few horn telling you to get out of the way!
We both know the culprit and it's getting to be about that time to quit putting off the inevitable and updating the rear end to obtain so respectable speed and more important to save that engine from all that unnecessary strain.
Their are several options available in your quest for speed:
1) Stay with the stock rear end and order up some 3:55 gears from Patricks.
2) Obtaining a rear end out of an early 50's Chevy Car with a power
glide that uses the torque tube and adapting it to the truck
3) Swap out that rear end for an open drive from a 54 Truck which will
mount up with the spring perches
4) Swap the rear end out for something newer and with better highway
gears.
I realize the problem of attempting swap #4 to a newer rear end leads to the question of what to do with the stock transmission that relied on the torque tube? You can always upgrade to a newer transmission that can accept an open drive drive line.
I've yet to see a rear end that's a direct bolt in for the 1947-54 trucks
and places the tires in the center of the fender openings. If it
does happen to do that, then the pinion angle is excessive and that leads
to premature u-joint failure.
SO HOW DO YOU DETERMINE PINION
ANGLE:
The best method is to measure the angle from the rear end you just
removed from the truck.
Steps to measure pinion angle:
1. Balance the rear end on two jack stands.
2. Place a bottle jack under the center of the rear end just below
the pinion gear flange.
3. Place a level on the spring perch "pads"
4. Place a magnetic protractor on the face of the pinion flange.
5. Raise or lower the bottle jack until the level on the spring perch
"pads" is level and then read the degrees on the protractor.
6. This is the angle that you will set the new rear end angle to.
ALTERNATIVE METHOD IF YOU DON'T HAVE THE ORIGINAL REAR END:
1. Roll the donor rear end up on the spring perches
2. Raise the leaf springs and attach them to the hangers.
3. Center the rear end between the frame rails by:
a) measuring from the inner edge of the backing
plate to the outer edge of the frame
b) a straight edge laid against the backing plate
and a square off the frame makes measuring easier.
c) once the rear end is centered mark the location
of the spring perches on the rear end
NOW IT'S TIME TO SET THE PINION ANGLE:
1. With the rear end in place and ALL four tires on the ground
a) place a magnetic protractor on the transmission output shaft to
measure the angle.
1) if you can't get to the output shaft, slide in
a yoke to measure from.
b) move over to the rear end and measure the angle off the front of
the pinion flange
c) The sum of the two angles should add up to 180 degrees.
d) Rotate the rear end to obtain the desired pinion angle.
I PERSONALLY SET UP MY REAR ENDS WITH A DOWNWARD ANGLE OF 1 TO 2 DEGREES BECAUSE ON ACCELERATION OR WITH LOAD THE REAR END WANTS TO ROTATE UP!
It's really not that big of a deal to determine the gear ratio without pulling the rear cover. If the tag listing the gear ratio is missing from the rear end all you do to determine it is:
1. Place a mark on the axle say at 12:00 O'Clock
2. Place a mark on the pinion gear flange.
3. Rotate the pinion flange say 30 times while someone else counts
the number of turns of the axle.
The higher the number of turns the more accurate the reading.
You'll divide the drive gear by the driven gear and that will give you
a close estimate of the rear end gear ratio.