1948 Columbia overdrive
- Thread starter 6201241hg
- Start date
4dFord/SC
Well-known member
It is operated by engine vacuum. The switch engages the unit. Flip it on, step on the clutch, and it will shift up into overdrive. This is best done at speeds of 45 mph or higher. Flip the switch off, step on the clutch again, and it will shift down from overdrive. This can be done at speeds of 25 mph or higher.
6201241hg
Junior Member
Your answer seems okay, but mine does not operate that way. I have an electric switch, but it is only a one way switch. When i want to shift into overdrive i push in the clutch toggle the switch and the speedo and rear end shift. But lately it is not coming out of overdrive. What brings it out of overdrive? I have owned this car for 15 years and it has worked fine. The last two years or so I noticed it is not down shifting. I need help to find the problem. I Would appreciate any input.
blucar
Well-known member
The '46-48 Columbia's are vacuum/electric. A two solenoid switch controlled by a self canceling toggle switch mounted to the dash, and a switch connected to the clutch, switches the engine vacuum to the high/low ranges of the Columbia unit.
There is also a S/W vacuum controlled speedometer switch incorporated into the system to allow for the two gear ratios.
The high range shift process is controlled by briefly engaging the toggle switch, briefly releasing the throttle, while depressing the clutch. THIS IS LIKE PATTING YOUR HEAD AND RUBBING YOUR TUMMY ALL AT THE SAME TIME.
The low range shift is accomplished by simply releasing the throttle and depressing the clutch.
I generally do not shift to high range at speeds above 65, and do not shift to low range at speeds over 35-45...
The gear ratio in my '47-48 Columbia is 3.78-1.
blucar
Well-known member
There are a number of items that effect the shifting of a Columbia, as I have outlined in my earlier contribution to this thread.
If the unit is not down shifting I would suspect the clutch switch and/or low range solenoid.
Do you know if your controls are a stock Columbia setup? If they are they are all contained on one bracket mounted to the left head.
The toggle switch should be a spring loaded self canceling switch.
4dFord/SC
Well-known member
x2.
6201241hg
Junior Member
I think my unit is stock as I have a two solenoid unit bolted to the left head and another unit going to the speedo. Your description of how the unit should work matches my unit. I will check my clutch switch. I think I can short the solenoids to see if they are working. I certainly appreciate your help. Now I know what to work on. Than you.
Take the 2 hoses off the shifting cylinder mounted on the rear. Look
for black oil being sucked from the rear into the hose closest to the
center of the rear, that's the suction hose that pulls the Columbia
in. You can also remove the entire shift unit and shift the rear into
or out of Columbia. The shift arm sticking forward from the rear moves
to the left or right. Easy to remember "in is in", "out is out". When the
arm is moved OUT towards the wheel it is OUT of Columbia and IN
towards the center of the rear it is IN Columbia. If there is black oil
in the IN SIDE the oil seal in the cylinder where the shaft go's into the
cylinder is bad and leaking air and oil form the rear. This leak provides
a lose of power on the cylinder. These seals are available from bearing
and seal companies and should be in stock at Napa, the seal number
is on the seal. The leather cups that are like large pistons in the cylinder
could be so dry they can't move. Put MMO in some small bottle with a
little spout and put a good load of the MMO in both metal tubes the
hoses go on. If you have a vacuum pump you could put a hose from
that on the tubes to shift it. Or a long hose from the intake manifold.
Check and see if you have vacuum on the hoses coming from the
solenoid valves on the head back at the rear. If you have good vacuum
on both when you shift the solenoid the problem is in the back. G.M.
Last edited: