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DilloCrafter
11-28-2005, 12:31 PM
I searched the forum first, but can't find the answer to this question, so here goes:

My truck (champion six, 3 sp. w/OD) originally had a 4.55 ratio rear end, but I have had new gears installed for a 4.09 ratio.

The speedometer cable probably needs lubing or replacing, as it jumps around too much to tell the actual speed. Once I get that fixed, I may find that the gauge speed is far off from the true speed, between the new gear ratio and larger tires than original. I saw a "Studebaker speedometer adapter" for sale recently. Does anyone know if there is an "adjustable" adapter, or if they made ones specifically for when changing rear end ratios, as I have done? Or should I simply not worry about it, and get a GPS unit or something that will tell me my true speed (like I can afford that after all the money that's going into this truck).

1955 1/2 Ton Pickup
http://rocketdillo.com/studebaker/misc/images/current_AvaCar.gif

Roscomacaw
11-28-2005, 02:06 PM
There's speedo gears that are specific to the tranny/rear combo that you have. The parts books spell out whichever one your truck requires. In your case - 3spd O/D with a 4.09 rear, you need to find speedo pinion gear (the one on the end of the speedo cable that goes into the hole in the tranny)-part# 520087;)

Those adapters you mentioned allow the really higher geared rear axles to work in unison with the standard Stude speedo. Easier to use an adapter than carry a second type of speedo in stock.
There's another adapter that operates in conjuction with the two-speed rears on bigger trucks. It shifts ratios to match the ratios in the 2-speed rear.:D

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

hank63
11-29-2005, 09:01 AM
A jumping speedo doesn't have to be the cable. It can also be internal wear in the speedo. If that's the case, get another speedo or have a "clock-repairer" fix your speedo (i had to do that once - the clock-fellow replaced a bushing and that solved the problem and was cheap at 6 bottles of beer).

The speedo drive is about "how many teeth" on the speedo gear. Go talk to truck rear axle people if you can't get the right P/N you need. Truck people often change diff ratios to suit the work their truck is doing.
A simple calc shows that you've "slowed down" your rear wheels by about 10% (in relation to engine speed). That much change will definitely throw the speedo out.
As an example, say your engine did 3000 rpm at 60 mph before the ratio change. With the 4.09 ratio, you'd do about 66 mph at 3000 rpm, BUT the speedo would still show 60 mph. That's just an approximate calc, but it shows what's happening.
/H

Roscomacaw
11-29-2005, 12:45 PM
A real simple first step is to take a long-spout oiler and put a couple drops of oil in the tiny, brass oil cup that's at the rear of the speedo head. It's just above where the cable connects.[:I]
I was surprized to realize that even my 58 wagon's speedo has such an oil port on it![:0] But in taking the dash apart the other day, that's what I discovered.
When the speedo in my 57 Truck started jumping and squealing, two drops of oil were the fix and I didn't even have to take the speedo out to do it. ;)

Miscreant at large.

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe
1957 President 2-dr
1955 President State
1951 Champion Biz cpe
1963 Daytona project FS

DilloCrafter
11-29-2005, 03:09 PM
Thanks, guys. I went out to my truck and found that hole on the speedo housing, above where the cable connects. I wouldn't have known that was an "oiling point" if you had not pointed that out. It's now oiled, and I'll find out next time I drive how it does (I had previously removed, cleaned and relubricated the cable itself, using white lithium grease from a spray can (but the jittery speedo was unimproved).

I also have ordered one of those old lube chart cards for my vehicle from a guy on eBay who says he has thousands of them. I plan to laminate it, and take it out with me when it's time to lube everything. We certainly are spoiled by modern cars, in comparison to how often these older ones need lubrication, and at so many points. I think I could nickname my truck, "The Tin Man".

1955 1/2 Ton Pickup
http://rocketdillo.com/studebaker/misc/images/current_AvaCar.gif