What transmission do I have?

[jd21476]

My truck is a '73 K20 Scottsdale and the Gear selector shows: P-R-N-D-L1-L2 but it only shift to 3 gears. I thought the 700R4 has that type of gear selector.

That brings me to another issue. The gear selector does not change when I shift gears. How do I fix that?

[Tom]

700r4 wasnt until the 80's. You have a th350 or th400 3 speed. a 4sp's shifter will have 1-2-3-D

[gchemist]

700R4 were not installed until '82. Does your have one installed? The selector for a 700R4 is P-R-N-(D)-3-2-1. K20 could be a 350TH or 400TH. What does the pan look like? A square pan with a cut corner is a 350th. An island shape is a 400TH. A mainly square is a 700R4. There is a string attached to the column that moves the selector. Remove the lower metal and plastic covers under the steering column. Shift it down. You should see the screw. You may need to remove the instrument bezel to find the string. If it's broken, you can buy a new shift indicator from www.lmctruck.com.

[jd21476]

Originally Posted by gchemist

700R4 were not installed until '82. Does your have one installed? The selector for a 700R4 is P-R-N-(D)-3-2-1. K20 could be a 350TH or 400TH. What does the pan look like? A square pan with a cut corner is a 350th. An island shape is a 400TH. A mainly square is a 700R4. There is a string attached to the column that moves the selector. Remove the lower metal and plastic covers under the steering column. Shift it down. You should see the screw. You may need to remove the instrument bezel to find the string. If it's broken, you can buy a new shift indicator from www.lmctruck.com.

I'll climb under it tonight and take a look.

[jd21476]

Wow, a 3 speed I didnt realize they used them up until the 70's. Is a swap to a 700R4 a good idea?

[Tx Firefighter]

Why would you want to swap from what you have now ?

A swap on your 4wd truck is no small job. Much more involved than a 2wd truck.
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[jd21476]

Originally Posted by Tx Firefighter

Why would you want to swap from what you have now ?

A swap on your 4wd truck is no small job. Much more involved than a 2wd truck.
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In San Diego you have to do alot of highway driving to get anywhere and I think having more gears would help. Right now it sounds like the tranny is being pushed to the limit on the highway.

[Tx Firefighter]

A good first step would be to find out what gearing you have in your axles and what height tire you're running. Then, we can plug it into a calculator to see how many revs you're turning at highway speeds. From there you can do some figuring to see what the best option is.
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[67swb72klb]

you could look at a bigger tire combo ?

[tlawre87]

still remember. Im going to spend X to get Xmpg more per mile. How long will it take to make that cost up?

Being a 3/4 its most likely a TH400. It'll have M40 as the RPO on the label in the glovebox.

[donut]

Being a '73 K-20, odds are it's a tbh 350 (and 4.10 gears). If your uncomfortable with the RPM, slowing down is the cheapest option, other drivers will go around.

That said, it's a 40 yr old truck. Who knows what a PO put in, verify.
Tx Firefighter was correct on many counts.

In my case, it was far cheaper to get the turbo 350 rebuilt, and spend the savings on gas. I did have a turbo 400 in the shed and access to a 700r4...

[Tx Firefighter]

I saw a picture of your truck on another thread. It sits pretty tall with what looks like oversize tires. Even if you have a non overdrive and 410 gears, it should be fairly reasonable cruise rpm up to a reasonable speed. Those tall tires offset the deep rear gears.

The reason I was pushing you to determine what you have for gearing and tires now is that I suspect you're either.....

1) expecting too high of a cruise speed. 80 miles per hour for example

2) have a different issue like a seized fan clutch which will make the engine seem like its screaming.
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