What transmission do I have? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jd21476 · 08-13-2013, 04:08 PM

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 · 08-13-2013, 04:51 PM

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 · 08-13-2013, 04:52 PM

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 · 08-13-2013, 04:53 PM

Quote:

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 · 08-13-2013, 04:52 PM

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 · 08-13-2013, 06:32 PM

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 · 08-13-2013, 06:48 PM

Quote:

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.
Posted via Mobile Device

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 · 08-13-2013, 06:52 PM

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 · 08-13-2013, 06:53 PM

you could look at a bigger tire combo ?

tlawre87 · 08-13-2013, 08:05 PM

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 · 08-14-2013, 07:24 PM

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 · 08-14-2013, 07:58 PM

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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08-13-2013, 04:08 PM	#1
jd21476 Registered User Join Date: Aug 2013 Location: San Diego, CA Posts: 236	What transmission do I have? 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?

08-13-2013, 04:51 PM	#2
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Re: What transmission do I have? 700r4 wasnt until the 80's. You have a th350 or th400 3 speed. a 4sp's shifter will have 1-2-3-D __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

08-13-2013, 04:52 PM	#3
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: What transmission do I have? 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. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

08-13-2013, 04:52 PM	#5
jd21476 Registered User Join Date: Aug 2013 Location: San Diego, CA Posts: 236	Re: What transmission do I have? Wow, a 3 speed I didnt realize they used them up until the 70's. Is a swap to a 700R4 a good idea?

08-13-2013, 06:32 PM	#6
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: What transmission do I have? 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. Posted via Mobile Device

08-13-2013, 06:52 PM	#8
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: What transmission do I have? 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. Posted via Mobile Device

08-13-2013, 06:53 PM	#9
67swb72klb Registered User Join Date: Dec 2010 Location: livingston co.mi Posts: 2,471	Re: What transmission do I have? you could look at a bigger tire combo ? __________________ California 65 GTO---Texas 64 burb 283 ---Oklahoma 67 CST SWB BBW wood bed 327 2004r---New Mexico 72 k10 350 350 auto---Georga 72 short step project

08-13-2013, 08:05 PM	#10
tlawre87 Registered User Join Date: Jun 2012 Location: Meeker, ok Posts: 146	Re: What transmission do I have? 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. __________________ Trevor 74 C20...work in progress. 04 Saturn Ion...Daily Driver

08-14-2013, 07:24 PM	#11
donut Registered User Join Date: Aug 2009 Location: S.C. Posts: 1,593	Re: What transmission do I have? 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... __________________ '86 C-30 dually, 454/tbh400 '73 K-20 350/350/205 (sold ) I'm kinda like duct tape- no real purpose, but handy to have around.

08-14-2013, 07:58 PM	#12
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: What transmission do I have? 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. Posted via Mobile Device



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