700R4 Speedo Question

[HookedUpGTP]

I received my '61 with a 700R4 tranny. The truck has an electronic VDO Speedometer that has not worked since I got the truck. There are two wires that go from the speedo to a two wire plug the driver side of the tranny. Does it matter which wire terminal the wires are connected too?

 

[dvalentine]

There needs to be a Pulse Generator in line with those wires....

It looks like this-

The wires you are talking about coming off the trans just might be for the back up lights.

Val

 

[HookedUpGTP]

The particular 700R4 that I have already has the pulse generator built inside the tranny... it doesn't have a gear for a gear driven speedo.

 

[drabo]

Sounds like you have a 4L60E and not a 700R4. They are basically the same tranny but the speedo on a 700R4 is cable driven. Other than that I try to stay away for adding any electronic stuff so I'm not much help.

 

[dvalentine]

If this truely is a 4L60E there would need to be a control module of some kind. The trans is meant to be connected to an electronic control unit, (ECU) that controls everything including when the trans shifts and speedo input.

I've seen conversions that involve changing the trans tailshaft but those were to drive a mechanical speedo.

So I guess we need to know what trans you have, and if there is an ECU already there.
You didn't say anything about if the truck shifts gears OK.

Val

 

[HookedUpGTP]

The truck shifts fine and there is no ECM, PCM, ECU or anything else electronic. There are two electrical connection on the tranny. A multi-wire plug on the drivers side about 1/2 way back on the body of the tranny (I assume that is where a torque converter lock out control wire goes, but nothing is currently connected there) and one two-wire connector on the tailshaft where a mechanical speedo would normally be connected. When I say it shifts fine, I should say it's a little soft going in to 2nd,3rd and 4th, but it shifts OK. I'm ordering the correct Holley brackets to connect the TV cable to the carb with the proper geometry and I'm hoping that will firm up the shifts. The speedo has worked at some point in the past as it has about 2000 miles on the odometer.

The tranny is stamped with:

8676358
MD8

I'm certainly no expert on the 700R-4, but from what I read, I though some of the 4L60's were shipped with a mechanical servo and some an electrical servo.

This is the only decent pic I have of the tranny... can't tell much from it..

 

[Arlo]

it is a MD8 TRANSMISSION,4-SPD AUTO (THM700R4)

http://www.hotrodders.com/forum/images/bulk/TH700-R4_1.jpg
this may help.

if you can count how many splines are on the output shaft that would help identify
27 splines for 82-84 tranny's.
30 splines for 84 and later models.
85 and later 700R4 are the best to rebuild.
87 and later models are the most reliable in stock form.

 

[drabo]

Okay it is a 700R4. The speedo gears go right in the tail shaft. You will need to order the right ones though. Try www.bowtieoverdrives.com , they have a calculator to tell you which ones to get. You will need a pulse generator to make the speedo to work.