Speedo cable question

[southside_jon]

After my trans swap my speedo on my '87 didn't work. when I went to the parts store they asked me if I needed the upper or lower one. I wasn't sure so I went home and pulled mine out so we could compair and get the right one. Problem was, I only have one speedo cable. and it crossed reffrenced with an '85 model year. Anyone know if there is suppossed to be another speedo set up that's not on my truck?

The other question I had was; On my trans (TH400) the speedo cable doesn't thread directly into the transmission. There is this other thing that threads into the speedo hole, that come off the trans and then turns a 90 degree angle and my speedo cable then threads into that. What is that? lol.

And my speedo cable will not work cause there is this little plastic thing that slips over the end of the cable to spin what ever that 90 degree thing is. My plastic thing is broke and none of the parts stores knows what is. Does anyone have any idea where I can find another one?

Sorry Idont have any pics. I know they would help explain what I'm talking about. But any help would be better than none.

Thanks, Jon.

[givengold]

I don't know about your little elbow thing, but trucks with cruise control have two cables. One from the tranny to the cc, the other from the cc to the gauge.

[Burlinator]

you should be able to remove that 90 and hopefully attach your speedo cable directly to the trans. The ones I have seen are just screwed on just like the cable, they are an over/underdrive for the speedo when you change rear end gears or tire size

[piecesparts]

My guess would be---the UPPER cable and LOWER cable thing is associated with the old style cruise controls, where there was a drive unit on the inner fender well. That was on the Older Chevy trucks not the 87s. The drive units and module controls were very antiquated inthose days.

The 90 degree unit is exactly what was stated above it is a gear reduction or multiplication unit for addressing gear ratio issues. These things could be ordered in various number ratios. This was required on many GM trucks due to the fact that the internal speedo gears on the tranny did not come close to the rear end gears ordered by the owner. REMEMBER those days when you could actually order what you desired in a truck and not have to take what is the most popular package on the list. Odds are, if you take this off and take time to get the proper drive and driven gears for your rear end gear set, then the 90 degree thing can go to the E-Bay list. I have one laying around the shop somewhere, myself.

[southside_jon]

So if I just put the cable right into the trans my speedo should work without harming anything and will just be off?

[southside_jon]

until I figure out the correct gear I need?

[piecesparts]

The speedo cable should screw right into the same spot the adapter is mounted and then you have to work with the gears inside the tranny and POSSIBLY the driven gear housing on the side of the tranny.


Try this for a start: http://www.73-87.com/7387garage/drivetrain/speedo.htm

[southside_jon]

Well I got lucky. I went to a local GM dealer and they had 2 of the little plastic things in stock. (I bought both) I put the speedo cable from the '85 on with the plastic part on the end and threaded it into the grear reduction unit. Now everything works great...... well as far as the speedo and trans. Much more work to do on the rest of the truck.

Thanks for all the info guys.