My cruz control started dropping out and I noticed that the speed needle was fluctuating. When the major fluctuatuons slowed down, the needle settled down to around 85% of normal indication.
The pickup shaft turns freely at the transfer case end, so there can't be drag back up toward the speedo end. (can it?).
For grins, I replaced the worm, as it seemed that it had a little deformation. No change.
Now, no fluctuations, but still down in speed by the 85% or so.

Q. is there anything in the transfer case that can give up that would cause a constant slip to the speedo drive? I don't remember the Mfg of the transfer case. Possibly B-W but not certain.

Am I being wrong about the thinking back toward the speedometer? I hope the problem is back that way. The odometer is still tracking, so that part is good. Could it be simply that the speed indicator has developed drag?

I know that the speedo input shaft has a magnetic coupling that interacts magnets and Aluminum plate to induce motion to the needle.
Please advise any expiriences.
Eric Egland

 

What size tires are on it......

 

OK, stock tires. 235-85R16. I don't think my tire size would have changed driving down the road.
I got to thinking, however, and I believe the cruise info comes off of the transfer case attachment for the speedometer/odometer drive cable. So...since the cruise was dropping out as well as the speedometer needle fluctuating, the problem seems back toward the gizzards of the transfer case. Changing the worm made no difference, so that makes it back farther into the transfer case. Dang me!!

Any thoughts?

Eric

 

Moreover, now that I think about it, since the odometer is tracking fairly well+-5 to8%, I better go back to the system diagrams and such. I'need to do some more study. I did order the factory books when I bought the rig in '90.
Thanks for any input.
Eric Egland

 

1990 has a completely mechanical speedo, so your problem is likely in the in the speedo cable or transfer case, I have heard of other cases of the drive gear in the transfer case getting damaged. Its not a big deal though, its fairly cheap and easy to replace, but it involves dropping the driveshaft and pulling the tailhousing of the transfer case.

 

The 90 model should have a BW 1356 transfer case.

Isn't there an electrical conection right outside the transfer case that ties into the cruise control?

 

on my 90 w/5-speed, there's a connection on the gizmo that the speedo cable goes into that feeds the cruise control. check your connections on both the connection (female) and the spade terminals on the plug. since mine is tied off on the frame with a wire or two broken (hence, no cruise) i can't tell you for sure this is your problem, but a check point. also, check the control "buttons" on the steering wheel as if they get loose or corroded a little, it might cause a variance in the signal. just a guess since as i said mine ain't working right now. hope this gives another place to check.

speedrdr

 

Correct, but the speedo will work with or without the electric sensor hooked up. That same sensor (VSS) is is also how the computer knows how fast the truck is going, and adjusts shift timing accordingly.

Since he mentioned a fluctuating speedo, I figure it would still have to be a mechanical problem. Another fellow had a very similar problem, and it turned out that his speedo drive gear was chewed up and causing shifting errors.

 

yep, you're right about that. forgot that mine also jumped around a little bit because the cable that passed through the gear was worn letting things slip around. new cable fixed that.

speedrdr

 

Thanks very much for the hints.
This gives me some more helpful info and hopefully, a solution when I get the system figured.
Eric