erratic speedometer

[CYant]

Hi, y`all

I bought a `90 D250 5-speed reg cab back in Feb. I love the way this truck starts up and performs. It gets good fuel mileage and pulls a trailer well.

One problem it has is the speedo. Its very erratic now. When I first got the truck it was slightly erratic but got worse over time.

I replaced both nylon gears and put on a new speed sensor with a new adapter, and that didn`t improve things at all. The yoke on the back of the trans is tight. The speedo will swing even when the truck is stationary which sounds like to me there is some stray voltage getting to the sensor wire. Called a speedo repair company and they thought the problem was not in the speedo itself. I removed the speedo unit and checked the three pins on the back where it plugs in. Everything checked out according to the service manual. One pin is ground, another is +12v and the third has continuity to the sensor. Anybody got any ideas about how to fix this?

Another problem is that since I use a pressure washer to clean it, the paint is flaking off in patches. It`s red and white and only the white is flaking off. Probably will repaint only the white, but do y`all know if the red is free of problems. If I could match it I might paint the white part red to match the rest.

AC had already been converted to r-134 but it ran out of charge. Had anan AC shop check it out and it took a new compressor and the valve on the firewall. It just doesn`t cool very well.

I `enjoyed reading on this forum for a couple months. Impressed with the technical expertise on the

TDR website. Looking forward to participating and hope to help out some of you guys someday.

 

[ETOBICOKE]

Speedometer

Just had a look through my manual, best I can tell, the speedometer sensor works as a ground return. What this means is that most likely your problem is in the wiring harness, between the speed sensor and the speedometer, possibly grounding out to the chassis.

Others have had similar paint problems such as you describe, although it is not very common. But then again 10 years plus, with original paint is not bad at all. In Canada about half of the first gen trucks that I see on the road have some degree or other of rust holes.

If you do a search for R134a you will find that others have a similar complaint to yours. It would seem that as the system was designed to work with R12, that when converted to R134a it is less efficient. There are other refrigerants that can be used in R12 systems that are hydrocarbon based and from the limited testing that my brother and I have done seem to work very well. R134a although it doesn't deplete the ozone it is toxic and is corrosive in contact with water, due to it's small molecular size it will also leak out more easily.



Hope this helps

Neil

 

[Scot]

Another thing you might check: The speedo drive gear is held in place by friction due to the yoke nut on the tailshaft of the transmission. There is NO keyway. Mine was quite loose when I went in to the transmission.

 

[Rockcrusher]

I had a lot of trouble also with speedo going crazy. Replaced sending unit several times (not cheap!) and finally found out it was the cruise control causing the trouble. Replaced same and no more problem.

The other thing that goes out about every year is the voltage regulator. Its located on the fire wall and picks up too much het. I keep saying I'm going to move it inside the cab but it's one of those "round tuits".