MoparDieselPowe

Hey everyone I have finally found a 1992 W250 that I picked up about a month ago and have given it a once over. What I am going to do is remove the aux cooling system the previous owner installed (which is leaking at every joint, and he has the cooler/fans on top of the fuel tank which is clogged to hell) and install a new one up front with fresh gates hose and A&N fittings. So my first question is, does anyone know the size/thread of the fittings at the transmission (A518) and at the heat exchanger? Also I was reading on some forums that the trans goes into overdrive based on temp, which some people said the heat exchanger was giving them some trouble in that area, is that true? Well I do have an issue with overdrive, it likes to act up when cold while cruising in 4th gear it will randomly drop out of 4th into 3rd and back for a while and shoot my rpms way up. I have looked into this and heard it could be due to the TP sensor or the output speed sensor on the trans. I have looked for the output speed sensor and cant seem to locate it, does anyone know where the speed sensor is located? Thank you for any help!

oliver foster

I know the 4x4 trucks trucks get there speed signal from the sensor in the NP-205 T-case.
It is the one with two wires that come off a clip on style wire connector on the back of the T-case.

lz_68

The heat exchanger has 3/8 npt fittings and the transmission is 1/4" straight thread fittings.

j_martin

OD shifting is controlled by the PCM, which uses inputs from the CPS, TPS and speed sensor. If the alternator isn't quitting at the same time as OD drops, the CPS is OK. Likewise, if the speedometer is steady, the speed sensor is OK. That leaves the TPS, which is one of the worst parts on this truck.

They're expensive and made of unobtainium. There are multiple threads on work arounds from fitting an automotive TPS to a manual potentiometer.

j.fonder

Could it also be the temp switch in the line near the trans? I believe it keeps trans from going into OF if too hot or too cold. Hopefully ofelas will chime in as he's an auto trans guru.

j_martin

If I recall correctly, engine water temperature low will lock out the OD, and also transmission temp high.

Hillbilly66

I stumbled across this possibility for a TPS last night on eBay. Item number 191808780792

oliver foster

I have several TPS units for 1st gens...