Hi everyone,

I have a 1989 diesel F350. It had a new engine and transmission put in 2 years ago and got test driven then was parked in a warhouse since then. I recently purchased it and am having problems shifting gears as its an automatic and will not shift gears properly unless you let your foot off the gas and then put it back on again. It will not shift if you keep your foot applied to the pedal. I had a mechanic take a look at it and apparently there is no speed sensor on the trans which originally I thought could be the problem. Anyone know what could be causing this? Any help or info would be greatly appreciated! Also, I have very limited knowledge on diesels, if you have any suggestions on other issues or parts that may need to be replaced that would be great...

 

speed sensor is in rear end its listed in the parts store as rear abs sensor do you have a tach check the tach sensor im asuming you have an e4od they have electronic shift sylinoids they dont like to sit

 

No speed sensor on the trans is your speedo working. and is your tach working.

 

the tach is working but the speedo is not

 

also i dont think its a e4od trans i think its a c6 ? sorry i dont know much about trans. thanks for helping me out

 

Well if it is a C6 it is a lot cheaper to fix and if it was just installed and parked, it is probably noy gettung vacumn right. Somebody will be along shortly that is up on them.

 

'89 trans could be E4OD or C6. There needs to be a VSS in the trans tailshaft housing, and also a cable - the cable drives the speedometer, and the VSS is for the E4OD computer. There is also a VSS in the rear axle, however this is for the ABS only - it was in '92 that the axle VSS started to get used for the trans computer and the speedometer gauge too, and you need a PSOM for this to work which an '89 truck does not have.

To determine if it's an E4OD or a C6, answer this - do you have an "OD" button on the dash to the right of the steering column? Also, under the hood, on the driver-side of the injection pump, what device do you have there - one that has a harness plugged into its side, or one that has two vacuum hoses hooked up to its top?

 

no od button and it has vacuum hoses hooked up

 

and thanks again for all the help and advice you guys are giveing me

 

the trans has less then 30 miles on it but it did sit for 2 years it starter right up after i dumped fresh deisel in it and jumped it i drove it home but the trans did not shift had 2 let foot on and off gas 2 shift but i also only live 10 miles from where truck was and did not have 2 go over 40 mph it does have cruise control if that matters ?

 

That's a C6 then, no VSS on the tailshaft housing of that. There is a cable, however, and those sometimes seize up, try pulling it off the trans and spinning it by hand and see if it turns easily.

 

Your problem is vacuum related I would think. A vacuum pipe is taken off the vacuum pump and goes to the the Vacuum Regulatory Valve on the side of the injector pump which modulates the vacuum according to throttle position and supplies it to the transmission.
So you need the vacuum pump to be good (around 20in. of vacuum at idle). You need the pipe to the VRV to be good. You need to check that at idle there is good vacuum coming out of the VRV (if not it may be bad). You need to check that the pipe from the VRV to the trans is good. Finally pull the rubber vacuum pipe off at the trans modulator and look for signs of ATF. If any found replace the modulator.
Get the vacuum sorted and I think you will be good to go.

 

I had an 85 with a c6, put a new flywheel in and forgot to hook up my vacuum, it did just what you decribed.

Austin

 

thanks 4 the help

 

Thank for everyones help, it was a vaccum problem and my truck is in the shop now getting fixed. Does anyone know where I can get performance parts like exhaust, etc.? It has the 7.3L non power stroke. I have been lookin online but can't find any for that particular year. Does anyone have any suggestions for the exhaust I wan't it to sound really good. Thanks again for everyones info and suggestions! Its greatly appreciated...

Anthony