Bought this truck for $400 last Monday with known tranny issues, after further diagnosis I've narrowed it down to a speed sensor coming off the transfer case (I think) I ordered in the part from the internet and its expected to arrive Wednesday. I'm posting to just get some info as to if my diagnosis was correct. Got it, noticed the speedo didn't work and when it did it would bounce around from zero to 30-35 mph only running in second gear (limp mode) I checked trsnny fluid, clean. Checked the shift solenoids by disconnecting the ecu signals to tranny and driving with a "co-pilot" having them manually activating, deactivating the solenoids and the truck shifted beautifully. So this gave me the assumption that all is well in the tranny. I then went ahead and researched the speedo issue and led me to the speed sensor or speed sensor buffer. I couldn't find a replacement buffer online so I went with just the sensor itself for now. But I also checked continuity through all the wires from both sides of the sensor all the way up to the buffer, and from the buffer to the back of the gauge cluster assy. All pulled a perfect 0.00 or sat at 0.01 for a few seconds and dropped to 0.00 flat which is normal considering the length of the wires.

So my assumption with the vss will either be good or bad, not 100% sure though.if it doesn't solve my problem then I'm either gonna repair the buffer myself, or go to the picknpull a couple of towns over and snag up some.

Could a faulty gauge cluster be the problem?? The clock reads 291,xxx but the engine was replaced in 2003 (brand new crate engine, not rebuilt) with unconfirmed mileage (installing company didn't jot down any info other than a date). Idk however notice that when I start the truck I hear a winding sound like plastic gears grinding. Could this be a gear mechanism in the speedometer cluster grinding away not allowing it to spin correctly, or something else??
Tachometer and all other gauges work perfectly, just no speedo or mile counter.

Also abs light is on, not worried about this yet. Could just be a bad wheel sensor, or something unplugged, previous owner said light has been on for 3+ years and no issues.

Would it be wise to contact previous owner and ask if speedo went out around the same time as the tranny shifting issues??

Sorry for the long drawn out posting, just trying to give as much info as possible.
Also if words are spelled way wrong it's because im typing from a cell phone (will try to correct spelling after posting)

Thanks for any responses, help, info in advance and have a great Monday!!

 

I know this was a while ago, but did you ever get this issue fixed? If so what was problem?

 

red wire with black tracer just above and center of the loom (you can see the bare wire) was grounded out on that bracket. I fixed that and speedo started working and it came out of limp mode and shifted through all gears perfectly as well. This harness if i remember correctly was driver side under vehicle by the bellhousing. Could have been passenger side however

 

Thanks a ton, had a near identical problem and ended up with the same fix. Wire was grounding out on transmission housing.

 

I hope someone can help.I see similar issues.the other night I came out if store and when I started truck the speedometer would jump up To 80mph but return to normal when I would start driving.I made two other stops and each time speed would jump to high then drop when I would shift and start moving I drove home 30 miles with no problems.next day when I started it speedometer did not move.I have low and second but not 3rd or overdrive and no speedometer. I replaced speed sensor but still nothing.problem is wife has stage three cancer and I'm out of money.spent last on part and now spending night in rig not enough gas to get home.I will go collect cans to get gas to get home but need to get this figured out.I can't keep driving twice a week in second gear.

 

Crawl up underneath and follow the wiring harness from the transmission everything is electronic on these, the speedo jumping happened to me as well, find the broken wires and splice them back up and you should have no issues, you're tight on cash right now so just to get you by, get the wires all separated and electrical tape the hell out of them, took me months of replacing sensors and wasting money just to find out it was a couple wires grounding out. Don't waste your money anymore just have some patience, crawl under the truck and find the big round connector going into the tranny (passenger side on mine I believe) it runs up along the firewall through a metal round clamp/bracket as seen in the picture above. You'll get it.