I replaced the speed sensor in the differential yesterday, but it didn't make a lick of difference. I've been having intermittent problems with the speedo ever since I bought the truck. When the speedo starts acting up, the truck will sometimes momentarily cut out and buck a couple of times. It was first mentioned this post, post # 35. I had the truck in the shop for a new oil cooler, EGR delete, standpipes, dummy plugs and STC fittings, and when I got it back it ran worse than before as detailed here in post #1. It turned out I had a torn IPR screen. I replaced that and it cleared up all of the problems I had except for the speedo problem I originally had. The truck actually ran perfectly on the way home from work yesterday, about 20 miles. No speedo problems and no cutting out. This is not unusual, as the problem is only intermittent. I put the new VSS in last night but did not drive it until this morning. This morning, same thing again, speedo swinging crazily. When cruising about 70 it the speedo would suddenly jump up to about 90 and that is when the truck would cut out and buck a couple of time. The VSS is a Dorman product and proudly displays "MADE IN CHINA".

Should I try a better quality sensor? Rock Auto sells an Airtex/Wells sensor that seems to be of good quality, but I can't determine where it was manufactured. The only reason I bought the Dorman is because I could get it next day from Amazon. Should I be looking at another source for the problem? This is very discouraging because this one thing is what is keeping the truck from being mechanically sound, and I'm trying to get it ready to tow an RV this summer.

 

First, for sensors I would not use any other then Motorcraft.

There have been incidents where the wire drop from the frame to the axle's sensor have broken from fatigue.

 

Thanks, I'll look at the wiring. I like Motocraft products, but do they really have to charge $100+ for that sensor?

I also should have mentioned that my fuel gauge sometimes does that thing where it might go to E or it might go to F, and then go back to the correct position. Maybe I need a instrument cluster repair. But that shouldn't effect how the motor runs. Do you think the VSS problem would contribute to the running problems I've mentioned?

 

So, I'm not an expert here and I hope someone more knowledgeable chimes in: I thought when this came up before we were talking 2 different VSS units, one in the rear diff for the ABS and one in the trans that is the one that affects the speedo. Why didn't you replace the trans module?

Or did I miss something? Did you ever call White bear Autonation parts and talk to them about this part?

 

Well I'm confused about the function of the two sensors. I thought the one on the rear was for speed (VSS) and the one on the trans (TSS) was for shifting. I'll pull the one on the trans and take a look at it...

I never did call White Bear.

Edit: I just signed up on their site and will call after I look around a bit.

 

I believe the one in the rear diff is just an ABS sensor. When mine acted up it would just shut the cruse control off and the ABS light would come one. It never did mess with the speedo.

 

Trans is speed

You can ohm it out iirc

It can't shift right if it don't know correct speed

 

So I guess the bucking is it trying to downshift or something? Doesn't sound good for the trans. I was looking at a diagram on fordparts.com and it showed two sensors on top of the trans. One at the tail, which I think is the one we are talking about, and one more forward. I'm on my way to get a floor jack. Tired of the bottle jack and I'm too big to get up under the front of the truck.

 

If you don't believe me (we used to tap that for speed with our DAS):

https://www.ford-trucks.com/forums/1...l#post12712763

 

Thanks for the link jack

We'll mark is the trans god so I'm inclined to believe him

I read something the other day that said vehicle speed comes from the rear most sensor on the trans but I better double check
It could very we'll be the case I read it too fast and saw speed thinking it was vehicle speed when it was really turbine speed

But I would also think turbine speed would be figured into shift points


Depending the type sensor you maybe able to test with a DVM

 

I think I've gone through this about a hundred times on different forums. With those two sensors on the trans and some of the literature there is a lot of confusion.

But since there are so many changes since I got out of the industry in 2008 I'm always ready to be wrong. Most of the vehicles we had always took the ABS sensors output, processed in the ABS computer, then sent the speed out to PCM, cluster, etc. We just spliced into one of those circuits post ABS. It would be rare but we also spliced into some harness off the sensors themselves, but it might not be as strong.

 

Thanks as well from me Jack for the link. So now that I have that all straight, I know that I have replaced the right sensor. As stated earlier, the speedo did act up the morninig after the sensor was replaced. However, I drove the truck about 100 miles last night, making maybe three or four stops, and it ran perfectly the whole time, I even used the cruise control with no problem. The only thing that wasn't right was the occasional fuel gauge thing, with it being full or empty now and then.

So could my problems the gauge cluster? I don't know where else to look, I don't even know if the sensor I put in is any better than the one I took off. Still need to look at that wiring.

Here's an interesting thing I read yesterday from Circuit Board Medics:

"The Super Duty (or SuperDuty) instrument cluster has several common issues including stuck gauges and the battery saver relay circuit. The most common problems are:

Gauges sticking, inoperable, or giving incorrect readings (speedometer, tachometer, coolant temp, fuel, voltage, turbo (Powerstroke) etc.)

Intermittent power to radio, power windows, (driver's side only on mine, intermittent,) or interior dome light

Intermittent power to all gauges

Low fuel indicator on at all times with fuel gauge also reading empty" (except that mine might also read full).

The only difference between my issues and those above is that my speedo does not seem to be sticking, but instead bounce around. Although, on a few occasions it did just sit at 0 MPH while I was driving down the road. Still doesn't account for the stumble in the motor though.

 

If your having those issues (posted above or some of them), I'd be sending the cluster off.

 

The sensor on the rear axle is used to measure vehicle speed.

There are three speed sensors on the 5R110 transmission. The one near the bellhousing is the turbine speed sensor (TSS,) the one in the middle of the trans is the intermediate shaft speed sensor (ISS,) and the one at the tail of the trans is the output shaft speed sensor (OSS.)

 

Thanks Mark. I assume the TSS is for shifting. Could you tell me what the other two sensors on the trans do?