Speedo jumping around

emilyyjustine · Jul 17, 2017

So I need some help! I have a manual 2002 f350 and my speedometer has been jumping a lot. It sits at 0 if I'm going 20mph or slower but as soon as I go over 20 it is all over the place. What could be causing this? Someone told me it was because I had a leak in my rear diff but I opened it up and changed the oil yesterday and put a new seal on it and it doesn't leak anymore but the speedo still jumps around. So I'm pretty sure they were wrong....

I have also changed the speed sensor and checked the wiring and still nothing... hopefully you guys can help me out! (I am new to working on my truck so if I sound dumb I am sorry)

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Arisley · Jul 17, 2017

Do you have front ABS. If so, that could be jacking with it.

emilyyjustine · Jul 17, 2017

I think I do... and my abs light is on so I'll check that. Thank you!

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Arisley · Jul 18, 2017

If you only have rear ABS, and the light is on, that is the rear VSS, the tone ring on the ring gear or the associated wiring. Which would also mess with your speedo.

Magnum PD · Jul 18, 2017

The tone ring on the differential needs to be in good shape as well

emilyyjustine · Jul 21, 2017

So finally got around to checking the tone ring and it's not in good shape

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Arisley · Jul 21, 2017

You need to tear into that and check things out.

sootie · Jul 21, 2017

there will be more wrong than the tone ring....holy crap!

Arisley · Jul 21, 2017

I am betting on spiders torn up.

8WR_ZJ · Jul 21, 2017

Yeah not to mention with that much metal in the oil bearing surfaces are going to be rough and pitted. Hope the R & P finish is still good. How long has the speedo been jumping and or abs light been coming on? See it a few times on these rear ends.

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emilyyjustine · Jul 21, 2017

The speedo has been jumping around since the 11th. I opened it up on the 13th to change the gear oil and I didn't notice anything. I changed the speed sensor and it still didn't work. So I pulled out the speed sensor and saw that. But I have moved it back and forth and it only seems to be that one spot. It doesn't make any noise or anything.

Do you guys think this is something I could fix on my own or should I take it in?

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Magnum PD · Jul 22, 2017

Take it in. Needs to be looked at. New bearings and ring.

heavydoc · Jul 22, 2017

emilyyjustine said:
Do you guys think this is something I could fix on my own or should I take it in?

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Without knowing your skill level and tools it is had to say, but there is ton of info out there for these rearends. The hardest part is setting the bearing preload and backlash

8WR_ZJ · Jul 22, 2017

I think its easy but then again ive done thousand of times. Are you confident using hand tools, being overly clean, and taking precesion measurements? Bare minimum pull the cover, clean it out, take pictures of the ring gears. If you put more 200 or so miles on it i would pull the carrier out and inspect the carrier assembly, carrier bearings and pinion bearings. Take pictures. Then pull the rear hubs and have a look at those as well. Take pictures. Then clean everything remarkably well. If i was doing the work and you had it all pulled apart and cleaned extremely well i would take 200 to 300 of the price. I hate doing gears repair on rearends thay are full of shavings. Last where are you located.

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emilyyjustine · Jul 22, 2017

I have never done anything like this before... I have tools but I feel like I prob won't have the tools for this... and I don't want to mess it up. I just had it open and changed the gear oil but the person that told me how to do it said I don't have to clean the gears and stuff. There wasn't a bunch of metal in it which is weird. Also nothing looked messed up when I looked at it.

this truck is starting to be a money pit

thanks for all your help guys. I think I'm done trying to fix this one. I'll be taking it in

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emilyyjustine · Jul 22, 2017

8WR_ZJ said:
I think its easy but then again ive done thousand of times. Are you confident using hand tools, being overly clean, and taking precesion measurements? Bare minimum pull the cover, clean it out, take pictures of the ring gears. If you put more 200 or so miles on it i would pull the carrier out and inspect the carrier assembly, carrier bearings and pinion bearings. Take pictures. Then pull the rear hubs and have a look at those as well. Take pictures. Then clean everything remarkably well. If i was doing the work and you had it all pulled apart and cleaned extremely well i would take 200 to 300 of the price. I hate doing gears repair on rearends thay are full of shavings. Last where are you located.

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I am in Logan Utah

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