speedo n trans problem linked together? - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 23 (permalink) Old 08-09-2014, 12:33 AM Thread Starter
Bobs 7.3
 
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speedo n trans problem linked together?

My 02 speedometer will stick at 35mph and when I stop alot of times it will stay there and not return to 0 mph and cause the tranny to be in second gear upon take off. Sometimes it will take off in 1st gear but alot of times it stays in second no matter weither the o.d. button is on or off. I get a blinking o.d. light when it all happens but as soon as it corrects itsself the o.d. light stops blinking and it wont store no codes (well atleast the torque app pro is saying theres no trouble codes stored).Also when it does this and going from drive to neutral or reverse the engine will rev up for 2 seconds and drop back down. It also will add miledge to the odometer when stuck at 35 mph when in park and running. If I let it sit shut off for a couple of hours it goes to normal and everything works as it should until after an hr of driving or so and sometimes it doesnt act up at all for 2-3 hrs. I changed the vss and the oss in the top of the tranny, checked all the wiring and cant figure it out. Sometimes it will go to 0 mph and stay there and when it does that ther trans shifts normally when taking off. Any help is greatly appreciated. The trans never acts up until the speedo does then when the speedo corrects the trans is perfect again.
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post #2 of 23 (permalink) Old 08-09-2014, 12:35 AM Thread Starter
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Re: speedo n trans problem linked together?

Also it started this 2 days after I changed out the rear diff fluid to royal purple with the frictiom modifier already in it and installed an extra capacity finned aluminum cover. No abs light ever (unless a wheel bearing goes bad).
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post #3 of 23 (permalink) Old 08-09-2014, 12:52 AM
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Re: speedo n trans problem linked together?

IDK for sure
but i would just unplug the rear VSS and see what happens

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post #4 of 23 (permalink) Old 08-09-2014, 01:00 AM Thread Starter
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Re: speedo n trans problem linked together?

Ill try that Zmann. I had a wire off my tru-speed about 4 years ago and ran with no speedo for about 8 months till I found the problem but it never messed up my trans not to go into first when taking off from a start it was just a dead speedo and trans worked great.
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post #5 of 23 (permalink) Old 08-09-2014, 01:19 AM
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Re: speedo n trans problem linked together?

i just wonder if the hall effect sender can be sending a false signal ?

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post #6 of 23 (permalink) Old 08-09-2014, 02:25 AM Thread Starter
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Re: speedo n trans problem linked together?

Hmmmm, where would that hall effect sender be located? It seems like its getting a signal from elseware when stopped. I changed the vss and the oss. Just ordered a new oss for the front by the converter (forget the correct name they use for that one) but its the same sensor as used in the rear. Figured well then they all will be new. Ive also heard where the alternator will cause speedometer problems but what would cause the speedo and transmission combined problems. Whatever it is once it corrects itsself they both work flawlessly. If the speedo stays at 0 mph I noticed the trans is always in first gear when taking off but when stuck at 34-35 mph alot of times it starts in second or third like somethings telling the trans to believe its still moving at that speed and always shifts great with no slipping or anything else unusual. The big question is whats telling the trans its still moving or letting it think it has stopped but it really hasnt?
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post #7 of 23 (permalink) Old 08-09-2014, 02:30 AM
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Re: speedo n trans problem linked together?

the hall i was referring to is the VSS it uses the hall effect to read speed so if you replaced it that blows my theory

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post #8 of 23 (permalink) Old 08-09-2014, 12:28 PM Thread Starter
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Re: speedo n trans problem linked together?

I put a new ford one in it and then yesterday went and got another new one and tried that but it wasnt 3 blocks and it was stuck at 8 mph and shortly after corrected itsself again. The trans shifted as it should from take off due to it only seeing 8 mph whitch it would be in first at that speed anyhow still. Whenever it sticks it will up shift right when it should threwout the gears its just when you stop most of the time the trans will hang in second or third (what gear it would be in at that speed). when you pass that speed (going by torque pro) it will shift fine to the next gear at the right time and into o.d.
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post #9 of 23 (permalink) Old 08-09-2014, 12:29 PM Thread Starter
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Re: speedo n trans problem linked together?

Wheres Mark K he should have some good input on this also.
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post #10 of 23 (permalink) Old 08-09-2014, 12:48 PM
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Re: speedo n trans problem linked together?

Something's wrong. There is my input. ;-)

A speedometer problem will affect the transmission. The PCM uses the VSS signal to decide what gear the transmission needs to be in. It's not going to downshift to 1 when the truck is going 35 MPH.

Have you removed the VSS to see if there is something stuck on it? The sensor is magnetic. A piece of metal stuck on there can cause weird symptoms.

Mark
Former Ford Automatic Transmission Engineer

“The good thing about science is that it's true whether or not you believe in it.” ― Neil deGrasse Tyson
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