Speed sensor and shift points?
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Elder User
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Speed sensor and shift points?
I just changed my speed sensor.The a.b.s. light on and the o.d. light flashing.Before I changed the speed sensor the truck used to shift into o.d. to early,I think.What I mean is it would shift up through the gears.and as soon as it hit the last geart it would just dump into o.d. My question is ;does the sensor heve any control over shift points.Also it never really felt like it would shift in anygear properly.What I mean in this is it would also dump in all gears a little too early,in my opinion.Just by the seat of the pants feel.Now it seems perfect and rock solid.
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Elder User
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Originally Posted by John311t
Are you sure its not your T.C locking up when it shifts into O.D.
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Joined: May 2007
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Originally Posted by dryfly
No, I'm probablly not describing it properlly.But Just dont know how else to describe what it did in the past,before yesterday.But to say that it just dumps into the next gear real fast.It wouldnt let the rpms build up.Like the carburated cars you used to be able to adjust your kick down cable.And if it wasnt properlly adjusted it would just drop to high gear fast.
This might sound crazy, but my truck acted sort of how you are describing when I forst got it. I pulled the battery cables on both batteries to clean the posts and left them off for 30-45 minutes. I did this because I had read that the tranny has adaptive learning that adjust it's shifting, and can be reset when the bats are left disco'd for about 30 minutes. I but the cables back on and took it for a spin and it shifted like a different truck. It holds each gear a little longer now, and seems to shift more crisply. If you have your owners manual it also goes into a series of steps such as running the AC for a minute or two after prolonged battery disconnection. I don't think removing the battery cables is a magic bullet, but it helped me for sure.
Post Fiend
Joined: Jun 2006
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From: Central, Al
The speedo is fed from the ABS system but the PCM takes in input from the VSS on the pumpkin and uses it for shift calibration. So if yours was bad the speedo could continue to work (with the front wheel sensors) but the PCM wasn't getting a clean VSS signal and making crappy shift decisions.
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That what happened to me, it can also cause poor cruise control operation. My VSS was crappin out for a long time, i had a front wheel bearing go out and i had 2 spare NON abs wheel bearings laying around so i put those in, and my speedo went bye bye. Replaced the VSS and everything was much better than before. So your condition sounds exactly like mine. That sensor does ALOT more than i thought it could, expeically since my speedo worked into the front ABS sensors where pulled.
Post Fiend
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From: Central, Al
Originally Posted by bdalton
I had read that the tranny has adaptive learning that adjust it's shifting
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Originally Posted by amiller93
Only on the gassers, the diesel 4R100 has no learning curve.
Good info. Weird how I did nothing but what I posted above and it seemed to correct my problem. Must have been something else...
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Thread Starter
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Elder User
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That sounds like a probable reason.I dont have front abs but I certainlly did have a bad speed sensor.
Originally Posted by amiller93
The speedo is fed from the ABS system but the PCM takes in input from the VSS on the pumpkin and uses it for shift calibration. So if yours was bad the speedo could continue to work (with the front wheel sensors) but the PCM wasn't getting a clean VSS signal and making crappy shift decisions.