Sonnax issue?
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Senior User
Joined: Dec 2003
Posts: 170
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From: Union Grove, Wisconsin
Sonnax issue?
About 6 months ago, I installed the sonnax kit. Everything seemed to work the way it was intended. Letely, I've been noticing then when shifting from 3rd to 4th, it takes longer to shift. It seems worse when I'm easier on the throttle. The RPM's climb to approx. 2300. First to second to third all shift fine. Could this be a sticking valve?
Postmaster
Joined: Nov 2003
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From: Utah County, UT
How many miles on the tranny? There is a sensor towards the tail end of the transmission that with some clever math by the PCM determines the amount the transmission is slipping. If the clutches for 3rd are wearing out and starting to slip more, it will hold it in 3rd longer before it shifts. If you ease up on the throttle will it shift?
Thread Starter
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Senior User
Joined: Dec 2003
Posts: 170
Likes: 0
From: Union Grove, Wisconsin
Cangim - Yes, if I let off the throttle over 40mph it will go directly into O.D. That's the thing I didn't like about the sonnax when I first installed it. It seemed like the truck would go from 3rd to O.D. and skip 4th all together. Especially when I'm easy on the throttle which is all the time. If I do give it more throttle, it will go into 4th then O.D. I don't remember the tranny waiting till about 2300 rpms' to shift when I first installed the sonnax. The truck and tranny have 105k on them. The trans oil was changed when I did the sonnax mod.
Postmaster
Joined: Nov 2003
Posts: 3,595
Likes: 0
From: Utah County, UT
Sounds like it is slipping, sensing a more torque being put through the transmission therefore it holds gears longers. Also, the 4r100 is a 3spd w/OD. There is only four gears. Why most think there is more is because the T/C locks and drops the RPMs down giving the impression that is shifted again.
