4r100 1-2 shift problems, HELP!!

[codyrock87]

I have a 12/99 f-350, most mods in sig. If you let the truck idle less than 1-2 mins and take off it will make the 1-2 shift once, after that it will only shift if you lift off the throttle. Sometimes the o.d. light will flash but it only gets a code 1-2 shift malfunction? Does this mean its in the valvebody? I'm lost here, after it warms up you have to be at 20mph and 23-2500rpm and let off the throttle and it will shift. It does have a banks transcommand on it and I have used the bypass plug with no change.

[ToMang07]

First I would lose the banks trans/crap, both for diagnostic purposes and so it doesn't dammage the tranny more.

Second, time to get it scanned and find out whats actually wrong, could be a shift solenoid, could be a TC lockup problem, or the transmission could be toast.

Only way to know is to find out whats going on. Need a good scanner (NOT a generic one, they won't work) like Auto Enginuity or a Snap-On, etc.

[codyrock87]

We have a Mac mentor scanner at my work, I will see if I can find the trans shift solenoid status. It shifts up and down in all the other gears fine

[codyrock87]

Got a scanner hooked up, it will command 2nd gear at about 10-15mph but wont shift until 20mph and letting off the throttle. It shows no fault for the shift solenoids and When switching gears the lever position is correct. If you manually put the truck in 2nd then it will slip, pop it in drive and it will pull anything in the same gear

[codyrock87]

I'm going to swap some stock tires in the rear to see if it will fix it, the speedometer is off a little

[slamb862]

i have the exact same problem with a 2000 f350. any luck?

[codyrock87]

I recently installed a superlift speedometer re-calibrator for the tires and got it set up properly so that my speedometer is accurate now, no change in transmission operation at all and it is still doing the same thing. What do i check now? Replace the solenoid pack or the valvebody?

[gijohn48]

what the problem is is the early 4r100 had a sprag that was replaced with a bad unit... and then they went back to the original sprag which does the shifting from 1-2... you have the bad sprag is my guess (same here) and the only way to fix the problem is have the transmission rebuilt. all the power programmers just help this problem along so get a high quality rebuild and you will be fine from there on out.

[gijohn48]

By the way I had a highly recommended transmission shop scan my truck for me and all it said was 1-2 shift malfunction....

[Bailout]

I had the same problem - a BTS valve body fixed mine... Just throwing it put there. It was a 1-2 shift problem.


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