Had transmission rebuilt. since then the truck will drop in and out of overdrive around 40. this is only after 30 min of driveing on warm days and when very slightly accelerating, like keeping up with traffic on a slight incline. if I hold the gas pedel steady the car starts to increasingly occilate in and out of gear. If i just hold the brake pedal enough to turn on the lights, not slowing the truck, the problem goes away. had complete tune up including coils and wires, exact same. Fuel pressure I am told is good 38 psi (filter changed anyway).
Lock out the overdrive until you are cruising at over 45 MPH…
This is a post that Transman618 should be able to answer, so Bump.
In the mean time please provide the year of manufacture for this truck.
The year is important, are the transmission shift points controlled by a TV cable (700R4) or by the PCM (4L60E). I have a 2000 S10 Blazer with a 4L60E. The torque converter lockup engages around 39 - 40 mph. At this speed, any application of gas will disengage the lockup. Is this occuring or is the truck downshifting from 4th to 3rd? If the battery is not fully charged (12.6 V), the torque converter lockup will not engage until my Blazer has been driven for 25-30 minutes. Also the idle will be a few hundred rpm higher.
If it’s an older truck with a 700R4, the TV cable may need to be adjusted.
it is a 1998 chevy s10 pickup. L460E. hard to tell if it is downshifting or just coming out of lockup. rpm’s do increase but which is causing the increase??? i dont know.
The rpms will increase when the lockup disengages because of the normal slippage in the torque converter.
That sounds like the TCC falling in and out of lockup. Heres what I would do if I were checking it. 1. I would scan it and see whether the TCC action is being commanded by the computer. If it is then I would be checking to see what, electronically is causing the computer to command the lock and unlock of the TCC. A bad TPS comes to mind. I would also find out whether the rebuilder addressed the TCC regulator valve in the valve body during the overhaul. These year 4L60E’s had problems with the TCC regulator valve wearing out its bore in the valve body. ATF would leak by the worn valve and cause the converter clutch to chatter slip and fall in and out of lockup. The valve body should have been modified during the overhaul to prevent this problem.
When you hold your foot on the brake, the TCC will be inactive. Therefore the shifting you feel will stop. I think your truck is acting normally. Just lock out the overdrive until you reach cruising speed.