Engine/Transmission (1994 - 1998) transmission problem

[CBrabec]

I have a tricky problem going on here. When the truck sits outside in cold weather (under 40*) for more than 3 hours, I'm having an issue with the truck shifting into OD. The truck will shift through all the gears until it reaches 3rd gear and then the truck's rpm's keep climbing and it won't shift into OD. Now I'm noticing that when the truck's engine temp gets up to around 160* all the problems go away and the truck starts shifting normal. I replaced the transmmission temp sensor and that didn't help and I had the transmission rebuilt by Floor it Diesel about a year ago. Since these trucks are so sensative with vaccume pressure, does this sound like a possible vaccume pump issue or electrical? This only happens when its cold outside, had no issues during the summer. I'm stumped with this one



Chris

 

[HBarlow]

I think the trucks with automatic transmissions are programmed to lock out OD until engine coolant and ATF are up to normal operating temp.

I'm not sure but it probably protects a cold engine from lugging at low rpm and the transmission from shifting into OD with cold fluid. Perhaps ATF is thicker when cold . . . ?

 

[CBrabec]

Not sure if that's it because this problem didn't occur last winter when I bought the truck. The funny thing is when I put the truck in the garage and plug it in, I have no issues which is why I think its electrical. But on the other hand, when it is outside, not plugged in, when I start the truck my red "BRAKE" light is on but is dim and it stays on till the truck warms up and the transmission still does the same thing which is why I'm wondering if it could be vacuume related. I don't know...

 

[Dieseldemon]

Vacuum does not have anything to do with the transmission not sure but I think the engine temp sensor has something to do with it I think it is susposed to upshift at 59 Deg.

 

[JMcCoy]

I think the trucks with automatic transmissions are programmed to lock out OD until engine coolant and ATF are up to normal operating temp.



I'm not sure but it probably protects a cold engine from lugging at low rpm and the transmission from shifting into OD with cold fluid. Perhaps ATF is thicker when cold . . . ?

x2. I believe that is normal.

 

[RCorbeil]

Right on Harv.



RCorbeil

 

[BigPapa]

it is supposed to up-shift at 59 Deg.

There's the correct answer.

 

[CBrabec]

I think you guys are right! What's throwing me off is I talked to 4 other friends of mine all with automatic 12V's and not one of them has this same issue with the truck not shifting into OD even when cold. Maybe its just my truck

 

[BigPapa]

My '95 would do it. I've not noticed it with my current truck. I've changed jobs and I have a couple of miles of driving before I get up to OD speed now.

 

[CBrabec]

John at Floor it Diesel who built my transmission said I can't run ATF +4 in the transmission so he told me I can run Dextron/Mercon III. With that being a thicker transmission fluid, do you think that could part of my issue when its cold? I was thinking about trying Amsoil's synthetic fluid, but not sure if that would cure the problem.

 

[JMcCoy]

John at Floor it Diesel who built my transmission said I can't run ATF +4 in the transmission so he told me I can run Dextron/Mercon III. With that being a thicker transmission fluid, do you think that could part of my issue when its cold? I was thinking about trying Amsoil's synthetic fluid, but not sure if that would cure the problem.

Why can you not run ATF+4? Your friends probably don't realize what their trucks are doing. Not everyone is as tuned with their vehicles like us TDR members :-laf