Engine/Transmission (1994 - 1998) another transmission tale

[bill threlkel]

Well on monday i took my truck to a shop because the transmission was shifting in to overdrive when it was in low. Thats right when you push the button and you should be in low it will sometime shift into overdrive, very unhandy. They first thought it was the solenoid pack for the overdrive, changed that because it gave a code for that. Then when it was driven it did the same thing. Next came checking the wiring harness and the pins on pcu, they checked out ok. The next thing they are going to do is check the valve body as they think they maybe leaking across to the overdrive.

This problem only happens when the truck has been driven at least 40 miles and trans. is good and warm.

If any body has any ideas lets have them, sure would like to get it fixed.

Bill

 

[Howard Durand]

You may have a problem with the PCM.



First try unpluggaing the TC/OD control cable at the transmission. That should prevent the transmission from electrically shifting into OD.

If that is the case, then your problem is either in the wiring or the PCM.

Bear in mind that not only does the transmission heat up in 40 miles but so does the rest of the truck. The PCM could be failing as it heats up.

 

[bill threlkel]

Yesterday i call them at the shop and they had changed there mind and said that the think it was the pcm. they have one on order and should be in on tuesday. Thanks howard i will tell them about unhooking the wire at trasimission to test if the part not here on tuesday so they can look some place else for the problem.

Bill

 

[Reb.B]

its not the PCM. You can manually energize the solenoid, but it will only shift into O/D when the shifter is in drive. If it goes first to o/d while in drive then you have a pressure/gov. problem, if the shifter is in first on then goes dirrectly into o/d, then there is a shift valve problem. You must remember, the first three gears in your transmission are controlled hydro. not electric.

 

[bill threlkel]

It goes into overdrive after it shifts into third, if you put it in first it will stay there, if you put it in second it will stay there. But when you put it in drive and it shifts from first to second then to third it then shifts to overdrive. Also it won't do it when the truck is cold it has to be driven at least 40 miles. The truck has always been a problem ever since i got it even on the last transmission, put the BD products on it and the trans shifted better but would take times acting up. Hope this will fix the problem if it doesns't then i will find a donner and put a standard trassmission in it. You can only put up with so much trouble from that auto trans.

Bill

 

[Reb.B]

hmmm, those 47 rh are usually so reliable. So it sounds like it wants to shift too fast when its in drive, but if you go through the gears manually, it okay. Please specify what problem is with the transmission and how you want it to shift.

 

[Joe G.]

Bill,



The 40 miles to get it to shift to OD is probably the temp sensor in the cooler line. Try removing the connector and putting a 1K resister in it. That should take care of the 40 miles problem. If it does take care of the 40 miles problem you can leave the resister in there or replace the sensor with a new one. I doubt very much you need the sensor since you live in Cool.



If the OD shift is the only problem then check the TPS voltage. If all of the gears shift too quick then you may have a governor problem. You will need to check the governor pressure in the latter case.



If the TPS is causing this then take a look at this thread:

https://www.turbodieselregister.com/forums/showthread.php?t=130979

 

[Howard Durand]

Bill,

Your first entry states that it would shift into overdrive when the transmission shift lever is in low. Is that statement still valid?

 

[bill threlkel]

With the overdrive locked out the truck will shift into overdrive after 3rd gear.

 

[Joe G.]

Bill,



Are you sure that it's not the torque convertor clutch locking up? It will do that in 3rd if OD is locked out. The shift sequence is 1 - 2 - 3 - LU if OD is locked out (indicator light on). The shift sequence is 1 - 2 - 3 - OD - LU if OD is not locked out(indicator light off).

 

[bill threlkel]

up date got my truck back the pcm was ok they tryed a new one with no difference. what the truck did was the 1-2-3 shifts with the lite on the lock out switch it would continue to shift to over drive. They checked the wire and every thing. Could not find the cause. So they put a switch in to manual turn off the overdrive solenoid. works great now i can choose when to have overdrive by the flip of the switch.

thank for eveybodys help Bill