Archived no or intermittint 3-4 shift

[PetesonM]

Kinda stuck. truck 99,Gorend fully built trans. problem, trans random shifting it will shift fine up to hwy speed (sometimes) and then randomly down shift into 3rd. it is not in limp mode. no code. It just will not shift into 4th (sometimes) or will downshift into 3rd#@$%!. tv is ok, trans fluid ok, and apps voltage correct. all conectors cleaned any thoughts on what else to check before droping the pan? speed sensor? or am i headed for a gov or shift solenoid? Thanks for help in advance

 

[JLandry]

Did it suddenly start doing this one day, or has this been happening ever since the rebuild?



Have you called Goerend for advice?



Best regards,



John L.

 

[PetesonM]

Just started thursday, yes i called Dave but has not had time to call back yet. I picked up my trans pressure gauge tonight so tomorrow i hope to have some readings. This old girl is suppose to make a 200 mi trip sunday night and i for the first time in 9 years im worried she will not get me there. Anbody else??

 

[JLandry]

Just started thursday

How many miles on this transmission?



I noticed you replied to a post back in January indicating your transmission had a problem. Was that problem different from this one? Was it repaired?



Anyway, the current problem sounds like it could be either a malfunctioning overdive (3-4 gear) shift solenoid or an electrical fault (wiring or PCM).



It's a long shot, but since the output shaft speed sensor is inexpensive and easy to swap out, it can't hurt to replace it on the chance it might be contributing. If that doesn't help, at least you'll have spare.



John L.

 

[PetesonM]

Thanks I'll start there. And hook up the pressure gauge. do you know what the pressure reading should be? If that doesn't work I have a valve body from the broke imput shaft trans I can swap and see if that fixes it. My fear is its a wire somewhere.

 

[JLandry]

do you know what the pressure reading should be?

See the information starting on page 21-658 of the 2001 Factory Service Manual HERE.



Good luck,



John L.

 

[PetesonM]

Not to be a pain or you may not know but do you think that the pressures will be diff on the gorend??

 

[cerberusiam]

Yes, the pressures will different on a built transmission. What the pressures are are not as important as how they rise in most cases.

Typical problem with intermittent OD can be the gov solenoid\transducer, OD solenoid, or a problem with the OD unit itself. Your best bet to narrow the problem down is a switch to the OD sense wire and see if you can get it to manually activate and hold. That will tell you if it is an electrical or mechanical problem. Pin #6 on the trans control harness is the OD circuit, tap a 18 gauge wire to it thru a switch and then to ground. When oyu ground that wire it should engage OD and stay there. You might get a CEL and limp mode with a resistor betyween the switch and ground but it should give you an idea if it is electrical or mechanical. If you add the resistor you can then drive it all the time with manual switch.

You will want to check gov pressure and make sure it is rising smoothly as you speed up. If you see hangs, dead spots, or jumps the solenoid may be sticking or the transducer not reaidng correctly.

Checking the OD circuit to see if it is trying rise in pressure when it should be in OD. You may need the switch to validate that it is demanding OD or you will need a scanner capable of seeing the commands.

 

[PetesonM]

Awsome your on the ball! One more thing then off to test new speed sensor. The pressure port above the tv cable is where i can pull all the pressure readings correct?

 

[JLandry]

Not to be a pain or you may not know but do you think that the pressures will be diff on the gorend??

Assuming a high pressure valve body, accumulator line pressures should be 25-35 psi higher than stock... 90'ish psi at idle and 120-150 psi at full throttle. As cerberusiam pointed out, the exact pressure isn't critical so long as the pressure rises immediately as the throttle is advanced.

The pressure port above the tv cable is where i can pull all the pressure readings correct?

It's port number 3 in the attached diagram.



John L.

 

[PetesonM]

ok so i replaced the speed sensor this morn and installed the pressure guage on the port driver side above trans line, no pressure till comand for fourth gear psi will go up to 50psi 4th gear will enguage and then hold at 100 to 140 depending on tp. however it seems strange to me that fourth gear will not disengage/pressure drop till very low speed like 15-20mph. The 4th gear problem seems to have gone away?? however the tc is doing the lock unlock thing?? I have a switch for that so i can work with that. Starting to think pcm or wire because it was raining out when this started.

 

[PetesonM]

checked also at port #3 in drive 90psi moves with tp up to about 150-160 psi tc locked and heavy gas??? im going to say speed sensor for now. i have a long drive tonight about 200mi so i will throw in some extra parts and tools and hope for the best, worst case drop the pan and put in the used gov sol! truck stop repairs wish me luck!

 

[cerberusiam]

The OD does not sound right, IIRC that should jump to 90 psi on engage then go up depending on throttle position 10 110-140.

Port #2 is the gov pressure, thats the the rise should eb smooth up to about 65 psi then jump to 90 or better when OD enages.

Port #3 is the apply pressure regulated by the TV cable, more throttle equals more apply pressure.