Cat It28G intermitten shift

[Jonmiller]

I have a cat IT28g prefix 8CR i have a issue with the machine intermittenly not wanting to shift trans was rebuilt recently and looked great inside FNR lever doesnt fall in to the known problem group i have checeked all the wires from the FNR lever to the ecm as the manual says to no issue there just the wire from the key switch reading 10 volts only diffrence my fellow techs had swapped the ECM and that didnt fix the issue all of the solenoids on the trans look and function good and wires to the solenoids all have the proper Ohms readings also there is no codes and im lost and need help any one else have this issue before or can some one help it would be greatly appreciated

 

[Nige]

What doesn't want to shift..? Direction or speed - or both..?
Are you sure there are no Codes..? How are you pulling the Codes..?

 

[Jonmiller]

The machine doesnt want to shift out of 1st gear there is no shift when the lever is switched to 2nd 3rd but 4th you feel a shift but it is second speed and according to ET there are no codes and ET also says that the control lever is commanding the ecm correctly

 

[Nige]

First question. Why was the transmission rebuilt..? Some kind of problem..?

Have you checked the downshift (kickdown) switch circuit..? The switch is mounted on top of the hoist control lever.
What you feel when you shift to 4th forward must be #2 (forward high) clutch coming in. That is the only speed either forward or reverse that uses that clutch. What's confusing is that the clutches for 4th speed FWD should be #2 (fwd high) and #5 (3rd speed). If you are not getting a genuine 4th speed something is not right there either.

I take it that you only get 1st speed in reverse ..?

It would appear that the following clutches are working
#1 - forward low
#2 - forward high
#3 - reverse
#6 - 1st speed

What are the P1 & P2 pressures for each of the 7 transmission (4 FWD, 3REV) speeds at both Low & High Idle..?

 

[Jonmiller]

The trans was rebuilt previously we recived it with a over heat issue and found a plug in the tourqe converter was missing allowing it to bypass the cooler
The hand lever was replaced for the FNR portion being inop
As for the shift when i select 4th gear it shifts normal just has the same speed as 2nd gear wont go any faster
Correct on only haveing 1st gear in reverse

Also as of right now the machine is working correctly i have not done anything to corect the issue just went to pull it in the shop and it shifted great now i have a operator out running it till it acts up again

 

[Nige]

When it presents the problem again get the pressure gauges on it and take P1/P2 readings in all speeds would be my first suggestion.

 

[Jonmiller]

Alright ill try to keep you updated on what gos on thanks for your time

 

[Nige]

Another question. When the transmission is playing up you have 1st speed, when you shift the control to 2nd speed do you get neutral or is it just that you don't get a shift out of 1st speed..?

 

[Jonmiller]

Machine stays in first

 

[Nige]

So if you shift 1->2->3->4 FWD after the machine starts moving nothing happens until you hit 4th speed, at which point you say you can feel the high range clutch come in. That sounds very much like something electrical/electronic, however I'm amazed that there are no codes.

It might be interesting to somehow jumper the necessary solenoids right on the transmission and see if you can find all seven speeds that way. To make sure you were getting the right speeds you'd have to do it with the machine in motion though, which could be a bit dodgy.

Have you tried the downshift switch on top of the lift control lever..?

 

[Jonmiller]

Yes i have when it was acting up it made no diffrence and i have blocked up the machine and jumped the solenoids and all gears engage correctly that way to thats whats got me lost also when it acted up before my fellow techs said there was no power at the solenoids i wasnt on the project then so i cant confirm their findings but thats what they keep telling me thats why i was thinking ECM good inputs but outputs vary but they replaced that and that didnt fix the issue thats why im on here to see what you guys think could there be a possible re flash for the computer and could that even effect my issue

 

[Jonmiller]

ok machine is acting up again and now im really confused i checked the voltage at my solenoids and the voltage at my solenoids 1-6 was 3.93-4.61V in every gear and direction why would that be

 

[Nige]

All the solenoids use wire 975 white as a ground back to Pin 39 on the autoshift control (ECM). That same wire also grounds the Ride Control relay and the Park Brake Alarm relay. Could you have a fault on that wire somewhere..? It goes through at least 1 major connector between the transmission and the cab. On second thoughts if there was a partial break in that wire it ought to register a Diagnostic Code on all 6 solenoids. Maybe if it's just a partial break it won't, I suppose it all depends on what resistance in the circuit the control is looking for to determine whether or not to throw a Code.

I recall you said earlier that the autoshift control had been changed for another one and it made no difference so I guess you've ruled that out. The control is not flashable.

 

[Jonmiller]

Nige my boss wants to know what the actual voltages should look like at the solenoids per gear selected i cant find that info would you by any chance know and would you be able to send me that info thanks

 

[Nige]

24V - it's right there on the electrical schematic. The voltage is supplied to the F-N-R/speed control via a wire from the ignition switch, then to the autoshift box. If you want a copy of the schematic send me a PM with your email address and let me know if the machine Serial Number is above or below 8CR1162.

 

[Jonmiller]

I Pm'd you and the serial Number is 8CR3832

 

[Jonmiller]

Ok i back probed the controller and got my voltage readings and from pin 23-27 read 0 volts pin 28-29 read 1.4 volts each and pins 30-40 had 0 volts and also i tryed to match these numbers and colors to the two schematics i do have and they dont match either why would this be ?

 

[Nige]

If you're using the schematic SENR1277 that I sent to you then you should see 24V between Pin 39 (solenoid ground) and any 2 pins out of pins 31 thru 36 that are the 6 solenoids depending on which gear you have selected at any time.

TBH I would start at the shifter control in the cab and check that you are seeing 24v at the right times. The wires that have 24V in them at any time should correspond to the chart right beside the graphic of the shifter control.

 

[Jonmiller]

I didnt get the email with the Schematic

 

[Jonmiller]

I have gotten some new data i pinned out the ecm when it was working and inop i emailed you nigel and was wondering what you get of the data thanks for your help