First Post - new to me M1078 MD3070PT with Shifting Problems

[isaacnasar]

Hi there,

This is my first post. I searched the forum and didn't see any previous posts on this topic so I'm hoping someone out there can help.

I recently bought a 1997 M1078 - It's in pretty good overall condition. I changed all the fluids and filters in the engine, trans, and differentials.

I have a few small problems that I am sorting through with the help of previous posts on this for,.

My biggest problem is with the Allison Transmission - It isn't throwing any codes if I press the up and down arrows at the same time on the WTEC.

It will shift from 2 t0 3, then 3 to 4, then 4 to 5 - from 5 to 6 and sometimes 6 to 7 it will shift to the next gear, hold it for 3 seconds then bounce back to a lower gear. i.e. 5 to 6 then back to 5, or 6 to 7 then back to 6. Once it downshifts to the lower gear (usually 5 or 6) it will lock in that gear and won't downshift or allow a shift to neutral or reverse. I have to shut the main power switch on the dash and start it back up again to select Drive, Reverse, or Neutral. In all other instances and prior to locking in a specific gear, the trans will shift and operate great, no slipping, weird noises, or jolting. It is full on fresh fluid and the fluid that came out of it looked good and had no burnt odor.

I've searched the hundreds of pages of manuals but can't seem to come up with something as the WTEC isn't displaying any codes.

My only thought is that it was sitting without batteries for so long and jump started by the military a bunch of times that possibly the Shift patterns and controls need to be wiped and re-loaded.

I was thinking maybe a speed sensor is an issue but if it was it probably wouldn't shift at all.

 

[NDT]

Welcome, you are correct, this issue has not been seen here. I would pull the WTEC out of the dash and send it to transmissioninstruments.com for a checkout.

 

[snowtrac nome]

pull the pan look at the harness where it jumps from the trans housing to the valve body. when in limp mode as I remember you have no reversa and it stays locked in a gear cant remember which one. we had a lot of harness failures in Iraq I have seen them here in the states too on commercial equipment usually a broken wire in the back of the cannon plug any Allison shop can plug in with a lap top and check codes you could also get a prolink 9000 off ebay with an Allison cartridge to do diagnostics your self

 

[Suprman]

Low voltage will cause all kinds of issues. Do you have 4 new batteries? The wtec2 trans control is grounded via the dash panel. Sometimes adding your own ground is good.

 

[isaacnasar]

Thank you NDT - I spoke with John over at transmissioninstruments.com. He helped me pull the codes off the WTEC and determined it is either a short between the ECU and one of the 2 Sensors on the transmission or that one of the sensors are bad. I am going to work with a multimeter this weekend and check all connections. He seemed to think one of the plugs are most probably loose or one of the connections are corroded. I'll clean everything and report back.

 

[coachgeo]

as you do that also check closely all the wiring to/from the alternator to ensure it is giving solid consistent voltage. Not verifying that Suprman's warnings about voltage irregularities in charging system is not an issue; will have you chasing gremlins that likely don't exist.

 

[NDT]

Take a look at mkcoen's M1078 build thread. About halfway through, you can follow the exact same diagnostics you are about to undertake. Also posted is the WTEC diagnostic/repair manual.

 

[Suprman]

What was the code?

 

[isaacnasar]

D1 3 5 then 0 0
D2 2 2 then 1 5
D3 5 6 then 2 2
D4 5 4 then 4 5

 

[Suprman]

22 is speed sensor. Cheap part easy to replace. Back bottom of trans. I have found one bad sensor can cause other codes if still being driven. I would clear the codes and see which ones come back first. I would replace the speed sensor especially if your speedo is erratic thats a dead giveaway. It will cause you odd shifts if bad. The trans harness comes thru the drivers side of the center hump its a cannon style connector. Runs along the drivers side frame rail, there is a branch off for the tps and then goes over to passenger side above the trans. There is a pigtail coming off the trans which mates to the harness. It almost looks like it unplugs from the trans but it does not. The trans and controller are very reliable. Most issues are sensor or wire harness related.
Will

 

[isaacnasar]

Thanks Will - I pulled everything apart from the WTEC to the Trans and cleaned the connections. WTEC is grounded and speedo and all other gauges work fine.

Still the same symptoms - but while cleaning everything I re-wired the heat and fixed the CTIS - those both work now which is a plus.

What's confusing is now it is throwing different codes

D1 2 2 then 1 5
D2 5 6 then 3 3
D3 2 1 then 1 2
D4 4 5 then 2 6
D5 4 5 then 2 3

I will order the speed sensor - found it online for $50 - hopefully that is throwing everything off

 

[Suprman]

Is your speedometer erratic? I have seen bad wiring harnesses it happens.

 

[isaacnasar]

Speedometer is not erratic - However the Volt Meter seems to bounce between 24 and 27 somewhat erratically.

I replaced the speed sensor - part # 29543432 and no improvement.

I decided to turn my sights on the charging system and here lies my confusion.

There are 5 connections on the alternator - one is the ground so lets ignore that for now.

There are two larger connections on the front and two on the side.

the front ones read 14.2 Volts and 28.3 Volts

the side ones read 28.1 Volts and -2.2 Volts

I'm not familiar with how the alternator works on this - can anyone shed some light on what may be wrong?

 

[isaacnasar]

I replaced the speed sensor on the transmission but there is no change.


I took coachgeo's advise and measured the voltage at the alternator

there are two connections at the front of the alternator - one reads 28.4 volts and the other reads 14.3 volts
there are two smaller connections on the side of the alternator which appears to be the regulator (76761-N3030) one reads 28.2 volts the other reads -2.2 volts

is it safe to assume the regulator is bad and that is causing all these issues? Does anyone know where to get these from?

 

[isaacnasar]

OK - So I replaced the speed sensor and the symptoms haven't changed.

I checked the output on the alternator - the two larger connections read 28V and 14V - the two smaller connections read 28V and -2V

Would it be safe to assume that the regulator is bad and possibly could be causing the weird shifting issues?

 

[Suprman]

Put your meter on ac and measure the back post on the regulator. Its an ac output. If you are charging at 28v thats good.

 

[Shark Bait]

Thanks Will - I pulled everything apart from the WTEC to the Trans and cleaned the connections. WTEC is grounded and speedo and all other gauges work fine.

Still the same symptoms - but while cleaning everything I re-wired the heat and fixed the CTIS - those both work now which is a plus.

What's confusing is now it is throwing different codes

D1 2 2 then 1 5
D2 5 6 then 3 3
D3 2 1 then 1 2
D4 4 5 then 2 6
D5 4 5 then 2 3

I will order the speed sensor - found it online for $50 - hopefully that is throwing everything off

For future searches it may be helpful to post the speed sensor part number and where you found it online, if it's a popular auction sight do not put the link.

 

[isaacnasar]

OK - will do

It was on an auction site - the description of the part was ALLISON B500 SPEED SENSOR 29543432

 

[isaacnasar]

Still drawing blanks - anyone have some ideas?

 

[NDT]

Still drawing blanks - anyone have some ideas?

Where are you in the process? All harnesses and solenoids ohmed out good? 100% good result from transmissioninstruments?