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M1079 only moves in reverse

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Bryteayes

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I recently purchased a 1998 BAE Systems M1079 LMTV from GP. I had it shipped to Texas. After new batteries it started fine. It will go in reverse but not forward. I suspect electrical controller at fault as opposed to needing a new transmission like the mechanic suggested. She only has 1234 miles. Any suggestions where to start?
 
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Ronmar

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You could still have a WTEC II in it. My 98 M1079 does… is your trans controller display square with red characters or is it rectangular with green characters?

yep, read out any codes, note if the mode light is lit when you read them as this indicates a current fault, not a stored memory…

So did it not go into forward, or did it indicate forward and just not move?
 
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B

Bryteayes

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San Angelo, TX
Ronmar said:
You could still have a WTEC II in it. My 98 M1079 does… is your trans controller display square with red characters or is it rectangular with green characters?

yep, read out any codes, note if the mode light is lit when you read them as this indicates a current fault, not a stored memory…

So did it not go into forward, or did it indicate forward and just not move?
Click to expand...
Thank you for your reply. She is locked up at the mechanic’ shop over the weekend. I’ll be there first thing Monday morning.
 
coachgeo

coachgeo

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before you assume anything transmission. Fully charge the batteries EACH to same level.... or better yet via battery diagram you can find in this forum.... drop it to two batteries. Will save you charge time. and in TX you won't need four anyway......... even up north TX. Your alternator will love you as well.

Point being these transmissions do horribly odd things when they dont have full 24v happily.

pull all the circuit breakers and relays. Clean them good, check them if you can.. plug them back in while batts charge. Plan on replacing.

look at where wires go thru the holes down by your gas pedal into area behind heater (if I remember it right). This is an area the wires can get chaffed. Also where they go up into the area behind the dash.

Is your gunners hole open in the roof or does it have the Metal cover? Rain and shift pad... not good.... and with rain in mind

Any hints of water coming down the left edges etc. along or down the windshield? The overhead running lights get leaks..... and that gets water into the Transmission Computer below the shift pad .. along with into the push buttons. All from leaking down from running lights. and if driver window out or left down.

Also RV forms with similar shift pad pointed out... those shift pad buttons might need to be exercised.... sometimes even exorcism ☦ . May even take a pretty forceful push with blunt tipped object (Pen Cap?)

all I can think of right now from past threads in here.
 
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B

Bryteayes

Member
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Location
San Angelo, TX
coachgeo said:
before you assume anything transmission. Fully charge the batteries EACH to same level.... or better yet via battery diagram you can find in this forum.... drop it to two batteries. Will save you charge time. and in TX you won't need four anyway......... even up north TX. Your alternator will love you as well.

Point being these transmissions do horribly odd things when they dont have full 24v happily.

pull all the circuit breakers and relays. Clean them good, check them if you can.. plug them back in while batts charge. Plan on replacing.

look at where wires go thru the holes down by your gas pedal into area behind heater (if I remember it right). This is an area the wires can get chaffed. Also where they go up into the area behind the dash.

Is your gunners hole open in the roof or does it have the Metal cover? Rain and shift pad... not good.... and with rain in mind

Any hints of water coming down the left edges etc. along or down the windshield? The overhead running lights get leaks..... and that gets water into the transmission below the shift pad .. and into the push buttons from leaking down from running lights. and if driver window out or left down.

Also RV forms with similar shift pad pointed out... those shift pad buttons might need to be exercised.... sometimes even exorcism ☦ . May even take a pretty forceful push with blunt tipped object (Pen Cap?)

all I can think of right now from past threads in here.
Click to expand...
Thank you. I’ll check her out Monday and report what I find.
 
coachgeo

coachgeo

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Bryteayes said:
Thank you. I’ll check her out Monday and report what I find.
Click to expand...
edited one of the things to check. The change is transmission "computer"

Any hints of water coming down the left edges etc. along or down the windshield? The overhead running lights get leaks..... and that gets water into the Transmission Computer below the shift pad .. and into the push buttons. All from leaking down from running light;. and if driver window out or left down.
 
Third From Texas

Third From Texas

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Another thing before you bend over for surplus replacement would be to check the wiring and connections. I've seen broken wires, wires pulled from connectors, chaffed wires, brittle/broken insulation, etc. At the very least do a CLOSE inspection of the connectors at the controller and at the ECU.

The first truck I purchased originally had "transmission issues" that turned out to be a single wire that had pulled loose from the ECU connector.

This thread is steering you in the right directions. Still, rule out what you can before spending money. I've seen guys replace a controller, then another....only to discover that it wasn't the issue.
 
coachgeo

coachgeo

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Third From Texas said:
Another thing before you bend over for surplus replacement would be to check the wiring and connections. I've seen broken wires, wires pulled from connectors, chaffed wires, brittle/broken insulation, etc. At the very least do a CLOSE inspection of the connectors at the controller and at the ECU.

The first truck I purchased originally had "transmission issues" that turned out to be a single wire that had pulled loose from the ECU connector.

This thread is steering you in the right directions. Still, rule out what you can before spending money. I've seen guys replace a controller, then another....only to discover that it wasn't the issue.
Click to expand...
that year wont have an ECU but the concepts are spot on... just applied to TCU (transmission CU) and likely that's what you meant. (or the TM's call it an ECU so your still right and I got egg on my face lol)
 
NDT

NDT

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Bryteayes said:
I lowered the engine RPM by pulling the hand throttle back and it went into forward without any problem.
Click to expand...
Learn something new every day. Will have to remember this for next time as the easiest repair ever. And your mech was about to bend you over.
 
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