macattack Posted December 9, 2011 Share Posted December 9, 2011 had this happen to me this morning in -30Celsisus. my 96 mr688s garbage truck had no reverse. picked my bin and selected reverse and nothing. put it in drive and the truck dies just like i pulled the red engine shutoff?. when i go to reverse all my backup lites.camera,alarm does not work. possible a short somewhere. but where do i look.do you think the nsbu switch?also when there is a misfire the driveshaft looks like it wants to turn?????the trans is an allison ht740rs automatic. would there be a relay or circuit breaker somewhere giving me trouble.thanks in advance. Quote Link to comment Share on other sites More sharing options...
GearheadGrrrl Posted December 10, 2011 Share Posted December 10, 2011 When a truck with an automatic with electronic controls won't go, shutting it off and restarting it resets the computer and that usually does the trick. If you've got a pre-electronic HT740, check the adjustment of the shifter mechanism and it's cable. Given that this happened at -30 C it could be that there's some stiff grease in there that won't let you shift all the way into gear until it warms up. Quote Link to comment Share on other sites More sharing options...
macattack Posted December 10, 2011 Author Share Posted December 10, 2011 thanks, truck was only out for about 10 minutes before she started acting up. this has a cable shift and that part seems to be fine. but this is what i found out today. truck is a 96(my avatar) it does not have a computer. i started the truck and let it idle for a few minutes. i just replaced the trans filters and topped up the fluid. truck is idling nice i then put it in drive and the truck dies instantly. i restart the truck and now about every 10 seconds or so a slight misfire happens. when there is this misfire my backup lites and camera flash on for a millisecond and my driveshaft wants to turn. does anybody know if the mack e7 300 engine would have a cam timing sensor or if my fuel inj pump is acting up. when it does misfire it only does for a very short time and then idles fine. 10sec later misfire then fine. i am thinking maybe a sensor or fuel inj pump and thats why it shuts off when i put it in drive. still no reverse though. dam i think this is gonna piss off santa. Quote Link to comment Share on other sites More sharing options...
macattack Posted December 12, 2011 Author Share Posted December 12, 2011 gonna try replacing the reverse and neutral relays. i found 1 of the 5 circuit breakers tripped. i reset it and now gonna replace the relays as soon as the part store opens. hope that is the problem.any help? Quote Link to comment Share on other sites More sharing options...
macattack Posted December 14, 2011 Author Share Posted December 14, 2011 relays did nothing. off to the tranny store. got a couple quotes. approx 8500.00 for a reman. holy sheeeeeaaaaaat. Quote Link to comment Share on other sites More sharing options...
shortstack Posted December 14, 2011 Share Posted December 14, 2011 Still sounds electrical to me. Did you say the transmission is not electronically controlled? Trey Quote Link to comment Share on other sites More sharing options...
macattack Posted December 14, 2011 Author Share Posted December 14, 2011 thanks for replying!!yes non electrical. checked the linkage all is good there. gonna check my mod valve. the truck has an air operated throttle control and just found out the modulator valve is a pneumatic type. mech told me to plug the hose end and plug the mod valve. start truck and see what happens. hopefully the valve. also the trans fluid is clean no smell at all. Quote Link to comment Share on other sites More sharing options...
macattack Posted December 15, 2011 Author Share Posted December 15, 2011 update. no tranny needed!!! did the mod test. basically bypassed the mod valve by plugging the air line and the mod valve. truck went into reverse and did not die in drive. i did not realize that an air operated foot controller would have a pneumatic mod valve.all my backups.alram,camera came back. gonna order two of those pneumatic modulator valves and keep one in the cab. maybe some others with air operated foot throttles had the same issues and got taken to buy a new tranny. check those pneumatic mod valves if your tranny is acting up. phew i came very close to buying a trans.dam drink is gonna taste fine. thanks guys. Quote Link to comment Share on other sites More sharing options...
MACKS Posted December 15, 2011 Share Posted December 15, 2011 There is a member here named Automaticmack,haven't seen him on in a while but he knows a lot about that trans and is always willing to help,he emailed me a whole owners manual a while back,maybe you can send him a pm for future reference. Quote Link to comment Share on other sites More sharing options...
GearheadGrrrl Posted December 15, 2011 Share Posted December 15, 2011 Actually, sounds like a rare failure. When I drove for the Postal Service they had a whole fleet of MR tractors with 740 series automatics and air throttles, and I never heard of that failure. About the only problems I heard of were occasional out of adjustment shift cables and the low hanging lines to the trans cooler getting caught on stuff and ripped off. Both were easy fixes- you could run an Allison dry and still not kill it! Quote Link to comment Share on other sites More sharing options...
randyp Posted December 15, 2011 Share Posted December 15, 2011 Glad that had a happy ending, good work! randyp Quote Link to comment Share on other sites More sharing options...
macattack Posted December 15, 2011 Author Share Posted December 15, 2011 thanks guys. a rare failure indeed! well it was the last thing i could check external wise and i lucked out. when it went down it was the strangest thing. no hints or strange noises but when i look back it did seem to shift from 1st to drive rather quickly. anyways so far so good. ordered 2 of these valves today got to keep one in the cab.85.00 dollars each. Quote Link to comment Share on other sites More sharing options...
shortstack Posted December 16, 2011 Share Posted December 16, 2011 Congratulations! Sure glad you didn't have to buy a transmission. Now hopefully you can get back to work! Trey Quote Link to comment Share on other sites More sharing options...
macattack Posted December 16, 2011 Author Share Posted December 16, 2011 yes thanks. as soon as the parts arrive. Quote Link to comment Share on other sites More sharing options...
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