macattack Posted February 5, 2017 Share Posted February 5, 2017 hi guys. this is on a 96 mr 688s refuse truck. this is freaking me out. got a ht740 allison 4 speed automatic. has air mod valve and air operated throttle. past week my trans temp gauge and speedometer gauge were jumping around in unison. usually in neutral, but occasionally at road speeds. anyways last week my gauges acted up again and the truck lost reverse and if i put it in drive the truck dies. changed out the air mod valve, but still no reverse. a couple times it went into reverse, the reverse lites came on my back up alarm worked and then when i tried again in wont go into reverse and no lites or alarm.. gonna replace the tcm. i was told there is a solenoid pneumatic that maybe my problem any ideas. thanks Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/ Share on other sites More sharing options...
j hancock Posted February 5, 2017 Share Posted February 5, 2017 Don't know but it involves electronics so check your grounds. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360812 Share on other sites More sharing options...
macattack Posted February 5, 2017 Author Share Posted February 5, 2017 thanks. which grounds? Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360827 Share on other sites More sharing options...
macattack Posted February 6, 2017 Author Share Posted February 6, 2017 got a new tcm for it. damn kind of a bitch to get at on these units. anyways got it out and the tcm looks pretty rough. hope the new tcm fixes it. got to wait till monday to get the proper connectors. anybody have wiring schematics for a 96 mr? thanks Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360860 Share on other sites More sharing options...
j hancock Posted February 6, 2017 Share Posted February 6, 2017 Sounds like you may be on to something with the module if it is looking like road kill. Your Mack dealer should be able to get you a wiring diagram. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360906 Share on other sites More sharing options...
Mackpro Posted February 6, 2017 Share Posted February 6, 2017 I believe there's a ground breaker under a black plastic cover mounted to the air cleaner housin bracket, this is all the ground to the cab. You might add cab to engine, cad to frame grounds. Worked on very few MR's as all the refuse companies and city owned MR/LE had their own shop's thank god! Lol. I looked for any diagrams that included the Allison and only had what I sent you the other day. We only have 1 old sheet on the VMAC 2 wiring . Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360910 Share on other sites More sharing options...
macattack Posted February 7, 2017 Author Share Posted February 7, 2017 thanks gang . i will check for the black plastic cover. thanks again Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-360999 Share on other sites More sharing options...
macattack Posted February 9, 2017 Author Share Posted February 9, 2017 anyone know how to test a oil pressure switch and also can a person run a test on a pneumatic/electric solenoid? this solenoid has 2 same color wires coming off of it. Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-361203 Share on other sites More sharing options...
macattack Posted February 10, 2017 Author Share Posted February 10, 2017 On 2/6/2017 at 8:40 AM, Mackpro said: I believe there's a ground breaker under a black plastic cover mounted to the air cleaner housin bracket, this is all the ground to the cab. You might add cab to engine, cad to frame grounds. Worked on very few MR's as all the refuse companies and city owned MR/LE had their own shop's thank god! Lol. I looked for any diagrams that included the Allison and only had what I sent you the other day. We only have 1 old sheet on the VMAC 2 wiring . would this breaker box be approx 3x4 inch. one wire on one side and 4 on the other. i found this under the center dash. maybe it is something else. Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-361327 Share on other sites More sharing options...
macattack Posted April 24, 2017 Author Share Posted April 24, 2017 happy days are here again!! yes got it figured out. my problem ended up being a worn trans governor. gear on governor looked fine but the inners were sloppy. replaced governor and put truck into reverse and she engaged every time. !!!!! Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-368252 Share on other sites More sharing options...
j hancock Posted April 24, 2017 Share Posted April 24, 2017 Glad you found it! Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-368254 Share on other sites More sharing options...
macattack Posted April 24, 2017 Author Share Posted April 24, 2017 thanks j hancock. took me a while, but got it figured out. came close to replacing the trans. what a relief. so after a couple filters, relays, and a shitload of testing also a tcm ended up being that governor. took 30 mins to change. Quote Link to comment https://www.bigmacktrucks.com/topic/48629-allison-740-trouble-96-mr688s-converter-locked-up/#findComment-368280 Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.