macattack

my 96 mr688s seems to loose a bit of air when releasing the park brake. so i thought quick release valves, but on mine they look different. instead of one supply there are 2 supplys and 4 outs? per axle??? here are a couple of pics

thanks bud. the oem is #3MT237P7 gauge. the one i got is from allison, but the sending unit with the new gauge is a single wire the original sending unit is 2 wire. the allison gauge has your basic send and ign terminals. but there is 2 smaller bolts with an insulator between them one is labelled + and the other - . dont know what that is about. but your probably correct. thanks again

gonna replace my tran temp gauge and the original says neg ground stamped on the back. the replacement does not say anything. is there a way to find out if the gauge is neg or pos ground? thanks

thanks for the info. i am thinking i will splice a long wire from the sending unit (ground wire) and route it inside the cab and when the gauge decides to act up i could touch that wire to a ground source inside the cab just to see if the gauge stops acting up. think i will leave the sending unit hooked up as original but run a jumper from the ground wire to inside the cab. thanks again

this is on a 96 mack mr688s truck. trans temp sending unit has 2 wires going to it. one is the send is the other wire for ground? dam gauge wants to jump all over the place.

does mack have instrument panel voltage regulators? cant seem to find out

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.

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. !!!!!

well still screwing around with this. anyways thinking possibly a switch issue of some sort. with engine off, if i shift into rev and back into neutral a couple times and then start the truck. it goes into reverse, but only once. seems something not switch, what do you think would the nss do this? could it also be an input speed sensor? any help would be great.

how could i check these. my rev switch is on the pass side and the nss is on the drivers side. what is the best way to test them? thanks for your info.

trying to do some diagnosing on my refuse truck allison ht740rs trans. sometimes reverse sometimes no. also at times it wants to kill the engine as soon as i put it into forward gear. with truck stopped and off if i put the shifter into reverse then into neutral and start the truck it will go into reverse ONCE. wont go twice until i shut off the truck shift into reverse then neutral and restart the truck, goes into reverse. also the acc/solenoid relay seems like its getting pretty warm more hot than warm. has anybody dropped the pan to replace the shift solenoids in the allison ht740 transmisson? want to know if its a tough job and why you changed them. thanks guys

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.

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.

thanks gang . i will check for the black plastic cover. thanks again

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

thanks. which grounds?

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

testing my temp gauge and sender on my allison auto trans. sender has a 2 wire pigtail. i believe one wire goes from sender to gauge , but does the other wire at the pigtail go to ground? thanks

thanks for the reply. yes its a 96 no electronics.

replacing a back up switch on my 740 allison automatic trans. what i need to know is should the truck be running or not when i thread out the switch on the trans. some say have the engine running so you wont loose any trans fluid. with engine off fluid will spill out. has anybody changed theirs and how much fluid will come out. thanks

fixed it. air modulator valve was bitched. need to keep a extra in cab just in case.

i got a 96 mack mr688s. this morning sitting at idle my speedo and oil temp gauge needles were jumping back and forth. all others were fine. did it a couple more times but always at idle. any ideas what i should look at. the speedo guage was replaced 8 months ago. would it be a relay? any help or things to check would be great. thanks

thanks gang. gonna fix her up today.

so i can use a barb fitting at the valve cover end also? thanks