m916 m920 jake brake 7155 cat trans whine

[Bolkbich]

I just bought my first M916... With a cat 7155 trans. Nice truck. I'm going to use it under a lowboy and a dump trailer. But first i have to work out some bugs. The wires from the jake brake pedal run into the 7155 trans. Can I bypass that (wire it like a civvy manual trans truck) or is it telling the trans to do something different when the jake is activated (holdback etc ). My jake is erratic ,it hits on all 6 a good part of the time. It stutters on 4-5 cyl here and there. Ive gone thru all the connections and jake servos. I'm wondering if its a neutral switch so the jake cant work unless the trans is in gear. On a different subject, My trans has a pretty noticable gear whine in the lower 8 gears. Its ALOT more noticable when hot. Do these transmissions all make this much noise on the low side ?

 

[Andy1234]

I can't comment on the jake brake, as mine doesn't work and I haven't had time to track it down, but the trans on my 920 whines at low speed and absolutely screams at higher speeds. It's full of oil and it shifts fine, so I can't say if it's good or bad.

FWIW,
Andy

 

[Bolkbich]

My oil is full and clean also. I installed RR's recommended filter/regulator/oiler and it definitley shifts nicer. My truck doesnt make much noise at highway speeds , actually I cant believe how nice and smooth it is at 55-60 (on the speedo). I ordered a low height sliding 5th wheel and im going to take out 2" of spacer leaves out of the rear springs. I have to get the 5th wheel height down below 54". The hydraulics on the truck will be fine once i set up the wetline connections. All in all im very happy with this truck and im anxious to use it.

 

[wreckerman893]

On the commercial trucks I drove (standard transmissions) you would flip a switch on the dash to engage the jakes. Usually they came on when you took your foot off the accelerator. It took some getting used to to have to push the pedal down on the M915/M916's I drove in the Army. I'm not sure if this has anything to do with the Cat tranny since the newer trucks with the Allison are the same way. You might PM Soni (M920) and see what he did when he converted his truck to a standard transmission.