I have a engineer friend that works for a utility in Cali. They had a large transformer delivered by Perkins and being a bit of truck/equipment nerd he hit up one of the drivers. Driver told him most of their trucks were Allison trans, which i knew already. What threw me for a loop as apparently some/most/all? of them also have an aux box and they shift the aux on the fly on heavy pulls. Maybe i'm being dense, but how do you shift an aux box without a clutch? Also, if the Perkins Macks at ConExpo 08 had aux boxes i missed that.
In the past I've helped Perkins when they were in my neck of the woods, I even had an older C500 with an Allison backed by a 4 speed aux. No different than a regular manual trans up front, with their's being air shift, flip the button, let off the throttle, hear it shift and get back on the gas. Easy peasy. Here's my old C500 helping them up a grade in Tulsa several years ago. They were a little light on ballast and the slick road gave them fits. I stacked every weight I had on my truck and drug em on up. I think we were 600k gross.
If it is an aux box I don't know what manufacturer or model it might be. Could it be 2 speed rears instead? I know some heavy haulers like those.
Perkins runs 70k Sisu planetary rears, single speed. Aux is the modern version of the 1241 Spicer. APO 1750-4 is the new model number. 2 unders, direct and over. You have to watch input torque with them as you increase gross weight. Ask me how I know
BOOM!?
I had two catastrophic failures that were more driver error than anything. You could get about 100k miles before you needed to throw bearings in it and give all the mounts a good look. It would egg the back mount holes, wear the input shaft/bearing/yoke pretty quick. It was worth it in the trucks I had setup with them. The rest of my trucks had the AT1202 two speed. Prettt simple and bulletproof.
Oh, air shift. I had a feeling i was just being dense. Neat pic Junkyard. While poking around the interwebs, i found Perkins' youtube and a video of them "building" a couple goldhofer modular trailers.
They have a lot of stuff that was engineered in house and built by Trailking or other mfg's. The Perkins brothers are sharp guys. One has retired and I think the other two will within the next few years. Their shop is immaculate. You could eat off the floor.
Years ago I bought a 55 GMC 370 2 Ton truck with a 270 6 cyl and an Allison 4 speed in it. It had a 2 speed auxiliary in it. More of a hi lo range. I learned if I shifted it up or down the auto would shift up or down 2 speeds to adjust and I would end up with a split speed. It was pretty slick on back roads and slow going. It was an ex liquor delivery van. I bought it as a cab and chassis and put a flat bed on it. Cab rotted away eventually.
Eaton 18sp ultrashifts can also run a 4 speed auxiliary and shift it for you. There is a bridge beam mover in Quebec with that setup.