Steering Wheel holders apply!

You guys are all amateurs. This guy knows how to get 'er done.

Merv Grazinski of Oklahoma City bought a new Winnebago motor home, the newsletter says. While driving it home on the freeway, he set the cruise control at 70 and went into the back to make coffee.

"Not surprisingly," the newsletter says, "the RV left the freeway, crashed and overturned. Mr. Grazinski sued Winnebago for not advising him in the owner's manual that he couldn't actually do this. The jury awarded him $1,750,000 plus a new motor home," and the company rewrote the manual "in case there were any other complete morons buying their recreational vehicles."

 

6-speed main and 4-speed deep-under auxiliary, double-over. Both up against the dash when you grab the big hole. Big Cam Cummins, no cruise control, louder than sin, tall rubber, and a crawl-through coffin-bunk.

 

Well, ######...

 

I have been told that twin sticks can't handle today's torque. True or false ?

 

My understanding is that Spicer was often very conservative in their torque ratings compared to Eaton. When the electronic engines started showing up, the torque started reaching points where Spicer wasn't willing to rate anymore and therefore, wasn't willing to warranty. That meant boxes went away because you couldn't get a warranty on them any longer.

The mainbox is rated for 1400lb.ft of torque, that being said, I firmly believe it is capable of far more torque than rated.

Back in the 70s there were guys wanting 425-horse 1693 Cats, but also wanted boxes. Even in that era, Spicer wouldn't warranty boxes behind a 425 1693 Cat, so, it was common practice to order your rig with boxes and have the 1693 set 350. Take delivery and run down to the local Cat shop and have her turned up, as there wasn't much to it. The boxes would last behind the 425 1693's for ages when driven properly.

It's all about how you drive it.

Overdrive in the auxiliary is the weakest gear in the entire set-up. When I'm loaded light and flatlanding (i.e. 80,000lbs or less, generally), I won't actually use overdrive in the auxiliary when in the low gears on the main. The "textbook" progression, starting from 1st-under (1st in the main, 2nd in the aux) is to shift through to OD in the auxiliary, then "cold shift" and split both boxes, going to 2nd-under, and ladder on up through the gears to 4th-over, then mainbox it to 5th and 6th-over (5th and 6th are close splits in the main).

However, as 1st through 4th are all underdriven gears, this means you're multiplying torque. Ultimately you're fighting the gears, effectively, by having one box in an underdriven gear and the other in an overdrive gear.

It's not uncommon for me to progress 1st-under to 1st-direct (1st and 3rd), then split to 2nd-under, 2nd-direct, then 3rd-under to 3rd-direct and 3rd-over. The split between 3rd and 4th on the main is a little wider than the others and you need to extra couple hundred RPM you'll pick up coldshifting 3rd-over to 4th-under typically.

However, the under-direct and then back into under shifts keep you from pushing hard on the OD gear in the auxiliary. I'll wind her up to 4th-direct, mainbox to 5th-direct (this puts me in direct gear, as 5th is direct in the main), and once I'm in this gear, I'm willing to push a little harder on the OD gear in the auxiliary as I'm no longer MULTIPLYING the torque I'm asking the gear and bearings to hold.

That being said, the gears are designed to handle these torque loads, even having the the main in first and aux in over. I just prefer not to hammer the gears.

Just so you know, OD is the weakest gear in any transmission.

I rarely work high power when I've got them against the dash. The torque load you're asking the bearings, u-joints, driveshaft, carrier-bearing, etc. is enormous, whether it's boxes or a single-stick, this is true. Unless I'm bobtail, sometimes empty, 6th-over is more or less a coasting gear rolling off of grades.

For those curious and unfamiliar with boxes, the "cold shift" (splitting both boxes) is when your hands are off the steering wheel.

Jump to about 0:23 in this video and you'll see the progression of a few shifts on a 5x4....



SIMPLE ANSWER:

"Technically" they're not rated to handle a 625 CAT.

Practically speaking? If you knew how to do it, yeah, it'd stand up to it.

I've only seen a handful of trucks with factory boxes and an electronic engine, both were behind N14 Cummins.

A friend of mine runs a 379 that he put boxes in behind a turned up C15 running about 650-hp.

With any transmission, it's all in how you drive it. You could put an idiot behind a 300-hp C12 with a 22918B and they'd still tear it apart, while you could put a quality driver behind a 700-horse 6NZ with a RTO12713 and they'd get it to survive.

 

I now have a headache after attempting to understand that. Kudos to you for the knowledge, tho.

 

They actually have an aftermarket kit that you can install to convert your current switch-based modern transmission to a 2 or 3 stick(depending on your transmission)

 

12gauge customs makes a twin and triple stick kit for most trannys

 

Here's my method. Old boot cut up wrapped around the spokes to soften them up. Leather wrapped around the wheel so my knee doesn't slip.

 

I hold the steering wheel with fingerless gloves. I want passers by to think what I'm doing is very intense, and shouldn't be taken lightly. I also wear a open face helmet and aviators to complete the look