M35 Top Speed increase?

Is there a way to increase the top speed of the M35 multifuel (without blowing up the engine)? Is there a trans or 5th gear change or tire change that can be made?

Thanks Guys

Think the super singles (12.5x20) will increase speed.

The transmission is already an OD at 16%. The drop-ins are immutable at 6.722:1. Yes, I have original drawings for final drive ar 5.20:1, but Rockwell did not make more than a handfull of gears for that speed.

The cheapest, easiest way is to run a set of regular 11.00-20 NDCC tires as found on a 5-ton.

Your wheels are designed to take up to a 12.00-20 tires, but those cost more. Radials will work fine with the original wheels providing you buy radial tubes for them. I have a set of Goodyear G386 radials in 12.00 I run and they are just the ticket.

Flipping the rear hubs and running singles on the rear will improve your ability to maintain road speed as well.

dg

Road Speed

Bigger Tires! 46" is the largest I have found to fit.

How tall are the 12.00 -20 tires?

Sizes

See if these help. Overall diameters (may vary by brand, type, or condition)

12.5x20 - 40.7"
9.00x20 - 40.9"
14.5x20 - 43.4"
11.00x20 - 43.5"
12.00x20 - 44.5"
395/85R20 - 46.7"

For even tire sizes (11.00, 14.00, 16.00) a quick rule of thumb is to double the number and then add 20" for the rim size. Using this theory:

11.00x20 = 42"
12.00x20 = 44"
14.00x20 = 48"
16.00x20 = 52"

It is pretty close with the larger sizes.

Since the 12.5x20 is essentially the same diameter as the 9.00x20 (actually smaller) you will not increase road speed with these tires. Similarly, the 14.5x20 is the same diameter as the 11.00x20 (just wider and usually a radial).

I think this has been discussed before, and the difficulty being space between transmission and transfer case. Some folks have mentioned the possibility of putting a "brownie box" between the two, allowing for a further multiplier of wheel RPMs (or reduction of engine RPMs at the given speed - same thing). The least laborious is the larger wheels. I can't wait until my old lady lets me buy some beadlocks & ginormous XMLs!!!!!

Matt

Bigger question is this, how fast do you want your deuce to go?

I think I'm starting to settle down and realize that I would be most happy with 11x20's if she would do 60 mph. It's a balancing act between driveability and the money / effort it would take to get there. 12x20's and the XML's still look very tempting though.

For me, speed is less important than ease of work. The big tires are an added bonus for going with a wheel style that I am more comfortable working with. Plus, with a bed-mounted spare, "Hello fuel tank #2!!"

Matt

When you up the size of your tires, remember to change the speedo adapter too.
60 mph is no problem with 1100-20 tires.

g744-- where did you get the 1200s and at what price, thanks

I found a set at American Truck Salvage in Phoenix. They were $100 per. I'd look at places that take in dead semi's and other big trucks. You will be surprised what they will sell tires for.

dg

BTW, you can look up htat Goodyear G386 on their site.

airmitch said:

Is there a way to increase the top speed of the M35 multifuel (without blowing up the engine)? Is there a trans or 5th gear change or tire change that can be made?

Thanks Guys

Click to expand...

Just wanted to update this thread.

If you feel handy cutting down your driveshaft to shorten it, I can get you a lead on a electronic splitter that will reduce each gear by 50%.

It shifts pretty cool, as all you do is put it in first, accellerate, let off, switch the button on the shifter, accellerate, button back, shift and so forth. It isn't the same thing as a splitting transmission on the semi trucks, but it is really close and a lot of people are using them on dodge cummins. they are rated/warrantied up to 1200 ft.lbs

Again, Robert, putting an overdrive box behind the tranny is not so much a matter of cutting down the driveshaft, as it is moving the whole transfer case back a foot or so to fit such a device in there.

See, the tranny and transfer case are pinned together by a tiny little "spud shaft", which is a driveshaft made from two u-joints with a slip spline between em. Once you put that spudshaft into the equation, there is less than an inch to do ANYTHING between tranny and the accompanying divorced transfer case.

Me, I went to a .695 tranny, with 45" tires. My "theoretical" top speed on the flats is around 80 MPH.

PS, final bit of info, rear axle spacing is at 48".

Ah - that makes sense. Why can't we change the final ratio in the tranny or the diffs? Is that possibe?

I'm just interested in the thread and the principal, I'm not interested in making a new world record 1/4 mile time for the deuce LOL!!!

I dontbelieve anyone makes different gears for rockwell 6.72 top loaders

sux

cranetruck,
Where do you get the different speedo adapters from? I have never seen different ones for the deuce available. I know on cilvian cars you just change the gears on the cable, is this what you are talking about? My 9x20 are taller than standard NDCC tires so my speedo is about 6 mph off & I would like to fix that.

Brad