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Transmission for 743 Cummins NHH220 horizontal Ann Hovdenes 10-5-03  
We just purchased a 1963 California CROWN BUS With a Mid mounted 743 cubic inch Cummins model NHH220 horizontal direct injection diesel engine. Four valves per cylinder, 220 HP at 2100 RPM. This engine is a "lay down" version of the NH220 truck engine and is mounted under the floor about 8 feet back from the front axel. With a -Fuller 5 speed transmission that can drive BOTH rear axles. The engine runs great but we can't get it to go over 57 mph. Do you know which transmissions would work with this engine, we would spend the money if we could get at least a top speed of 70-75 mph. We have fallen in love with the bus and are hoping to convert it into an RV. Any help you could offer on this matter would be greatly appreciated.
More info on the bus can be found at
Re: Transmission for 743 Cummins NHH220 horizontal Mark O. 10-6-03  
Your rear end gear ratio has more to do with your top speed than your transmission.

On my Crown I switched the original 11.00X20 tires with 11X24.5 tires and picked up almost 5 MPH.

If you decide to switch transmissions, there are some Road Ranger transmissions that have overdrive gears. You will need to research which one would be the best choice for you but the swap is a pretty straight forward swap. Your Fuller 5-speed uses the same shift tower and linkage the Road Rangers use.

Whatever you decide to do, the installation of a pyrometer should be a priority. 2-cycle DD's like to run hard and hot. 4-cycle Cummins will melt pistons if you run them as hard and hot as a DD. I have seen the pyrometer go to 900 degrees on a flat highway when I was driving into a headwind. Same day driving back on the same highway the pyrometer was less than 400 degrees at the same speed.

Good luck and happy trails.

Mark O.
Copied from the FAQ at yahoo... kd5kfl 10-6-03  
Perhaps the most popular of all the manual transmissions offered in the Crown Super Coach was the tried and true Fuller RTO/RTX-910 10-speed Roadranger.
This transmission was really cool.

This box combined in one case a 5-speed front section and an air operated 2-speed synchro rear section. The driver rowed through the 5 gears in the low side, then preselected the air shift button up.

Then he/she rowed thru the same 5 gears, only now in the high side.
Once a road speed of around 15 to 20 mph was achieved, the low range was never used. It was also common practive to skip gears, usually in the low range.

The gear ratios of this fun-to-drive box are:
.82 10th, 1.00 9th, 1.26 8th, 1.59 7th, 2.00 6th, 2.57 5th, 3.14 4th,
3.95 3rd, 4.98 2nd and 6.27 1st. The 4-5 and 9-10 rpm drop was 22%.

The other gear drops were around 26% with the only exception being the 5th to 6th (range shift) which was around a 1.285% drop.
This box was non synchronized but easy to shift with very little effort.

Some Crown drivers shifted the Roadranger without using the clutch,
a skill I never quite mastered. If done properly, the kids necks and heads
never even jumped, not even a little.

Fuller made most of the trannys for the late model Crowns with manual
trannys. The Fuller T-905M has been discussed. They also made two (2)
different T0-905 models with overdrive fifth gears.
These boxes will bolt in place instead of a direct fifth model.

One had about a 17% O.D. and was used with 2-speed axles and was called a short-forth model. The other more desirable O.D. model had, as I recall,
about a 28% or 32% overdrive. Do not remember the particular ratios, other than it was a progressive box more like the T-905M, except it was an overdrive model.

Fuller also made two models of the T-906 box, which had 6 gears instead of 5.
The direct model had a 1.00 6th, a 1.33 5th, a 1.91 4th, a 3.03 3rd, a 4.87
2nd and a 8.53 1st. The overdrive version had, I think, a.75 6th, a 1.00 5th, a 1.44 4th, a 2.28 3rd, a 3.66 2nd and a 6.41 1st.

Anyway, it is possible to speed up a low geared Crown without changing the
rear end gears. A tranny change is possible, but is a little more work.
Thought you guys would like to know this stuff.

Swapping a Fuller into a Crown:
I believe the bellhousing on the Fuller will be the same as on your Spicer if you visibly determine such. Probably an '0' or '00' housing, but not sure. You will need to visibly comfirm.

The Roadranger will be longer. Do not know how much. Your drive shaft will have to be shortened, but do not know how much. Except for all the do not know's, everything is great.

Your swap is doable, only somewhat lengthy. Lots of stuff will have to be
changed, including the rear yransmission-motor mounts.
A Fuller T-905 or TO-906 6 speed O.D. may be easier to do. Good luck.
Re: Transmission for 743 Cummins NHH220 horizontal Andy 10-6-03  
Pat Young told me that he has a bunch of the Roadranger 10 speeds. He also he said that they sell cheep ( I think like $250. You should be able to do at least 80mph with one of these.

Pat Young:
(559) 251-3814
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