10 spd or 13?

[TomC]

Spicer transmissions are old versions of Meritor (Rockwell) transmissions.  My guess it the 9 spd Spicer will have the same ratios as an A model 9spd Meritor.  I'll try to look it up for you.  Good Luck, TomC

[TomC]

A model Meritor 9spd A model overdrive- 10.50, 7.37, 5.21, 3.78, 2.76, 1.95, 1.38, 1.00, .73.  The B model is very close to the same except it has a 12.56 low-which you don't really need.  If you gear your bus for 1800rpm at 75mph, that will give you a good spread of speeds. That gearing would put you with 12R-22.5's (485rpm tires) at 2100rpm a top speed of 88mph.  If you have an electronic engine, you want to gear it for 1600rpm at 75mph.
1800 at 75 in overdrive is 2465rpm in direct, or 1972 at 60-divide by your 485rpm tires, and you need a 3.90 to 4.11 rear end ratio.
1600 at 75 in overdrive is 2191rpm in direct, or 1753 at 60-divide by your 485rpm tires, and you need a 3.55-3.70 rear end ratio.  Good Luck, TomC

[Iceni John]

Some disillusioned folks would say to "go for the bus" 

Maybe that's why my girlfriend ruefully calls my bus "The Mistress".   I think she's just envious of it.   Competition?

John

[buswarrior]

Another consideration is a true "Super 10"

Only 5 shift positions and a splitter. IIRC, gear ratios are evenly spaced for consistent engine rpm targets for shifting any gear.

Split when you want, just shift 5 when you want, no returning to do over the pattern.

Trouble with the transport industry, too many don't call things by the proper name.

Don't confuse a "Super 10" with a "Top 2" or with a "2 speed differential".

happy coaching!
buswarrior

[TomC]

Even though I like the Super 10, I would shy away from them.  They are not made anymore-they were problematic-so Meritor gave up on them.  Good Luck, TomC

[gus]

I prefer the 10sp even though it is overkill in a bus, 6sp would probably be more than enough. The main gears you need are an OD top and a pretty low bottom for low speed steep grades and maneuvering.

The 9sp I don't like because of the huge gap between 8-9 but that may have been just the model trans I drove.Son't know if it was an OD or direct type. 8 and 9 were either too low or too high, it could have used one gear in between.

[HB of CJ]

This comes from a poor memory from 1970 when assigned a Crown Supercoach school bus which had the RTO910 Fuller 10 speed Roadranger and there was a small 3"x3" pamphlet included in the driver's glove box under the side window.

.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 6.28 first gear.  These ratios might be a little bit off, but very close to what this cool tranny actually has.  Broomm, broomm, brooom.  Very cool.

Sosss...just add 22% to your present top speed and you are good to go.  Actually, I was told by the former heavy truck racers that the 910 series can handle 950 ft lbs torque in the "low side" and about 1500 ft lbs in the "high side".

And....never start a paragraph with a conjunction.  No...wait.  In 8th, 9th and 10th gears, the infamous RTO910 can handle over 1800 ft lbs. for a short time.  Humm.  Torque totals or something inside the tranny that flexes the case.

The overdrive 9 speeds, in my humble opinion, would not be a good choice in a Crown Supercoach because the bottom 2 gears would be wasted and never used.  However...the top 4 gears would work ok if you needed the road speed.

Gradeability/startability is fine with the RTO910.  My '74 ten wheeler Crown weighed right at 25000 stripped interior and I EASILY started up a 12% gravel forest service road ro 4000feet starting in 1st gear.  HB of CJ (old coot)

[TomC]

Gus-typically the difference between the 9 and 10 spds was between 1st and 2nd gears.  The top 4 gears on each are just about identical.
Top 5 gears on a B model 9spd- 2.79, 1.95, 1.38, 1.00, .73
Top 5 gears on a B model 10spd- 2.48, 1.83, 1.36, 1.00, .75
Top 5 gears on a C model 10spd- 2.64, 1.90, 1.38, 1.00, .74

Not much difference between them.  Good Luck, TomC

[HB of CJ]

Seems I can't post a longer answer.  You probably (might) have the RT905M which was the Fuller 5 speed of choice way back in the day when Crown Manufacturing offered the Fuller 5 speed in their busses.

Your present gear sets are right around...1.00 in 5th, (high gear) 1.32 in 4th, 2.04 in 3rd,  3.25 in 2nd and around 5.25 to 5.45 in 1st because I can't remember.  The Fuller 5 speed is a short tranny.  The older T906 6 speeds are slightly longer and the older...

and newer 7 and 9 speeds are slightly longer still and the same length, then comes the 10 speeds, then the 13 speeds and the 18 speeds which are the longest.  Remember the Crown drive shaft is kinda on the short side.  U-joint life becomes a concern. 

A 400-750 Cummins Big Cam 855 would love the TO14707 7 speed.  No air lines needed.  Your cool 220 743 would LOVE the RTO910.  Try to stay away from the Super 10...it had a truely weird shift pattern and many a 10 speed driver destroyed them.

Please don't ask how I know this personnally.  Embarrassing.  The RTO910 is now becomming rather hard to find.  Older equipment.  Most now recycled.  Expect to pay no more than $750 for a runner and about $1500 for a rebuilt.  HB of CJ (enough)

[Mex-Busnut]

Another consideration is a true "Super 10"

Only 5 shift positions and a splitter. IIRC, gear ratios are evenly spaced for consistent engine rpm targets for shifting any gear.

Don't confuse a "Super 10" with a "Top 2" or with a "2 speed differential".

happy coaching!
buswarrior

Mine had the "true Super Ten", and I absolutely hated it. No synchronizers. No problem up-shifting, as long as you do it fast and double-clutching. Down-shifting was another story.

[gus]

Tom,

Thanks, didn't know that. The gaps between the two top gears are a lot more in practice than they seem in the chart!

I have a 10sp on my '71 Dodge C900 but haven't driven it enough to notice the similarity. It is a work in progress!

[buswarrior]

The Super 10 I refer to is made by Eaton.

Splitter works the same as on an Eaton 13 speed.

Upshift, flick the splitter, lift throttle, change happens when you break torque, back on the throttle.

Downshift, on the throttle, flick the splitter, lift throttle to break torque, back on the throttle gently to raise revs, catch the shift as the revs rise, back on the throttle in the lower split.

As best as I had heard, they are prone to the same issues regarding the splitter as a 13 or 18 speed.

Tom, what else is wrong with them, I'd like to know, as I have one in a 2001 FLD 120.

happy coaching!
buswarrior

[TomC]

On the Super 10's, the splitter usually went south.  But the nice thing is you still have a 5 spd transmission that you can reasonably drive.  What was really destructive was if the splitter was floating between high and low splitter-usually took out the entire transmission.  Also, the Super 10 had a unique transmission case in that it takes a specialty trained mechanic to know how to work on it.
As with any geared transmission, you must keep the oil up to the level of the fill plug.  DO NOT EVER use your finger to feel in down to the oil and be satisfied with that.  A fingers depth of lack of oil can be enough to get the gears out of the oil.  Have seen too many transmission failures because of this.  Quite simply-keep your oil clean, up to the level of the fill plug, don't grind the gears and the Eaton Roadranger transmissions should last well past 1 million miles before overhaul.  When I changed my 13 spd to a 4 spd Allison (wished I had that setup while driving), I had 1.2 million miles on the original clutch and over 800,000mi on the transmission (the original owner blew the transmission at 400,000mi-just before I bought the truck).  Good Luck, TomC

[buswarrior]

Thanks Tom.

happy coaching!
buswarrior

[Busted Knuckle]

BW & TomC are correct about the "Super10" it is a 5 speed shift pattern that splits each gear as you go up shifting it like a 5 speed.


Steve I don't think yours had a true "Super10" in it. If it did the reason you hated it was because nobody taught you how to properly drive it.
On a true super 10 the only time a clutch should be used is taking off in 1st or reverse!
Let the throttle pedal do the rest!

TomC truth be known the biggest problem with the Super0 was re-teaching old hands to shift it like a the top end of a 13 spd all the time rather than shift 5 times and up shift and do it again and splitting it @ the top.

I know had a little trouble getting used to it, but once I did I loved it! (except I really was a fan of the 13's and 18's). I had 2 drivers who had been driving longer than I was old and they just never could get the hang of the "Super10" and I had to out them back in trucks that had 13's to make them "comfortable" and so I could sleep knowing they weren't destroying my transmissions!
  BK