Rear Gears

[MCI-RICK]

My bus has a 4.56 rear.  Yup 4.56!  I was wondering if it's possible to replace the gears instead of a full axle swap?

I believe my max speed is around 63mph.  I say I believe because I've not been able to get exact data.  Even from Mr DDEC!  I plugged my DDR into the ECM and found out the speed or rev limiter is OFF!  I picked this bus up from Idaho in April this year and had it up to and over 70mph several times on my 3,000 journey home with out a problem.

While I don't expect to drive over 70mph much, I'd like to have the option to do so.  I believe the tires on my bus are no longer in production so I haven't been able to obtain exact size or revs per mile. The tires are Good Year G391E 295/80R22.5.

OK - here's the info

Allison VR731 trans - ratio is -  .88
Rockwell rear ratio - 4.56
tire size? - 40.6" or 499 - 502rpm
1990 6V92TA DDEC 2  - max rpm 2100? - I've read in DD manuals but I'm not sure.

I want to thank Sean for the rpm info on the tires!

Going by this info, 4.10 gears should raise speed to about 70mph.

I don't know what's available or possible but is there gearing that would increase top speed to around 75mph? and does anyone have a cost idea?

BTW, I know the tires should be replaced soon.  They have less than 10,000 miles on them and are not dry rotted but the date on them is 1602.

Thanks,

Rick

P.S.  The Reliabilt tag on my engine does not have the camshaft info on it.  This is the engine serial #600FF9900 on the tag.

[RTS/Daytona]

I have an 1989 RTS 35' DDEC-II / California 277HP / V731 / 24.5 tires and 4.10 - I do 73-75 MPH

at 60-65 mph I get 9+ miles to a gallon

You can replace the ring and pinion gears - but you must have them set professionally (The removeable / replacement / gear-setup / l 5.13 to a 410) -> $700

Or replace the Pumpkin (aka chunk) - it's the ring/pinion/bearings/housing - but if your have driveshaft e-brakes - try to get a pumpkin that has the E-Brake mounting hole  in the pumpkin Housing Tab- Flx's do not have the hole (they have whelel E-brakes - But they tell me it can be drilled

New 4.10 pin and pionion runs about $2500 - used 4.10 gears or pumkins are VERY VERY rare

Pete

[MCI-RICK]

Pete,

Are there other gears available?  Maybe something like 3.73?  I have the 22.5 tires not the 24.5 tires like you have and would like the max speed to be no less than 75mph. 

I rarely drive above 65mph but I don't like the idea of driving my bus near or at its max speed.  I believe it's currently 63/64mph and I'd rather not drive at 55mph.

Rick

[RJ]

Rick -

Pete's got the "fastest" gearbox/axle combination you can get for a V-drive automatic.

With a DDEC, it's going to be hard to get it to turn more than 2100 rpm, unless somebody else has messed with the software.  92s don't like much over that figure anyway, unlike their 71 series cousins.

Rockwell/Meritor/Arvin (whatever they're called nowadays) never built a "taller" ratio for the V-drive axle than the 4.10:1.  Most are like yours or even lower (5.13, etc.).

Allison never made any bevel gears taller than what you've got - altho they did, for a very, very short time, make an underdrive bevel gearset that was 1.04:1 (These were special order for San Francisco Muni to cope w/ the hills).  Installing a set of these, even if you could find them, would slow you down.

There are some 11R24.5 drive axle tires out there that turn 470 revs/mile, which would help some (Bridgestone M726EL, 44.2" diameter).  I haven't seen any 22.5s that turn that few r/m, most are in the 490 - 510 range.

With your current rear axle, the above 24.5 tire would give you 69.24 mph @ 2100.  If you had a 4.10 like Pete, you'd max out at 76.99 mph @ 2100.  (And so you can cry in your beer some more, the manual gearbox would top 85 mph with these tires!)

FWIW & HTH. . .

[TomC]

As stated before the biggest gears for the Meritor (old Rockwell) was 4.10.  IF you change to 11R24.5, which are the biggest diameter tires you can get, you'd have 476rpm tires.  So at 2100 with 4.1 and the .88 overdrive your top speed would be 73mph.  I have the same 4.56 as you, but also have 11R24.5.  I cruise at 58 mph which gives me 1850rpm-which I get about 6.5 mpg.  Since I have an 8V-71, I have it turned up to 2400rpm (don't do that with a 92 series) and I get a top speed of 75mph.  Good Luck, TomC

[RTS/Daytona]

Rick

What you are looking for is:

Ring and Pinion gears (matched set)
Rockwell(Arvin Meritor) 4.10 (A-38152-1) gear set (Ring& Pinion 41/10)

The RTS# is 2055047
The FLX# is 04-0219-00362

2 years ago - I sold 4 sets - I used to sell them for ------ $1957 (INCLUDES shipping to a business address only) - don't know what the price is now
Meritor been increasing there prices year year  --- let me know if your SERIOUS - I'll ask my supplier  (I don't like bugging this suppler)

for used / takeout pumpkins
look for ROCKWELL V-Drive 14 bolt differential - 59000 series

Some RTS'ers that drive in mountain areas may want your  4.56 gears

Pete RTS/Daytona

[MCI-RICK]

Pete,

As a newbie to the bus world, I've been trying to figure out what's doable vs what's practical, sprinkled with a bit of, I want it.  I spend a great deal of time here gathering info to help me make decisions regarding our conversion. 

I'm considering the change over to a different rear and will drop you a pm if I want to proceed. 

I really do appreciate the input I get on the questions I post! 

Just a thought - Newbies are the guys that help keep "the basics" fresh in your mind.

Thanks for you patience everyone!

Rick   

[NJT5047]

You might wish to install a tach and see what RPM you really are operating at.   A DDEC II RPM limiter can be turned off, or adjusted wherever.  If it's turned 'off'...there's no rev limiter.   This is common in marine applications. 2100 is considered max RPM for a 92 series, but if the rev limit is turned off, it'll run whatever. 
A good many transits were limited to 1800 from the factory and for special operations (charter?) the low RPM setpoints were often defeated.   
I've got a chip in my DDEC 1 (different from yours, but yours can be reprogrammed similarly by DD) that simply removes the engine red line.  This is good if you watch a tach or have an inherently slow bus like mine, but unlike a'71/'53 series, extended operation at much over 2100 may result in a giant sucking sound in your wallet. 
Install an alternator tach.  Might be surprised at you max RPM.   Might not?
Depending on the terrain you plan to operate the bus, your 4:56 might be just what you need.  If you're in the flatlands, a lower numercal pumpkin would be good.  But, if you live in hilly country, you might find the 4:56 a nice item...albeit with a slightly slower highway potential. 
Unless a 6V92TA is kept spooled up, they are quite poor hillclimbers.   
You can check for a rev-limiter by using your DDEC reader and simply run the RPMs up in neutral...if it goes above 2100, let off.  Your limiter is off.   
The bus won't really go any faster with a 4:10...it'll just operate at lower RPM.  On any roads other than flat, it'll likely be slower.  Your transmission is limiting for a 2 stroke.   The top speed might be a little over the 2100 mark, but maintaining 65 might be much easier with the 4:56.   
My dos centavos...

JR 

[MCI-RICK]

Jr,

I'm not trying to high jack a thread I started but can you tell me more about an alternator tach? 

I will spend some time searching for info on that but some input would be appreciated.

Thanks,

Rick

[JackConrad]

   An alternator tach receives a signal from the R terminal on the alternator. Obviously, the alternator has to have an R terminal, and the tach has to be programmed based on number of poles in the alternator and the alternator/engine speed ratio.  Jack

[luvrbus]

Jack, the alternator does not need a R terminal we just went through this on Texas Border Dudes Eagle his didn't have a R terminal but the guy at Prescison Speed helped work it out.       good luck

[JackConrad]

Jack, the alternator does not need a R terminal we just went through this on Texas Border Dudes Eagle his didn't have a R terminal but the guy at Prescison Speed helped work it out.       good luck

Thanks for the information, I jst learned something new.  How did ya'll connect to the alternator?  Jack

[MCI-RICK]

Luvrbus,

Jack, the alternator does not need a R terminal we just went through this on Texas Border Dudes Eagle his didn't have a R terminal but the guy at Prescison Speed helped work it out.       good luck

Thanks for the information, I jst learned something new.  How did ya'll connect to the alternator?

PLease, share info!

Rick

[NJT5047]

If you have a 50dn alternator, you likely have an "R" terminal.  If not, you can read off the "B+" term.   The 'before rectified' alternator output can be used as a signal. 
Look at the backside of your alternator and you'll see small letters indentifying the various terminals.  The "R" is the most common signal tap for a tach.
ID your alternator and let your tach supplier know what you need.   
Your DDEC II ECM also has a tach signal built into it...and cruise control (cruise may be disabled, if so, it can be enabled).   
Check with the local DD for a compatible tach.  The tach wiring is probably dead-ended behind the dash.  Most coach wiring harnesses have an assortment of unused front to rear leads and a dedicated tach lead.
I would guess that your DDR will give you an RPM readout too?   Once you know what the RPM is in the various gears, it's going to be repeatable.   
The important thing is don't over-rev the engine.   Most buses don't have tachs because they cannot be over-revved.   Coaches with the DDEC rev limiter removed obviously are an exception.   
JR
 
 

 

[donnreeves]

Rick,
I have an RTS with 4:10 gears and sometimes wish for a 4:56. I believe you are from NJ like me, so will spend most of your time in the Northeast. The speed limits up here are 65 max with constant hills to climb. My engine seems to like running at 2100 rpm, or 70 mph. At 1900 or 65mph it is a little sluggish on the hills. Another problem with the 4:10's is the shift from 2nd to 3rd. in my bus it happens at 2350rpm and 55 mph. It can drop down to 52 before downshifting. The problem is that there are a lot of 50mph roads that I have no choise but to run at 2250rpm in 2nd. To sum up, if you are going to spend alot of time out West or down South, the 4:10's are best, but for the Northeast I would stay with the 4:56's. By the way My RTS is  96"x35' with a 350hp 6V-92. Your bus, being bigger and heavier, with less hp would have more trouble with the taller gears. Pete lives in FLA with 70mph speed limits and the biggest hills he sees are the overpasses, so his gears work well for him. I have an Isspro tach with a crankshaft sensor, works great.  Donn