Transmission swap?

[5B Steve]

     I know this question has been ask before, I have the chance to change mine from the 4 spd Spicer to a 10 spd

     roadranger.  Would it be worth the time and expense to go this route?  My bus is a 1976 MCI-5B. I know if it works

    "DON"T FIX IT" Thanks for any insight. BTW, engine is a 8V-92 N.

   Steve 5B....

[bevans6]

Compare the length of the Spicer, flange to flange, to the length of the Roadranger.  The Spicer is about the longest transmission that will fit in there behind the 8V engine, and the issue is that the drive-shaft gets too short.  Your 8V92 is (I think) 3/4" longer than the 8V71 already.   FWIW the Spicer is about 28.5" from the drive-shaft flange to the flywheel housing flange.  Since people can successfully fit a 640 series Allison in there with an 8V71, you might also look into how long that tranny is.

Brian

[TomC]

I would personally be more interested in the Spicer 7spd.  It is available with overdrive and has more than enough gears for you.  Plus, there are no air lines that have to be run, unlike the 10spd for the range selector.  I had a truck with the 7spd, and worked well.  I believe it is shorter than the 10spd.  Good Luck, TomC

[5B Steve]

    Brian,  thanks for that info!

   Tom, I was hoping that I would get your impute.  Where can one get a 7spd spicer and what would be the cost?

   Steve 5B.........

[Lin]

I think Boogiethecat did that switch but than went to a 6 speed with synchro.  You might get want to see what his experience was.

[TomC]

The maximum torque rating for the 6spd overdrive with synchros is 860lb/ft.  I believe the 8V-92NA is rated at 365hp and 1050lb/ft-so you're too high for that transmission. 
Both the 7spd and the 9spd (9spd will have air operated range selector) are 28.9" long
The 10spd is 29.9" long.
Both the 13 and 18spd is 33.1" long.
Personally, would still stay with the 7spd for simplicity.  But- 7spds are a rare bird in the trucking industry-although not impossible (only takes one). Check with Truck Trader, Ebay Motors, My Little Truck magazine, etc.  Good Luck, TomC

[HB of CJ]

My old Crown Supercoach had the (in)famous RTO 910 10 speed.  At 55 mph the coach could be run in 8th, 9th (direct) or 10th.  The gears were very close together and the shifter moved only an inch or soss with very little effort.  Again...more like shifting a dirt bike than a truck tranny.

However..having said all of this, in your particular application,  (weight, power, wind resistance, road speed) the Fuller TO 14707 overdrive might be an actual better choice, mainly because it is the same overall length as the Fuller 9 speed, which is a couple or three inches less than the 10 speed.

Still a very big, fairly long, wide and flat tranny, since the twin countershafts are horizional instead of vertical like most single countershaft trannys.  I think your DD 8V92N would absolutely LOVE the rpm drops the 7 speed would provide, plus give you a .75 to 1.00 overdrive for high warp speed.

In addition, the overdrive 7 speed still has a low gear of around 9.25 to 1.00 or soos, which, along with the low reverse, would laugh at ANY gradability or startability concerns, as long as your open differencial could optain traction.  The gear ratios are AROUND .75, 1.00, 1.37, 2.06, 3.22, 5.45 and 9.24.

Don't worry about the long single shift rod that moves back and forth along with twisting to shift the thing.  My Crown Supercoach as about a dozen grease zerts along the rod which, if greased, allowed VERY EASY SHIFTING.  You will love the 7 speed Fuller.  HB of CJ (old coot)

[Len Silva]

The maximum torque rating for the 6spd overdrive with synchros is 860lb/ft.  I believe the 8V-92NA is rated at 365hp and 1050lb/ft-so you're too high for that transmission. 
Both the 7spd and the 9spd (9spd will have air operated range selector) are 28.9" long
The 10spd is 29.9" long.
Both the 13 and 18spd is 33.1" long.
Personally, would still stay with the 7spd for simplicity.  But- 7spds are a rare bird in the trucking industry-although not impossible (only takes one). Check with Truck Trader, Ebay Motors, My Little Truck magazine, etc.  Good Luck, TomC

Tom,

Not questioning your numbers, I'm just wondering if it really matters that the trans is under rated for the engine torque.

If you drive conservatively and are not hauling 80,000 lbs., is there a real chance of damaging the transmission in anything but the lowest gears?  I mean, if you were tooling along and dropped into 4th and punched it to pass someone, are you risking the transmission?

Just wondering what it all means in real life experiences.

[artvonne]

I mean, if you were tooling along and dropped into 4th and punched it to pass someone, are you risking the transmission?

Just wondering what it all means in real life experiences.

  If you mash the pedal down, the engine WILL develop full torque as it accelerates. Anything downstream of the engine that cant tolerate the torque the engine produces is going to fail. The only question is when. It doesnt matter if your running light or heavy, all that matters is if the engine is producing full power into the drivetrain. Ideally you want something over rated, not under.

[TomC]

Len- if you had for instance a small injector 6V-92TA putting out 277hp and around 900lb/ft torque, then I'd say it probably wouldn't matter-because the turbo engines turn on the power relatively slowly.  But Brian has a natural 8V-92 that has an effective 4 stroke equivalent displacement of around 1100cu/inches.   With any Detroit non turbo engine, the torque turns on immediately-so would most likely blow the 860lb/ft rated 6spd transmission.
This is why it was so hard to keep a transmission behind the 12V-71NA-when you mashed the pedal-the engine made torque right now-at most any engine rpm.