Thread Tools Display Modes
Old 08-31-2010, 02:05 PM   #1
Bus Nut
frank-id's Avatar
Join Date: Nov 2003
Location: Twin Falls, Idaho
Posts: 808
Changing rear gears

To begin the gear changing process, gather all the information possible. Decide the rear gears presently in your application. Make some measurements about the present complete unit. Go to a truck salvage yard or gear shop for big trucks.These places can give information about what other trucks use the same model or size rear axle assembly. New gears are expensive, so changing a complete rear axle is more cost effective. I got a used rear assembly from a Freightliner with a 3:55 for my 1968 Crown bus. The used unit was $1500, drum to drum. The 3:55 has all the upgrades from 1969-1996, with good brakes, drums and no leaking seals. The u-joint was $25 and near new. All the air brake stuff was good, and only some new u-bolts were bought. My bus had a 4:10
when purchased and could go 57 mph, as now the bus will travel about 79mph. Frank
frank-id is offline   Reply With Quote
Old 09-02-2010, 10:45 AM   #2
Bus Geek
lornaschinske's Avatar
Join Date: Jun 2004
Location: Roswell, NM
Posts: 3,587
Year: 1986
Coachwork: BlueBird
Chassis: 40 ft All American FE
Engine: 8.2LTA Fuel Pincher DD V8
Rated Cap: 89
Re: Rear end gear ratios

I think the gear ratio in our bus is 5:10 (don't remember, don't care). Folks can just pass us. Bring the bus out west, some semi's would pass, others ended up dropping either just behind or just in front. With a fully loaded bus, the stopping distance is ... long, even when going slow. Since we like to run the back roads/scenic highways we think the original gearing will end up working just fine. As close as we can tell, we were getting 10 to 15 mpg bringing the bus out, going slow. David recently got the governor readjusted so that will probably change... hopefully not drastically.

The Class C does 80 mph and is heavy (my brakes are good... the RV is just very heavy... it's maxed out weight wise on the chassis). It also is a PITA to get it stopped (those little cars either are hiding at my rear bumper -- if I'm lucky I can see their antenna in the rear window -- or trying to fit into my front grill), I'm always worried that I can't the thing stopped in time. I worry that I will run over some little speck of a car, and I do mean run over it.

You may want to rethink doing higher speeds. It's not a question of can you go faster, it's a question of can you stop it.
This post is my opinion. It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
Fulltime since 2006
The goal of life is living in agreement with nature. Zeno (335BC-264BC)
lornaschinske is offline   Reply With Quote
Old 02-23-2011, 10:47 PM   #3
Almost There
Will's Avatar
Join Date: Feb 2009
Location: Columbus, Indiana
Posts: 79
Year: 1991
Coachwork: Thomas
Chassis: International
Engine: DTA 360, Fuller 6-speed
Rated Cap: 53
Re: Rear end gear ratios

Mostbig box trucks have the same axle gearing--I've been looking. Just like when you buy a pickup--engine power has everything to do with what gears are installed. An old bus with a gas engine, or a non-turbo diesel probably had something near 6:00-1 gears. I owned a straight truck with an FT361 with a 2-speed axle and the gears were 6.50/9.00. If you see a medium- duty box truck going 70mph you should know 2 things: the driver is an employee and doesn't own the truck; his foot is to the mat. Won't hurt anything, but I don't drive my bus that way.

A bus is delivered with a straight-truck drivetrain. A typical bus has a maybe 26,000# GVWR and weighs 10,000# less. The bus my kids rides is about half full (2-per seat, not 3) with kids from K-6. It's an 11-row, a 6th-grader is 100# tops maybe (guessing) and a K is maybe 40#. You've got maybe 1,600# in that bus. Besides that, your chassis is probably rated at 50,000# GCWR (my old straight-truck mentioned before was) which means you have to have enough power/gearing to get a small dumptruck pulling a backhoe going, but you are dealing with only 18-20,000#. Can you safely gear it up? Hell yeah.

I have a Fuller 6-speed but I don't use first. It's not a barnyard gear either--it's a smooth shift from first to second. I just don't need first because I don't have enough weight. If I start in first, the engine slams into the governer before I can get the clutch up. With 50,000#, yeah, I could use it. I plan to go down to 3.70s, when I can find them. It's not easy though, because people don't order medium-duty trucks with 300hp.

As far as brakes go, you should have excellent brakes or something is wrong. My bus is hydraulic disks and they are great--very surprised at the stopping ability, especially since they are only 15" disks. Disk brakes are THAT much better. I'm actually frightened by private owners with old air brakes and manual adjusters. I hate laws, think everyone should own a gun, etc., but air brakes do need to be adjusted to function properly. If you have them, go get a class on operating and maintaining them so you don't kill someone. Hydraulic disks are the same as what's on your Hyundia--just bigger.
My bus conversion
Will is offline   Reply With Quote
Old 03-03-2011, 11:52 AM   #4
New Member
Join Date: Mar 2011
Posts: 5
Re: Rear end gear ratios

I agree about the air brakes. If you have them know how to adjust them. I drove truck for 10 years and even when drivers have to go through scales and get safety inspections it always amazed me how often I would get a tractor/trailer with out of adjusted brakes. Major problem when most of your driving is through the Sierras! When set right air brakes are very effective.

Ounce you get a feel for it, it is not difficult to do and takes 5-10 min. (Note: do not trust "self adjusting" air brakes)
Life is simple if you simply live
moving_on is offline   Reply With Quote
Old 03-03-2011, 01:32 PM   #5
Bus Crazy
opus's Avatar
Join Date: May 2010
Location: Montana
Posts: 1,615
Year: 1995
Coachwork: Blue Bird
Chassis: All-American R/E
Engine: 8.3 Cummins
Rated Cap: 72
Re: Rear end gear ratios

Originally Posted by Cotton
Even though it sounds like a good amount of work, it seems like a rewarding project to be able to go 79 in a bus! Thanks for the advice!!!
And you feel 79mph in a bus is a safe thing to do?
opus is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Rear axle gear ratio. To change or not to change. slade Conversion General Discussions 15 04-24-2017 02:33 PM
changing gear ratios Cygnusaa Mechanical and Drivetrains 36 03-05-2017 01:20 PM
rear end gear ratio change Atridox GM | Chevrolet Drivetrain 2 08-13-2012 09:24 AM
Engine,Gear ratios, GVW, mph???input JoeA Conversion General Discussions 8 01-15-2007 11:42 AM
Rear storage / Rear door ideas allanwcoty Conversion General Discussions 0 05-17-2005 11:52 AM

» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 03:11 AM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.