GEAR RATIO, REAR END ?

5B Steve · February 16, 2010, 04:12:42 PM

HELLO,

I CALLED MCI TODAY TO FIND OUT WHAT GEAR RATIO I HAVE FOR MY 1975 (AUG) 5B. I COULDN'T BELIEVE THE TECH

COULDN'T ANSWER THE QUESTION ON WHAT IT HAS IN IT. HE DID GIVE ME SOME NUMBERS THAT IT WAS BUILT WITH.

THE NUMBERS LISTED BELOW.

R 164-WX27

491408

THE QUESTION I HAVE DOES ANYONE KNOW WHAT THESE ARE? HE DID ASK IF IT WAS BUILT FOR THE MOUNTIANS OR

FLATS? I REPLIED, HOW WOULD I KNOW!

THANKS FOR ANY HELP,

STEVE 5B....

John316 · February 16, 2010, 04:15:56 PM

Who did you talk with at MCI, Steve? I might have some tips for you...I have learned a thing or two...lol.

God bless,

John

DaveG · February 16, 2010, 04:16:26 PM

Have you gotten under your bus and looked at any of the tags on the rearend? Generally there is one on the housing itself and that might have the ratio of the original drop-in, but there may be a tag on the drop-in itself and that would be far better.

Worst case scenario you could look at the end of the pinion (after you clean-up all that dried grease and crap) and look at the numbers there.

Of course, there will be real bus guys here in a minute that can help you out too!

rv_safetyman · February 16, 2010, 04:42:59 PM

Steve, there are a couple of things you can do to determine your ratio, if MCI can't help you. Also recall that someone may have changed the rear end since it left the factory.

If you have the typical bus size tire (~~ 490 revolutions per mile), you can get a feeling with the tach. If you are doing about 70-72 at 2100 rpm, you probably have a 3.73. You can factor from there to get other rear end ratios.

The other way is to jack the bus up and rotate BOTH rear tires one complete revolution (make sure that both go 1 revolution so that your spider gears don't mess with the results) and count how many times the drive shaft rotates. It is a two man job, but it will be darn accurate. Usual cautions, as you will have to release the parking brake -- be sure to block the bus!

I don't know about MCIs, but the typical Eagle rear ends are 3.73 and 3.36. Since you have a 5 with a drop box, I would think it might be the same.

Jim

Ed Hackenbruch · February 16, 2010, 05:00:33 PM

The book for my 68 5A says 3.36:1 is standard and 3.7:1 is optional. Since your 5C is 7 years newer it may be different. Do you have the maintenance manual? That is where my info is from, in the section for the rear axle, first couple of sentences.

5B Steve · February 16, 2010, 05:22:12 PM

JOHN,

I WAS PUT ON HOLD FOREVER, I THINK THE TECH NAME WAS JOHN. I DID HOWEVER SPEEK WITH SEVERAL.

STEVE 5B.....

luvrbus · February 16, 2010, 05:26:20 PM

My spec books call for 3:36 for the 8v71 with a manual transmission and 3:73 for 6v71 with a Allison 740 only 2 gears they show

good luck

5B Steve · February 16, 2010, 05:32:36 PM

JIM,

LIKE THE FORMENTIONED WEATHER IS THE FACTOR NOW. THAT IS GOOD TO KNOW

STEVE 5B...

Lin · February 16, 2010, 05:37:05 PM

I remember spinning a wheel to get my rear end ratio. It's been a while, but I only remember having to jack one side. Have I gone senior?

5B Steve · February 16, 2010, 05:39:47 PM

HEY ED,

THE MANUAL, I HAVE IS FOR ONE SEVERAL YEARS OLDER PROBABLY THE SAME AS YOURS. IT NOWS HAS AN 8V-92 N.

WOULD THIS REQUIRE TO CHANGE THE REAR END?

STEVE 5B......

5B Steve · February 16, 2010, 05:46:03 PM

LUVRBUS,

IS THAT RATIO FOR THE INTERSTATES OR THE MOUNTIANS LIKE THE TECH ASK?

STEVE 5B....

rv_safetyman · February 16, 2010, 05:48:29 PM

Lin, you can use just one wheel. However, you will have to divide the number of drive shaft revolutions by 2, as the spider gears will mess with the count.

Jim

DaveG · February 16, 2010, 05:53:11 PM

Is someone shouting?

luvrbus · February 16, 2010, 06:05:43 PM

Sorry but I don't know the answer,but the ratio of 3:73 for the 6v71 and Allison makes sense to me I doubt a 6v71 would have enough power to leave a 7/11 with 3:36 gear.
If you have a tach and tell us what rpms at what speeds it is a no brainier or tell us your top end speed if around 80mph you have a 3:36

good luck

John316 · February 16, 2010, 06:19:19 PM

Okay, Steve. Here is what I would suggest. Try calling back and speaking with either Jim Mclean, Jim Salsbury, or Terry (I am not sure how they spell their names). Ask them if you can get the build sheet for your bus (the original build material sheet for your bus). One of those guys should be able to help, because if you have your build sheet, you know what the original rearend was.

God bless,

John