Need some MC8 differential info

[MC8Mike]

Hi all,
   After some absence from the board I'm back with some questions about my MC-8 differential gearing. Since the engine swap to the 8v92 I'm now running up against the governor, 2100 rpm at 70mph. The way the gearing is now the trucks that pass me on the flat I have to re pass on the hills. Anyway from what I have read in doing a search in prior posts about this subject my 8 has a 3.70 gear and would like to get a higher ratio, somewhere in the 3.30 range. My parts manual only lists a 3.70 and 4.11 ratios available even though I find discussion on the boards of the existence of higher gears. I guess my question is a source for a used 3rd member in the desired ratio, or if it is possible to find a new ring and pinion for my 3rd member will the higher gear ratios fit my ring gear carrier. I know on so many rear ends if you change the ratio too much you also have to change the ring gear carrier to match the new gear.  Thanks in advance, Mike.

[luvrbus]

I got my 3:36 ring gear,pinion and carrier from Pro/Gear in Orlando FL for my MCI 8 when I went to the 8v92 .Then I was told later the MCI 9 pumpkin with the 3:36 gear was a direct bolt in for the 8 with a  3:70 pumpkin

[MC8Mike]

Thank you, that gives me a place to start.

[lostagain]

I swapped 4;11 to 3:36 gear ratio in my 5C. Best thing I have done to this bus. A 5C is the same bus as an 8, without the drop box, and 5 feet shorter of course. I have the Allison HT740 that has the 1 to 1 ratio in top gear. At 65 mph, the revs are about 1800 rpm. Top speed is 80 mph in 4th, 55 in 3rd, 40 in 2nd. The loss of power is negligible, more than made up by the higher speeds in each gear. And start ability is not an issue with the Allison automatic. I found the gears at a charter outfit in Alberta that has kept every bus they ever used for the past 40 years. Swapping those gears is heavy work. I used a transmission jack, along with other bottle jacks, and some strong language. You have to raise the bus high enough to get the gears slid under it. Higher than you would think. I seem to remember in and out in 2 days. Well worth it.

JC  

PS: 11R24.5 tires

[MC8Mike]

I like the 5C bus, if I had not already had the 8 I would have gone for the 35footer. One of the Saudi buses would have been great for me out here in the desert with the double roof they had.
I run the same tires and trans as you. Did you replace the whole pumpkin? And what was it from it that was the case? Having the ability go run 80 if need be would be great. Limited to 70 you just don't have enough extra speed to pass safely at times.
I know it will be a heavy, dirty job but I agree it will be well worth the effort.
Thanks for the input, Mike.

[robertglines1]

CK with B-K I think he has a couple MCI's he is parting out.

[MC8Mike]

Who is B-K? Thank you, Mike.

[chessie4905]

Also check with Luke. Or maybe the place near Danville, Pa. on I-80; he has several MCI'S. That's  if you have no luck out there.

[lostagain]

Mike, I swapped the gears inside the pumpkin. First, drain the oil, pull the axles out, then with the cover off, slide the gears off. Putting the new gears in is tricky, because they have to be slid in just right: level and straight. I had borrowed a transmission jack that adjusts not only for height, but also for sideways and fore/aft level. It is not difficult, but the parts are heavy, and you are working under the bus...

BK is Bryce Gaston. He posts here occasionally. He owns a charter bus company in Tennessee, or somewhere back East.

JC

[eagle19952]

Who is B-K? Thank you, Mike.

Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
Huntingdon, TN 12 minutes N of I-40 @ exit 108


http://www.busconversions.com/bbs/index.php?action=profile;u=8

http://www.kylakesidetravel.net/

[robertglines1]

check your messages 

[B_K]

I spoke with Mike for a moment today and I am going to see if either of the MCI's I still have has the right ratio for him. ( ::)sorry Mike didn't get it checked today, but will in the morning just before I start working on putting my bike back together! I promise bus before bike ~ this time anyway!  )
  BK 

[TomC]

Course another way is to swap in an Allison B500 transmission. Same 1st four gears of the HT740, but with a .74 and .64 overdrive. Then you don't have to fool with the rear end. Good Luck, TomC

[MC8Mike]

Yeah that is a consideration but I already have a bunch of bucks in my rebuilt ht740. In hindsight that may have been a better option for me. Thanks, Mike.

[luvrbus]

Even going with the B500 you would need to change the gear ratio to a lower gear for the overdrives