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Veteran
Location: Kingsley Michigan | I am in the throws of reworking the 440 engine again---for reasons this time that I cannot explain---anyway---the trans is out now--as it too has mysterious vampires that have infested it too-----Sooooo-- in talking to Valley Truck here in Michigan and they said they would redo the Differential ratio from the factory 4.65 to a 4.11 for $1000. Sounds good with all of the high speed motor rpms required to get ole 801 down the road. Just wondering if anyone else has gone thru this and what was the overall satisfation with the change---Or not!
Thanks for the input; Barn |
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Expert
Location: Cottage Grove, OR | Barney, At one time I discussed this with Leslie. He said that a number of people had done so and not had any problems per se. It does have all of the effects that you can imagine that result from a taller ratio. Until you hit the mountains here in the West or some specific grades in the East, it is probably a non-issue. Basically, you will have less torque applied to the wheels at a given engine rpm and therefore slower acceleration and a little less hill climbing ability. FMC's accelerate faster and hill climb faster than many coaches so you will be in good company. I delayed responding as I was hoping someone that had the changed ratio with a gas engine would respond. Of course diesels require a much greater change in ratio to get the operating rpm down into the range that diesels work.
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Veteran
Location: Kingsley Michigan | Thanks Stephan--
How do the diesel guys do it?? I am now in a world of hurt as I took the rear end out and now the shop says they can't make a faster ratio than what is in there---what changes can you make outside of an overdrive trans or taller tires ---both of which have their drawbacks????
Barn |
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Expert
Location: Cottage Grove, OR | I believe the diesel guys change the entire differential. MCR has had differentials built that are heavy duty and have a taller ratio. As you know, the diesels have a much lower operating rpm so if they don't have an overdrive transmission they need both a differential change and also the larger wheels. I believe they also have had the ratio's changed to what you are looking for in a standard casing. Not sure why they could do it, but your local guy can't. If I did a change to a diesel, I would change the transmisson to the Allison 6 speed which would give me 1900 rpm with the stock rear end. If you left the rear end stock, but went with the Allison 5 speed you would have some lower gears for acceleration and mountain climbing, but a cruising rpm of about 2200 rpm. You would probably have to control it as an "automatic stick shift".
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Contributor
Location: Bluevale, Ontario | Hello Barney,
A Rockwell RS15120 differential is different but can be adapted to work in the FMC housing. The housing flange needs to be drilled for the RS15120 bolt pattern and custom axles need to be fabricated because of the different splines and length, it gets quite expensive. Also a straight axle such as a Dana model 80 can be cut down and made to work but this requires alot of machining and axle fabrication. Both ways give you many options for ratios. We have done both setups for other coaches. If you install larger wheels you will accomplish your ratio change and get close to what your looking for. There are 22.5" 5 lug wheels out there that will fit onto an FMC coach, but hard to find.
Looking forward to the GLASS rally in May. Frank. |
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Veteran
Location: Kingsley Michigan | Thanks Frank;
I have been kicking the whole issue around with Chris Hoagland and came to the final conclusion that changing the 4.65 to a Mcc bus 4.33 was not of much benefit and considerable cost. My differential went to Valley Truck in Grand Rapids where they found the ring gear rivets were loose. The rebuild was going to cost---with new bearings and seals $400. Chris offered the MCC 4:33 differential to me for $1200 plus shipping with a driveshaft--which had different u joints on it due to the smaller pinion and would require an adaptor plate to make up the shorter length---but not a biggy--have a couple of machine shops---but the whole issue was time and money and only a 9% lessoning of the RPMs. The better way to go seems to be with new wheels as I still sport the 17.5" split rim conventionals. They look great as they are chrome but----they ride like a truck with 5 flat tires for the first 10 miles and are hard to find service with. The Alcoas are a lot of work to look good so 22.5" steel and chrome might be my next move. The overall lowering of RPMs of 12% with maybe a similar increase in the milage as well as being tubeless appears to be of greater benefit. If this doesn't do enough---there is the change to the 4:33 that might payoff--but we will wait and see---
Thanks for your input and hope to see you, your wife and kids at GLASS 09; Barn |
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Contributor
| Barney, I know this thread has been quiet for many years, but what did you end up doing? Did you go with the 22.5's? Where did you get the wheels?
Other solution? |
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Changing the Differential Ratio?