Rediculously Slow Rear End Gearing, Enine Problem

[wmah]

I used to run about 3000rpms at about 55mph. Until I had the rear gears change from 5.57 to 4.33 and now I cruise along much nicer and cheaper on fuel. It did cost me almost $2400 to make the swap but I figure after 18,000 miles it will have more than payed for itself.

[KC10Chief]

48 mph? Wow. Mine plods down the highway at 55mph and about 2700 RPM's. I can do 65 but it's over 3,000 RPM's then. I thought about changing the gears, but it is VERY expensive. More than I paid for my bus in fact. I'm going to do the conversion on mine and drive it like it is. If I just can't stand it anymore, I'll change to some better gearing. But my bus is already a dog with its current gearing. Not too much of a problem in Oklahoma though. When I looked into new rear end gears for my bus, it was about $1,500 just for the parts. Geez. And I'm a pretty savvy mechanic and it's not a job I would want to do on my own. I plan to convert this bus and maybe in about 5 years, buying a bigger, newer skoolie to convert. One of the flat front transit skoolie's!

[the_experience03]

My 6.6 governs out at ~2600 RPM which is getting me to ~63 mph with 4.56 gears and 10.00R20 tires, the same size you have. Unless you have horribly low gears I don't think that is your problem.

Are you getting all 4 gear shifts? My bus will top out at ~46 mph in third gear. If your linkage is messed up and it isn't shifting into 4th could this be your problem? Your rear axle will have the ratio stamped into it. If it is the Rockwell rear like mine it is stamped on the front passengerside axle tube. Start there and figure out what your ratio is.