Ride Height (slow day)

[Lin]

Must be a slow day if I am thinking about ride height, but I actually went and measured the airbags.  According to the book, the rear bags should be at 7 1/4 inches.  They are maybe 3/4" less.  Does that make a difference for me in any way?

[Ed Hackenbruch]

Ummm, almost an inch less clearance?  and maybe a little softer ride but i doubt that you will notice the difference. 

[TomC]

Ed has a typical response to ride heights.  Unlike what would seem to be the logic, actually the higher the ride height, the smoother the ride will be. Why-because with more air in the air bag, the distance between the two extremes of the bag are farther apart with more air separating them-hence it reacts less to bumps.  On the other hand, lower the ride height down bringing the air bags down so the two ends of the air bag are closer together, there is less air in between which means the bag will react faster to bumps-hence a more bumpy ride. Sounds in reverse, but I got that straight from Neway.  Good Luck, TomC

[skihor]

The P.O changed out the 8V71 4 speed to a 6V92 with a 5 speed Allision Auto. Slightly longer setup.   As such the driveline is a little shorter. In our case the ride height is very critical. Too low or too high and I get vibration from the drivetrain, (it can be ujoint breaking/exlploading). Voice of experience talking here.  On a stock set-up one could prolly get away with slight variations in ride height but the manufacturer designed it for a reason, as in ride quality, parts wear, etc... On the other hand my own, (older), parts aren't aligned like they were in my 20's, and I get by just fine. So unless you notice  a drop in ride quality or premeture wear I wouldn't worry too much.

Don & Sheila

[artvonne]

As such the driveline is a little shorter. In our case the ride height is very critical. Too low or too high and I get vibration from the drivetrain, (it can be ujoint breaking/exlploading). Voice of experience talking here. 

  In a large Bus or Truck, there is an enormous amount of torque being transfered through the driveshaft into the axle. Far more than any car or light truck. An 8V71 produces 800 lb ft of torque, turboed 8V71's and turbo 6V and 8V92's can have well over 1000 lb ft. Multiply it by the gear ratios in the transmission, and you may be twisting that driveshaft with more than 5000 lb ft of torque. Angle the line between the ends, and you force the U-joints to experience loads many, many times greater than the straight through torque.

  Ride height is very important, and should be watched closely. While 3/4 inch is not likely much of a worry, several inches could become a real U-joint/driveshaft killer.

 

[TomC]

Driveline torque- 8V-92TA that produces 1450lb/ft torque, multiply that by a 3.51 1st gear, and then multiply that by the 2.0 torque converter and you have 10,179lb/ft torque going through the drive shaft-which only happens if you hold the brake and pump up the engine to torque converter stall speed (not suggested). But even normal starting where the engine is producing around 900lb/ft of torque when you pull away from a stop-that's still over 6,300lb/ft torque at dead stop that lowers quickly as the bus increases in speed.  Good Luck, TomC

[artvonne]

  Not such a slow day afterall? Here are a couple links that might scare the crap out of us.

http://www.rinomechanical.com/pdf/Tech-Notes/universal_torque_determination.pdf

http://www.pirate4x4.com/forum/showthread.php?t=584506

http://en.wikipedia.org/wiki/U_joint

[Lin]

There are several interesting things brought up.  One would be that ride height adjusts the position of the drive shaft and therefore could be critical.  However then, the factory spec ride height would only be applicable to the original drive train configuration.  As Don points out, a change in the engine and/or transmission (as has occurred in my case) would change the drive shaft alignment.  Therefore the factory spec could be irrelevant.  It would seem that in all cases other than OEM, one would have to adjust the ride height based on how straight he could make the drive shaft, measure that air bag expansion, and consider that the new spec.  Sounds like fun!

[artvonne]

However then, the factory spec ride height would only be applicable to the original drive train configuration.  As Don points out, a change in the engine and/or transmission (as has occurred in my case) would change the drive shaft alignment.  Therefore the factory spec could be irrelevant. 

  Typically, anyone smart enough to do a mod to the driveline, you would hope would be wise enough to keep the new powerplant driveline along the same line as the original, or, reset the ride hieght to compensate. So yes, checking the alignment would be a very good idea if this has occured.