Hello all, been a lurker here for a while and have gotten a lot of great info that has helped me with my bus project thus far.

Here's my question. I have a 1994 7.3 IDI shuttle bus that is built on an e350 chassis. I'm having some wicked vibrations that feel mostly through the seat, not the steering wheel. I've run the gamut of usual suspects and have put new rims, new tires, new u-joints, and even new leaf springs on the bus in an attempt to make the chatter/shudder/vibration go away and nothing seems to help.

It occurs rather intermittently, though it doesn't appear at takeoff or at low speeds that much. It typically kicks in pretty bad at 40 - 45 MPH and then goes away around 60 MPH on the highway. Once you reach highway speeds it rides pretty much fine but will still start to shudder really bad and then just go away.

From everything I've read, I'm inclined to lead to a driveline issue. One of the big questions I have however is the "box" that is located between the two driveshafts. I have no idea what this is and am wondering if it could be the source of my shudder. I'm posting a pic to see if one of y'all would be kind enough to identify this for me and/or let me know what its purpose is.

Thanks in advance!

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You got me? It appears to be some kind of a brake. It looks like a rotor on the front. Maybe a electronic parking brake? It could very well be the source of your vibration/shudder. My first thought was driveshaft out of balance. But that usually gets worse the faster you go. You might try talking to one of the mechs. at a shop that services similar vehicles. City, or a private fleet.

 

yeah, I was kinda hoping someone would at least know what it was so i could research it before taking it to the shop. Honestly, with all the guru's here I'm a bit surprised no one knows what this is, lol.

 

You cant figure it out yourself?

Is there wires going to it? Caliper(s)?,

 

I am wondering if it is some kind of electric motor. Make bus function like a hybrid. If that is the case it should have some very large battery cables running to it. Or connections where they used to be.

 

Got an answer from someone over @ skoolie.net. It is a telma driveline retarder, sort of like an electromagnetic jake brake. Anyway, this may very well be the source of my driveline vibration, so I'm probably going to grab a standard driveshaft from a pick and pull, yank the telma unit out and see if it makes a difference. I figure the $35 I'll pay for a ds from pick n pull is the cheapest route to eliminate (or implicate) the telma unit as the problem

 

Just make sure the new driveshaft is not bent. Junkyards are notorious for lifting a vehicle with forks underneath and bending the driveshaft.

 

x2 I was looking for one when I made my truck 4wd, and every truck I looked under the driveshaft was screwed up from forklifts.

And measure first, being a bus, that might have some funky odd size driveshaft that you might not be able to find so easily. Though maybe not... I dunno.

 

it's just the standard 138" wheelbase, so a replacement should be pretty easy to find. However, in the meantime, it turns out it was just that my rear shocks were shot and were providing essentially zero dampening.

I ended up taking it to the shop and they lifted it and spun the driveline and there was no driveline issues, though I am still probably going to take that driveline brake unit off, as it doesn't really serve my purpose and is just one more thing to go out (not to mention that everything I read about them says they are notoriously hard on u-joints)