1974 MCI Tag Axles

[Glennman]

I just purchased a 1974 MCI converted bus. I had to drive it 900 miles to get it home. In the past, I owned a bus that didn't have a tag axle. Whenever I stopped I would check the tires for heat, etc, and noticed that the tag axle tires were cool, where the rest of the tires were warm. It does not appear that the tires have any weight on them, and they smoke quite easily when making a somewhat quick stop. It looks like they don't do anything but take up weight and room.

My questions are: 1. Would it hurt anything to remove them; 2. Is there a way to raise them when turning; 3. Is there a way to adjust them to take weight off the drive axles, also making the breaks more effective?

I know that is a lot of questions. Thanks in advance for any replies I might receive. Any ideas or education will be appreciated... Glennman

[GnarlyBus]

All good questions.

The tag axle helps carry the weight of the coach. They cannot be removed. The tag on an MCI of that era cannot be lifted while turning either. It can only be lifted using a jack and chaining it up. This is an emergency operation. The tag helps keep the bus going straight down the road.

They can be unloaded using a switch near the driver that is usually covered with a red protective cover. I've never had to use it but it could be used to drain the air out of the tag axle air bags so that the weight of the coach rests on the drive axle to help with traction in a tight spot. Sometimes people take a good tire off the tag to replace a flat to get them down the road to a tire shop.

The tag axle takes weight off the drive axle during normal operation. It has its own brakes as well. Not sure I understand your third question.

It's possible that the tag axle air bags are not filling up to proper psi causing the axle to not carry it's share.

The switch near the driver will drop the psi in the air bags on the tag to 35 psi and there are valves in the engine compartment on the right side right above the drain daily sticker that will drain the rest of the pressure out to 0. If either of these were set to drain then it could cause the cold tires. It's possible tag tires don't get as hot because they aren't loaded as much as the other tires. The tag carries I think around 4k normally while the drive carries around 20k lbs. The steer axle is around 11k lbs.

Get a manual for your bus when you can. The maintenance manual but also the operators manual includes instructions on how to tell if the tag airbag pressure switch and valves are setup properly.

Tag axles can get seized when not greased regularly. Search the forum for seized tag axles and you'll read some solid threads about it. It's an ordeal.

Hope this helps.

[buswarrior]

Check for the air to be turned on to the tag axle first.

2 Manual valves, up high, curb side engine door access.

Sliding a tire under moderate braking gives you flat spotted tires, which go thump thump thump down the road.

There are two regulators mounted on the bulkhead, just down through the engine room floor access. One for road pressure, one for the tag unload pressure.

Previous Owners (PO) cannot be trusted to have done anything correctly, the condition of a coach must be held in great suspicion, until you prove it out as performing according to the manuals.

Wouldn't be the first time someone screwed up the tag axle on a coach, quite misunderstood sometimes.

Just return it to proper function, and service the brakes.

Happy coaching!
Buswarrior

[Glennman]

Thank you both for the great replies. I'll look at the manual (I believe one was provided, as there was a whole box full of books and manuals provided), and seek to restore the original operation, if indeed it is not functioning properly.