MC-7 tage axle question

[gtd]

I have a 1973 MC-7 Combo.  I am noticing in pics of other MCI buses that their tag axles have a different wheel style then mine.  They look like a steer axle.

Mine looks like a drive axle  like it should have duels like a semi truck, but I only have one tire on each side of my tag. 

My questions.  Whats up with this?  If I should have duels, Is it hard on the axle to run single wheel?

[makemineatwostroke]

I never seen but one mci7 combo and it was a tandem drive not a tag axle

[Tony LEE]

"but I only have one tire on each side of my tag.  "

That is normal for MCIs - at least for 7's and 8's. It tracks roughly in the middle of the duals. Later models (I think) did have castored tags to reduce the turning circle

[makemineatwostroke]

Gtd,both axles on your bus are drive axles like on a truck and i don't know if it good or bad not to run the duals on it but they look better with the duals that it was design to have maybe some MCI people will have an answer for you

[Tenor]

GTD-
MCI 7's have a drive axle toward the front which is attached to the tranny by drive shaft.  It has dually's.  Behind that is the tag axle.  It never had more that 1 tire per side.  It is not attached to the drivetrain of the vehicle.  It is there to support the load of a full bus.  As for a different wheel, perhaps some companies put a lighter or smaller wheel on (I am guessing here), but usually it is the same wheel as the rest of the wheels.  They are mounted just like the steering wheels.

Glenn

[Stan]

The MCI-7 Combo was a covversion done by Greyhound. The rear lower third of the bus came from a GM 4501 Scenicruiser. The 4501 had duals on the back axle but the back axle is a tag. You can run single wheels on that axle, either as an inside or outside wheel. To run as an inside wheel, (looking like a front wheel)  you just put it on facing in using the inside nuts. To use it facing out, you have to have a spacer under the inside nuts and then mount the wheel with the outer nuts facing out.

With single tires on the rear axle, you have to reduce the weight carried by that axle by reducing the air pressure on the rear air beams. You can still leave in the tag axle air dump valve which reduces the pressure even further.

You have to reduce the braking force on the rear axle with single tires by installing smaller brake cans or using a maximum pressure regulator to stop wheel skid. The pressure regulator only stops wheel skid and the tag axle will be doing more than its share of braking if you don't use smaller brake cans.

If anybody has seen a MC-7 Combo with tandem drive, please post the info as they were not tandem when used and sold by Greyhound. I don't think there would be room for a differential housing and I have never heard of a tandem axle for reverse mounting. Crowns are midship engine so the drive axles face forward.

[makemineatwostroke]

Stan maybe i am wrong but the one at Southern Oregon Diesel had 4 axles in in the tandem it could have been their set up 

[ChuckMC9]

Well first of all, it looks cooler!

But look at the hub on that axle in your photo. They look like drive axle hubs???

[Tenor]

Wow Stan!
I should have looked at the picture closer!  I've never heard of one of these.  I'll just shut up for a while in humble silence!

Glenn

[roadrunnertex]

Folk's this MC-7C conversion is a ex Greyhound combo car true and like one posting said it does have the PD4501 Scenicruiser rear suspension and drive with the front axle being the drive axle and the rear being the tag.
When these MC-7C's were in Greyhound service they were called combo coaches and Greyhound gave them a model number of MC-7C.
Blitz Body in Chicago,IL got a contract from Greyhound to take portions of the PD4501 Scenicruiser underbodys and put them under the  MC-7C.These coaches operated with a total of 10 wheels on the ground like the Scenicruiser.
They also had a automatic transmission and MC-8 dash and a single large radiator.
Portions of the above information came from the book Modern intercity Coaches by Larry Plachno.
jlv

[Stan]

For those who are interested some more MC-7 Combo facts. The rear hubs are identical, as are the brakes. IIRC, Greyhound ran equal weight on both axles. In the picture. note that the rear bay door is only half a door. In the conversion, the drive axle was moved forward 18" shortening the wheelbase (for better weight distribution) and giving a very short turning radius. Also it was the most rugged bus ever built, weighing 1500 pounds more than a MC-8. A six cylinder in-line Cummins or DD can be stuffed in without modification. !00 buses were originally converted and were the first Greyhounds to run automatics (Allison HD740) and four of the coversions had experimental Cat 3408 engines. I think Plachno did a feature article on a cross country run to compare HP and fuel use with the Cat engine.

[TomC]

Unless the PO installed a limiter on the pressure to the air bags of the rear tag axle, you should be running duals on that axle too.  The best way is to have the bus weighed by axle to see if you're exceeding the single tire rating of the tag.  My suggestion is that if both your rear axles have the same weight on them, you need to be running duals on the tag also since it has the same weight bearing and the same brakes as the front drive axle.  Let us know what you find.  Good Luck, TomC

[Stan]

My MC-7 Combo with all solid oak interior and loaded with fuel, water, tools, groceries, clothes and everything else used by full timers came in at 34155 pounds with the Greyhound drive line (8V71 & 740)
Front axle - 8092 pounds
Drive axle - 19602 pounds
Tag Axle - 7100 pounds
Drive & Tag - 26063 pounds.

Drive axle close to legal highway limit but no problem with axle or tire ratings (12R-22.5) I don't think I had room to add another 400 pounds over the drive axle!

[mikelutestanski]

hello     Combos were built to cary passengers and freight..  the raised section in the rear was used for parcels when Greyhound was looking to pull more money from routes that were mandated by the icc but had less than optimum passenger loads. Primarily used out west..   AS far as the 3408s  I know of only 3 that were built.   One crashed out west.  one was dismantled and one is in Canada.  The fellow that has it is near Banff.   He wrote an article that appeared in bus conversions   years ago..yellow colored unit..  I have some pictures of that coach. 
      Dont know about the rear dual having to have duals but one reason not to have duals on the rear axle is that the rear tires scuff going around corners and wear quicker.   Two owners of combos passed that info to me  Is it right ??  dont know..  as far as weight limitation the standard 7 goes to  about  34900  so the combo should be able to carry more?  how much dont know..   anyway more stuff to think about..     happy bussin    Mike

[roadrunnertex]

Some more interesting MCI combo car information.
Greyhound had converted 2 MC-8's to combo cars.
They had the PD4501 rear like the MC-7 Comb Cars.
The only one that I saw was in for maintenance just after the Trailways take over by Greyhound and it was in the old Trailways shop in Houston,Texas.
jlv