The Conversion

Let the conversion begin… First thing is to remove the old gearbox.

Here we go… First problem.. It seem that the tag axle sit right in front of the gearbox, so to remove the gearbox, we need the tag axle out first…

Sometimes I  really wonder if I ever going to get an easy one on this vehicle… None the less by lunch time we were making good progress and most of the 28 bolts required to be removed for the tag axle to come out where undone. Because of the axle design we also need it to remove the tailshaft as it goes right trough the axle. Looking at this axle a serious worry began to invade my mind, as the Allison transmission was still missing some connection at the back for the cooling of the retarder. But considering that this transmission came recommended specifically for this engine frame combination, I though that it would have definitely fit, maybe just, but definitely fit. While unbolting the axle we started to take measurement just to have a better picture of actually how much room there was under there for us to play with adapter plate and cooling pipes for the retarder.

  All bolts are out except for those two, so that the forklift can be positioned to take the massive weight of the tag axle. In this picture you can also see of why the tailshaft had to be removed for the tag axle to come out. An interesting design to say the least. Definitely strong and possibly one of the reason why this coach is so good on the road. The torsion bar is also of good quality and size and the bushes seem to be in good order.

 

 

 

The tag axle is finally out!

In this picture you can see the three point linkage, the two bottom plate for the airbag and that incredibly strong design of the axle to go around the tailshaft. Now that the axle was out we began to take all measurement required for the conversion. To convert from a manual gearbox to an auto transmission, you need a flexyplate that can be of three different kind based on your engine configuration… In my case, I needed the one that replace completely the original flywheel. And this became the first serious problem. To fit this flexyplate you also need an adapter to space correctly the gap between the flywheel housing and the Allison transmission. Simply another 30-40 mm of space that we really didn’t have…

The 10 speed Eaton gearbox. A great gearbox but unfortunately with no retarder, one of the main reasons for this conversion.

This was one of the few times in my life, where I wished we had more choice of parts in this country in a similar way as it is, in the US, where you can find almost anything you want/need for most of your projects.

Now the 8 bolts holding the gearbox to the flywheel housing had to come out so that the gearbox could be finally remove from the chassis and let us start to play with the new transmission. At this stage I got quite excited at the idea that in a week or two I could have put the whole thing back together and move to stage 3 where the body conversion actually begin…

The gearbox is finally out!

Now is just a matter of removing the clutch and start to take measurements to see what is what and what is not. As it turned out the clutch disk was in good shape. The first good news was that indeed as per recommendation the MAN Engine did came with the SAE model 1, an essential requirement for the Allison transmission to fit.

The day was coming to an end, so we decided to wait the day after with better morning lights to actually take the measurement and see what figures we had to play with. Upon having the two gearbox side by side it appear they were very similar in length.

One may think that’s a good think, but in the back of my mind a terrible though was beginning to formulate…

The two gearbox looked virtually identical in length but as mentioned before the Allison still has few bits missing in the back for the retarder. I didn’t understand why this was happening. The gearbox model was recommended to us by the Allison team here in Australia. So why there was so much little room to play with in the first place? I had enough for the day and decided to go home and check again on the trail of paperwork and various emails, to see if I could find a reason for the new problem of space…

The day after back in the workshop, and after two hours of some unbelievable calculations and numbers, we finally came to the sad conclusion that for the Allison transmission to fit, a serious modification to the tag axle was required…

I decided to take the rest of the day off and check again the email to see if I could find what went wrong. I eventually did find the reason of why this was happening. It seem that someone went under the presumption that my coach was more like a bus (where you have only two axles) and therefore plenty of room between the engine and the differential to play with. I’m however to blame as much as he is, as I fail to realised while the emails were exchanged, that I never specify that I had a coach and not a bus…

Now was the time to decide if to continue on this path and modify the chassis, pay for an engineer and do all the paperwork required for such an operation… Problem is that I don’t really have either the time, money or the inclination to deal with bureaucratic matters and considering that I’m building this to get away from all that, plus the uncertainty of the final cost of modify a tag axle, I made the decision to cut my losses and to look for another coach where this conversion can be made in an easier way without major modifications especially regarding the chassis, something that I consider not to be taken lightly.

Back to the drawing board…