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       As I had decided on an automatic transmission , the next problem was were to get one and what did I need . The Americans use autos a lot so there was my start point .

      I spent many hours on Google and U tube researching what had been used successfully used in specials in the States , one name came up more often that not and that was Allison Transmissions. 

      I was defiantly going to want a secondhand one because of the cost , The model I decided on was an Allison  AT 545  automatic transmission used in many applications in the States such as school buses and dustcarts etc. the spec. shows it is used in vehicles up to 30,000 lb or 13.39 ton. I was hoping that the Flyer was going weigh in a lot less than that , so It should be strong enough , it was not designed for the amount of torque  I had to play with but I was ever  hopeful.

 The next two days were spent phoning almost every commercial vehicle breaker in the country , I had no luck until  I got through to one about thirty miles away. He had a large auto box  that had come from a medium size bus and better still it had been driven into the yard for breaking, the trouble was it was a Mitchel Powersystems transmission a make I had not come across in my research and not an Allison but I had to go and look at it anyway.  When I inspected it apart from being very dirty and one small broken bracket, under the stick on Mitchel Powersystems  label was the Allison AT 545 makers plate, plus it still had its  torque converter with it.


     The Torque converter is basically a fluid clutch between the engine and the transmission .It has a set of impellers with transmission fluid flowing between them to transfer power from the engine in to the transmission .All automatic transmissions have torque converters but the AT545 does not have the ability to lock, it always has a small amount of slip like slipping the clutch with a manual gearbox, a transmission with the capability of locking the converter after third gear connects the engine directly to the transmission,causing less heat, I wanted a non locking system in the hope it would be better with high torque of the Meteor Engine.

     I will admit that I have rebuilt several gearboxes but I only know what I have read about auto transmissions and having down loaded a manual from the Allison web site I dont think I would want to go inside one . After cleaning I did remove the sump to look at the internal fluid filter and it was spotless . I am told that if there has been a problem with clutch slippage the fluid shows discoloration the liquid I removed was also perfectly clean , so apart from the clean a couple of small external repairs and a coat of paint I put it to one side.

   At this point I also fabricated the front and rear mounts for the transmission as it was going to be rigidly  mounted in the chassis, I would be able to do the final shimming up at a later date.


Torque ConverterTorque Converter

Temporary Position Temporary Position

Front and Rear MountsFront and Rear Mounts 

Allison AT 545 Automatic Transmission Gear Ratios

           1st      3.45-1           2nd     2.25-1
           3rd     1.41-1           4th     1.00-1

                Rev.    5.03-1

    Now I had all the information I needed to calculate the ratio of the step up gear box between the engine and the transmission I was going to need to get  the forward speed I wanted .

     I calculated that if I had a step up ratio of 2-1  I would end up with a rolling speed at tickover in gear speed of 5 mph and a top end speed of 100 mph at 2000 rpm , the max rpm of the Meteor is 2500 rpm so I was happy that my calculations would be close, now the search started for a gear box to do the job.

   The next part of the story of the step up gear box will best be told using mostly photos as after looking for what seemed like forever with no success , I decided to build one from scratch myself, not something that I under took lightly but It seemed that I had no other option.

Step up Gearbox Gallery 1.

   I started by sourcing the gears and oil seals also the circlips and castle nuts, which gave me the internal dimensions of the box itself  which was fabricated from 8 mm plate and 30 mm plate for the internal bearing carriers.

   The main input shaft from the engine I machined from the drive shaft of a Centurion tank clutch main shaft as it all ready had the correct spline and oil seal for the rear of the Meteor engine.

   Once the basic box fabrication  was finished I had all the bearing housing surfaces  professionally line bored, then I machined up the shafts and flange couplings. I then sent all the shafts and gears away to be splined and heat treated professionally.

    When they were back I did a number of provisional assembles to dress any burrs and check for backlash etc.


Gearbox Gallery 2.

 At this point both the step up gearbox and the auto transmission were mounted  between the chassis rails so that I could think about what to do next.

  There  eventual  positions would be finalized later with shims and adjuster bolts. I would eventually use 140 grade oil in the step up box, I tried 90 grade to start with but changed it to combat some of the noise of the straight cut gears.

    I decided to use straight cut instead of helical  because they will carry more load and I did not want to use thrust races in the step up box.

      The last job on the power train for the time being was to shorten and re balance the ford prop shaft , like most parts on the  donor vehicle it was in good usable condition and only needed a good clean and greasing of the U J s.