cav551:
Coomsey, I expect Windrush is your man on this. I have some ancient Foden 'box manuals including the 5 speed which I’ll look at this evening. There are mnay different 12 speed sequences depending upon whether it was an overdrive or underdrive box and the individual ratios.
Ah the Foden 5 speed , I remember it well . It was the weirdest set up to drive , normal 4speed and for crawler , select first , lift the clip and push , move to the left and pull back . It must have been a throwback to the days of 100 bhp pulling 20 tons . Low reverse was a similar movement . I never had cause to use it even in the FGs 1st gear was low enough . Dave
cav551:
Especially for CF the auxiliary section of a Fuller RTLO 147-13A. The most highly stressed part of the gearbox. Note especially the type of gear used. I have not listened to the commentary.
The straight cut v helical gear argument certainly seems to contain some contradictions.With numerous previous ‘heavy duty’ examples of the Fuller box actually containing a straight cut auxiliary section.
While the latest 18 speed versions certainly states a move to a helical auxiliary for reasons of both noise reduction and ‘durability’. In which case the obvious question in that case is why not move to a single counter shaft totally helical gear train like the I shift which certainly seems to have an ultimately higher torque input capacity than the Fuller.
Having said that it would be interesting to find out exactly what’s going on here and possibly why ?.
In addition to the question as to why the AK 6-90 at least seems to have been a helical constant mesh geartrain,except for 1st gear being straight cut ?.Or for that matter examples of after market performance car applications examples of an all straight cut gear train except for over drive top ?.
I may be wrong since it has got to be some 12/13 years since I had an auxiliary section apart, so without the offending bits in the hand it is not clear, but perhaps judging from the fact that he has kept remarkably quiet about what the fault was, I am going for the vlogger forgetting that mainshaft gears do not run on the shaft; they are effectively centralised by the two countershafts.
1st gear and/or the PTO gear will often be spur gears since they sometimes double up as reverse mainshaft gear which is normally engaged by sliding mesh action with the reverse pinion.
cav551:
The Fuller Roadranger gearbox was developed at a time when multi speed transmissions were required to cope with the comparatively narrow rev band of useful torque produced by the American made diesel engines of the day . Fuller wished to incorporate the extra ratios obtainable with twin stick designs which normally operated separately mounted transmissions, or booster boxes as they were called in the UK, into just the one assembly.
The designers needed to cater for the then foreseeable increases in input torque likely to be required. This focused attention on the combined limitations of spur gears, tooth loadings, and particularly the radial loadings which adding additional gear clusters to what would seem to mean ever lengthening shafts and casings. Straight cut gears and a single layshaft design looked like dictating that each gear was going to have to be thicker to reduce the tooth loading, and there were going to be more sets of gears added to the shafts. The extra shaft length was likely to cause problems with the radial load imposed on the shafts unless something was done. They could adopt the same solution which the UK’s David Brown used and utilise a horizontally split casing with an intermediate bearing and corresponding webs in the casing, or they could come up with something different.
They chose to place the mainshaft between two layshafts, so doubling the number of teeth in contact, reducing the tooth loading and allowing the thickness of the gears to be reduced. The mainshaft, being sandwiched between the two layshafts, was itself no longer under radial load and although the casing was still subject to all the radial loading, that resisted by the each layshaft and its bearings was halved. The bonus was that not only were they so far saving length, but also weight since components could be reduced slightly in dimensions. The lack of any need for bushes for the mainshaft gears to run on, allowed more weight to be saved by employing dog clutches which mated with internal teeth in the mainshaft gears, rather than the more common external designs in common use.
The need for additional ratios was dealt with by what was effectively a repetition of the main box primary gear train, but this time with a synchroniser and dog clutch enabling through drive or reduction drive via a gear train. The second stick was replaced by an air system operating the hi-lo range selector.
There were two versions of this design one for an input torque of around 600 lbft and a larger version for around 950 lbft. For torque ratings beyond that a significant level of upgraded parts were required which does in some instances include helical gearing for the auxiliary section; generally indicated by the figure 7 as the third digit in the model code.
Still running one of these in my old Foden, cable change which is a bit like stirring mud with a stick.
In which case the obvious question in that case is why not move to a single counter shaft totally helical gear train like the I shift which certainly seems to have an ultimately higher torque input capacity than the Fuller.
