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Gearboxes - 22G1832 Vs Dam3220 Vs Dam 4818


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#1 Moke Spider

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Posted 26 March 2020 - 12:32 AM

Following on from the thread I deleted :shy:  the main questions in that were based on the original Rod Shift Gearbox (22G1832) and how they differed to the DAM3220 and also if the DAM4818 was suitable for a Moke.

 

The Gear Ratios and in fact for the most part, the Gears between these Boxes were the same. While the Laygears in the DAM3220 and 4818 were the same and on later '3 Step' Layshafts, the Gear Profiles and tooth Counts were the same as fitted to the 22G1832.

 

The DAM3220 was fitted with A+ type Main Shaft and Laygear and retained the small Idler Gear in common with the 22G1832, however, the center web on these cases was weaker than the 22G1832.

 

The DAM4818 was the same as the DAM3220 except that the Idler Gear fitted was the A+ type, the first gearbox to do so, however the center web on these Gearbox seems weaker again than the 3220 series.

 

In regards to which gearbox of these would be best in a Big Wheel Moke, while they'll all fit and work (and at various times, were factory fitted), I'd have to say none are brilliant, though I'd suggest the 22G1832 would be the pick here.

 

Big Wheel Mokes are very hard on the Center Web on the Gearbox Cases and indeed the Final Drive, much harder than most Minis. This is all due to the fitting of the Big Wheels. The rolling diameter on a Mini wheel in in the ball park of 20 inches (500 mm) where as on a Big Wheel Moke, it is 24 inches (600 mm). In order to get an acceptable Final Dive Ratio and maintain the 'magic' 16 mph / 1000 RPM mark, it was necessary to fit a short Final Drive of 4.2:1, however, this also increased the torque mulitpication considerably at the Final Drive and also on the Mainshaft Bearing, that's located in the Center Web. Added to this is less than ideal (actual) Gear Sizing and things start to stack up.

 

On top of this added torque multipication at the final drive is a further multiplcation of torque added by the increase in wheel diameter.

 

These factors are not only on 'drive' but also on 'over-run'.

 

Overall, even before anything is done to increase power outputs or make the tyres more sticky, in totally standard form, the Center Web in the Gearbox and every other part of the drivetrain there after, 'see' an increase in torque of 50%.

 

For these reasons, when given a choice, the only gearbox case to use in a Big Wheel Moke is the DAM5626, which was developed for the MG Metro Turbo and then became standard across the range.



#2 TimDaly

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Posted 26 March 2020 - 02:56 AM

Thanks for the excellent response Spider.  I wondered why I couldn't find the post..... got a little excited with the delete button eh?  I have a fairly healthy selection of boxes here but no DAM5626.  I'll start a search to see what I can come up with locally.  If it is not available, or overly expensive, it sounds like you would suggest the 22G1832 next.  If I did use this box, what can be done to minimize the chances of failure?  I will be hauling a bit of weight between people and gear.

 

Thanks,

Tim



#3 Moke Spider

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Posted 26 March 2020 - 06:18 PM

The DAM5262 was fitted to Metros and Minis from 1983 on - just too late for the Australian produced Moke. They are thin on the ground here too but seem plentiful in the UK. If you can find one from the early to mid 80's they seem the best of the lot. There's a date cast in to the diff cap. The later ones certainly from the 90's seem to have had poor tolerances on the machining.

What else can be done?

While I have only spoken here of the Cases cracking, and other than getting a hold of these later '3 bolt' type cases, or short of welding up the 4th hole and having the case re-machined (as I was doing before the late cases became in to being), not much other than checking the case for cracks in this area. I also use a bearing Mount Loctite and never fit the shims here that are used on the C shaped Bearing retainer. Anything and everything you can do to hold that bearing firmly in place will help, though, the added measures I use here only add maybe 5% to that end. I have it on the 'to-do' list to either cut this web out and fit a steel one (doweled and bolted on position) or cast my own cases.Not really something for the guy at home, but, having said that, personally, I haven't broken a DAM5262 case - yet, but seen the odd one that has. I'm not entirely sure quite where the limits of these cases are, but they are light years ahead of the earlier cases - all of which I have broken at some point in time (some many times) and also seen loads and loads of them. To highlight that the DAM5262 cases are not immune to breaking, the factory fitted a Clutch Damper to the Metro Turbo so that 'dumping the clutch' wasn't possible or at least reduced.

Other issues in this part of the Gearbox in Mokes is with the Crownwheel & Pinion stripping teeth. Due to the ratio here and the difference in size between these gears, quite simply, the Crownwheel wants to 'run over' or 'over-power' the Pinion. Usually the Pinion strips teeth or shatters but this can also break teeth from the Crown Wheel too. Sometimes, these broken parts can get between them and then that results in the cases cracking as well.

I've found dropping the Ratio from 4.2:1 to 4.1:1 while a small change and not a cure, helps a lot. This ratio still uses a 15 tooth Pinion. I used to pull these gear sets from the ADO16 (1100 series) of cars. I always spend a few hours going over the gears in good light looking for chips and cracks, then where possible, polishing them out or rejecting them. A while back I actually designed my own sets and had 10 sets made. These were designed to increase the Tooth Contact Ratio from 1.3 to 2.1:1 and they were made in a superior grade of steel. I don't have any of these left.

 

There was a somewhat rare A+ type Final Drive Gearset available in these Ratios. I haven't tried them, however, while the have a higher tooth contact ratio, the tooth form in these is smaller, so, I feel these are inferior to the earlier types.

If you can put up with it, and if you can find them, you can drop to a 3.9:1 Final Drive which uses a 16 tooth Pinion. It seems at this point, you won't have issues with teeth stripping off the gears, but personally, I find it just too tall, especially with any load on board.

The earlier Diff Output Shafts also shear off. The later types, as fitted from around 1982 (DAM3114) and on are fine. All other diff issues found with Minis are the same on a Moke, but they happen sooner. I've been running with Quaife ATB type Diffs for over 10 years now and never had an issue with them, in fact, I'll never go back to a standard or open diff ever, though, keep in mind here, fitting any type of limited slip diff adds load to the center web of the gearbox.

Outside of the Gearbox, the other items that let go are the Driveshafts, but, while a nuisance, I'm happy for them to break, as they are a 20 minute roadside fix and in my own case, these now seem to be the weakest link in the drive trains that I build, so they act a s a fuse or weakest link in that chain and so protect the other drive train parts.

I hope the above hasn't put you off altogether. Keep in mind, while these are issues, there's many Mokes getting about that haven't had these issues. They are by no means limited to those with bigger engines or hard driving. When I had my workshop, there was no 'indicators' here as to what would be more or less likely to fail.

I will add on the back of that, that any 'impact' type driving will only increase the risk of this occurring, particularly in a forward motion on drive, thnigs like dumping the clutch, very hard starts with sticky tyres, continued wheel spin in slippery conditions, getting airborne and landing with power on etc etc will almost certainly lead to a broken gearbox case and / or final drive.



#4 GraemeC

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Posted 26 March 2020 - 09:12 PM

...... I also use a bearing Mount Loctite and never fit the shims here that are used on the C shaped Bearing retainer....

 

Can you clarify that Spider? You never fit shims or you never fit locktabs?



#5 Moke Spider

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Posted 27 March 2020 - 02:33 AM

 

...... I also use a bearing Mount Loctite and never fit the shims here that are used on the C shaped Bearing retainer....

 

Can you clarify that Spider? You never fit shims or you never fit locktabs?

 

 

Either.

No Locktabs on any of the fasteners, just Loctite 243 on those, with Bearing Mount Loctite on the Mainshaft Bearing.

I very seldom fit the shims back under the C Plate, only if the circlip groove face in the case isn't deep enough. In the past 20 years, I can only think of 1 or 2 boxes that I've fitted them.



#6 GraemeC

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Posted 27 March 2020 - 07:40 AM

Interesting. What’s your reasoning?

#7 Moke Spider

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Posted 27 March 2020 - 08:00 AM

Interesting. What’s your reasoning?

 

If you read the manuals, and shim accordingly, the bearing in the case can have as much as 0.002" float + the flex that the circlip gives and that's around 0.010".

 

You think that's a good idea ?

 

I don't !!!

 

By stopping the bearing floating back and forth, the Bearing Mount Loctite has a chance of doing some good to help hold this Bearing in place in the Web.

 

When you hit the loud pedal, this Bearing is trying to go skywards. Anything we can do to hold them is going to help. What I suggest isn't going to make the world of difference, but every bit helps.






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