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Archive for the ‘Gearboxes’ Category

Compromise is a word used quite a lot when it comes to classic Minis.  One of the big ones is to decide if highway driving is a priority over back roads and rapid acceleration.  Most of us really want to be able to drive our Mini places, and that means on the highway…. at least a good part of the time.   To accomplish this with most of the standard 4-speeds that virtually all versions of the Classic Mini came with,  we can choose to install a taller final drive to get our top gear RPMs down to a more reasonable number.

But, even with a big engine making plenty of torque, there is a compromise to be made!  Those nice high final drive gears for freeway driving now make it harder to get off the line, because they affect ALL the gears.  A very common complaint with Minis is that the clutch can get hard to engage smoothly, known as “chatter” or “judder”.   A high first gear will take more slippage to get the car moving, and the relatively primitive clutch of the Mini results in glazing the flywheel, disk, and backplate.   This will make your Mini shake and buck, particularly while reversing!  It’s not a coincidence that Minis that work great on the highway can rattle themselves – and your nerves – and your engine mountings with violent off the line shenanigans!

The solution?  The same one all modern cars employ!  Give the car longer legs with an extra gear!   Over the decades, a lucky few have experienced some of the custom 5-speeds that have been offered for the Classic Mini.  They have never been cheap or common…. remember, it was viewed as a major automotive milestone to package the Mini engine with FOUR speeds.  It was the first successful mass produced transverse front wheel drive layout after all!

Unfortunately, some of the 5-speeds have been frankly awful.   Poorly executed design and attention to details meant some could be nearly impossible to shift!  And if you needed parts?  Often, you needed a machine shop to make them!

But, take a look at what we managed to get and have in stock and on sale even…  probably the most refined of the five speeds for a street car, these have a lot more purpose-built components, rather than modified used parts harvested from the standard 4-speeds as done ‘back in the day’.  They feature very well thought out gear ratios with custom made input gear (also called ‘first motion shaft’) matched to it’s own laygear with revised tooth counts to achieve a very close match in 1st through 4th to the Cooper S of the 60s. 5th is a true overdrive, and with the 3.44 final drive results in an effective final drive of 3.03,  perfect for the highway!  And all in the latest A+ helical cut gears for durability and quiet operation. The MSG4 in stock has the standard open diff.  Also available for order is the MSG5 featuring a street-friendly cross-pin diff,  as well as other versions with full straight-cut gears and LSD.  These have been made for at least two decades by MiniSpares in the UK,  improved and refined over the years,  and have been the best supported and serviceable of the 5-speeds:

http://www.minimania.com/part/MSG4/A-5-Speed-Helical-344-Final-Drive

One of us had one on order for most of a year and when it was ready we were informed that another one from the production run was still available.  So we grabbed it to be able to offer it to you, so your Mini can be happy on America’s highways!  Over the last few years it has taken many months to actually get one, but here it is!  No compromise 5-speed overdrive means you don’t have to give up acceleration and back-road performance to relax on the highway!   Call and talk to me if you have any questions!

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Part One
Building a new gearbox for the Mini is exciting not because of the amount of work and thought that has to go into it but rather the thoughts of the sheer pleasure in looking forward to driving it. The “Dog Engagement system” as found in the latest sets of gears from Quaiff and often thought of as being special because of this ‘dog type synchro system’. But in reality the benefit is most significant when you are on the race track and need to use all 4 gears, they are a stunning close ratio that means you always can find the right gear for the right turn on almost any track.
Getting started in our case it was first required that we decide if we were going to go with the older remote set-up or the later ‘rod-change’ version. In either case it was going to require starting with process of cleaning, inspecting and modifying the case to accept the gears and Limited Slip. We took into consideration that for the drop gears in our somewhat economy minded project we would go with standard helical version. But again, as we were starting from scratch we had a choice of using the early size idler gear or the later ‘big shaft’ version. As the Big shaft was the very obvious first choice, it simplified the case selection as only the later model rod change housing used the big shaft type idlers.
As all of my choices for a starting point were absolutely filthy, the first step was to take a high pressure water hose to them in an attempt to at least blast off some of years of baked on gunk! But the solvent tank and had brushes were needed steps before even a good inspection could be done.
With the gearbox gutted and cleaned the next step was to drill out the holes where it bolts to the engine block. Mini Cooper Trans to Engine boltsOur experience tells us that even with the thick flange late blocks we can still benefit from using these larger bolts. We use a special bolts with small drive to allow for much easier fixing, 5/16”X24 bolts, 7 are 1” long and 5 of them are 1.5”.
Next in our process was the installation of the new shift forks required for this gear set, a pretty straight forward job after you mange to find a punch of the correct size to drift our the roll pin holding in place the 3rd/4th gear fork. All’s well that ends well!
The real change for the task thus far was the modifications needed to install a modern limited slip into any Mini Gearbox. IMini Cooper Stock Diff Housingt has been my experience that no LSD will fit into any housing without the need to grind some additional clearance in both the differential housing and the tranny case itself. The process is very much a grind a little and try it one that has to be repeated a numbLSD modifiled Diff Housinger of time until you are sure it will fit. And for sure you don’t want to install the gears in the housing before you know the diff will clear everything.
On the diff rear case you can see in the pictures with the stock ribs on the inside, these have to be ground off as shown in the after picture. The next step is to take the diff and see how it all fits.
Mini Cooper Rod Change BushingPS, whilMini Cooper Diff Bushinge we were working on the Diff housing, we also took the time to install a new bushing for the rod change linkage. Although we used a actual press, it can just as easily be done on the workbench.

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Gear Box Rebuild

Written By GuessWorks

Gearboxes may seem complicated but they are very simple in their construction, and surprisingly easy to put together. The main issues are having the right tools to do the job. So here’s a list of what you will need.

  • Torque Wrench with a maximum range in excess of 150lbft
  • 1 1/2″ deep socket ( a ball joint socket is ideal )
  • Small ratchet and a long extension is useful
  • Other sockets 1 1/8, 9/16, 1/2, 7/16, 3/8
  • Small cold chisel
  • Steel punch (1/8″ diameter)
  • Larger steel drift
  • Mallet (soft and hard headed)
  • Small screw driver

There are three main rotational parts in the gearbox, the 1st motion shaft ( or input shaft ) which carries the bottom drop gear and what could be called 4th gear, the laygear which transfers the power from the input to the rest of the gearset, and finally the 3rd motion shaft which carries all the remaining gears.

First of all make sure you have everything you need…

continue reading

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