4 replies to this topic

[scubaet]

A little help for those of you who are having trouble getting that pinion nut off that is torqued to 150 ft-lb.

I found the following instructions off the web on several mini sites, this set is from mini spares. but they failed to explain several problems you may come across.

I was changing my gearbox / transmission from 3.44 to 2.95.

Problem 1 - the pinion nut is torqued so tight I could not get it off. Did not want to pay a shop to use an air gun $50 to undo one nut, also the air gun can create microscopic stress fractures in the gears from the repeated banging.

Problem 2 - going from 3.44 to 2.95 requires machining of the C shaped outer plate, they failed to mention the 2.95 pinion does not fit the existing one.

Here are the existing instructions, photos below of how I did it at home. I added a few comments.


Rod-change types -
Removal of the speedo drive housing gives access to the pinion retaining nut (1.5”AF socket needed and a long bar).

To be able to undo the pinion nut (torqued up to 150lb ft !!) you need to engage two gears - 2nd and 4th - to lock the transmission.

Rotate the gear selection barrel anti-clockwise as far as possible then pull it back towards you, i.e. away from the gearbox. Make sure both the inner selector shaft and the outer barrel are as far back as they will go. Using a pry bar, or long screwdriver, push the 1st/2nd and 3rd/4th selector quadrants inwards. They will rotate towards the clutch end, and in so doing engage 2nd and 4th gears. Engaging reverse by sliding the gear away from the centre web and into mesh with the outer gear of the 1st/2nd outer track using a long screwdriver assists further.

(yeah, did not understand any of that, just wiggled the selector forks and moved the back under gear shaft toward the speedo housing, and it worked, sorry don't know how i did it really, just got lucky)

Through the speedo-housing aperture, use a small chisel to undo the pinion lock tab. Now undo the pinion nut. You are going to need help with this, somebody to hold the engine whilst you heave mightily on the pinion nut!

(yeah right, have a professional wrestler maybe, not your average strong man)

Carefully pry the pinion nut off of the shaft - NOT on the edges of the teeth as they can easily be chipped!

Re-assemble in the exact reverse order, adding the replacement parts, ensuring when you re-engage the selector outer barrel and shaft that all the selector quadrants are in line, especially the reverse gear one as this can not be seen. Test for engagement by pushing and pulling a little on the selector shaft at each quadrant level. You will actually be able to see the reverse lever moving if it is engaged. Then rotate the selector back to its standard position. Re-fit the diff as per the ‘book’. But before refitting the speedo drive housing check the speedo drive compatibility information.

[scubaet]

This is a 1275 Rod change gearbox / transmission

Photo of the big Pinion Nut in the center, requires a deep 1.5 inch socket
It is torqued to up to 150 foot pounds




note the C shaped bracket that surrounds the big nut. when going to a 2.95 the pinion gear is larger than the C bracket.
you will need to have a machine shop cut the circle larger so it fits.



this photo is hard to make out, taken from the hole where the differential and driveshafts bolts onto
the bottom middle cylinder is the rod that changes the gears
to the right of this you will see 3 forks stacked on top of each other
push and pull these to lock 2nd and 4th
there is a key on the bottom cylinder I had to wiggle out of the way to move the forks freely
and they do not slide easy
someone else may be better qualified to the exact methods


tools required
breaker bar
15 inch deep socket
the middle is an adapter from 1/2 inch to 3/4 inch
I broke 3 of the half inch extensions trying to get the nut off, so a 3/4 inch breaker bar is highly recommended



don't laugh too hard, this was the only way I could get enough weight on the gearbox to hold it in place.
(insert redneck or colonial joke here)
The steel pipe was required to get enough leverage to free the nut

[Pigeonto]

Hmmm.Well done. Seems that although we're miles apart, the job is the same!! Would be interesting to know how it has affected the car by way of fuel consumption and general driving,

[jonny f]

Thought i would say thank you for this!

Quite easy. Have had a little trouble getting the selector fork bits back in the right place but that's all.

[tiger99]

Well, that is very interesting. I had to change from an unknown ratio to 2.95 once, when my replacement engine/box from an insurance company was found to give furious acceleration and a very low top speed. Judging by the manifold, lack of bypass hose, and heater takeoff, it had come from a Metro. I did it in the car (radiator out, and much jacking, pushing and shoving, only for the patient or desperate!), but I did not need to replace any other parts except the speedo drive, so I assume that in some cases the C shaped piece may already be the correct size.

As far as I can determine from the Somerford Mini web site, the part changed twice, initially 22A522 for direct and remote changes, then DAM1756 (rod changes until 1984), and finally DAM5996. As far as I recall, the City E with 2.95 final drive appeared in 1984, so it seems that they standardised on the later part from then onwards. Somerford don't say that the change relates to the final drive ratio, but it must be.

Just one of these interesting little curiosities which pop up when someone mentions something that was different to your own Mini.