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MG Midget and Sprite Technical - Frogeye gearbox replacement

My frogeye is currently stuck in my garage with a broken gearbox and I could do with some professional advice to help me work out the best way forward to get it going again...so here I am!!
This is how it came about! Drove my 948,smooth case gearbox, frogeye home from France on Friday last, arriving in Plymouth by ferry about 10pm. The whole trip had gone well until I passed through passport control and formally entered the country. At that precise moment, as the passport control man waved me off saying...hope you make it home ok mate....the gearbox decided that second and third gears would not be helping to carry me home! As Devon is pretty hilly in places, this meant that the frog had to complete it's journey home on the back of a recovery truck.
So...what to do next?
Obviously, the engine and gearbox are going to have to come out so that the gearbox can be repaired or replaced.
But, should I continue with the smooth case, or should I try a ribbed gearbox?
I am tempted to fit the stronger ribbed gearbox in place of the smooth case, and by coincidence, in the back of my garage I have one.
The last few days have seen me cleaning it up and looking inside (internals looked clean and unmarked), but by counting the teeth on the input shaft at 19, I think I have identified it as being a morris minor gearbox?
So the possible ways forward, seem to be:
a. repair and continue using a smooth case gearbox
b. use the ribbed case I already have, which seems to be from a Minor.
c. Find a 1275 ribbed case, and if necessary get it reconditioned.
I appreciate that a ribbed case does not necessarily fit the 948 without a new engine backplate, but I'm sure others have done it??
Any help appreciated.
Phil
P J Dent

The ribbed case has better ratio's and improved synchromesh over the smooth case. You can get rib case internal inside a smooth case if you want originality.

The input shaft of the ribcase should have the same number of splines as the smoothcase. A morris minor box is not easy to identify without taking it apart but sometimes on the input shaft there is a part number the minor box is 22g 171 the midget box is 22g 229.

Personally I would rebuild a 1275 ribcase and fit that! You will need the later engine backplate
Bob Beaumont

The factory recommended way to fit a ribcase to a 948 Sprite as in the ST Manual.

'The 1098 / 1275 gearbox 38G374 is easily adapted to earlier models. Standard ratios are as 948 9CG. Use later engine backplate 12G 453 together with 1098 flywheel 12G 180 and 1098 clutch'.

Leyland letter dated 1977: 'The speedo pinion is common through all models and therefore it should not be necessary to re-calibrate the speedometer. Likewise the crankshaft spigot bush is the same diameter part 1A1559'.

Have you considered a T9 conversion using a Ford Sierra box. I cut the bellhousing off a smoothcase and adapted it to accept a T9. Apart from the driven plate the 948 clutch parts were retained.

Alan
www.masckent.org
Alan Anstead

Earlier Midget 'boxes had 22G172 on the first motion shaft.
Dave O'Neill 2

some late Spridgets have 22G1117 on the input shaft, so 3 possibilities.
Phil I confirm if the input shaft gear has 19 teeth it's a Morris Minor box, not much good.
David Smith

On the subject of broken Frogeyes, there was a red one on the back of an AA recovery lorry on the M40 northbound yesterday morning.
Dave O'Neill 2

Not me!
G Lazarus

Thanks to all for comments/advice.
Bob, I'm not too concerned about originality as long as changes are not visible. That said, my frog is currently all original apart from fitted disc brakes.
I'm pretty committed to going the 1275 ribcase route now, and think I've managed to source one.
The ribcase I had already, does not seem to have a part number on the input shaft, which is why I counted the teeth on the the input gear. Research suggests that 19 teeth means it is a 'Minor' box, 20 is a 1275 box, and 22 is a SCCR gearset.
Thanks Alan for the extract from ST Manual.I was expecting to change the engine backplate, but I didn't know that the flywheel and clutch had to be changed for ones from a 1098.
Presumably changing the flywheel and clutch is not essential, but is just an improvement which is worth doing, especially as the 1275 box can accommodate the increase in size?
I had though of going T9 route, but only if moving towards a 1275 engine.
Thanks Dave and David, but as mentioned earlier, I can't see a part number on the input shaft.
I've resigned myself to the ribcase I found at the back of my garage being be a 'Minor' one. Shame, as it looks to be in good condition.
So it looks as though I will be fitting a 1275 ribbed box, a 1275 engine backplate, and a 1098 flywheel and clutch assembly.
I assume I need to use the clutch fork and slave cylinder that goes with a 1275 box.I already use the 3/4 inch dia master cylinder, so they should go together well??
If anyone knows better, please let me know.
Many thanks
Phil
P J Dent

Your spec looks fine. You will need a 1098 or 1275 clutch fork with a 1098 clutch release bearing. the 3/4 slave will be fine.
Bob Beaumont

Thanks Bob.......it makes a change to actually know what I'm doing before I start!!!
P J Dent

Progress has been steady but a little slow on replacing the broken smoothcase gearbox in my 948 frogeye with a ribcase, but now it has come to a dead stop!
This is because when starting the rebuild of all the parts, I have found that the 1098 flywheel which I managed to source, doesn't seem to fit on the crankshaft boss of my 948 engine!
The hole in the centre of the 1098 flywheel is 2 inch across with the four bolt holes on 2.75 inch dia. The crankshaft boss to which it has to be bolted is 1.75 inch across the raised centre, with four bolt holes at 2.5 inch dia.

I didn't realise before now, but it seems that the flywheel on the earlier 1098 CG engine is different to the one on the later 10CC engine, and it looks like I have the latter flywheel whereas I need the former? Hope that makes sense!

Has anyone experience of this, and can confirm that I am right?

Assuming I am!!.....has anyone a spare 1098 CG engine flywheel in the back of their garage that I could buy?
Many thanks
Phil
P J Dent

Yes Correct you have the later flywheel from the 10cc engine which has larger main bearings. Its relatively rare given they were only fitted to the later 1098 Spridgets. You want the flywheel from a 10cg engine as fitted to Morris Minors, A40's early 1098 Spridgets etc. Should not be too hard to source as there were quite a few of these engines made.
Bob Beaumont

I have a 10CG flywheel with newish ring gear and I really need a 10CC flywheel ( with 2" hole ) what about a swap ?
P Johnson

Hi P
Sadly, since I last posted on this subject, I have managed to source and buy a 10CG flywheel, and I am fitting the engine/gearbox back into the car as we speak!
I planned to advertise the 10CC flywheel in the for sale section, but am happy to do a deal with you if you want it, at the price I paid for the 10CG flywheel plus postage.
Email me at philipdentattiscalidotcodotuk if you are still interested.
Cheers
Phil
P J Dent

Phil,
Sent you an email, I have an add in parts wanted, on this site, for the flywheel. Paul
P Johnson

Everything going together fairly well so far, apart from the glitch with the flywheel mentioned above which is now sorted.
Engine and gearbox are now together and with a bit of shoving and heaving bolted back in place.
I suppose the bit of force was needed because with the thicker 1275 engine backplate, the distance between forward and rear mountings is a bit more than it was originally?
Last thing holding me up is:
I'm trying to connect up my master cylinder to clutch slave cylinder using the original pipe I have on my 948 frog. However as I am now using a 1275 clutch slave cylinder with the 1275 box, the connection isn't compatible at the slave cylinder end.
I suppose this means that I will have to buy and fit the master cylinder to slave cylinder connection arrangement from a 1275, ie a new fixed pipe plus the flexible pipe that connects into the back of the slave cylinder.
That is...unless anyone knows better! I may be being really dense here?
Any help/ comments gratefully received....and anything to lessen the time lying under the car the better! I'm getting too old for this!
Many thanks
Phil
P J Dent

Hi Phil,
I went through that last year. I bought the adaptor to go on the dual master to convert small unions to larger unions. Then used the clutch pipe from a LH drive 1275 because it was longer. Then with careful bending, using a small aerosol can, I spiralled part of the pipe ala Frogeye Then with a bit more bending I could connect the pipe direct to the 1275 slave cylinder.

It's a pain to do but I wanted it to look like a Frogeye under the bonnet and also didn't want to install the bracket on the chassis to hold a flexible pipe.

700 miles later I trashed the 1098 gearbox and decided to go 5 speed!!!!!

Rob
Rob aka MG Moneypit

Where did you get your ¾" master from, Phil? They used to be as rare as calm acceptance from Lawrence.
Nick and Cherry Scoop

Some on ebay from MGBHive.

http://www.ebay.co.uk/itm/MG-MIDGET-3-4-DUAL-DISC-BRAKE-CLUTCH-MASTER-CYLINDER-GMC112-K2A-/311146219271?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Model%3AMidget&hash=item4871c28707

I bought mine last year from MG Centre Wrexham who had some AP/Capero in stock.

Rob
Rob aka MG Moneypit

That's not too bad. Eight years ago I had an old ⅞" unit re-sleeved in stainless steel to get a ¾" master. I recall that it was quite expensive.
Nick and Cherry Scoop

The AP Caparo is the one to have, I believe.

B-Hive don't state which brand they are selling.
Dave O'Neill 2

for the pipe, you can get a flexi end-to-end from Peter May, makes life easier, recommended.
David Smith

Hi Rob,
Thanks for the advice, I certainly hadn't thought of using the LHD 1275, longer pipe so that when coiled, it would look the same as the original. Good idea.
I want to keep the car looking as original as possible, but more than anything, I want it to be reliable. I'm hoping that with the very limited power from a 948 engine, teamed up with the later, stronger rib case gearbox, the engine/gearbox combination will last longer!
Thanks also David for the info on the Peter May flexi connection. Again, I didn't know this existed. Does it also need the adaptor at the dual master cylinder end to convert smaller unions to larger?
I can't remember where I sourced the 3/4 inch dual master cylinder from as I fitted it some time ago, but I think it may have been Wrexham.
I'm on the last stretch now, prop shaft connected up yesterday (more lying down under the car!), radiator back in and filled, all connections made to engine, and gearbox filled with 20/50. Just the clutch connection and bonnet on to finish. Can't wait to try out the new gearbox!
Thanks for all the help.
Phil
P J Dent

This thread was discussed between 16/09/2014 and 02/11/2014

MG Midget and Sprite Technical index

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