Straight cut gearbox

[morris1961]

Hi everyone!

I've just acquired a 1275 gearbox. After taking a look inside I found out it has straight cut gears. I'm aware they're pretty noisy... What does everyone think I should do? Does anyone else have one in their minor?

[bmcecosse]

Let's see a picture with the side cover off! Worth very good money if it is !! The noise is 'wonderful' but I suppose a bit wearing on a long run if you are not an enthusiast.......

[morris1961]

Here you go[frame][/frame]

[bmcecosse]

Ooooh YES! You're in the money! Lovely....

[morris1961]

Are they worth more then? I hadn't heard of them until I pulled the side cover off and thought it looked a bit different!!

[philthehill]

A new 1275cc straight cut close ratio gear set is £395 plus VAT from Peter May Engineering.
BMC Special Tuning Pt No:- C-AJJ3319
Whilst the straight cut gears do not loose/absorb power like the skew gears the gearbox is no stronger as all the rest of the gear components are standard MG Midget 1275cc.
I had a MG Midget SC/CR gearbox in my Minor at one time and it could not cope with the power and standing starts so changed it for a Ford 2000E/Rocket box which now has a SC/CR set installed.
The main advantage with the MG Midget SC/CR gearbox is the closeness of the gear ratios.
The 1275cc gearbox CR/SC ratios are:-
1st...............2.573.
2nd..............1.722.
3rd...............1.255.
4th...............1.000
As above the down side is the noise.

[bmcecosse]

It would be more likely to sell to a Spridget owner - although anyone with a 'fast' Minor would appreciate it too! Stick it on ebay if nobody on here bites your arm off for it!

[IslipMinor]

Very desirable! Presented well on eBay I would think that it could get at least £400 and maybe more than £500?

[bmcecosse]

Indeed!

[morris1961]

Thanks for the info guys! Worth much more than the price I paid then! I've got a 3.9 diff and bored out 1275 to go in too... So might have some fun with it and if the noise gets on my nerves sell it on.

[bmcecosse]

I certainly would ! Just make sure it hasn't been stored standing on the bellhousing - if so - wash out the 1st motion bearing before use..

[mike.perry]

I have a 1275 Midget box in my Traveller, now out of my Traveller. 1st gear sounds like a bag of spanners. Have not looked inside yet. Some say it is stronger than the 1098 box, others not.
My opinion of the close ratios is that on a well loaded Traveller, towing a trailer across hilly terrain they are less suitable than the 1098 ratios, particularly with a 3.9 diff. Ok these are extreme conditions but they illustrate the point
1275 1st 3.200 2nd 1.918 3rd 1.357 4th 1.000
1098 1st 3.628 2nd 2.172 3rd 1.412 4th 1.000

[philthehill]

Non of the BMC 'A' Series gearboxes are what I would call strong whether they be 1098cc or 1275cc.
Having had several 1275cc Midget gearboxes (including CR/SC) fail on me (including a customers 1275cc Midget gearbox whilst carrying out a performance road test ) brings home the shortcomings of the 'A' Series gearbox.
That is why when considering a serious increase in power an alternative gearbox should be considered unless the original gearbox is required by class regulations. And in some ways that consideration is no different to upgrading the rear axle to say Ford to cope with the additional power and increase in reliability.
Unless you require the close ratios for say motorsport the standard Minor gearbox ratios are more suitable for a fully loaded car/traveller/pickup/van.
The higher gearing of the MG 1275 Midget gearbox was determined after factory road testing of the vehicle and of course the MG Midget is no load carrier and as a substantially lighter vehicle does benefit from the higher gearing under acceleration.
Interestingly the BMC special tuning sheet for 948cc & 1098cc Midget/Sprite C-AKD 5097 gives the same part number C-AJJ3319 for the CR/SC gear set as the 1275cc but gives the following info:
Close ratio for AN5 only use with 22A 426, 22A 204 and 22A 207 - 2nd speed gear C-22A226, 3rd gear C-22A227, 1st gear C22A 228.

[morris1961]

Thanks for the comments everyone. I think I'll be putting it in next weekend... I'll let you know what I think!

[mike.perry]

The ratios I quoted seem to be different to yours Phil. Mine came from that font of all knowledge, Haynes MG Midget Manual, are yours the special tuning ratios?

[philthehill]

Steve
The ratios I have quoted came from the BMC special tuning pamphlet for 1275cc Midgets/Sprite....C-AKD5098.
Link attached.

http://www.scribd.com/doc/23809120/Spec ... g-for-1275

Special Tuning pamphlet...C-AKD5-97 covers the 948cc and 1098cc engines of which I have a hard copy.

Another good tuning reference is the Car and Car Conversions book 'Tuning BMC Sports Cars' of which I have a copy.

Phil

[mike.perry]

Your ratios are the Special Tuning C/R gears, mine are the standard 1275 gears

[bmcecosse]

Considering the difficult and cost of buying new gears for a box - the price you quote Phil for a Straight Cut set is quite reasonable. In theory the SC sets was supposed to 'absorb less power' - and reduced end loading, but I always suspected it was simply less expensive to make relatively low numbers of these special ratio gears with Straight Cut teeth. I had 2 X Mini SC boxes (in my Rally car and my Track car) but never managed one for my Minor !

[morris1961]

I have one last question! After putting the box on the bench to poke about I spotted this metal tag. Not seen one before. It's probably nothing but any Ideas?[frame][/frame]

[philthehill]

I have seen similar tags on re-conditioned gearboxes.
I am not aware of gearboxes being supplied direct from the factory with CR/SC gears already fitted only being supplied as an after market option to be fitted by the owner/tuner/modifier or BMC Special Tuning Abingdon.
I would suggest that at some time your gearbox has been re-conditioned and that is what the tag represents.