1275 midget gearbox and clutch operating arm

[moggiegeek]

Despite gearbox woes in last post still planning to fit working 1275 midget gearbox to 1275 engine I have built up - over years I realise!
So to test my assumptions so far....
1.Using 1275 back plate on engine
2.Using ESM redrilled flywheel
3. Uprated Minor clutch with roller bearing for release arm
4.Roller bearing in flywheel recess to accept 1275 input shaft nose.
5. Hydraulic clutch operating mechanism.
Checking:
Therefore should I use a minor clutch operating arm and make up a suitable fork ended push rod for clutch or use midget arm and fork ended push rod to slave cylinder?

[philthehill]

When fitting a 1275cc Midget/Sprite gearbox you should use a 1275cc Midget/Sprite clutch release arm. Any other arm does not have the correct operating arc relative to the release bearing as the release arm pivot points are different.
Use a hydraulic system as then you can alter the pedal pressure/effort by varying the size of the master cylinder and slave cylinder bores.

[moggiegeek]

Many thanks Phil, could you remind me of the two different casting numbers for the Minor and Midget arms?
Thank you

[philthehill]

http://gerardsgarage.com/Garage/Tech/TO ... arings.htm

[jaekl]

I understand that all ribcase gear boxes have the same pivot location. The only difference between clutch arms is mechanical or hydraulic actuation and thus different ends.

[philthehill]

The pivot point for the release arms are different. See link above for details.

[jaekl]

Yes, smooth case front plates and rib case front plates have the pivot point at different places. Gerard shows the Spritget 1098 and 1275 (10CC thru 12CE) being the same clutch arm. Wouldn't it then follow that a 1098 Minor clutch arm could be used with any rib case front plate. In other words there are only two different front plates, the RHD and LHD pair for smooth cases (803 and 948) and the pair for rib cases (1098 and 1275). This is also stated by Gerard.

[philthehill]

Unless the various release arms are compared for overall length and the pivot point to carbon thrust centre is compared I cannot give a qualified answer. Whilst I have a spare 1275cc Midget release arm I do not have a 948cc or 1098cc release arm. I do have a selection of gearbox front covers for both 948cc and 1098cc gearboxes so will have a look at the differences in due course.
What I do know is that when I first started modifying Morris Minors and changing the clutch assys and gearboxes way back I had to reshape the release arms and make the carbon thrust centre hole vertically elongated so that when the release arm was moved the carbon thrust did not foul the first motion shaft. The elongated hole was required because the pivot points of the release arms were different and there was no way around modifying the hole.
The current 1275cc Midget release arm fitted to my Minor has had to be reshaped and the hole through the bell housing enlarged to allow sufficient travel to allow release of the clutch.
Whilst many of the problems of interchanging gearboxes and clutches can be overcome with modifying the parts I have not found an easy solution to changing the gearboxes and clutches outside of using the factory fitted combination of parts.

[jaekl]

The throw out bearing must be matched to the clutch. There are three different heights of throw out bearings to accommodate the differences over the years. The only thing that stayed the same is the location and axial displacement of the throw out bearing attachment relative to the first motion shaft and front plate. You must have used a thinner throw out bearing requiring more travel of the clutch arm. Since the front plate is the same in all applications of the rib case gear box whether it be 1098 or 1275, then a Minor mechanical linkage clutch arm can be use in a 1275 installation provided the throw out bearing is designed for the clutch being used. All of this is explained in Gerard's web page. You may find that with the Spridget 1275 diaphragm pressure plate and the loss of mechanical leverage from moving the pivot point outward, the stock Minor linkage requires more pedal force. Many have drilled a hole in the plate on the pedal to bring the linkage attachment point closer to the clutch pedal axis to improve the mechanical leverage. The stroke of the pedal will increase which provides better modulation of the clutch action.

[philthehill]

Having dug out the gearbox front plates and the Midget clutch release arm.
The Midget release arm Pt No: 22G168 is compatible with the 1098cc gearbox front plate Pt No: 22G118.

[ampwhu]

I have a 1275 engine in one of my cars. I used

1275 backplate
1275 flywheel to match engine (early midget)
1275 3 piece clutch from midget
1098 clutch fork as its mechanical
1098 gearbox

And I fabricated my own clutch lever arm to change the pivot point so I have a light clutch. I can depress the pedal with my finger now.

[Chipper]

Would you happen to have a photo/diagram of your linkage?

[philthehill]

To lighten the clutch pedal pressure especially when fitted with a 1275cc Midget diaphragm clutch, you can modify the relay shaft as below.

Modified relay lever (1).jpg (74.42 KiB) Viewed 1223 times

[ampwhu]

I did exactly what Phil said above. It was posted a while back and I copied it. Works very well.

[Chipper]

Interesting. I did see that a while ago, in Technical Tips or similar, but opted to go the hydraulic route for my MG Midget clutch (which is also quite light - it was very heavy and 'in or out' with the standard linkage, and also wore through the bushes very rapidly).

[philthehill]

To get the best out of the mechanical linkage when a 1275cc Midget/Sprite diaphragm clutch is fitted the arm of the relay shaft needs to be lengthened as per the above diagram, the relay shaft rubber bush needs to be replaced with at least a poly bush and grease nipples need to be fitted to the clutch pedal shaft (and brake pedal lever whilst it is apart).
Minor Mania used to supply hard plastic bushes as a replacement for the relay shaft rubber bush. I had one fitted before I went for full hydraulic operation of the clutch, and it worked well.
Below is the link to the ESM relay shaft poly bush:-
https://www.morrisminorspares.com/clutc ... de-p829577