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Disc Brake Conversation to MK1 Midget


Freshman Member
I'm new to the Spridget World. I own a 1962 Midget and a 1970 donor midget. I'm currently in the process of moving the 1275cc to the '62. Someone recommended that I do a disc brake and rear gear swap as well.
Anyone have any suggestions or pointers about this? Is it worth it? Is it a straight forward swap? Any help is appreciated.

Joe Schlosser

Jedi Warrior
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All the sprite/midget chassis are the same except for the early cars with the quarter elliptic cantilevered rear springs. everything else is a straight swap out. The 62 Midget should have the 1/4 elliptic rear springs.
The 62 had a 4.22:1 read end ratio. The 1275 had a 3.9:1 ratio. I assume you are moving the 1275 motor and trans together to the 62 body. Moving the 3.9:1 diff over is not a problem and will give you lower revs at cruising speed.
If you have the front drum brakes you should have the old style rear brakes. Swapping them over is not a big deal but you do need to also swap the hand brake rod on the rear axle assy.
The front discs are not all that difficult. Easiest method is to swap out the entire assembly from the lower A are up through the connection to the connection to the shock.
However!!! The disk brake master cylinder is a different diameter for the disc brakes. If you want to stay with the single line MC you need to get a new 3/4 inch unit. OR you can use the 1275 unit but swapping that out is a lot more work.
Questions just ask.


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You'll also want to grab the Rear Backing plates off of the donor Car. That will allow you to use the later 3/4" Wheel Cylinders, and will allow the EBrake Rods as well as the EBrake Swivel/Balancing rod to bolt right up. Later brakes are easier to keep adjusted. You'll want the stronger axles from the Donor Car, mark them and make sure Left Axle goes in the Left Side on the Mk I.

You will need a new 3/4" Master as the Master on the Donor car is a dual line and won't fit the Master Cylinder opening without Surgery. If it is original to the car likely crap with rusty bores. Brake and CLutch piston rods from the Mk I are different lengths from the donor. Use the rods that came on the Mk 1. Examine closely the Wishbones, likely they are cracked and trashed. Check how much play is in the front end, Page 45 of the Moss Manual, Swivel pins may need to be rebushed and reamed to fit. It's worth the effort. And while you are at it replace the Shocks with an exchange from Peter Caldwell at World Wide Imports in Madison WI.Its a while it's apart... New Pads, New Brake Line Flex hosed Front and Rear. Replace rear wheel cylinders, Rear Shocks and all bushings back there as well. Radius Rod gets a lot of wear and tear. Pay attention to the shim on the Radius Arms. Goes on the inside IIRC. Not sure what Rear End a '70 has, think it may stil have a 4.22. there is a Casting mark on top / tab of the rearend two numbers separated by a /. Divide those numbers and it will tell you if it is a 4.22 or 3.9 rear end.
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