|The MGA With An Attitude
DOOR LATCH Repair - CP-113E
This article furnished by David Adams.
Many Coupe door latches have been repaired due to the failure of the mechanical connection between the ratchet star wheel and its shaft which connects to the external pinion. The first picture below shows an OEM RH latch recently for sale on EBay and the next two pictures show repaired latches.
Both the latches in my 1960, 130,000 mile Coupe have been repaired, one was brazed up solid and the other was repaired by welding. The brazed repair has a lot of play, axially because it was not pulled up sufficiently tightly before brazing and radially because there is wear either in the bearing or the journal of the shaft. The previous repair by welding did not properly address the problem, to fix the star wheel to the shaft, and was never going to work because the peripheral blobs of weld did not fuse with the star wheel. Any new repair would have to replace the original connection and address the axial and rotational fixings.
The earlier welded repair was hacksawed through and the components removed: the repair, hardened star wheel, hardened thrust washer and hardened pinion on its shaft are shown in the first picture below. The hardened components are believed to be case hardened. The star wheel was originally connected rotationally by a 9/32 AF double-D on the shaft and a mating one in the star wheel. There is a bearing for the shaft punch locked into the body of the latch.
I decided to drill the (unhardened) pinion shaft 1/4”, cut the head off a 1/4” bolt and cut it to length so the thread protruded from the star wheel end of the shaft. Then to weld the end of the bolt into the peen in the recessed face of the pinion, weld a washer to the star wheel and, having adjusted for end float, weld this washer to a nut and weld the nut onto the bolt running through the pinion shaft. Remember that the star wheel is handed, the picture shows a LH latch star wheel.
There was a lot of wear on the double-D of the shaft and to correct this the star wheel was turned against the direction of rotation before welding. Surprisingly, the wear between the shaft and the star wheel had thrown up a burr on the star wheel’s lower face and this was removed before reassembly. All the components were lubricated and the nut was adjusted to give a small axial float such that the pieces of paper could just be slid in and out without jamming. Rotation and feel were checked before welding the nut to the washer and to the shaft. Not as pretty as I would have hoped!
Thanks to David Halliday and George Horton for some of the pictures used.