Bronze Onions.(Trunnions)

Post by **RobThomas** » Wed Aug 12, 2009 8:59 am

Well. that's what my 3 yr old son called them.

I had some sad news to report. After 57 years, our 1952 MM has failed an MOT. Intermittent horn (dirty fuse), zero brake on right rear (Dirty cylinder and different to the 1098 ones I keep on the shelf

) and finally....wobbly top Onion on one side. I had a quick peek on the ramp at the station and they said that it might be OK with some driveshaft gaiter grease. After returning home I jacked the car up and popped the split-pins out (all shiny and grease covered), unwound the nuts (no trouble, all clean and greased) and popped out the rubber bushes (all crumbly and slack). The top trunnion wound off smoothly and I could feel areas where it was tighening on the stub but I took it all the way off. After a quick wash I discovered that it was an original bronze Onion that had survived over half a century of abuse before the seal fell off and lots of grit got into the threads.

Now for the good news. I had another MM leg (are 1098 trunnions different?) and merely popped the iron trunnion off the other leg and it was as tight as new. I guess that the bronze bits wear out without damaging the steel suspension leg? Going back for the MOT again later today. I've got a photoshoot with a well known Morris magazine at the weekend!

Bronze Onion, R.I.P.

Post by **mike.perry** » Wed Aug 12, 2009 9:45 am

Good to hear that the MOT failure was not too serious. Your brass trunion should not have originally been fitted to a 52 MM. They stopped using them about 1950. The idea was I believe that the wear would be taken by the trunnion, leaving the swivel pin intact. Trunnions are interchangeable, only the swivel pins are different, with changes of threads on the stub axle and different stub axles on the M1000 swivels. See G. Holt's article on suspension threads and the article on modifying front suspension in Tech Info.
I thought that the rear brake cylinders were interchangeable and only the fronts were different. I will have to check that one out. I never seem to get any trouble with the rears on the MM. I shouldn't have said that!
The photo shoot wouldn't be with a monthly Minor magazine would it?

Post by **RobThomas** » Wed Aug 12, 2009 2:16 pm

There are no signs that the bronze trunnions are replacements and I'm almost certain that the legs are the originals. None of the nuts and bolts appear to have any marks indicating that they'd ever been off. Might be that it was replaced carefully with 2 new legs. Were bronze trunnions ever given as an option for parts replacement?
The engine has a serial number a few thousand later than the car and I was told that it was replaced under warranty very early on.
The rear cylinders are interchangeable with later ones but the bore is smaller (3/4 instaed of 7/8) after about 1960. Fortunately, I had the cylinders, covers and shoes on the shelf from another car project. All the splitpins came out without needing pliers!

just passed 40, 000 miles.

Post by **mike.perry** » Wed Aug 12, 2009 9:34 pm

As far as I know, brass trunnions were replaced around 1950, but there is nothing in the parts book. There is a note about fitting a conversion set 301192 prior to car no 114924 which is 1951 so perhaps brass trunnions lasted until then.

Post by **RobThomas** » Thu Aug 13, 2009 10:49 am

Can the early legs be re-threaded 'oversize'to rescue them with 'rethreaded undersized' trunnions?

I've already found a set of 1098 legs (new) to put the Riley brakes on all round on our lowlight tourer. I bought a Riley project many years ago just to get the brakes off it but the rear axle was a bit rusty. The restorer had bought all new cylinders for it so £100 was a good deal!
I had been looking for a set of brackets to mount the Midget discs on the front but it would seem a shame not to go for the Riley bits.

Does anyone know if the rear brake backplates are different on the 'Austin' axle casing? Got a picture of one without the shoes and cylinders?

Post by **Dean** » Thu Aug 13, 2009 12:37 pm

Rob, club spares do the re-threading of legs. For £60 per leg you get re-threading and trunnions to suit. includes postage two. But you have to send your own legs to them which is a tenners worth of postage. So about £70 all in.

I had mine done, so it mean't I could keep my original early swivel pin set up.