Differential - what went first

[richardthestag]

Somewhat of an interesting Saturday. A404 / M40 interchange was closed for the entire weekend for resurfacing. Yeah thanks for that highways agency. Had to pick up #2 son from Maidenhead station, usually a 20 min drive became an hour... each way.

After following an ancient old cretin in a BMW driving at 25 in a 40 for miles I opted to whiz past him, some boyish exuberance may have been present.

Bang, clatter clatter clatter followed by lack of progress.

Luckily only a couple of miles from my workshop so a quick tow got it there.

question is what went first, the cage or the planet gears?

This is a 3.7 diff that I did nothing to but replace the shagged shims with new to get the endfloat closer to zero and seals. Quiet and tight diff until this.

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[richardthestag]

Replacement used old diff fitted yesterday and back up and running for our Indian Summer

I am considering installing a block of wood under the throttle or perhaps alternative fuelling system to prevent reoccurrence

[mole42]

I'd say that maybe the shims were a bit tight. Old planets running a bit tight, sudden increase in power. Been there, with a PI, not a Stag, on the M6 a few years ago.

[marshman]

Agree with Richard (mole32), It's nice to have a smooth running diff with little or no backlash, but they do get warm/hot when running so expansion comes into play (or lack of play!) so it all tightens up even more. I guess chugging along at low speeds probably wouldn't notice the extra "drag". Eventually, little planet gears "give" up and jam busting the cage apart. Either that or the hard gear surface of the little gears started to break up causing a similar effect. That's my theory anyway. Still a bit of JB weld and a couple of planet gears should sort it

I always err on the "sloppy" side when it comes to shims/clearance etc. to allow them to "close" up when hot.

Had a similar experience in my Land Rover on the M20 towing a trailer. Cruising along at around 60 (having stupidly ignored the strange "new" light tapping noise from the rear end. Suddenly the rear locks up with lots of smoke before freeing up leaving a horrendous noise and vibration. A swift drift over to the hardshoulder (when such things existed) and a look underneath revealed smoke exiting from the missing filler bung. No it hadn't fallen out and lost all the oil. I had checked the diff oil level before the trip and over tightened the plug (it's not a taper fit for some stupid reason and it is easy to screw it in too far. One edge had been catching on the cage as it rotated, gradually screwing it in further and further until it was "ingested". One wrecked diff - and it is a big Salisbury diff as well! Another lesson learnt.

[jbuckl]

Your car used to be automatic.
Maybe in the past it was put into drive when off idle.
That could have initiated a inspired fracture.

Wild guess.

I had a diff break like that. Very high load.

[richardthestag]

I never shim them to zero there is usually 3-4thou backlash. impossible to get them that tight.

Diff was running great and silent.

The diff that was in my car when it was auto was a 3.45:1 which I removed top fit this 3.7:1

I am going with slight uphill, sticky new tyres and a weapons grade hooligan at the controls