Differential Failure
Posted: Sun May 31, 2015 11:43 am
No photos of my Elan racing at the Winton Historic meeting this year as my diff failed during practice. I packed up early and came home on Saturday and pulled the diff out of the car today.
Getting the diff out was the usual challenge with the diff being a light press fit into the chassis. Fortunately with the hoist i now have, it did not drop on my face like the last time I removed it about 20 years ago!
When I pulled it I could see a large hole in the rear alloy case. No wonder it failed.
Getting one of the output shafts out was a challenge as the splines had jammed in the diff centre. Had to resort to using jacking bolts as I could not drive it out or get it out with a slide hammer puller
It appears the crown wheel to the diff centre bolts had failed in fatigue and 5 of the 6 had lost their heads. One of the 5 was missing so I presume it went out the hole in the case. I don't know why the bolt heads failed but they were the original bolts in the car - the CWP was also the original.
One of the failed bolt heads had been very badly chewed up and I presume this jammed in the gears and led to the final failure and shearing of the pinion gear teeth and the collapse of the pinion bearing.
I now suspect the bangs I had heard a couple of times in the past couple of races that I could not identify had been the bolt heads progressively failing. I think the hole in the diff casing actually occurred when racing at Phillip Island earlier this year as i had a couple of puffs of smoke out the rear of the car that I put down to engine or gear box oil leaks dripping on the exhaust - but it was diff oil as it now turns out. The fact that the diff ran with no noise until it jammed on a loose bolt head and failed and that the diff crown wheel carrier bearings are still perfect having run for some time with not much oil and getting very hot is a testament to Redline gear oil qualities.
Now just a new CWP , new alloy case, new bearings, shims and crush tube and teach myself how to set the Pinion depth correctly as I have never had to do it before and i will have a new diff .
I could probably get the alloy case welded up but the output bearing circlip grooves are badly chewed up and to fix them plus the hole plus another cracked area from an internal impact and it would probably cost me more than a new one.
cheers
Rohan
Getting the diff out was the usual challenge with the diff being a light press fit into the chassis. Fortunately with the hoist i now have, it did not drop on my face like the last time I removed it about 20 years ago!
When I pulled it I could see a large hole in the rear alloy case. No wonder it failed.
Getting one of the output shafts out was a challenge as the splines had jammed in the diff centre. Had to resort to using jacking bolts as I could not drive it out or get it out with a slide hammer puller
It appears the crown wheel to the diff centre bolts had failed in fatigue and 5 of the 6 had lost their heads. One of the 5 was missing so I presume it went out the hole in the case. I don't know why the bolt heads failed but they were the original bolts in the car - the CWP was also the original.
One of the failed bolt heads had been very badly chewed up and I presume this jammed in the gears and led to the final failure and shearing of the pinion gear teeth and the collapse of the pinion bearing.
I now suspect the bangs I had heard a couple of times in the past couple of races that I could not identify had been the bolt heads progressively failing. I think the hole in the diff casing actually occurred when racing at Phillip Island earlier this year as i had a couple of puffs of smoke out the rear of the car that I put down to engine or gear box oil leaks dripping on the exhaust - but it was diff oil as it now turns out. The fact that the diff ran with no noise until it jammed on a loose bolt head and failed and that the diff crown wheel carrier bearings are still perfect having run for some time with not much oil and getting very hot is a testament to Redline gear oil qualities.
Now just a new CWP , new alloy case, new bearings, shims and crush tube and teach myself how to set the Pinion depth correctly as I have never had to do it before and i will have a new diff .
I could probably get the alloy case welded up but the output bearing circlip grooves are badly chewed up and to fix them plus the hole plus another cracked area from an internal impact and it would probably cost me more than a new one.
cheers
Rohan