92a Posted January 15, 2023 Share Posted January 15, 2023 Hi Everyone, had a horrible vibration on my wolf 90 as I left home ,reversed back 50 yards and jacked it up to check the propshafts, they both seemed ok, drive forward to park and heard a clunk, got out to find the front propshaft hanging down with the diff flange on the end , bolt had sheared off, it was an 8.8 , I replaced the flange when I put a D2 front prop on and guess the bolt came with the flange kit , should it 10.9 as its torqued to 100nm ? Quote Link to comment Share on other sites More sharing options...
Gazzar Posted January 15, 2023 Share Posted January 15, 2023 Lucky there was no major damage! Over torqued? What's the torque specification? Buy a genuine parts bolt and see. The 8.8 should stretch more than the higher grades, something isn't right, somewhere. Quote Link to comment Share on other sites More sharing options...
92a Posted January 15, 2023 Author Share Posted January 15, 2023 Diff is proper stiff now and as wheels move freely ( until you take up the slack ) I think it may well have done serious damage, and I’ve only put the flange on with a random 8.8 bolt and a spring washer but not torqued it yet 😕 Quote Link to comment Share on other sites More sharing options...
Gazzar Posted January 15, 2023 Share Posted January 15, 2023 Yes, I suspect you are seeing the results of something, not the cause. I'm not familiar with the latter diffs, I didn't realise they used a bolt to hold the flange on. I presume the pinion bearings must be set up some other way than by torquing the bolt, but is it possible that the pinion bearing has failed, I wonder? Either way, I think you'll have to drop the diff out. Quote Link to comment Share on other sites More sharing options...
uninformed Posted January 15, 2023 Share Posted January 15, 2023 What is the dia of the bolt/thread? Quote Link to comment Share on other sites More sharing options...
92a Posted January 15, 2023 Author Share Posted January 15, 2023 The bolt is M12 Quote Link to comment Share on other sites More sharing options...
Wytze Posted January 15, 2023 Share Posted January 15, 2023 Could be just me, but i would go 12.9 Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 15, 2023 Share Posted January 15, 2023 As @Gazzar says I suspect this failure is a symptom not a cause, and remember HT bolts are brittle and that's not always good - I remember Rog shearing all 6 hub flange bolts on his Toyota as he'd rebuilt it in a hurry and used stainless ones, they pinged off like bullets Quote Link to comment Share on other sites More sharing options...
Gazzar Posted January 15, 2023 Share Posted January 15, 2023 8.8 can be more forgiving, in that they stretch before they bend, so higher numbers are just that. Not better, just higher. Horses for courses. Really interested in how this is resolved and grateful that you've shared the learning process. Quote Link to comment Share on other sites More sharing options...
uninformed Posted January 16, 2023 Share Posted January 16, 2023 If that is a genuine bolt, and the torque spec correct as per the WSM, I’d go with that , just add a bit of medium strength loctite. And for it to fail, something else has gone wrong. Poor threads, not clean etc. I also think that there is miss information regarding grade/class of bolt that has become popular. All grades get “stretched”. Generally for bolts that get reused the pre load will be something like 65% of proof load. The joint design or job requirements dictate the pre load, then the bolt size and grade/class is chosen. Substituting higher class bolts doesn’t always benefit, not because they don’t stretch or are brittle, but because tightening to the same pre load doesn’t get the bolt performing as it should, or the base material isn’t capable of a higher pre load (something like cast iron…..) and substituting lower grade or class bolts is definitively not good, you might get away with it, but it’s not a good idea. BTW “Grade” is for SAE bolts, “Class” for metric and whilst they are a representation of strength they are not the same values or measured the same way. 1 Quote Link to comment Share on other sites More sharing options...
Snagger Posted January 16, 2023 Share Posted January 16, 2023 19 hours ago, Gazzar said: Yes, I suspect you are seeing the results of something, not the cause. I'm not familiar with the latter diffs, I didn't realise they used a bolt to hold the flange on. I presume the pinion bearings must be set up some other way than by torquing the bolt, but is it possible that the pinion bearing has failed, I wonder? Either way, I think you'll have to drop the diff out. They are set up with shims for depth and preload exactly as per the other Rover diffs, just with a bolt into a drilled and tapped pinion end instead of a nut onto a male tapped pinion end. Other generational changes that occurred in Rover diffs were roll pins securing the cross pin instead of circlips on each end, which was a cost function and weakened the diff (the roll pin shears if the carrier hole is even slightly ovalised, so the pin then slides out radially and hits the pinion head) and the replacement of the punched side bearing loading nut pawls with roll pins, which again seems weaker but cheaper. But they are all set up the same way. 1 Quote Link to comment Share on other sites More sharing options...
Gazzar Posted January 16, 2023 Share Posted January 16, 2023 Okay, so why did the bolt fail? Curious. Quote Link to comment Share on other sites More sharing options...
92a Posted January 16, 2023 Author Share Posted January 16, 2023 I have just taken the diff out and there is no sign of anything breaking up and nothing in the oil ( plenty of oil ) I guess I must of over tightened it , but I did it up by hand lying under the vehicle , hence my original question as to the correct grade or class of bolt ? I bought a 24 spline Truetrac from XCESS4x4 before Christmas so I’ll put the one I take out the back in the front for now Quote Link to comment Share on other sites More sharing options...
Snagger Posted January 16, 2023 Share Posted January 16, 2023 50 minutes ago, Gazzar said: Okay, so why did the bolt fail? Curious. My suspicion would be overtightened, or loose bearings allowing shunting of the pinion that shock loaded the bolt. That could have been because the bolt bottomed out in the hole on dirt or grease, reaching correct torque without pulling tight, or an issue with bearings or shims. Or it could just have been a defective bolt. Quote Link to comment Share on other sites More sharing options...
western Posted January 16, 2023 Share Posted January 16, 2023 The M12 bolt under that LR part number is correct for your rear axle, I checked it yesterday. Quote Link to comment Share on other sites More sharing options...
uninformed Posted January 26, 2023 Share Posted January 26, 2023 (edited) I just went through my diff parts draw. Here are two pinion flange bolts, as supplied in Rover diff pinion flange kits. I’m pretty sure these are from Ashcroft. The gal looking class 10.9 is definitely from Ashcrofts kit… If my memory serves correctly (probably not…) I bought some of the earlier square profile flange kits, then changed to the round. I suspect the Gold zinc class 8.8 is from the earlier type. The gal looking 10.9 is definitely from the later round type. Just a note. A thick washer is required with these bolts. Did you have that? Edited January 26, 2023 by uninformed Quote Link to comment Share on other sites More sharing options...
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