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crownwheel bolts loose


Daan
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I am giving my landy a bit of a once over after having served myself pretty good for around 5 years.

Part of this is by pulling the diffs to have a look. I was worried to see the rear crownwheel bolts were only fingertight.

This is on a detroit diff with 4.7 KAM crwonwheel and pinion and a 4.7 spacer. I run 35 inch simex.

The whole thing has obviously been worked pretty hard over the last 5 years. I fitted the whole setup myself, using loctite and 40-45 LB-ft of torque as per manual. I seem to remember that the required torque seemed quite low.

My question is whether I can up this a bit, say 50% to prevent this happening again. Anyone done this? It is fitted with BSP bolts and thick washers. Another trick I was thinking is to use Schnor washers, to stop them getting undone.

I have heard of more people having had this problem and the question is obviously whether people have solved the problem succesfully.

Cheers, Daan

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Daan,

I've had the same problem on my ARB centre with a Rover 3.54 crownwheel. They were Loctited in place but, as per the ARB instructions, I didn't clean the threads first to remove the factory oil. Hence, Loctite didn't work and the bolts came out! I'm just finishing fixing my Lathe before I can repair the centre, and then I'll be thinking about how to secure the bolts in place. Current thinking (seeing as I don't trust Loctite any more!) is either to drill the bolts and use locking wire, or to put a tack of weld on the bolts.

I'll be interested to hear how you get on....

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Daan, these are all of the guys I know who have KAM 4.75s (seem to be badly affected due to the width of the crownwheel).

  • Ali Read had this happen - diff was rebuilt and no issues when vehicle was sold about 18 months afterwards.
  • Jules Read hasn't had a failier although, AFAIK, he hasn't pulled his diffs since he killed his truck
  • Graham Antill had this happen at an event - not sure if he ever solved the problem.
  • Mark McFarlane (aka Tonks) - no problem AFAIK
  • Trev (aka LR90) - no problem AFAIK

IIRC KAM started selling stronger bolts to try and solve the problem.

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i just took my front diff out, bolts were really loose. true track with ashcroft r&p. didn't install it myself, so don't know whether loctite was used, didn't see any traces though so i would think not. re-tightened the bolts to the correct torque, using stronger (red) loctite. did them one by one + used lots of brake cleaner on bolts and threads to make sure everything was clean. tried undoing the bolts a day later, really thight. put the diff back in no keeping my fingers crossed.

cheers

orange

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you could always drill the bolts and lock wire them so it cant happen

I dont think lockwire stop them getting loose, but they do stop them getting undone, once they are loose if you see what I mean.

I have a more direct question to Mr ashcroft (who is on this forum): what torque are you using for the crownwheel bolts with this kind of setup?

Thanks, Daan

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I dont think lockwire stop them getting loose, but they do stop them getting undone, once they are loose if you see what I mean.

I have a more direct question to Mr ashcroft (who is on this forum): what torque are you using for the crownwheel bolts with this kind of setup?

Thanks, Daan

funnily enough we have been looking into this last week after also having had this problem,

we go to 45 ft/lb a med strength loctite on brake cleaneered threads but this is still not good enough for some applications,

KAM use a 3/8 BSF thread like the older 4.7 series diffs, this is quite a corse pitch not as good as the later 3/8 UNF, all 3.54's and our 4.11's use the 3/8 UNF ,

you can buy higher tensile 12.9, 3/8 UNF bolts but they are all socket caps and thus do not have a shank which is very important to locate the crown wheel,

the later P38 diffs use the same thread in 12.9's, hex head with integral washer but have no shank, not ideal. (and they are £ 2 each),

we are doing 3 things :

1) costing up a batch of 2000, 3/8 UNF, 12.9 tensile, 1 1/8", hex head with 3/8" shank and integral washer,

2) being higher tensile we can fit to a higher torque, waiting to speak to a guy tomorrow who has these figures,

3) buying high strength permanent fixing loctite.

should do it,

Dave

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Mine were fine when they were pulled last March after 3 years. Ade, did you use new bolts?

No! old bolt's but with thread lock after cleaning with brake cleaner! if (when) i brake a shaft i'll be having a close lok at the bolt's! <_<

Only one year of actual use though, :)

Chris

yeah! but not a whole year!!! ;):lol:

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funnily enough we have been looking into this last week after also having had this problem,

we go to 45 ft/lb a med strength loctite on brake cleaneered threads but this is still not good enough for some applications,

KAM use a 3/8 BSF thread like the older 4.7 series diffs, this is quite a corse pitch not as good as the later 3/8 UNF, all 3.54's and our 4.11's use the 3/8 UNF ,

you can buy higher tensile 12.9, 3/8 UNF bolts but they are all socket caps and thus do not have a shank which is very important to locate the crown wheel,

the later P38 diffs use the same thread in 12.9's, hex head with integral washer but have no shank, not ideal. (and they are £ 2 each),

we are doing 3 things :

1) costing up a batch of 2000, 3/8 UNF, 12.9 tensile, 1 1/8", hex head with 3/8" shank and integral washer,

2) being higher tensile we can fit to a higher torque, waiting to speak to a guy tomorrow who has these figures,

3) buying high strength permanent fixing loctite.

should do it,

Dave

Hi Dave, thanks for this quick reply on a sundaynight, its weekend mate!

I had fitted capheads initially, but on fitting the diff to the casing I had an 'oh my god' moment: capheads catch the diff casing.

So hexheads it is. BSF bolts are not ideal, if only from a supply point of view, but with these crownwheels, I am stuck with it. I dont think tightening them harder by 25% would make them break, would you? In the case of new custom bolts, the best would be to have the shank as short as possible. This allows the threaded part more stretch wich decreases the tendency to come undone. This might also be the clue with the p38 bolts. I think friction is really what keeps them together and the fully threaded bolt is the best in stretch.

My plan currently is to use loctite, tab washers from a s3(or 2) and schnor washers and give them 25% more welly.

To be continued....

Daan

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i had both of my crownwheels come loose after fitting my lockers. i'd used locktite & cleaned the threads, they where the original bolts though. my current plan is if it happens again im getting those lockwashers series diffs had (or making my own) as i trust a mechanical solution much more than some fancy glue.

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Daan, these are all of the guys I know who have KAM 4.75s (seem to be badly affected due to the width of the crownwheel).

[*]Ali Read had this happen - diff was rebuilt and no issues when vehicle was sold about 18 months afterwards.

IIRC KAM started selling stronger bolts to try and solve the problem.

It was not 18 months later , it was about 2 months later i sold it

But went again 2 weeks after i sold it :ph34r::ph34r:

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That's my understanding too. Worth giving them a call Daan

Eh.... yes the website mentioned them, and yes I ordered them. Then wondered where they are. Phoned back and the reply was: We never had BSF bolts, but we can get them for you; 2.30 pounds ech, which is fine, but: minimum order 2000....

i got mine out of a ser 2a diff, i think ser3 didn't have them

Now ordered, cheers tonk.

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