Is it necessary to replace the crown wheel bolts on 8-3/4 ?

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70Hardtop

70Hardtop

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We say crown wheel, Americans say drive gear (or ring gear) and the service manual says to discard the old bolts when it is removed/replaced for service or ratio change or rebuild etc. Also I see there are many kits online with the new set of bolts.

So I am wondering how much stress do these 12 bolts take normally? The service manuals are not assuming the cars will be abused, but for normal road use? And isn't most of the stress on the bolts a shear force, rather than a tensile (pulling) force? My diff assembler said I will never break them - the car is a Challenger, engine a 400hp 340, nothing too serious. Although tyres are large, 295 Sumitomo's. The pumpkin is all assembled but still out of the car, I can still easily replace the bolts, but I just thought I would ask here, actually how important it is to replace them. And the main reason I would is because I don't know the history of this chunk, it may or may not have had huge torque through it in a past life. Thanks!
 
Better safe than sorry.
The factory isn't in the business of selling bolts, they are more about protecting their warranty and their image.
The bolts themselves do take a lot of stress when the car is abused.
When the rear diff's crown gear was installed, i bet they used loctite thread locker on the threads and that stuff is hard to get off completely especially on fine thread bolts.
If you don't get it all off, the torque reading would be off on re-assembly.
Time is money at a dealership.
So, unless you idle around town and never drive the car with sticky tires and abuse it .......EVER.........i would just change them out. Same thing if you don't know the rear diff's history or how it was treated.
It's cheap insurance.............
 
Dartnut said:
Better safe than sorry.
The factory isn't in the business of selling bolts, they are more about protecting their warranty and their image..............
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thanks for reply, I think I will, yes it is, well not really cheap, as I have to get them imported in but it is easy insurance. And good point about the Loctite and dealerships etc, hadn't thought of that. In my case however, there was no thread locker on them and I was helping the guy that assembled it, I cleaned up all the threads and we applied ARP Ultra Torque to the threads and underside of the heads.

However as I said, I don't know the history of the unit and a bolt can look just dandy but may be ready to fail with a little stress.
 
70Hardtop said:
thanks for reply, I think I will, yes it is, well not really cheap, as I have to get them imported in but it is easy insurance. And good point about the Loctite and dealerships etc, hadn't thought of that. In my case however, there was no thread locker on them and I was helping the guy that assembled it, I cleaned up all the threads and we applied ARP Ultra Torque to the threads and underside of the heads.

However as I said, I don't know the history of the unit and a bolt can look just dandy but may be ready to fail with a little stress.
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Cool.
And don't forget that this stuff is over 40 years old now.........
I hear you on the cost, the shipping and exchange rate on money can be brutal, even here in Canada!
 
IMHO replacing these bolts is not necessary, I have built several rear ends and reused old bolts, these units are crossing 300k miles with no problem. When I build an engine that has TTY bolts they always get replaced, but ring gear bolts are not TTY, nor do they torque close to 100FT LBS, nor are they reaching any kind of stretching while torquing, the use of locktite is something I do believe in, so I would definitely do that. I agree that it is quicker to build with new bolts, due to cleaning, but remember and extra $20-30 when selling a ring and pinion set is a nice average ticket boost for the seller!
 
Dartnut said:
Cool.
And don't forget that this stuff is over 40 years old now.........
I hear you on the cost, the shipping and exchange rate on money can be brutal, even here in Canada!
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Yeah, it's easy to get ripped on the shipping. I have bought a few things for my Mopars from Canada and shipping wasn't too bad at the time (sellers helped out). Re the bolts - I just priced some, Doctor Diff has some for A$54 (incl shipping cost by First Class) and there are some ARP ones here on Australia ebay for $76.
 
Unless he knows they're left hand thread, he'll likely need at least one.

I changed lotsa hi/po, regular rearsets thru the decades, seldom changed bolts, never ever had a reason to regret that decision.
 
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moparownr said:
IMHO replacing these bolts is not necessary, I have built several rear ends and reused old bolts, these units are crossing 300k miles with no problem. When I build an engine that has TTY bolts they always get replaced, but ring gear bolts are not TTY, nor do they torque close to 100FT LBS, nor are they reaching any kind of stretching while torquing, the use of locktite is something I do believe in, so I would definitely do that. I agree that it is quicker to build with new bolts, due to cleaning, but remember and extra $20-30 when selling a ring and pinion set is a nice average ticket boost for the seller!
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Thanks for advice - but I cannot work out what TTY is? Something to do with torque values? Are head bolts and main cap bolts TTY? As I said in another reply, in Aust I will have to pay between $56 (OEM) and $76(ARP) for them. So not exactly cheap.
 
inertia said:
Unless he knows they're left hand thread, he'll likely need at least one.

I changed lotsa hi/po, regular rearsets thru the decades, seldom changed bolts, never ever have had a reason to regret that decision.
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haha, that reminds me of a funny situation when I was removing them, happened to be about 2am and cold and I wasn't fully alert. Yes I knew they were LH thread, so I was undoing them with a ratchet and every time the ratchet eased up to finger tight I pulled it off and started undoing with my left hand. However I couldn't work out why they were not coming out and why they kept getting tighter. Back on with the socket and started undoing again, same deal, went to finish off by hand and same thing happened! Then realised what I was doing - the left hand was automatically going the normal way while the brain was asleep. Had to laugh at myself.
 
70Hardtop said:
Thanks for advice - but I cannot work out what TTY is? Something to do with torque values? Are head bolts and main cap bolts TTY? As I said in another reply, in Aust I will have to pay between $56 (OEM) and $76(ARP) for them. So not exactly cheap.
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TTY=Torque to yield. Don't mean to be confusing, all TTY bolts must be replaced, non TTY do not.
 
moparownr said:
TTY=Torque to yield. Don't mean to be confusing, all TTY bolts must be replaced, non TTY do not.
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Ah ok. But what bolts on the engine are TTY then? The service manual doesn't say to replace the head bolts but it says to replace the ring gear bolts.

BTW, what exactly does torque to yield mean? Is that at the limit of a bolt's stretch? I thought torquing bolts is meant to prevent a bolt going near it's tensile failure point?

Anyway, going to bed now, so I can't reply at this time

Thanks
 
I twisted off 2 in the same ring gear when I was torquing them (55 ft/lbs) with a snap-on non ratchet torque wrench. I believe the PO overtorqued the bolts trying to get them off ( Left hand threads) and damaged them, 2 more had obvious hyper-stretching. Good part was the twisted off bits threaded right out with a punch. This was after I ran them out and chased the top 3 threads with a tap I bought. LHT taps dont grow on trees but I got it in 3 days for $7. Ebay...:)
100113202921.jpg
 
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70Hardtop said:
Ah ok. But what bolts on the engine are TTY then? The service manual doesn't say to replace the head bolts but it says to replace the ring gear bolts.

BTW, what exactly does torque to yield mean? Is that at the limit of a bolt's stretch? I thought torquing bolts is meant to prevent a bolt going near it's tensile failure point?

Anyway, going to bed now, so I can't reply at this time

Thanks
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Again sorry for any confusion, your thinking on TTY is in line, there are several sites that can explain it way better than I can, my point was that your bolts don't need replacing, and your car has no TTY bolts on it.
 
pishta said:
I twisted off 2 in the same ring gear when I was torquing them (55 ft/lbs) with a snap-on non ratchet torque wrench. I believe the PO overtorqued the bolts trying to get them off ( Left hand threads) and damaged them, 2 more had obvious hyper-stretching. Good part was the twisted off bits threaded right out with a punch. This was after I ran them out and chased the top 3 threads with a tap I bought. LHT taps dont grow on trees but I got it in 3 days for $7. Ebay...:)
View attachment 1715196040
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Good story and I'd say that has happened more than once around the world, maybe even more than twice... A good reason to replace them if you didn't know the previous history of the unit. You did well to get that LH tap, ebay can be a saviour sometimes.
 
moparownr said:
TTY=Torque to yield. Don't mean to be confusing, all TTY bolts must be replaced, non TTY do not.
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I just did some reading on the Torque to yield bolts. Very interesting. And I'm glad you mentioned it, as now I know about it and have learnt a bit more. However, as another fellow here said, and I don't mean to knock your post, but it is not relevant in our ol' skool world, unless we used them on aluminum heads. And also, just because they are not TTY bolts on the crown wheel, is not really a reason to not replace them. If you knew the full history of the vehicle and exactly how it has been driven, eg if you had owned the car from new, and the diff had never been worked on, or if it had and you knew the bolts were all correctly torqued etc, then you could confidently reuse the bolts. But otherwise, for the cheapness of them in the USA, it would be just good practice to replace them. The mistaken overtorquing trying to undo them due to the LH thread is a very good reason to replace them. My main reason for asking in the OP is why, in normal circumstances, would they need to be replaced. To save time at the dealership is a very good reason but how much load are they under in normal circumstances? They must be under some considerable load for the service manual to say to always replace them. As the pinion exerts load on the ring gear, it is only one particular area that is under load each time and I would guess, only about 3-4 bolts each time are taking the force of the pinion. The load would not be evenly distributed on each bolt. I think (and I'm only guessing) that there would be both a shear and a tensile force component on these few bolts. As I read that the gears ride up and down on each other under load and on coast etc. Sorry for the long post.
 
The bolts themselves aren't supposed to take any sheer force, their purpose is a clamping force (think clutch pressure plate) creating friction/(stiction)? between the two surfaces.
Would that not mean they all share force equally if tightened equally ? ?

EDIT
 
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