[gtobird]

I already know this is being cheap. I was about to install a ring gear on the posi I bought and thought I would just use the ring gear bolts I had from an old open unit I had. They look perfect to me. Nicest bolts you'll ever see cause they were of course constantly dunked in gear oil as the ring gear turned.

Anyway, the instructions for my posi say to only use new ring gear bolts... Huh? Just wondering why. I re-use engine block cap bolts and head bolts without concern, so why is this an issue?

Inquiring minds want to know.

OJ

[TedRamAirII]

Originally Posted by gtobird

I already know this is being cheap. I was about to install a ring gear on the posi I bought and thought I would just use the ring gear bolts I had from an old open unit I had. They look perfect to me. Nicest bolts you'll ever see cause they were of course constantly dunked in gear oil as the ring gear turned.

Anyway, the instructions for my posi say to only use new ring gear bolts... Huh? Just wondering why. I re-use engine block cap bolts and head bolts without concern, so why is this an issue?

Inquiring minds want to know.

OJ

GM service info says to always replace them. They stretch upon final torque, so I would replace them, why chance it? One thing to do is be sure the ring gear and the face of the carrier is FLAT. Run a stone across them both, be sure of no high spots. Then loc-tite the bolts and torque them evenly.

['ol Pinion head]

Depends on the ring gear bolt size and the intended use. Have gone through or set-up R&P's multiple dozens on early 8.2's with the 3/8" rh thread ring gear bolts. With a 4sod and lower gears in the car, have always sourced new bolts for the reinstall . Refreshing bearings in a 2.78 or 2.93 geared early 8.2, have usually reused current ring gear bolts. Gray iron 8.2's, I wont blow bucks "upgrading" them for high torque applications, been there, they wont hold up, instead build up off an 8.5 A body hsg.

[TheSilverBuick]

Almost every rear end I've done has been with used gears and I re-used the bolts that were in my carrier when I swapped them over. The only time I actually put new bolts in was when I used a ring gear spacer and it came with new longer bolts. Then I ended up re-using them when I changed the gears out a few years later.

[gtobird]

Originally Posted by TheSilverBuick

Almost every rear end I've done has been with used gears and I re-used the bolts that were in my carrier when I swapped them over. The only time I actually put new bolts in was when I used a ring gear spacer and it came with new longer bolts. Then I ended up re-using them when I changed the gears out a few years later.

I appreciate the responses from everyone. I have never had anyone tell me they actually broke the bolts in a "non-racing" application. I fully understand the bolts stretch when installed, but unless they were over torqued or in the prior installation they were abused, I can't see how there would be a problem.

I'm probably going to live dangerously and re-use them.... if for no other reason, I just want to prove to myself this isn't an issue. When I look at our hobby today, I hear about all of the things we HAVE to do in building our cars, yet I recall 40 years ago when I had little money and built everything with discarded parts I scrounged from friends. In my old age I'm not much of a daredevil, so I guess I have to enjoy this kind of a big risk... LOL

OJ

[TheSilverBuick]

Put loc-tite on them, torque them to spec and call it the day. The only time I've ever heard of the bolts being an issue is from vibration loosening them up. The teeth on the gears usually break long before the series of bolts on the ring gear strip.

[TedRamAirII]

Originally Posted by TheSilverBuick

Put loc-tite on them, torque them to spec and call it the day. The only time I've ever heard of the bolts being an issue is from vibration loosening them up. The teeth on the gears usually break long before the series of bolts on the ring gear strip.

It's not a case of the threads stripping, its the heads popping off that causes a problem. GM, Ford and Chrysler wants the ring gear bolts replaced, whenever they are taken out, but what do they know? ; ) Doesn't matter to me, its not my car.

[tanksteve]

I was curious about this. I looked and I dont see that the 1967 or 1970 Pontiac service manuals called for replacing ring gear bolts while servicing the ring gear. If you do install with new ring gear bolts, one has to wonder are the bolts USA or ??? I just went through this and the new "grade 8" bolts I received had the grade 8 markings stamped off center.....

[tanksteve]

Probably the biggest danger in all of this is forgetting to torque all the ring gear bolts to correct spec. I tore apart a 8.2 BOP a few months ago that I got from somebody who said the rearend had a problem. I found that two of the ring gear bolts had backed out. It was a pity, they had installed Richmond gears.

[TedRamAirII]

Originally Posted by tanksteve

I was curious about this. I looked and I dont see that the 1967 or 1970 Pontiac service manuals called for replacing ring gear bolts while servicing the ring gear. If you do install with new ring gear bolts, one has to wonder are the bolts USA or ??? I just went through this and the new "grade 8" bolts I received had the grade 8 markings stamped off center.....

All newer truck Service Information specify when taking off old ring gear bolts and DISCARD THEM. Looked up a 2013 Camaro and first thing it specifies is DISCARD RING GEAR BOLTS, REPLACE WITH NEW ONLY. If anyone wanted to "save money" its auto manufacturers. So why would they discard them, if they were OK to reuse? If it was me, I would check with ARP for bolts.

[TheSilverBuick]

What are you torqueing them to that cause the heads to pop off?!?!?!? They only have a paltry 55/65 ft-lbs torque setting (8.2"/8.5") and the bolts are huge and fine thread.

And the "save money" logic doesn't really apply because it'd be dumb to find enough used bolts to put in new cars and how many warranty rear ends was GM anticipating doing? My bet is most rear end work was outside of warranty and it's another dollar they can charge to the customer.

[gtobird]

Originally Posted by TheSilverBuick

What are you torqueing them to that cause the heads to pop off?!?!?!? They only have a paltry 55/65 ft-lbs torque setting (8.2"/8.5") and the bolts are huge and fine thread.

And the "save money" logic doesn't really apply because it'd be dumb to find enough used bolts to put in new cars and how many warranty rear ends was GM anticipating doing? My bet is most rear end work was outside of warranty and it's another dollar they can charge to the customer.

The more I think through this, the more I'm questioning why GM recommends replacing these bolts. I also wonder if it may be insurance that the correct length of bolts are used when ring gears are changed and spacers are added.

[TedRamAirII]

Originally Posted by TheSilverBuick

What are you torqueing them to that cause the heads to pop off?!?!?!? They only have a paltry 55/65 ft-lbs torque setting (8.2"/8.5") and the bolts are huge and fine thread.

And the "save money" logic doesn't really apply because it'd be dumb to find enough used bolts to put in new cars and how many warranty rear ends was GM anticipating doing? My bet is most rear end work was outside of warranty and it's another dollar they can charge to the customer.

I'm sure GM doesn't care a wit how much money they make on a few bolts. When they do warranty work, the Engineers decided the old bolts were not good enough to reuse, and THEY are paying for it, so I doubt they want to pay for parts that not needed. I'm sure they have their reasons, and if you are smarter than the people that design and build them, then go ahead. Don't listen to me, what do I know.

[RAJ7395]

He's my take on this.

One 3/8-24 fine thread grade 8 bolt dry torqued to 50 ft.lbs produces a clamping force of 7900 lbs. Torquing a 3/8-24 grade 8 bolt higher than 50 ft.lbs causes plastic deformation of the bolt. Plastic deformation causes the bolt to grow in length and shrink in diameter.

My guess is that reusing an already plastically deformed bolt is not recommended as the longer length may cause it to bottom out in the blind ring gear bolt hole and the bolt is weaken due to the decreased cross section.

[gtobird]

Originally Posted by RAJ7395

He's my take on this.

One 3/8-24 fine thread grade 8 bolt dry torqued to 50 ft.lbs produces a clamping force of 7900 lbs. Torquing a 3/8-24 grade 8 bolt higher than 50 ft.lbs causes plastic deformation of the bolt. Plastic deformation causes the bolt to grow in length and shrink in diameter.

My guess is that reusing an already plastically deformed bolt is not recommended as the longer length may cause it to bottom out in the blind ring gear bolt hole and the bolt is weaken due to the decreased cross section.

You are on to something, but I don't think the issue is reusing a bolt that is plastically deformed from use or factory torquing. Rather, it may be because you can no longer torque it reliably after it's been used. Please allow me to explain.

Being a geek who did all sorts of physics experiments in college I had the opportunity to test the tensile strength of bolts and actually did the elastic to plastic deformation tests. Your point helped me remember that lubricating a bolt lowers the amount of torque you can apply to it. The theory is the bolt will turn easier with lubrication, but is still stretching at the same rate as it would without the lubrication. So, in essence you will reach the point of "plasticity" at a lower torque level. It's not a small amount either. It could be anywhere from 10% up to 50% depending on the type of lubricant that's used. Seeing that used carrier bolts would have been continuously soaked in one form or another of lubricant and likely some form of posi additive, it would be hard to predict just how much the applied torque would change on a used bolt. Even if you clean them well, they can still retain quite a bit of oil on them (and for that matter, so can the ring gear threads). All this to say, a given torque on a dry bolt will have a lower load than on a well oiled bolt and that could be yet another reason not to rely on "used" bolts.

[tanksteve]

gtobird -what year and type is the rearend? What the 2013 GM service manual says is not going to apply to 8.2 BOP and 8.5. Newer rearends may very well have torque to yield ring bolts.

[TedRamAirII]

Originally Posted by tanksteve

gtobird -what year and type is the rearend? What the 2013 GM service manual says is not going to apply to 8.2 BOP and 8.5. Newer rearends may very well have torque to yield ring bolts.

The Service Info states to torque the bolts. If it was a TTY setup, it would state to torque the bolts to #30, then another 90 degrees (for example) I'm just stating my opinion on reusing bolts in a highly stressed area. No one needs to follow my advice. Its your car, do what you want. Just trying to save some heartache if the heads pop off. Seems like a bolt head got between the pinion and ring gear, I've seen it happen, and it wasn't pretty, unless you sell rear axle housings. ; ) This guy was kinda lucky. http://www.nastyz28.com/forum/showthread.php?t=244801

[RAJ7395]

Originally Posted by gtobird

You are on to something, but I don't think the issue is reusing a bolt that is plastically deformed from use or factory torquing. Rather, it may be because you can no longer torque it reliably after it's been used. Please allow me to explain.

Being a geek who did all sorts of physics experiments in college I had the opportunity to test the tensile strength of bolts and actually did the elastic to plastic deformation tests. Your point helped me remember that lubricating a bolt lowers the amount of torque you can apply to it. The theory is the bolt will turn easier with lubrication, but is still stretching at the same rate as it would without the lubrication. So, in essence you will reach the point of "plasticity" at a lower torque level. It's not a small amount either. It could be anywhere from 10% up to 50% depending on the type of lubricant that's used. Seeing that used carrier bolts would have been continuously soaked in one form or another of lubricant and likely some form of posi additive, it would be hard to predict just how much the applied torque would change on a used bolt. Even if you clean them well, they can still retain quite a bit of oil on them (and for that matter, so can the ring gear threads). All this to say, a given torque on a dry bolt will have a lower load than on a well oiled bolt and that could be yet another reason not to rely on "used" bolts.

Sounds like the best answer yet! It only takes 30 ft.lbs of torque with a lubricated 3/8-24 bolt to achieve the same 7900 lbs of clamping force. 65 ft.lbs on an oiled bolt could very well pop the bolt head off.

[HO Kenny]

Maybe I'm living on borrowed time. I reused mine in about 1980. If I had $1 for every time I've dumped the clutch or speed shifted I'd be rich.
Great explanation on lubricant on the bolts though. I believe A fine threaded bolt will yeald a stronger clamping force than a coarse threaded bolt using the same torque.
Use a torque wrench.
I have a question. Can loc-tight act as a lubricant?

[gtobird]

Originally Posted by HO Kenny

Maybe I'm living on borrowed time. I reused mine in about 1980. If I had $1 for every time I've dumped the clutch or speed shifted I'd be rich.
Great explanation on lubricant on the bolts though. I believe A fine threaded bolt will yeald a stronger clamping force than a coarse threaded bolt using the same torque.
Use a torque wrench.
I have a question. Can loc-tight act as a lubricant?

I don't know if loctite could act as a lubricant or not. I'm guessing it might cause drag and therefore change the torque required if it is starting to dry (opposite of lubrication). I'm about done with this conversation over $10 worth of bolts, but it has been fun bantering about theories.

In theory you could perhaps (maybe) prove the loctite thing by installing a new dry bolt and torquing it to spec. Draw a line on the head of the bolt and extend the line onto the part it's mating to after torquing. Try repeating this procedure to make sure the line on the bolt and mating part continuously line up after torquing. There probably will be small variation.

Then apply loctite to the bolt and re-torque to the same amount and see if the lines still line up. If not, you know that loctite changes things. This won't be perfect science. When I did this kind of stuff in college we had a press with double acting cylinders, pressure gauges and a jig to test the actual loading from a given torque.

Last, but not least even after all of this applied science, I'm still of the belief that there is little chance you will have a failure with used bolts. I say that only because back in the day our cars were built, most things were designed with a safety factor of 2X, but I can't argue with the logic that it's $10 worth of bolts to avoid a possible failure.

OJ