Thinner control arm bolt make any difference?

[tookien]

Originally Posted by thescreensavers
What is the OE torque spec? What is the size and grade of the replacement bolt?



Can't remember exactly at the moment but around 70-80 foot pounds.

The original bolt was half an inch thick.

The replacement bolt is 0.462 inch thick and the grade is 10.9.

 

[tookien]

Originally Posted by thescreensavers
What is the OE torque spec? What is the size and grade of the replacement bolt?


The bolt at the bottom is the old bolt with the nut (whatever is left of it).

 

[mattd]

Compressing the bushing will not change the diameter of the bolt bore. The clearance that is in there will allow the control arm to loosen up much easier, as wel wear the bolt or control arm busing, whichever is softer.

Change it out to the proper size.

 

[tookien]

Originally Posted by mattd
Compressing the bushing will not change the diameter of the bolt bore. The clearance that is in there will allow the control arm to loosen up much easier, as wel wear the bolt or control arm busing, whichever is softer.

Change it out to the proper size.


Thanks

 

[zzyzzx]

How long do you intend to keep this vehicle?

 

[eljefino]

.462/2 ^ 2 x pi = .1676 in^2.
.500/2 ^2 x pi = .1963 in^2.

You have 85% of the strength of the original bolt. (Not getting into how a metric 10.9 doesn't directly cross reference to an SAE 5 or 8.)

And as others say, you're hammering on an undersized fastener, and in three pages of this thread, failed to acknowledge the problem and are blowing off the people who are correctly telling you to just get the proper bolt.

And how are you going to "keep an eye on it"? Will you remove it annually and perform NDT tests on it?

 

[thescreensavers]

Originally Posted by tookien
Originally Posted by thescreensavers
What is the OE torque spec? What is the size and grade of the replacement bolt?



Can't remember exactly at the moment but around 70-80 foot pounds.

The original bolt was half an inch thick.

The replacement bolt is 0.462 inch thick and the grade is 10.9.


From what you said it would appear the replacement bolt is an M12(.472") . A class 10.9 corse thread can be torqued to 93ft/lb. If your OE torque spec is less than that then your fine and I wouldn't loose sleep over this.

Bolted joints resist shear by clamping and friction, the bolt to bushing spacing is not relevant as a gap always exists for installation. The .028" diameter difference is negligible in that regard. This would be different if we were discussing a shoulder bolt.

In this case at 75ft/lb ( if correct) applies 9000 lbs of clamp load (assuming a clean plain nut and bolt), which an m12 bolt is sufficiently capable of producing without breaking. (93 ft/lb is 11,000 lbs)

 

[eljefino]

^ I like the science behind this-- it tickles my nerdy senses. But if that clamping force were all it took, a giant, appropriately torqued c-clamp around the subframe, holding the bushing in place with friction, would be all we need. But that's a recklessly goofy way to build a car. What if OP hit a curb, and a shock load went through the control arm and rubber, jarring that bushing within the frame pocket? That extra .97mm, on top of the nominal (.25mm?) clearance for ease of assembly, would not be good news.

 

[thescreensavers]

Originally Posted by eljefino
^ I like the science behind this-- it tickles my nerdy senses. But if that clamping force were all it took, a giant, appropriately torqued c-clamp around the subframe, holding the bushing in place with friction, would be all we need. But that's a recklessly goofy way to build a car. What if OP hit a curb, and a shock load went through the control arm and rubber, jarring that bushing within the frame pocket? That extra .97mm, on top of the nominal (.25mm?) clearance for ease of assembly, would not be good news.


Clamping force is what a bolt delivers when torqued. If the bolt loosens up then double shear is at play and yes in this regard the m12 is 11% less. minimum double shear load of 1/2 bolt loaded through the shank is about 34k lbs. So 30k lbs for the m12 which is more than adequate.

The load the bolt will see is dependent on the joint stiffness ratio, which means it's much less than the shock load received by the control arm.

No the bolt/bushings isn't moving around if torqued appropriately, once a bolt is torqued the load is carried by the bushings metal sleeve via friction and clamp load.

Long answer that the m12 is likely fine. OEM is the safe answer though.

 

[tookien]

Originally Posted by zzyzzx
How long do you intend to keep this vehicle?


It's an old vehicle. A 2003 rav4.

But I did lots of work to it and plan to drive it for at least another 10 years.
The entire suspension system is new, did quite a bit of restoration (given I'm here in rust belt) and did all the maintenance.

 

[tookien]

Originally Posted by thescreensavers
Originally Posted by eljefino
^ I like the science behind this-- it tickles my nerdy senses. But if that clamping force were all it took, a giant, appropriately torqued c-clamp around the subframe, holding the bushing in place with friction, would be all we need. But that's a recklessly goofy way to build a car. What if OP hit a curb, and a shock load went through the control arm and rubber, jarring that bushing within the frame pocket? That extra .97mm, on top of the nominal (.25mm?) clearance for ease of assembly, would not be good news.


Clamping force is what a bolt delivers when torqued. If the bolt loosens up then double shear is at play and yes in this regard the m12 is 11% less. minimum double shear load of 1/2 bolt loaded through the shank is about 34k lbs. So 30k lbs for the m12 which is more than adequate.

The load the bolt will see is dependent on the joint stiffness ratio, which means it's much less than the shock load received by the control arm.

No the bolt/bushings isn't moving around if torqued appropriately, once a bolt is torqued the load is carried by the bushings metal sleeve via friction and clamp load.

Long answer that the m12 is likely fine. OEM is the safe answer though.





Great explanation. Thank you.

 

[tookien]

Originally Posted by eljefino
.462/2 ^ 2 x pi = .1676 in^2.
.500/2 ^2 x pi = .1963 in^2.

You have 85% of the strength of the original bolt. (Not getting into how a metric 10.9 doesn't directly cross reference to an SAE 5 or 8.)

And as others say, you're hammering on an undersized fastener, and in three pages of this thread, failed to acknowledge the problem and are blowing off the people who are correctly telling you to just get the proper bolt.

And how are you going to "keep an eye on it"? Will you remove it annually and perform NDT tests on it?



Given that it's a front lower control arm, if that bolt loosens the first noticeable issue that will come up is torque steer which can also offset the alignment.

Lifting the front wheel up and just moving the wheel side to side will reveal play at the bolt.

But yeah it's better to just have the right bolt in the first place.

My concern was really whether this will come lose if torqued properly.

 

[tookien]

Originally Posted by thescreensavers
Originally Posted by tookien
Originally Posted by thescreensavers
What is the OE torque spec? What is the size and grade of the replacement bolt?



Can't remember exactly at the moment but around 70-80 foot pounds.

The original bolt was half an inch thick.

The replacement bolt is 0.462 inch thick and the grade is 10.9.


From what you said it would appear the replacement bolt is an M12(.472") . A class 10.9 corse thread can be torqued to 93ft/lb. If your OE torque spec is less than that then your fine and I wouldn't loose sleep over this.

Bolted joints resist shear by clamping and friction, the bolt to bushing spacing is not relevant as a gap always exists for installation. The .028" diameter difference is negligible in that regard. This would be different if we were discussing a shoulder bolt.

In this case at 75ft/lb ( if correct) applies 9000 lbs of clamp load (assuming a clean plain nut and bolt), which an m12 bolt is sufficiently capable of producing without breaking. (93 ft/lb is 11,000 lbs)




Thanks once more for the info.

 

[Mainia]

Originally Posted by SLO_Town
The biggest problem with using a smaller diameter bolt is that it does not fit precisely into the bore of the bushing and holes in the frame mounting points. Using a smaller diameter bolt may work for awhile, but eventually it was loosen and start elongating the frame mounting point holes. Then you're screwed.

Scott



I agree with this poster. My main concern is you have a higher risk of elongation of you subframe's mounting hole.
No worries on the size as far as safety as they are ALWAYS over engineered, as long as the bolt is grade 8. Whats the big deal on ordering the right one, $8?

 

[philipp10]

What is the original diameter verses the new diameter? Reducing a 1" bolt by .038" is different than reducing a 1/2" bolt by the same amount. But in general, get the correct bolt. If this is a critical bolted connection, I would not risk my life on it. .038" is quite a change.

If failure of the bolt is not dangerous, then I would not be so concerned, Depends upon application, but in general, a car is engineered for certain fastener sizes and should not be changed. I am quite surprised this is even being discussed.....

And yet there are people here worrying about 0w vs 5w....lol

 

[mattd]

The posts regarding the control arm bolt hole elongation is also a very high risk and concern.

 

[tookien]

Originally Posted by mattd
The posts regarding the control arm bolt hole elongation is also a very high risk and concern.



This is incorrect in this case.

The control arm isn't just swinging on the bolt. It's the bushing sleeve that when clamped down holds the control arm in place when torqued down.


The previous commentator is correct:

"No the bolt/bushings isn't moving around if torqued appropriately, once a bolt is torqued the load is carried by the bushings metal sleeve via friction and clamp load."

 

[tookien]

Originally Posted by Mainia
Originally Posted by SLO_Town
The biggest problem with using a smaller diameter bolt is that it does not fit precisely into the bore of the bushing and holes in the frame mounting points. Using a smaller diameter bolt may work for awhile, but eventually it was loosen and start elongating the frame mounting point holes. Then you're screwed.

Scott



I agree with this poster. My main concern is you have a higher risk of elongation of you subframe's mounting hole.
No worries on the size as far as safety as they are ALWAYS over engineered, as long as the bolt is grade 8. Whats the big deal on ordering the right one, $8?



OK, I'll let you know what I have to do to replace the bolt.

I have to take off the transmission pan.

Then cut out the welded hole in the subframe to access the nut.

Then remove the welded nut.

Then weld in the new nut.

Then weld the hole back.

Then prepare, prime and paint the surface.

Install the transmission pan.

Then refill the transmission fluid.



Not so easy for one bolt. This is rust belt.

People in the south just don't understand what it takes to get some trivial things done....It's a whole different ball game here.

 

[mattd]

Originally Posted by tookien
Originally Posted by mattd
The posts regarding the control arm bolt hole elongation is also a very high risk and concern.



This is incorrect in this case.

The control arm isn't just swinging on the bolt. It's the bushing sleeve that when clamped down holds the control arm in place when torqued down.


The previous commentator is correct:

"No the bolt/bushings isn't moving around if torqued appropriately, once a bolt is torqued the load is carried by the bushings metal sleeve via friction and clamp load."



If the bolt were to loosen up, yes that would be the case. That is what I was referring to. Obviously the bushing will not just "swing" on the bolt.