Purpose of serrated A-arm washer.

[Steve L.]

What's the purpose of the serrated washer on the Lower A-arm mounting bolt. The one at the rear with the big 9/16 bolt.

Looks like the serrated side should be facing the frame and not the nut since the nut is a smaller diameter than the serrated surface.

The serrated surface can't be used for retaining the nut torque.

[John H.]

Re: Purpose of serrated A-arm washer.

What's the purpose of the serrated washer on the Lower A-arm mounting bolt. The one at the rear with the big 9/16 bolt.

Looks like the serrated side should be facing the frame and not the nut since the nut is a smaller diameter than the serrated surface.

The serrated surface can't be used for retaining the nut torque.

Steve -

Don't know about C3's, but on midyears, that serrated washer goes at the top, under the bolt head, not at the bottom under the prevailing-torque nut.

[Alan S.]

Re: Purpose of serrated A-arm washer.

Hi Steve,
As usual I'm referring to the notes from my 71. As John stated, I too listed a serrated washer under the head of the bolt not under the nut.
The washer is similar to the serrated washers used for some bolts on the bumper brace assemblies, but smaller in diameter.
Regards,
Alan

[Steve L.]

Re: Purpose of serrated A-arm washer.

opps, sorry, I should have said serrated washer under the head. This is the way I assembled it.

My question remains, what is the purpose of the serrations? The bolt is fairly tight in the hole so it can't move around much, if anything. the serration diameters on my original washers are larger than the bolt head so I assumed the serrations are against the frame.

[John H.]

Re: Purpose of serrated A-arm washer.

To keep the bolt and washer from rotating, thus loosening the nut on the other end? Keep in mind that the bolt 'clamps' the inner metal sleeve to the frame. The a-arm rotates by torsioning the rubber. There's fairly high torsion forces being transmitted to the frame, that relies on that bolt staying tight.

As an aside, you did wait to final torque the a-arm bushing bolts after the car was on the ground, and the suspension loaded at normal ride-height, correct?

Dave -

Steve's talking about the big bolt that attaches the rear of the lower control arm shaft to the frame, not the bushing bolt in the end of the shaft.

[John H.]

Re: Purpose of serrated A-arm washer.

opps, sorry, I should have said serrated washer under the head. This is the way I assembled it.

My question remains, what is the purpose of the serrations? The bolt is fairly tight in the hole so it can't move around much, if anything. the serration diameters on my original washers are larger than the bolt head so I assumed the serrations are against the frame.

Steve -

In the 60's, there were lots of varying philosophies among fastener engineers about how to maintain clamping force in joints; I worked with many of them - some preferred split lockwashers, some liked hardened serrated external-tooth washers, others liked prevailing-torque locknuts, some liked Marsden nuts, etc. You'll see examples of many different approaches, depending on the inclination of the releasing engineer and the fastener engineer he consulted with.