Sombrero bolts

[Ed S.]

Can anyone provide a description (or a picture) of the bolt that secures the cross member - through the sombrero to the frame on a 1964?

By description I mean head mark and finish.

AIM says the part # is 454933. Cannot find a description or a picture of it anywhere. The Judging Guide does not give a description or it or discuss it.

Paragon shows it with a zinc finish and "WB" on the head
LIC shows it as being a grade 5 bolt, black ph with an "O" on the head.

The one's I removed from my car were painted black by a previous owner and have an "M" on the head.

Thanks

[Edward J.]

Re: Sombrero bolts

Ed, that is the correct head mark (M) grade 8, hex head, thick flat lock washer, black phosphate, about one inch long. maybe slightly longer.

[Ed S.]

Re: Sombrero bolts

Ed,
Thank you. You saved my sanity.

Ed

[David B.]

Re: Sombrero bolts

GM #454933 plain 7/16 - 14 x 1 1/8 long

[Wayne M.]

Re: Sombrero bolts

One other point -- Tech Service Bulletin Nov 29 1965, on subject of rear X-member suspension mount bolts. The torque in the AIM is too low (20-30 ft.lbs), resulting in loosening in '63, '64 and early '65s. Revised torque is 50-65 ft.lbs.

[Ed S.]

Re: Sombrero bolts

One other point -- Tech Service Bulletin Nov 29 1965, on subject of rear X-member suspension mount bolts. The torque in the AIM is too low (20-30 ft.lbs), resulting in loosening in '63, '64 and early '65s. Revised torque is 50-65 ft.lbs.

Wayne - thanks for bringing this important torque spec to my and other's attention. FYI, I checked my '64 AIM, Sect 4, Sheet B3.00, torque value for the bolts that secure the cross member (through the sombrero cushions) to the frame is 55-65 LBS. FT. I wonder if the AIM the Service Bulletin is an earlier version.

[Duke W.]

Re: Sombrero bolts

That revised torque spec concerns me because I don't think the weld nut is hardened. I recall on my SWC the nut felt like it might be striping so I only when to the value in the AIM.

Duke

[Ed S.]

Re: Sombrero bolts

Wayne's & Duke's comments have my attention and concern. I am a bit confused, not by what either of you said but.... the date of the Service Bulletin re the revised torque values is Nov, 29, 1965, yet I have an AIM for a 64 Corvette - I am assuming that this document existed before the date of the SB, yet the torque value in my AIM is 55-65. Did GM go back and update obsolete AIMs. Would they have updated a 64 AIM in late 65 when the guys on the assembly line are no longer using that version of the AIM?

Question to others that have replaced cross beam cushions - did you follow the AIM torque values and if yes, did anyone experience thread damage? I don't have my shop manual handy, will check to see what it recommends for torque values later and will post what I find. This is worth discussing further.

[Duke W.]

Re: Sombrero bolts

The short answer is no... a change made for '65 production would not be reflected in the '64 AIM.

This issue has been bugging me for 40 years. The '63 AIM, 4/5.00, shows a change to 55-75 lb-ft dated April 23, and the change records shows that the previous spec was 20-30. I could not find a spec in the '63 shop manual, and thee AIM does not show a frame or bolt (454933) part number change change.

So it appears that the change was only an increase in the torque value, but weld nuts are typically not hardened because the process of welding them can also anneal making the material weaker, which is why I question the higher torque value.

It could be that the service bulletin was not written until '65 as a precaution for the early to mid-production '63s that were torqued at the plant to 20-30.

When you think about it the axle and rear suspension are held on by only five bolts - the two for the axle cross member, the front carrier bracket, and the two trailing arm bolts. Normally, vehicle weight alone should hold the axle cross member to the frame, but what if the car gets airborne?

If anyone has the TSB, please scan and post it, and I'd also like to hear if anyone has ever stripped the sombrero weldnut.

Duke

[Wayne M.]

Re: Sombrero bolts

Another source for rear X-member bolt torque revision (quote from Chev Service News, Sept-Oct 1965.) I should also mention that this was the timeframe when the sombreros were modified to add more attaching tabs. My early '65 still had the old version. My '65 AIM shows 20-30 ft.lbs.

"1963-1964--1965 AND 1966 CORVETTE
All service operations of the rear suspension should include retorqueing the crossmember attaching bolt to 65 ft. lbs."

Here's some more: TSB reprinted in Vette Vues:











c

[Bob B.]

Re: Sombrero bolts

Ed, A lot of repro bolts come zinc that were originally black phosphate or the dark, heat-treated steel. Black oxide is a good way to go on the zinc ones. - Bob

[David B.]

Re: Sombrero bolts

Repeat Thread: GM Standard parts list bolt #454933 as: Plain 7/16 - 14 x 1 1/8 long
By GM definition Plain means: "clean (free of dirt, rust,die or drawing compounds) coated with a light oil film."

[Ed S.]

Re: Sombrero bolts

The TB says "the torque spec of 20-30 ft. lbs. in the 1964 and 1965 Corvette Shop Manual Supplement and the 1966 Chassis Service Manual are incorrect.

So.... the AIM always had the correct torque values, it was the shop manual that was wrong. Discussion up to this point has been suggesting that the AIM had the torque values wrong.