Rear spring correct oem bolt length ?

[Jim R.]

Anyone have a drawing of the correct rear outer spring bolt length for the mid year standard suspension, or under side of bolt head to cotter key hole. (trailing arm to spring)

[Alan D.]

Re: Rear spring correct oem bolt length ?

Here is some past history on the subject (unable to find link)

Joe Lucia 3/27/11


I believe the original bolts were black phosphate-finished. However, I have seen some bolts that I believed to be original that were dull zinc plated. I have also seen some that were natural steel. The latter seemed to have had machined shanks.

The "cups" (outer retainers) were natural steel. The "washers" (inner retainers) were natural steel. The "castle nut" (actually, a SLOTTED nut; GM rarely used castle nuts) was "plain" finish (sort of a "brownish", as-manufactured finish). Cotter pin was natural steel.

All of the bolts ever used by GM in PRODUCTION or available from them in SERVICE were GM 290M material grade with FIVE radial lines.


Wayne Midkiff 3/27/11

both bolts are 6_3/8", measured from just under the hex head to the tip. This agrees with P&A30 Rev July 30 1965, Gr 7.506: # 3831585, 1/2"-20 6_3/8.

Same Oct '65 P&A30; Same Oct '66 P&A30; Same Oct '67 P&A30.

But then, by my 7-1-69 P&A30B, the description changes [part # remains 3831585] but size goes to 9/10"-18 --6 1/2", and remains so thru 10-1-69 P&A30 and 1-1-70 of P&A30B. To me, this bolt size doesn't make sense.

[John H.]

Re: Rear spring correct oem bolt length ?

Jim -

I have several sets of older GM replacements; they measure 6-5/16" from the underside of the head to the end of the bolt, and 6-3/32" from the underside of the head to the centerline of the cotter pin hole. The threaded portion is 9/16"-18, and they have Grade 8 markings (six lines).


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