Rear spring outer bolts/castle nut

[Michael F.]

Re: Rear spring outer bolts/castle nut

Joe, you should write a book from all your notes and experience over the years for the rest of us.

[Ronald L.]

Re: Rear spring outer bolts/castle nut

I managed to sift through a box of over 40 used bolts...

Half were C head marks with most being heavy zinc coating, that 400 hour stuff, I don't recall the spec off hand.

Down in quantitiy from there were Z head marks.


Of the black C head mark, there was one real interesting, the threads were more like 10/11 versus 13 and it matched a couple others, ones that looked real old had a RBC and P head marks, and all had only 10/11 threads.

[Alan D.]

Re: Rear spring outer bolts/castle nut

Later service replacements, pn 351592, still hold the 6 5/16 length.
The head has a two digit number in center and "Rockford" on outside.
The "585" was still available in 1973 since my records show me purchasing many of them under that number @ $1.15 each.

[John H.]

Re: Rear spring outer bolts/castle nut

I bought several pair about 15 years ago that I still have - necked-down shanks, 14 threads, Grade 8 (six radial lines), "C" headmarks, black phosphate; photos below.

[Joe L.]

Re: Rear spring outer bolts/castle nut

I bought several pair about 15 years ago that I still have - necked-down shanks, 14 threads, Grade 8 (six radial lines), "C" headmarks, black phosphate; photos below.

John-----


I'm going to have to go and dig out some of my GM #458982 bolts. I could just about swear that every one I've seen and every one I have are 5 lines (GM 290M) as opposed to 6 lines (GM 300M). Obviously, though, based upon the ones you have, there were at least some made that are 300M.

By the way, I've always figured that there was some good reason that GM used 290M material for these bolts. I just don't see it being a cost sort of thing. GM-290M bolts are so unusual I would think that it would cost more to have the bolts made from that material than the far more common material used for 300M (SAE grade 8). Plus, for suspension bolts GM most commonly used 300M bolts. So, why vary that for these bolts?

My guess has always been that there was some property of GM 290M material that the design engineers felt was important for these, particular, bolts.

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Joe, yes I am going back too, to see if I over looked this difference in some of these.

[Alan D.]

Re: Rear spring outer bolts/castle nut

All 4 of the new (592), still in GM package, are 5 marks (grade 7)
The bolts on the car are also 5 marks with head markings of SBC, however these are service replacements (unable to find receipt on them so far)

The threaded area on the (592) measures 49/64 from end of bolt to sholder start, ie does not include shoulder. If one measures to top of shoulder its 15/16

[Wayne M.]

Re: Rear spring outer bolts/castle nut

Later service replacements, pn 351592, still hold the 6 5/16 length.
The head has a two digit number in center and "Rockford" on outside.
The "585" was still available in 1973 since my records show me purchasing many of them under that number @ $1.15 each.

Like this ? So I guess the center number "92" is not the year of production. From a box of suspension bolts I got off eBay.

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Wayne, I bet that is the one, what are the other dimensions, and then... is this even safe to use?

[Alan D.]

Re: Rear spring outer bolts/castle nut

YES, Wayne - that's the 592 bolt, all mine look the same.
Also my receipts show I was purchasing the 585 still in 1973.

[Joe L.]

Re: Rear spring outer bolts/castle nut

Like this ? So I guess the center number "92" is not the year of production. From a box of suspension bolts I got off eBay.

Wayne-----


There was a definite purpose behind having the last 2 digits of the part number on these particular bolts. That's because there were 3 other bolts in this series that were used selectively to adjust rear bumper height for the 1975-76 models that these bolts were original used on. Those bolts were GM #351191, 351193, and 351594. Also used were GM #6271686 and, of course, 351192.

The 351191, 351193 and 351194 were never available in SERVICE, though.

[Joe L.]

Re: Rear spring outer bolts/castle nut

YES, Wayne - that's the 592 bolt, all mine look the same.
Also my receipts show I was purchasing the 585 still in 1973.

Alan-----


The GM #3831585 was discontinued in December, 1974.

[Wayne M.]

Re: Rear spring outer bolts/castle nut

Wayne, I bet that is the one, what are the other dimensions, and then...

Here's the other end of the Rockwell; again, from nut screwed on finger tight to collar edge, then back off 10_1/4 turns to removal. Overall shaft length is 6_5/16".

[Ronald L.]

Re: Rear spring outer bolts/castle nut

I went back and looked at what was in this box...

11 C headmark with 6 bars, black, 6 3/8 long
13 C headmark 5 bars zinc 6 5/16
14 C headmark 5 bars black 6 5/16 but three were longer 6 3/8
9 Z headmark 5 bars more like 6 1/4

Then the good stuff:
2 Rockford 92's 13 threads and 6 5/16

2 P headmark 11 threads 6 5/16

3 really old SBC headmark 5 bars 11 threads.

More that I think about this, I am pretty sure I had P in the car 30 years ago but these I'd be concerned about with wear and corrosion on the bolt shank.

And that newer black coating was not black phos, it was a much heavier coating that took lots of effort to scrub off and verify head marks.

[Russ S.]

Re: Rear spring outer bolts/castle nut

Ron -- 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.

Another thing -- when I screw the castle nut to finger tight against the collar, then back off until nut comes free, it takes 11_1/2 turns. Also, I'd say these are zinc or cad plated; the finish is well protected against the elements by the rubber cushions.

That size must be a misprint. It should be 9/16-18-1 1/2"