VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 39 Chevrolet rear shocks

Can anyone tell me what size bolts should go thru the Frame to hold shocks on,Has 7/16 x 20 x 3 3/4 long,Threads were stripped out not sure if they should be sae fine or coarse.
Do you think a Heli coil would work 21/32 long?

Is it a Master 85 (single acting shocks) or a Master Deluxe (double acting shocks)....?

It is a Master Deluxe, Sorry Gene I forgot There are two.

Gene will most likely correct me but I think the bolts should be unc but the other dimensions seem right. Fitted correctly Heli-coil should work fine as I have used them in some high stress situations that are still in service several years later. I know of 1 company that uses Heli-coil in the original manufacturing as it is less affected by corrosion and tension.
Tony

The shock mounting bolts on my '37 Master are 7/16 - UNC.

I agree with Tony that you could consider a Heli-coil repair. The primary limitation for using them is to make sure there is enough material around them to still support the load. You have to drill and tap larger than the original size to fit them. If the remaining casting wall is too thin it could split when you install the Heli-coil.

One other repair method to consider is to drill the hole out to 7/16". Then use a longer bolt and nut to secure the shock.

My Edit: I just looked at the front shocks on my '37. You cannot drill through. I was thinking it was a shock body with separate "ears" for the mounting bolts. Sorry for the confusion.

Thanks just ordered 7/16 x 14 Thread repair kit,I think P O had taped over coarse threads to put fine thread 7/16 bolt in,Thanks to All.

Sorry to chime in a little late, but 1939 double acting rear shock absorbers use 1/2" UNC bolt , and not the previously discussed 7/16 threads. I have a NOS set here, and checked them. The same size threads go back to 1930-31 delco shock absorbers.

Thanks Jack,It had 7/16 sae fine in it,Not surprised whole car has been a cobbled up mess,Will see if I can chase treads out to 1/2 ,Was going to use heli coils to replace threads .

Jack,Chased threads out with 1/2 x 13 tap , 1/2 bolt went right in feels real tight,Will go get proper length now.
Don't know how shocks were staying on frame,That explains why holes in frame were so large,And was making so much noise,Shock feel real good as far resistance.

If the shock is bolted through the frame rail there must be something inside of the frame riail to prevent it from collasping.

Glad you got it sorted Robert.

Gene, Yes there is Jack put it back together no knocking or banging, Drove it around Mile section rough dirt gravel road 1/2 way around.