Okay from what I can tell some cars had bolt, some studs, some with locktabs etc.

What do I want to use or get hold of?
I'd like to just throw some long 3/8 inch bolts in there with spring washers, is that okay?

I had mine taped out and use grade 8 bolts and washers. Total pain in the bum to line up but great for strength while racing.

The stud type were 3/8" into the subframe and 5/16" thru the cross member. The cross member has a tube spot welded in as a guide and compression piece for the bolts. You might have to carefully run a 3/8" clearance drill[1/64 or 1/32 bigger] down the tube to help with the line up of 3/8" bolts. Also make sur the length is exactly right or the bolt end will bottom out on the subframe mounting plate for the cone or they will be too short and not get enough thread into the subframe.

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Thanks David, that explains why they were originally studs.
I think I'll have to have a closer look at things to work out what to do.

I think Hydro frames had 5/16 bolts, not studs and also had no spacer.

I think the studs were also stepped with 2 different diameters on them, probably to locate the subframe with the body.

I'll have a look at my spare front frame when I get home.

Andrew

I have a deluxe body with a dry suspension subframe.
I've never noticed little spacer tubes in the firewall before.
Wouldn't be hard to make.

The tubes are inside the cross member and you can not actually see the ends on the ouside of the cross member. Get a piece of wire and slide down thru the hole and you can feel them. Just make sure that they are still attached. I have found ones that have either rusted away or broke off. If you tighten the bolt up without a tube it will just crush the cross member.
The bore of the tube should take a 3/8" bolt but check on the aglinement to the subframe. During construction some of these tubes were not quite welded in the exact position. I have always wondered why they had a stepped stud

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
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The tubes are welded in the firewall/crossmember, as David said.

But if your going from a wet to a dry frame, you'll also need the flat spacers that sits on top of the frame (I think they are about 1/4" thick with 3 holes in them)

Andrew

I think someone mentioned using head bolts, i haven't actually had a close look but i guess it would be about the right length and thread. Just an idea