Ridetech first gen rear cradle fitment solutions

[streetk14]

Just wanted to see if any others have run into this and what your solution was. We’re working on getting the ridetech 4 link rear cradle fitted to my 68 Firebird. We had a few hurdles to overcome, but it’s mostly there. Still dealing with some floor pan interference that’s preventing the tabs to mount totally flush on the frame rails, but I don’t think that’ll be a huge deal to resolve.

The bigger issue is that I have close to a 1/4” gap between the frame rails and cradle on the sides; meaning the cradle can shift left to right and isn’t a tight fit between the rails as it should be. We did a bunch of measuring, and decided to center the cradle, which leaves us with gaps on both sides. The thought was to fab up some 3/16” or 1/4” plate to use as shims.

I was suspecting I’d run into something like this. The car is really original and hasn’t had any floor pan or rail work done. It still has all the factory undercoating back there. These cars clearly weren’t built to today’s standards, so I’m not blaming ridetech on this.



Ideas?

[srode]

Not uncommon - yes shimming is the way to deal with it.

[dhutton]

Most guys have to take a BFH to the floor to get it to sit flush on the frame rail.

Don

[Dwdrummr1]

Im currently experiencing the exact same thing on my '68 Firebird. As far as shimming it, does that mean welding strips of metal in before installing rivnuts? Was really hoping to avoid welding...because I can't. I was going to have someone stitch weld a bit after full install.

[srode]

welding would be best but you after you have them fit and marked for location you could take the ridetech frame somewhere and have someone weld it the shims to that and have it stitch welded to frame rails after you have it installed.

[streetk14]

Im currently experiencing the exact same thing on my '68 Firebird. As far as shimming it, does that mean welding strips of metal in before installing rivnuts? Was really hoping to avoid welding...because I can't. I was going to have someone stitch weld a bit after full install.

We were looking to fab up some 3/16” steel plate pieces that could just be wedged between the frame rail and cradle before bolting it in.

The issue here is that the riv-nuts do stick out some. Unless I’m doing something wrong with the supplied install tool, they create a gap that prevents the cradle from sitting totally flat on the rails. That also means that any plates we make would need larger holes so they can clear the riv-nuts and sit totally flat on the frame rail. That seems like the best solution to me, since I really don’t like the cradle pulled up against the riv-nuts with a gap between the cradle plate and frame rail.

[Josh@Ridetech]

Most guys have to take a BFH to the floor to get it to sit flush on the frame rail.

Don

Shims will work, however, most of the time it is the front floor area that Don is mentioning here.

Some cars are a little more forigiving than others and don't take as much work, some need that BFH. All you're shooting for is to get the cradle pushed all the way forward up against that pan area and the rest of the cradle should sit flush on the frame rail areas.

On the sides of the frame rail, you can definitely add some shims to help with that inside-inside frame variance. These frames were all over the place as you mentioned!

[streetk14]

So here’s the riv-nut situation I mentioned. The cradle is sitting tight to the heads, creating a gap between the plate and rail. I just don’t see how it could sit flatter.

[Pro Touring Store]

I have also had shims made before. Thinking I should make it a product lol.
On one of the last vehicles I did, before riv nuts.. I got it mostly into place using the self tappers, and slid shims in (yep like a body shim) and tacked to the body. I slightly tightened the cradle, and used a jack to get it as close as I could.. Then welded it in. Ended up doing only 1 shim on one side, 2 on the other... but everything ended up pretty square. Like the rails were off in height side to side.

You should be able to find a local cnc plasma shop and give them a cardboard template or something and have them cut some out for you.. 1/8 steel is what I had done.
Hope that helps a little, good luck

-Dale

[Josh@Ridetech]

That looks good to me, you will have a tiny gap due to the head of the riv-nut. You could make a shim as Dale mentioned above too just to alleviate that gap though too, no worries at all!

[Dwdrummr1]

StreetK14, how do you think you might address the side to side shim situation?
I am guessing you have already put the rivnuts into the frame, so you could just slide some shims in and stitch weld to the frame and cradle to ensure they don't move. You may need a longer bolt on the inside of the cradle to ensure you have enough thread engagement. This may be the route I take, unless I am feeling ambitious and follow srode's suggestion of having someone weld some shims to the cradle before install. But ultimately, as long as the shims are in there and secured so they don't find a way of vibrating out then it will be fine.

[CSG]

I don't like that rivnut situation. With that setup all the force is applied to the bolts instead of the friction between the two "plates" being forced together. It may work but I would try a shim with an oversized hole for the rivnut to sit inside.

[Dwdrummr1]

With the situation shown in the pic above, if it is truly just the rivnut keep the cradle from seating you could just use a unibit or grinder on the backside of the cradle to slightly open up the hole in the cradle.

[streetk14]

I’ve thought about both of those options. I would feel better about a solid contact of the cradle flange and frame rail vs it sitting on the inserts. Adding a countersunk hole on the cradle or an 1/8” plate between the frame and rail would both work.

For the sides, I’ll need some type of shim or spacer. Anyone have thoughts on just doing a 1” x 1” square piece of plate between the frame and cradle (with a large enough hole for the rivnut head to fit inside) at each rivnut location? A solid plate matching the contour of the cradle would be ideal, but more work for sure.

[Josh@Ridetech]

I don't like that rivnut situation. With that setup all the force is applied to the bolts instead of the friction between the two "plates" being forced together. It may work but I would try a shim with an oversized hole for the rivnut to sit inside.

This was also an option that we talked about over the phone. We have done a ton of testing over the last few years with these with good results, however, we're always doing our best to make things better. I'll do some talking on my side and see if there is an option for us to add something like this shim in the future as part of the kit.

Thanks,
Josh

[streetk14]

This was also an option that we talked about over the phone. We have done a ton of testing over the last few years with these with good results, however, we're always doing our best to make things better. I'll do some talking on my side and see if there is an option for us to add something like this shim in the future as part of the kit.

Thanks,
Josh

I appreciate the help, Josh. I have no doubt this has been tested on cars that get driven harder than mine ever will.

Some shims that match the contour of the cradle would be a nice addition to the kit, but I have no idea how much these things vary. I think we’re going to do some 1/8” plate between the underside of the rails and the cradle to take up the gap seen in my picture from earlier. If nothing else, it’ll make me feel better about the install.

[streetk14]

A little update on this. Maybe it’ll help someone else with their install.

I ended up having some shims made that matched the mounting flange on the cradle. 1/8” per side gave it a nice, snug fit between the frame rails. It’s really never going to be perfect, as (at least on my car) the rails aren’t perfectly flat. It’s pretty good though, and I’m happy with it.

2nd thing to mention is the riv nuts and tool supplied with the kit. I found the supplied tool was responsible for creating that tall cone shape seen in my photos earlier. That’s what created the gap I didn’t like. I have a riv nut tool, but didn’t have a 3/8” mandrel for it. I ended up buying one, and the riv nuts came out much flatter. I ended up drilling out all the originally installed riv nuts and replaced them.

Since I needed more riv nuts (ridetech doesn’t give you any extras), I got some with a thinner head that really allow the cradle to sit flat under the frame rails. Maybe not as strong, but I’m ultimately not concerned about the riv nuts pushing into the frame; I’m much more concerned about them pulling out. Anyway, this really got rid of any need for countersink drilling the cradle or anything else.

[Panoz78]

I know I’m a bit late to this post but here’s a suggestion.
In Australia there’s no way we would pass a registration process using Rivnuts,
what we would have to do is drill out the bolt location hole and insert a 1/2 or larger rod/ tube all the way through the frame rail and the weld it into place .
With a hole big enough for the bolt and nut on the other side .
Or thread the rod /tube to take the bolt and have a couple of threads out the other side .
The rod stops the frame rail From squashing and helps spread the load to both sides not just one side like a rivnut . And also would sit flush with the frame rail once ground down .
And make it easier to shim then pull tight

[streetk14]

The riv nuts are actually really tough. I can’t remember all the numbers from the chart I saw, but it’s a lot of tensile strength. If the cradle is snug between the rails, it isn’t going anywhere. I feel like the riv nut attachment to the sides and bottom of the rails is somewhat of a compromise, but the cradle has bolt locations at the front and rear that go through heavy sheetmetal and bolt into reinforcement plates.

I know ridetech has been thrashing on these things for a long time on some fast cars. I know if it can take that kind of abuse, my car will be more than fine. For a bolt on kit, it’s pretty good. I like the frame rail idea, but I probably would have just gone with a Quadralink if I wanted to do a bunch of welding/fabrication.