Subframe bolt question - need opinions quick

[Nate047]

Hey guys, trying to put my rear end back in the car today. I have a rear 6-point brace which included its own hardware. I’m trying to decide if I use these or if I reuse the old bolts. Reason being the spacer provided for the new hardware is thicker than the “spacer” built into the front subframe mounting bolts. Makes me wonder if the subframe will sit properly or not. I’m using CMP subframe mounts. Take a look at the pictures and I think you’ll see the size difference.

[bigjae46]

I think you'll be OK.

Is this a bolt through design on the front and rear? If so, I'd upgrade to a 1/2"-20 grade 8 bolt or a slightly bigger Class 12.9 bolt. Get rid of the aluminum spacer. Drill through the floor, use a large fender washers. I drilled the hole to fit the bolt precisely (make sure you drill straight - I used two old subframe bushings. I minimized the length of the bolt that is threaded - I had to drive the bolts through the floor. I torqued my bolts to 120 ft/lbs (takes two people or some really created ways to brace the breaker bar on the top...long story...haha. Overkill? Maybe but ain't nothing moving. Will it be a nightmare to remove? Absolutely!

[bmwfnatic]

Well you can't use the original "stud" because it would simply not be long enough and not work with your brace.

But I understand your concern, this would not be a problem with rubber bushings that can take up the slight change in subframe angle, but with the solids this is perhaps not ideal, I say perhaps because we don't know if the original hardware even makes the subframe exactly sit exactly level.
Personally I would measure the hex shape on the original stud, and then grind down the new spacer on a belt grinder to match that measurement.

[bigjae46]

Well you can't use the original "stud" because it would simply not be long enough and not work with your brace.

But I understand your concern, this would not be a problem with rubber bushings that can take up the slight change in subframe angle, but with the solids this is perhaps not ideal, I say perhaps because we don't know if the original hardware even makes the subframe exactly sit exactly level.
Personally I would measure the hex shape on the original stud, and then grind down the new spacer on a belt grinder to match that measurement.

Wouldn't the CVs in the driveshaft and axles account for any minor height changes? But...you'd also need to account for the thickness of the reinforcement plates. IIRC, I ended up using a grade 8 fender washer which was about the same thickness as the steel plate and the spacer on the OE stud.

[discoelk]

Use the OE. The subframe "bushings" look like the PBM ones that are designed to "clamp" the subframe to the trunk floor. Using the other ones will clamp the subframe to the bushing and it will not sit flush to the unibody.

Edit. bmwfnatic is on the right track. You can order spacers from McMaster-Carr that typically arrive in a day or two if you're in a rush and don't want to grind your existing spacers.

[Nate047]

Thanks guys. I went with the stock bolts. The difference just wasn’t comfortable for me.

As far as how to mount the brace still, there is a solution. You basically take some stock bolts, cut off the threaded ends, and use those as studs and thread them in from above. There is enough thread to get a good, solid connection.

No pics but the rear end is back in the car!