Notching Rear Subframe

[ShutterSpeed]

Back in May I broke my stock axles at the inner CV joint. The cradle snap and all the ball bearings fell out. Well instead of replacing it with a stock unit, i upgraded to the Driveshaft Shop Stage 2 axles. Rated for 650hp i figured they would be more than capable on my stock motor FRS.

Fast forward about 6 months. I'd just arrived in Houston for Wekfest Texas 2014 when i begin to hear the all too familiar axle clicking sound. After quick inspection i notice the two inner cv boots are ripped and all the grease has been flung out of them. My diagnosis is that the joints aren't lubricated enough so i pack in some grease for the long drive back to Louisiana.

Get it home and bring it over to my fabricator, Justin Rosen, at EFI Services in Harahan, LA. I figured while I was over there i would have him install the Powered By Max rear subframe risers and differential risers to help alleviate the angle the axles sit at after lowering the frs.

***Note If you plan on removing the rear subframe bushing to install these solid mounts, I'd suggest skipping the air chisel all together and breaking out the oxygen torch and burning them out. Granted the smell is toxic and bad for you, it worked 10 fold better than any other method.

We begin the teardown on the car and notice that this time it is the outboard CV joint on the DSS axle that is frozen solid. So I'd have to send it back to have them replace or warranty the part, luckily it was warrantied. They aren't cheap.

After installing the risers we noticed that the DSS axles would now hit the subframe right as they were exiting the diff. So out came the grinder and cutter. Justin originally thought that we could notch out a small chunk of the subframe but we later realized that we would have to take out a large portion of it and then weld in new 1/4" plating to reinforce it.

The DSS axle just came back from being serviced and the car should be back tomorrow, when I hope to update this post with how the axles sit now after the risers and notching. Enjoy the crazy, anxious process i went through to keep all the upgraded parts.

Ripped Inner CV Boot


Subframe Dropped


Torching Stock Bushings Out


Clean Bushing Hole


Diff Dropped Out


Welding In PBM Solid Diff Mounts


Raw Finished Result


Front Diff Risers Installed


Notching Process Begins with some Grinding


Initial Subframe Notches


More Grinding


The New Size of the Hole


Sanding to Bare Metal


Ready for Filler Plates


Mocking Up Floor Plate


Floor Plate TIG'd In


After the Sides were Welded In


Comparison


Both Welded In


Notch Back on the Car


PBM Solid Diff Mounts Installed on the Car


Waiting to pick the car up from the shop tomorrow and then I will post pictures of how well the axles sit after being raised and a review on the NVH of the whole setup.


Picture for Reference

[puma]

nice, thanks for sharing, i installed the same bushings (or lack of bushings) but didn't need to notch the subframe as our axles are stock.

Have you had a problem with the driveshaft? we installed an aluminum driveshaft at the same time and it was too big, it would hit the transmission tunnel and fuel tank, had to lower the diff a little.

[ShutterSpeed]

The driveshaft sits about a half inch away from everything. It'll be interesting to see what happens. Haven't driven the car yet.

[ShutterSpeed]

Driving Impressions:

Car feels solid. The power feels like it is making to the ground much better now with the solid rear end. The noise and vibration is much less than i thought it would be. There is a whine from the solid diff mounts during acceleration, most notable in higher gears 4-6, but is noticeable in lower gears. The exhaust is just louder than the whine.

Overall i am very happy with the risers and notched subframe. Was definitely worth going the extra mile to do it right. The clearance of the driveshaft and the tunnel is very minimal so i do not believe that a one piece driveshaft from DSS will be possible.

[Calum]

I'm surprised they didn't use any gussets where the frame was notched.

[Thorpedo]

Agreed with Calum. While it might not make any difference whatsoever, they severely weakened that in a few ways. Not bashing their work, I hope for your sake there aren't stresses that will make it matter. Keep us updated and TBH I would check it fairly often for deformation/cracking.

Beautiful car BTW.

[Alpha_noob]

This thread is exactly what I needed! Is it possible to just install the subframe risers without the welded solid mount diff mounts?

[ZDan]

You've reduced the stiffness of the subframe *tremendously* in that area. On the order of -75% or more. It's worse than that really as the welded plate lines up with voids on either side so no direct load path into the intact front and rear structure. A lot of work for what looks to me to be serious reduction in stiffness and structural integrity. For what? I don't get it...

[TylerLieberman]

Originally Posted by ZDan

You've reduced the stiffness of the subframe *tremendously* in that area. On the order of -75% or more. It's worse than that really as the welded plate lines up with voids on either side so no direct load path into the intact front and rear structure. A lot of work for what looks to me to be serious reduction in stiffness and structural integrity. For what? I don't get it...

Well luckily this was 6yrs ago and the car never exploded, so you don’t need to lose any sleep worrying over it.

[dragoontwo]

Originally Posted by ZDan

You've reduced the stiffness of the subframe *tremendously* in that area. On the order of -75% or more. It's worse than that really as the welded plate lines up with voids on either side so no direct load path into the intact front and rear structure. A lot of work for what looks to me to be serious reduction in stiffness and structural integrity. For what? I don't get it...

Dat stance lyfe, yo!

[TylerLieberman]

Originally Posted by Alpha_noob

This thread is exactly what I needed! Is it possible to just install the subframe risers without the welded solid mount diff mounts?

Yes, a few people have done it. Though most of the axle angle correction (if that’s what you’re after) will be gained from the diff risers.

[ZDan]

Originally Posted by TylerLieberman

Well luckily this was 6yrs ago and the car never exploded, so you don’t need to lose any sleep worrying over it.

Missed the thread necro...
Still IMO a not great idea extremely poorly executed as far as the basic design. Likely mitigated by more stiffly-mounted front and rear of subframe. But still...
*If* i were to notch the frame there, I'd go with a curved upper plate to of 2x the wall thickness or greater. So front and rear of curved upper meet up with the structures fore and aft.

[Scalzo]

I just went through the same damn process
Wish I would of seen this sooner