Reinforced IRS sub-frame

[SlowSVT]

I finished reinforcing my IRS sub-frame and I thought I would share what I did. Some of this stuff I would not recommend but there are a few that I think should be considered by anyone who is looking to improve the stiffness on some of the suspension pivot point. All the gussets are .090 thk chromoly steel (4130).

Note the large ears on either side of the sub-frame. Those are pick-up points to attach to the upper control arm brackets used on the SRA. This mod triangulates the mounting points which will stiffen the entire backhalf of the chassis.

The 4 bushing tubes are wrapped with a curved metal finger extended up from the support arms to provide a better support for the bushings.
In this shot you can also see the staggered bolts holes for the new mounting point (there is a bracket that slides in after the sub-frame is installed where a bolt goes thru both ears on the sub-frame and UCA mount).

Any gaps in the welding from the factory were filled in. 100% seam welded. Funny thing is after it was all welded you could tap it with a hammer and it sounded like a tuning fork

The upper and lower control arm pivot ears were reinforced. The rear lower in particular had a huge gap on 2 of the 3 sides where the lower front-to-rear tube meets the frame. I made a thin "L" bracket and welded it filling the entire gap. This is an area as well as other I think any Cobra could benefit from.

Here are photos of some of the patterns I made used to fabricate the gussets. I should have taken detail shots before it was powder coated because it hides just about everything.

I will post more detail shots of areas that should maximize the structure where I think it is needed for the most benefit for the least amount of work for anyone who would be interested in beefing-up what they have.

 

[raym5_0]

nice work as always in your projects...:thumbsup:

 

[03 TOPLESSSVT]

Looks awesome no doubt!

 

[gabe1530]

awesome work!

 

[2k2leenin]

Awesome mod. Sub'd for more info... Keep it coming

 

[SlowSVT]

Thanks guys

I'm eager to get the rear suspension complete so I can get the car back on all 4's so I can get the chassis painted. The mod list on this assembly alone is frightening!

I even managed to get the diff in there after all said and done :burnout: It's a tight squeeze :nonono:

 

[SlowSVT]

OK I took a few pics of some of the more critical points I think are worthy of any IRS should any of you consider stiffening up your sub-frame.

These first 2 pics are a "Biggie". That little triangular metal gusset welded between the rear LCA bushing and the "L" strip (2nd photo) at the base of that same bracket will do wonders to stiffen both the pivot ears and the lower front to back sub-frame tube.

The "L" strip is a little hard to see. It's the goobly guck just above the toe link bar mounting hole. That use to be a big friggen gap! :fm: There are other gusset in this photo but they are hard to point out.

Here is the front LCA reinforcement gusset. Note the mounting hole for the pivot bolt in the lower LH of the photo. These mounting ears were unsupported where I filled in the gap by boxing it in with the folded triangle.

(keep in mind these ears have to endure the cornering, acceleration and breaking forces. Any reduction in movement will allow the suspension to hold it's setting more accurately which is the whole reason for this exercise)

Here is one of the sub-frame mounting points. You can see where the tube was wrapped to provide support around the circumference of the mount. Small strips were added to both sides to extend the support out to the ends.

Here is a view of the front diff mounting ears. I added a strip connecting it the main frame tube reinforcing the end of the mounting bracket

These are areas I would recommend reinforcing. The other stuff on my sub-frame are a lot more involved and may not provide much benefit unless you address other areas downstream of the chassis.

These are all photos from the bottom of the IRS. I'll take some from the top side after I turn the thing over.

 

[03' White Snake]

Very nice work. I need to learn how to weld.

 

[nxs450]

Nice work! What are the blue slotted washers in the last pic?

 

[SlowSVT]

Nice work! What are the blue slotted washers in the last pic?

IRS differential mounts, aluminum, pinion angle adjustable, 1999-04 Cobra [MMIRSB-40.1] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

 

[CobraBob]

I give you a lot of credit for that great workmanship. That setup is about as stout as you can get. :rockon:

 

[03cobra#694]

:coolman:

 

[gabe1530]

how much for you to do mine?

 

[SlowSVT]

how much for you to do mine?

I'm still trying to get over the trauma of building the first one! LOL

Did I tell you how much I hate chassis work :cuss: Yet for every hour I do engine work I do 10 hours of chassis work :nonono: I have learned it's best to bring the rest of the car up to the level of the engine.

Here is the mod list for the rear suspension. Feel free to comment on anything I have done here. Sometimes I overlook things and it nice to have a Peer Review .

Reinforced IRS sub-frame with 6 point mounting
FTBR Delrin sub-frame bushings
Reinforced front diff mounting ears
FRP diff cover with added cooling fins and internal reinforcements
Magnetic drain plug
220 degree snap switch for diff cooler
Torsen T2-R torque biasing posi carrier
Mark Williams steel bearing caps with a flat machined across the beam
Extra long SHCS screws for bearing caps
Studded diff cover with 12pt nuts
MM solid front and rear diff mounts
PHP aluminum toe link bars
Level 5 axles (I hope this was not a real big mistake)
MM delrin A-arm bushings with SS thrust faces and grease fitting
MM sway bar end links
FTBR eccentric camber adjustment bolts
MM coilovers and Hyper springs (don't recall rate)
Urethane sway bar bushings
93 Cobra R aluminum calipers
Wilwood 12 x .88 2 pc brake discs
Reinforced rear IRS sub-frame mounting bracket
9/16th front IRS mounting bolts
Extended wheel studs

I wonder if I forgot anything :??: A friend of mine is shimming the ring & pinion which will allow me to assemble this IRS and get it installed. I'll post more pics of the build some of which I have already posted but this is a good thread to consolidate everything so everyone can get the "big picture". After all the work I've done it's nice to see things starting to gel :rockon:

 

[SlowSVT]

Here is the Mark Williams steel cap next to the OE aluminum caps plus a comparison of the various bolt lengths. The short one on the MW cap is what it came with and is now part of my metric fastener collection and was replaced by the longer bolt that required a bottom tap. I don't recall the length but I have it posted on another thread and will put that info here.

Here are "before" & "after" pics of the modified Mark Williams caps. The "flat" was machined to remove the arch where the backstop pads that are screwed into the FRP diff cover contact the caps distributing the load over the entire pad and not focusing to the crest of the arch which is not ideal.

Here is a photo on the interior of the FRP diff cover prior to welding. Note the cavity where the rear mount and the backstop rail just to the left.

Since I was welding the cooling fins I decided it can't hurt to reinforce this by boxing them in especially the area the supports the mount. In this pic you can see the temp snap switch, the backstop pads the MW caps engage and the magnetic drain plug. The polishing was done to aid drainback and prevent debris from sticking to the walls.

Studded cover
These are available from Grainger but you will need a bottom tap for these as well to maximize the thread engagement minimizing thread stretch. This I would recommend this to anyone over bolts and you can torque them to a higher rating.

I wish the short end was fine thread :nonono:

This thing is the bomb :coolman: I am using the MM rear mount to help wick heat off the diff which is why I milled in some slots to increase the outside surface area. You can see the gussets added to the front mounting ears. The diff cooler hose fitting can be seen at the bottom. The mandrel bent barb fittings are not available so I made one.

"OVERKILL" you ask?

Defiantly! :burnout: That's 1/2 the fun :rockon:

 

[Blackedout]

WOW... some very nice details.... You interested in doing others...

 

[SN8KBYT_1]

Excellent work. Looks beautiful. Whats your address? I am sure there are a few us that would like you to do ours!

 

[SlowSVT]

Excellent work. Looks beautiful. Whats your address? I am sure there are a few us that would like you to do ours!

Take route 66 and head west

 

[01Jes]

Looks really good man. Good skills as always.

 

[black 10th vert]

Excellent work! Are those MW caps just a straight bolt on replacement, or do they require line boring to match the case? I ask because I have a spare aluminum case that is missing caps so this might be a good way to make it usable again.