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trees 06-26-2003 07:37 PM

Mustang II Kit Failure
Some months back we had a long thread on Mustang II kit failures and I had expressed great confidence on the kits, if properly installed. Well, I had one this evening on my way home and will share it with those that may be interested. The 36 Ford 5WC in my Avatar was completed in 1999 and I have put 26,000 trouble free miles on it (til this evening) It has a Fatman's stage 3 kit in it. The 1/2 inch bolt that fastens the tublar lower control arm failed about 1/2 inch inside the cross member on the front side of the XMember and about 3 inches from the bolt head. the back side of the lower control arm remained attached to the cross member, but the front side of the arm went down and out. The wheel assembly tilted out at the top and this fractured the heavy MOPAR upper ball joint seat. The tire took the beautiful paint job to the shiney bare metal on about 10 inches of the wheel opening bead. I was slowing to make a right turn so was only doing about 15 mph and just touched the brake. I jacked the car tho get some relief for the fender and examine the damage. I pulled the bolt end from the control arm eye and saw that it had basically sheared. The bolt had been about 90% sheared for some time from the rust on it and the last 10% was a shiney new brake. The remaining part of the bolt appears to be frozen in the tube that is welded inside the cross member. Now the scarey part: I had driven the car yesterday about 200 miles thru the twisting mountain roads in Western North Carolina and many of these turns at speeds high enough to have a comfortable drift. Great fun, but could have been disasterous. I'll be having a conversation with the Fatman in the AM and see if there other failures such as this. These bolts are grade 5 and the fracture would be indicative of over torque, but since I installed and assembled the front end, I know it was not over torqued.


RAW 06-26-2003 08:13 PM

That is awful! Sorry to read the bad news. The worst of a rodders night mares, dropping the car on the road. Good luck, r

302 Z28 06-26-2003 08:38 PM

Please keep us informed of this event, I am very interested.


Deuce 06-26-2003 09:26 PM


It will be interesting to hear what.....THE CHUBBY ONE has to say.

I am not bashing anyone or their products..........but it does seem to me that he gets MORE than his fair share of these :surprised :surprised

Maybe he sells more than anyone else??

Glad you are OK..:cool:


horvath 06-27-2003 06:18 AM

I'm eager to hear your next report, Trees! And very sorry to hear the terrible news!

How could I go about checking mine? Is there something specific to look for in advance?

54 Chevy Pickup

Centerline 06-27-2003 08:10 AM

I'm very glad no one was hurt.

You're failure is somewhat different than those seen previously but still seems to reinforce the argument that eliminating strut rods may not be the ideal solution to making the Mustang II suspension "look" better.

Keep us informed.


TooMany2count 06-27-2003 08:27 AM

seriously, this is the one company I wouldnt buy a kit from, yes I know lots of folks who run The BIGG GUY's stuff, BUT out of all the companies that make M2 kits he's the one I have heard all the complaints about & NEVER anyone else. The odd thing the complaints are, everyone who complained had a different problem w/his kits. SOOOOOOOOOO if it's up to me & I'm using a M2 kit, you know who I WONT buy it from..........joe

4 Jaw Chuck 06-27-2003 09:19 AM

Why a grade 5 bolt? I know they perform better under certain conditions like tensile loading but honestly why grade 5 for a critical shear bolt like a suspension bolt?

Somethings not right there, are you sure? Does the bolt head has three, five or six ticks on it?

Which one here does it look like? 06-27-2003 12:20 PM

That is why I have been adamant about only using stock MII X-members and hardware in my installations and advising everyone who asks to do the same. These aftermarket guys are probably not engineers and I am 100% sure they don't do fatigue testing to check the long life implications of their designs. I recall one guy posting on a thread similar to this last year that he tested a new suspension he was planning on selling "all weekend, over potholes and rail road tracks" and didn't have any failures so he was confident in selling it to the public.

I know for a fact that Heidt's 'economy' X-member has a serious flaw in design that will invariably fail with enough fatigue cycles. There have been a couple of pictures of the failure posted on this board in the recent past. I am not familiar with Fat Man's design but it sounds from your description that it has some serious long-life design flaws too.

If you have one of these after market X-member, be very diligent in doing your monthly inspection looking for cracks, bends, and evidently, failing bolts.

horvath 06-27-2003 01:36 PM

Willys36 : Could you give us greenhorns a basic inspection list? How would I look for a failing bolt? I mean, what would be the early signs? I have a FatMan Mustang II in my truck and I sure don't want any surprises!


54 Chevy Pickup 06-27-2003 02:48 PM

To check the bolts, you only option is to take them out and look at them. The lower A-arm bolts on strut rod eliminator units like Trees' are the most critical and should be checked at least semi-annually. The rest of them are relatively lightly loaded. If you have strut-rods, all the rest of the bolts are probably not over stressed.

The rest of the system needs to be checked for corrosion and cracks. The former is pretty straight forward.

If you have strut rods, the strut rod mounting point on the frame is the critical point. I don't know how many rods I have seen at rod runs that have these mounts cracked and usually not even hanging on the frame. If it is welded to the frame, check that weld. Preferably the bracket is welded and gusseted to a 1/4" or 3/8" plate or 1/4"x4"x4" angle iron and bolted to the frame. Check the body of the X-member around the lower A-arm bolts for cracks also.

Front ends with strut-rod eliminators are living on borrowed time, IMHO. All of the aftermarket X-members I have seen are not robust enough to withstand fatigue stress so will eventually crack. This is totally different from tensile stress. Tensile strength is the resistsnce to being pulled apart by a single load application. Fatigue strength is much more subtle and a lot lower value than tensile strength. In fatigue stress failure, a part is stressed to a level far below ultimate tensile stress thousands or millions of times (could be vibration or just normal service - pot holes, joints in the highway, etc.). Even though none of the individual loads can possibly fail the part by itself, the accumulation of the loads initiates a crack at a stress riser (sharp inside corner, hole, nick in the metal, etc.). Heidt's economy X-member is the worst example I have see. It has right-angle joints in the plates that make up the body of the unit that are in the highest stressed place they could be. Check very carefully around the entire bottom bolt hole area for the first sign of cracks or bending.

Th rest of the system should be ok, just check for problems.

horvath 06-27-2003 05:17 PM

Okay -- well, my Mustang II kit was totally welded onto the frame, and my mechanic said the job was done very well ... the geometry is all correct, level, etc.

Does that eliminate some of the concern of what we're discussing?

54 Chevy Pickup 06-27-2003 05:40 PM


Originally posted by horvath
Okay -- well, my Mustang II kit was totally welded onto the frame, and my mechanic said the job was done very well ... the geometry is all correct, level, etc.

Does that eliminate some of the concern of what we're discussing?

54 Chevy Pickup

Nope. The weaknesses aren't a fuction of how well the thing was installed. They are inherent in the unit itself.

horvath 06-27-2003 06:07 PM

Thanks, man.

There's a really cool (reputable) hotrod guy about a half-hour from me that I've been meaning to visit. I talked to him on the phone recently and he's very familiar with the Fatman's IFS, so I'm gonna take my truck to him and have him check everything out in detail as you've outlined.

Then, I'll rest easier and drive more comfortably, too!

54 Chevy Pickup

trees 06-27-2003 07:48 PM

Ok, I have an up date since I have removed all the parts on the failed side. Tomorrow, I strip the other side. First, my dealings with Fat Mans Fabrications. I have been to their facility and will say they are a firsct class operation. They do have a design function and use prototypes and extensive testing. They also do structural analysis and Fatman himself is an engineer with lots of metalurgical background. I explained the problem to a technician, who looked up my record with the company and knew every thing I had purchased and when I purchased it. He proceded to tell me they had problems with some of these bolts in the past and my most recent kit had special 5/8 inch bolts built to made to their specifications so they could maintain quality control. They were going to send me all new bolts (5/8") , bushings, and ball joints, no charge, and that Fatman himself wanted to talk with me as soon as he could break away from some customers. He called me at the shop about an hour later and wanted all the details. He said this was the same type failure as 5 others and they had done metalurgical testing on them and determined they had received a bad batch of bolts that had not been properly heat treated. The part of the bolt close to the threaded end was softer than grade 5 and near the head and the fracture, it was closer to grade 8, which was indicative of flexing (working) hardness. Neither he not the technician tried to BS me and readily acknowledged a discovered weakness and had taken corrective action. He also offered to pickup the tow bill (did not have one) and will pay for the alingment when I provide him with the bill. After talking with him, I discovered the Carrera shock shaft is bent next to the eye and I'm sure there will be a new one here by the time I am ready for it. He did say this was the 6th 1/2 " bolt failure out of approximately 40,000 they have put in service, so their track record is really good. There is one thing I did not do on assembly that I should have done, and you can bet will be done in the future. I did not put any lubrication on the bolt because I did not consider it to be a wear item. This bolt is rusted in (the hole (Fatmans welds a thick wall tube inside the crossmember for the bolt to pass thru). The next ones will be installed with a good coating of Never Seize. For Chuck, the bolt had 3 hashs, signifying grade 5. I, nor Fatman, think grade 8 is the answer because while stronger in tensil strength, they are weaker in shear, which is what became lacking when the bolt work hardened. Going back to some of the other responses. I still think Fatmans is producing the strongest aftermarket units. His cross members are over kill, his thick walled tublar products are indestructable and the MOPAR ball joints are so much better than the flimsey OEM Mustang II. The bolt failure, for what ever reason, can occur on any other kit. Willys 36 is right in that the strut rod geometry of the origional equipment can not be beat ever by strut rod eliminators. Fatman did offer a solution to the cracking of the frame where the strut rod bracket is welded on and that is weld a 1/4 inch plate to the frame and then weld on a 2nd 1/4 " plate to provide the proper thickness for the strut rod bushings etc. This was to reduce the heat required to weld a 1/2" plate to the much thinner frame rail. Thanks for all the information sharing, guys.


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