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Old 11-11-2002, 02:30 AM
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Exclamation Must II Front Suspension Warning

I came across this post on another message board, but thought some of you might find this interesting. The poster had a catastrophic failure with his crossmember (Heidt's) and his dealings with the manufacturer.

<a href="http://www.jalopyjournal.com/ubb/Forum1/HTML/026126.html" target="_blank">-Suspension Component Failure-</a>

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Old 11-11-2002, 05:02 AM
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I'm familiar with this web site and some of the people that frequent that place. They are traditionalists that don't hesitate to bash anything that isn't 100 percent old school. They hate billet and anyone who uses it. Most of them have no honor; since they have in the past raided other forums and disrupted them with foul language, impersonation, and obnoxious posts just for fun. Needless to say they arenít my kind of people, but enough editorializing.

The failure of this particular Mustang II unit can be attributed to two things. Poor repair work/maintenance and the use of strut rod eliminators. Neither of which would have caused the problem by itself but together it spelled failure.

I personally don't use the strut rod eliminators because they transfer all the tortional braking and front/back movement forces (caused by bumps etc.) to the lower "A" arm pivot point. Ford didn't design the system to work in this manor and since they spent millions of dollars designing this suspension system I see no reason to change it. The strut rods are designed to take the tortional forces and transfer them to the frame where they can be absorbed/disipated without damage to the other suspension components. This is a much better and safer design. That being said, it is only as safe as your welding. If the strut rod mounting on the frame comes loose (and I've seen one or two over the years) you will notice it immediately. Under braking it will pull very hard to the broken side. The good news is that it won't catastrophically fail like the one in the linked post did. Every strut rod failure Iíve seen has been caused by poor welding and not by the design itself. Thatís why I always use gussets when welding the strut rod frame mount to add strength. Better safe than sorry.

Even if you have the highest quality installation possible it wonít last if subjected to poor maintenance or repair work. As you can see in the photos there is a lot of rust in this area, which indicates poor maintenance and possible damage prior to the initial installation. Also Heidts determined there were some previous repairs that were less than adequate. Personally my experience with Heidts tells me that they are telling the truth here and not the owner of the car.

Overall the Mustang II suspension system is a very safe and strong IFS that can be easily installed at home by the average shadetree mechanic as long as he has adequate welding skills. Just like anything else though, if the installation is substandard or isn't maintained you'll have problems.

There are literally thousands and thousands of Mustang II front ends out there on all kinds of street rods that work very well every day. Just because one guy had a problem (which he caused) don't let that influence your decision when it comes to using one of these systems. They are safe, strong and functional.


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<a href="http://www.hotrodsandhemis.com" target="_blank">http://www.hotrodsandhemis.com</A>
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Old 11-11-2002, 08:52 AM
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I agree with centerline. This catastrophic failure was bound to happen due to poor design. Those sharp intersections of the welded plates are stress risers and occur at a very high stress point in the x-member. Add to that the strut rod eliminators and it was bound to fail. Had either of two things been done differently - Heidt's continued the bottom plate clear to the top of the shock risers or the owner used the strut rods, this probably would not have happened. The MII is a very good and safe design as Ford did it but back-yard engineers must be careful when modifying it. Heidt's is partly at fault for ending the bottom plate where they did, causing the stress riser.

This is why I not only always use the stock Ford MII x-member in my installations, but I also go to the trouble of using the entire rubber mounted strut rod brackets and x-over member from the donor car. I have seen many, many strut rod brackets fractured off frames where they were welded to the stock frame rails. Although the welds are good and they are gusseted, the frame material isn't up to the stress and it cracks. If I was to do it this way I would weld the strut rod brackets to 3/8" plate and bolt the plates to the frame with grade 8 bolts.

[ November 11, 2002: Message edited by: willys36@aol.com ]</p>
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Old 11-11-2002, 09:47 AM
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That thing looked pretty rusted! In that illistration in the differance between Heits and TCI. Makes me feel better about going with the TCI instead of the Big company. I have seen that way that Heits, Fatman's and some other attach that lower A arm to the crossmember with out it going all the way thru and had concerns about that. TCI as shown in that pic goes all the way thru and is welded by TCI not the installer. Think I will run a round file thru that corner on the bottem to chamfer that corner to help prevent cracks. My opinon here is poor quality in parts and owner negelect. You cant just build these things and drive the heck out of them. You have to inspect and check things. I check my sheet everytime I work on it and it hasnt even rolled out of the drive way yet! That is scary though makes you wonder how many are out there that are poor craftmanship either from the parts supplier or the installer/owner!
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Old 11-11-2002, 01:55 PM
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Got a question. On that picture of the end of the TCI crossmember. I tried to copy that pic here. Wonder if I should box this area in to make it stronger??? I can see how this area can take some abuse. Its the open area showing were that lower A arm attaches. Thanks!
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Old 11-11-2002, 06:20 PM
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Maverick; In answer to your question, yes I highly recommend that you continue the lower x-member boxing all the way up to the top of the shock tower. Leaving the plate with sharp edges where the manufacturers do is putting a stress riser exactly where the strss is very high due to the proximity of the lower A-arm pivot. If you are using a strut rods, the problem is lessened but if you are using stand-alone lower A-arms, you are inviting stress fractures and eventual failure. It doesn't need to be 3/8" plate either, 16 ga or 1/8" max plate thickness should suffice. You will be getting strength from the shape of the box, not necessarily from the plate itself. That is how Ford gets away with making their x-members of several pieces if 18 gauge sheet metal with strength to spare. The formed shapes, boxed sections, multiple layers where necessary and spot welds all yield a very strong section while discouraging crack formation and propogation since stress risers don't exist and if a crack did by chance start, it would be confined to a single layer of sheet metal. That crack couldn't propogate to adjouning layers because they aren't solidly attached so there is no crack propogation path.
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Old 11-12-2002, 06:08 AM
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Yep think I will do that. Think Ill even weld a angle plate on the bottem side of the frame were the cross member meets it to make that area stonger also. So that angle plate will fit in the corner of the bottem side of the frame and the side of the cross member. Then box the rest of the side of the cross member and the bottem. Goody I get to weld somemore!
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Old 11-12-2002, 06:32 AM
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Be careful with placement of your gusset that it doesn't form a stress riser itself!
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Old 11-12-2002, 10:26 AM
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Whatchu talkin about Willys? Which gusset? Were would the stress riser occure? <img src="confused.gif" border="0">
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Old 11-12-2002, 11:50 AM
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One thing that's being overlooked here is the choice of lower arms. If the Mustang II suspension is to be used under a fat fendered car, where it's not an appearance consideration, it would be wise to use a lower control arm with a strut rod. This forms a larger triangle which will spread the braking forces out more efficiently. I don't like the A-frame lower because of the way the forces transfer into the mounts. Of course it is also a good idea to have an installation such as this performed by a competent welder who also has a knowledge of structures and proper connection techniques.
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Old 11-12-2002, 12:49 PM
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The angle plate you mentioned. I guess I don't have a mind's eye view of what it will look like.
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Old 11-12-2002, 01:25 PM
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Wish I could draw on here. Looking at the frame from the side, under the frame rail welding about a two inch angle iron so that it it attaches to the underside of the frame rail to the opened up area of the cross member. Then box in the rest of the cross member.
Mabe Ill draw it out and PM you if you dont understand.
I think the gussets your think of would be placed on the front and back of the cross member up to the bottem of the frame rail. In this case I could see a stress riser on the crossmember were the gusset is attched.
Iam I making any since. Think I need to draw it out just so I understand!
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Old 11-12-2002, 03:21 PM
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Got your PM and now I understand. Good plan except I would carry the boxing plate all the way thru instead of stopping it and finishing the ends with angle iron. The continuous surface will be much stronger. Any time you introduce a sharp change in direction, that is a stress riser. As I said in my PM response, I don't think the extra gussets will be necessary if you box the x-member.
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Old 11-12-2002, 09:46 PM
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Something else to think about doing is to drill those bolt holes out to 1" and put a 1" tube all the way thru both sides and then use a long grade 8 bolt all the way thru... Just a thought cause thats the way I built mine......GlennK
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Old 11-13-2002, 05:14 AM
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Thanks Willys think I will box it all in. It seem pretty strong but stronger is better.

46 that is a good idea I got my kit from TCI and that step is all ready done for you by TCI.

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