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Old 07-21-2020, 06:23 PM
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Default Differential bracket issues Superformance early Mod. 100's

Regret Posting anything. I'm asking for help and really didn't get it. Just the opposite.

Last edited by Moto Guru; 07-26-2020 at 04:09 PM..
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Old 07-22-2020, 08:39 AM
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Quote:
Originally Posted by Moto Guru View Post
My opinion is it could of been built better.
My opinion is that it was never engineered to withstand 800+ HP. Glad you're lucky enough to be here posting about it vs. something more tragic.
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Old 07-22-2020, 09:15 AM
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Yes. Think I heard about diff mount issues in the past. I guess take it to a race car fabrication Shop?
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Old 07-23-2020, 11:30 AM
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I've seen the front mount break on the passenger side where it just tore the mount off the frame rail at the welds on a friends car. We just welded a 3/16" plate over the frame and welded a thicker bracket on there. It's been working fine for years.
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Old 07-23-2020, 11:53 AM
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Old 07-23-2020, 11:58 AM
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can you provide detail of the design? the location of the bracket is difficult to get to, it's difficult to weld because of the location, if you could get to it from from above then for sure it could be done easily. Unless you open the cockpit somehow to do it from above. any insight would be greatly appreciated..

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Old 07-23-2020, 02:08 PM
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Old 07-23-2020, 05:28 PM
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Old 07-23-2020, 10:17 PM
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Your link to photobox does not allow non photobox members to see it. Just post up the photo on Club Cobra. Photo sharing sites have a habit of not sharing once they decide they want you to pay. If you put the photo in your album on this site and post from your album on this site or your desktop that can't happen.


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Old 07-24-2020, 07:38 AM
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I suggest contacting a Superformance dealer. If there is a way to get to it from up top, they should know how to do it.

Here is another easier said than done thought. Build a cage that holds the entire IRS. Remove everything that is attached to the frame (those parts could be moved to the new cage). Repair any frame damage, but I think stripping would remove what is broken. Now the new cage would simply bolt into the existing frame. At least 4 heavy anchor points, the further apart the better. Obviously the cage must be designed to fit into the frame.

I see this as a way to beef up the entire assembly and make it more serviceable in the future when all that Hp finds the next weakest link. Also there is a hope that you may eliminate a handful of the next weakest links with the cage design and maybe never have anymore failures.
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Old 07-24-2020, 09:04 AM
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Are you a member of SCOF? There is plenty of useful information in their tech library, plus many SPF owner there with experience with this and many other issues specific to SPF. If you are not a member, do yourself a favor and join and gain access to tons of useful information specific to SPF.

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Old 07-24-2020, 10:13 AM
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Rick's (olddog's) suggestion about a cage or mounting cradle is a very good idea. When Ford did their own IRS packages they used this approach. This is what the OEM IRS cradle for an SVT Cobra with IRS look like;



You can see the four attaching points at the top and bottom and left and right in the picture. There is a lot of "stuff" in the OEM implementation that we do not need. A company called Ronin Speedworks offers kits to marry the Ford 8.8 IRS up to a variety of performance cars.

Ronin likes the Ford Explorer version of the IRS housing for its added strength (so do I) but their mounting approach works with either the Explorer or Cobra versions of the 8.8 center section.

Here are a few pics of one of their kits. They have several other and I suspect would be willing to work with you if you wanted something out of the ordinary. This kit is particularly nice because it provides for a simple vertical install and retention of the IRS center:



This rear mount style gets away from the ever present danger of cracking the thin rear cover on most of the Ford offerings. The cover in the picture is from an Explorer and is substantially stronger than the OEM Cobra style rear cover. Their rear mount style allows the center to be installed vertically and easily secured with two vertical fasteners.

This is a view of a front mount package to address the pinion mount for the center section;



This cradle in the picture is mounted into an Explorer subframe. You would mount it into the SFP rear frame rails instead.

When you use this style of mounting the install is as close to bulletproof as you are likely to get. The real nice attribute when you are finished is the ease of installation and removal of the IRS center section. Four vertical bolts and it is out, making service much easier — not a snap but much easier.

If you have good fabrication skills the pics should give you some ideas for a start on building your own design.


Ed

p.s. While you have the whole shebang apart give some thought to changing out the passenger car IRS housing that SPF provided for the more robust Explorer SUV IRS version Ford built for the Explorer. If you do be sure to use the version with the two large front mounts not the one with the single large front mount.
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Old 07-24-2020, 12:02 PM
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Old 07-24-2020, 04:07 PM
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Old 07-24-2020, 05:01 PM
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Old 07-24-2020, 05:44 PM
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Quote:
Originally Posted by Moto Guru View Post
I was able to pry out the metal from the frame that holds up the front differential. As you can see from the metal close-ups the material is very frail.
I am uncertain how to visually measure the "frailty" of any metal. Can you explain the process?


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Originally Posted by Moto Guru View Post
The actual alloy was bad on this one,
That may be. Please tell us more about the chemistry of the alloy steel that failed and what it should have been. Please elaborate a bit on what elements you found in the steel and what elements were missing. If there were no elements missing please advise us the actual concentrations of the elements you found in the steel vs the correct concentrations that you believe should have been present.


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and was missing some welding.
How did you determine there was missing welding? Did you compare the component to another SPF Cobra or perhaps did you have manufacturing documentation that called out for a different type or location of weld?



Quote:
Originally Posted by Moto Guru View Post
I'll keep looking at this thread to see if anyone can give me pointers.
Please read post #10 and post #12. They will give you excellent guidance on improving the diff mounting in the chassis.


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Originally Posted by Moto Guru View Post
The passenger side bracket is a PAIN to get to especially taking out the top bolt, there is almost no room to work at all. I'm talking fingertips here.
These bodies are fiberglass. You should have no difficulty getting at the top of the location to weld. Just cut a hole in the fiberglass floor above where you want to weld. Remove the now liberated piece of fiberglass. Clean the surface to be welded. Position the pieces you wish to weld. Go in with your TIG torch weld what every you would like to weld. After cool down, clean the surface for painting. Paint the surface to prevent rusting. Re-glass the piece of flooring you just cut out. Paint it to look pretty and you are done!



Quote:
Originally Posted by Moto Guru View Post
Take a look at the metal, looks like there was a bad heat sink or bad cast when they made or heat-treated this particular metal. Something doesn't look right.
I have an SPF and I have never found a heat sink anywhere on the chassis. In the picture you posted I also do not see a heat sink.

If you mean that you think the heat treatment is incorrect you probably ought to know the steel used in that section of the chassis (and I think everywhere else) is not heat treated it is almost certainly condition "N" steel, possibly condition "A" steel but likely condition "N" steel.

In your determination of heat treat status what type of test did you use to determine the heat treatment?

In the FWIW category the piece of damaged mounting hardware you displayed in the photograph looks as if the mounts were not tight. The freedom of movement the loose mounts afforded the nose of the differential housing, allowed the differential nose mounting hardware to hammer against the mount eventually tearing the mild steel. This would have taken some time to accomplish.

Just looking at your photo it would appear the damaged component approximates 0.125" in thickness. That thickness of mild steel, in a properly designed mounting, should be more than adequate to restrain the nose of the IRS housing.

All that being said, if you want to very securely mount the IRS center section to your chassis the solution / answer is in post #12 above.


Ed
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Last edited by eschaider; 07-24-2020 at 05:48 PM.. Reason: Spelling & Grammar
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Old 07-24-2020, 07:48 PM
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Quote:
Originally Posted by eschaider View Post
I am uncertain how to visually measure the "frailty" of any metal. Can you explain the process?




That may be. Please tell us more about the chemistry of the alloy steel that failed and what it should have been. Please elaborate a bit on what elements you found in the steel and what elements were missing. If there were no elements missing please advise us the actual concentrations of the elements you found in the steel vs the correct concentrations that you believe should have been present.




How did you determine there was missing welding? Did you compare the component to another SPF Cobra or perhaps did you have manufacturing documentation that called out for a different type or location of weld?





Please read post #10 and post #12. They will give you excellent guidance on improving the diff mounting in the chassis.




These bodies are fiberglass. You should have no difficulty getting at the top of the location to weld. Just cut a hole in the fiberglass floor above where you want to weld. Remove the now liberated piece of fiberglass. Clean the surface to be welded. Position the pieces you wish to weld. Go in with your TIG torch weld what every you would like to weld. After cool down, clean the surface for painting. Paint the surface to prevent rusting. Re-glass the piece of flooring you just cut out. Paint it to look pretty and you are done!





I have an SPF and I have never found a heat sink anywhere on the chassis. In the picture you posted I also do not see a heat sink.

If you mean that you think the heat treatment is incorrect you probably ought to know the steel used in that section of the chassis (and I think everywhere else) is not heat treated it is almost certainly condition "N" steel, possibly condition "A" steel but likely condition "N" steel.

In your determination of heat treat status what type of test did you use to determine the heat treatment?

In the FWIW category the piece of damaged mounting hardware you displayed in the photograph looks as if the mounts were not tight. The freedom of movement the loose mounts afforded the nose of the differential housing, allowed the differential nose mounting hardware to hammer against the mount eventually tearing the mild steel. This would have taken some time to accomplish.

Just looking at your photo it would appear the damaged component approximates 0.125" in thickness. That thickness of mild steel, in a properly designed mounting, should be more than adequate to restrain the nose of the IRS housing.

All that being said, if you want to very securely mount the IRS center section to your chassis the solution / answer is in post #12 above.


Ed
I think first I'd like an explanation of how almost 900hp was not the major contributing factor. This sounds like a case of pilot error to me.
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Old 07-24-2020, 09:05 PM
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I think first I'd like an explanation of how almost 900hp was not the major contributing factor. This sounds like a case of pilot error to me.
I would normally agree, Tony, except the OP indicates he is extracting that power from a 354" naturally aspirated small block. The numbers work out to essentially 2.5 hp per cubic inch. While not ProStock power levels (3 hp per cubic inch) it is close enough to raise the question of, "it it real or is it memorex" to steal a line from years gone by.

I suspect the represented engine power level is an optimistic wish with no dyno paperwork to support it. The real world power is probably closer to 550 FWHP, likely less, that will work out to about 450-ish at the tire — best case.

The real problem is a maintenance issue not a power, chassis design or strength of materials issue. Someone abused the car and when they heard the clunking in the back continued to beat on it until it failed. Once failure arrived the blame game begins. There are enough of us with SPF replicas that make more power, more torque and do not seem to suffer these sorts of failures. It is an abusive operation / lack of maintenance type failure — nothing more and nothing less.

My questioning was just to point out that the OP was sprouting potential problems like a popcorn machine at a movie theater without any knowledge of what he was talking about - let alone testing to provide some sort of basis for the representations.


Ed
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Old 07-25-2020, 09:08 AM
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I believe it was wheel hop that caused the damage if you want a drag car go with a solid axle ford 9"
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Old 07-25-2020, 01:19 PM
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I agree with the OP that this failed slowly over time. The picture of the edge shows beach marks where a crack was formed and the metal was flexing, for quite a while. Very little metal was left at the time of the final failure.

I would expect everything to do with a frame to be mild steal. Heat treatment makes metal harder, and brittle. Hard makes it stiffer and flex less, but not necessarily stronger. It's brittle like glass. Mild steal is flexible, weldable, and bendable. All the things you want in a frame.

I have no way to say for certain, but my guess is that a long time ago some single event of abuse set things into motion, and the rest happened slowly over a long time. Sense it happened so slowly and there was so little metal left holding it together at the time of failure, I would rule out a design or manufacturer flaw. The design was at least 4 times stronger than the final failure put to it. Most likely 5 or 6 times stronger maybe more. This based on a small sample of total area of failure, so don't rely on this as gospel.

I also agree that 800 Hp out of 354 CID NA engine is doubtful, even with 12:1 compression. Maybe 354 is a typo and it's a 534 stroked big block.
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