Original 427 Street Cobra Suspension Rebuild

[David Kirkham]

Gents,

We had a TON of comments on our assembly manual thread (still working on it) and we just got an original 427 Street Cobra in the shop...so, I figured you guys would like to see a "check out/rebuild" of an original 427 Cobra Street Suspension. This suspension is almost identical to a 427 SC Cobra suspension. The main difference being the brake caliper and rotor. I will get into the specific details later.

The customer asked us to go over his car and see if there was anything that needed to be done to make his car "right" so he could drive it. Owning one of these babies is not for the feint of heart. It is not unusual to spend $10,000-$20,000 to go through the suspension of an original car. Parts are unobtainable in most instances and so you end up making them--usually out of UNOBTAINIUM, of course!

When we got the car it was supposedly "completely concourse restored." Well, I am sure most of us know what that means. There was a little TLC that the car still needed. The alignment needed some love and I was sure there were other gremlins lurking in the woods that needed to be ferreted out as there seem to be on all these cars. They are now over 40 years old, after all, and that is a LONG time for things to happen!

Feel free to comment and ask questions! I am happy to answer what I can.

Here is the first picture. This is a shot of the left rear suspension. The first thing you notice, of course, is that original 427 Cobras had INDEPENDENT rear suspensions! You would not believe the amount of people who have called us and told us they went for a ride in an uncle's, cousin's best friend's original 427 Cobra and they knew it had a solid rear axle...

Well, they DON'T!

Original 427 Cobras had a true independent rear suspension. (The following has been corrected due to a brain short on my part. ***Incidentally, Jaguars do NOT have a true independent rear suspensions*** Should read, Incidentally, Jaguars do not have a true upper control arm as they use the 1/2 shaft as the upper control arm.) Sorry!

Cobras do not use the 1/2 shaft as the upper control arm. They have a true rear upper control arm with plunging 1/2 shafts. You can see in the picture the top of the upright were the upper control arm bolts into the upright.

Another interesting thing is you notice the on rear suspension, ORIGINAL COBRAS HAVE OUTBOARD REAR BRAKES. On this car (street 427) the original calipers are cast iron. They are HEAVY!!! Notice an original Cobra has rear wheel disk brakes. It was one of the 1st production cars to have 4 wheel disk brakes.

[David Kirkham]

Here is a picture of the interesting "locking" mechanism for the rear hub bolt. I am sorry the picture is not 100% in focus, but Sandwich is working faster than I can take pictures and post them on the web!

Anyway, this it the infamous locking tab the English were so enamored with. At first glance it looks like a good answer to the question of keeping the bolt in place...in practice it is incredibly stupid. But, as they say, "Hind sight is 20/20" and who knows what people will be posting about me on the web 20 years from now!

This is how the locking tab is "supposed" to work. First you place the locking tab into the two little drilled holes in the drive flange. Then you tighten up the bolt to the required torque (we use 225 foot pounds BTW) and then bend over the tabs against the flats of the bolts to prevent the bolt from loosening up. Very BAD idea.

In order for the tab to even be able to be bent, they have to be made out of a SOFT steel. Soft steel will pound out as you drive down the road. The rear suspension takes an incredible abuse. If you have ever driven with a professional driver, you know what I mean. If the steel yields (which it will surely do) YOU WILL LOSE ALL PRELOAD ON THE BOLT! ONCE YOU LOSE THE PRELOAD ON THE BOLT YOU LOSE THE PRELOAD ON THE BEARINGS!!! This means your hub bolt is about to play "Free Willy" and exit the premises. This means your hub is now loose and is about to fall off--which will loosen the preload on your sphincter as you face Turn 1 going 150 mph with a Miller Motorsports instructor showing you things you didn't know cars could do.

Talk about a YOU TUBE moment! "Original Cobra into the wall at over 100 mph!!!" I bet there would be 1,000,000 hits the first day alone.

[David Kirkham]

Here you can see Sandwich taking a screwdriver to the tab to bend it out of the way so he can get a socket on the bolt. (Don't worry, it isn't a Snap On screwdriver!) I guess this is the one that is in bad focus! Sorry! Notice the little divots in the bolt where someone else had taken the upright apart earlier in its life.

[David Kirkham]

Here Sandwich is taking a socket to the rear hub bolt to loosen it.

[David Kirkham]

Here you can see the bolt, washer, and "locking" washer have been removed. In the "locking" washer you can see the two ends that are bent AWAY from you as look at the washer in the car. In this picture, they are bent up. Those two tabs stick into the flange and are "supposed" to prevent the tab from turning.

BUT,

Already we are starting to see problems.

[David Kirkham]

Here you can see Sandwich putting the straight edge of some calipers across the washer. You can see it is severely bent! The steel of the washer indicates is is probably mild steel and so it has no spring to resist permanent deformation from the pounding of the rear suspension. As the suspension beat on the washer over time, it has yielded letting all the preload out of the suspension--major bummer waiting to happen in the driver's seat.

[kris-kincaid]

The Navy uses lock-tabs on a lot of secondary nuclear steam valves and conventional main steam valves. Shelby continues to use them on the suspension. I've never seen one fail, either in a Cobra or on a ship.

I've never questioned them, so it's interesting to see your opinion. Have you had problems with them failing?

BTW, nice thread. Always nice to see original parts.

Originally Posted by David Kirkham

Anyway, this it the infamous locking tab the English were so enamored with. At first glance it looks like a good answer to the question of keeping the bolt in place...in practice it is incredibly stupid. But, as they say, "Hind sight is 20/20" and who knows what people will be posting about me on the web 20 years from now!

[Jim Maxwell]

David, this is a fantastic thread. Having and driving one of these wrecks waiting to happen, what is the cure? Jim Maxwell CSX 3288

[mylesdw]

Originally Posted by David Kirkham

Incidentally, Jaguars do NOT have a true independent rear suspension as they use the 1/2 shaft as the upper control arm. Cobras do not use the 1/2 shaft as the upper control arm. They have a true rear upper control arm with plunging 1/2 shafts.

I can't see why you consider the Jag IRS to be not a true IRS. An independant suspension is surely one that transfers no suspension forces from one side of the car to the other and the Jag unit clearly fulfills this. It is not a double wishbone IRS; that is obvious, it's just a different design.

[FIA-ERA]

Front spindle shafts and rear drive knuckles... Couldn't answer on the alloy? Heat treated for maximum hardness and strength.

[FIA-ERA]

Front Stub axle- Front hubs and rear drive hubs. Did I win??

[David Kirkham]

FIA-ERA

I am not sure what a rear drive knuckle is?

You are right, however on your next post. There is a rear hub, front hub, and a front axle.

You win the first question.

Bonus question?

Why do we have a front hub AND a front axle in the oven?

Still open--alloy and heat treat specs????

David

[mylesdw]

Originally Posted by David Kirkham

FIA-ERA

Bonus question?

Why do we have a front hub AND a front axle in the oven?

Still open--alloy and heat treat specs????

David

Is it something to do with the hard steel (bullet proof) fasteners you are using? The hub and the spindle have to be equally hard to avoid erosion?

[David Kirkham]

mylesdw,

Actually increasing hardness generally increases the risk of corrosion. The reason we have both front hubs and front spindles in our oven is because we have our own front hubs we use on our billet suspension along with the front spindles for original Cobra restorations (and our very early cars that ran that suspension).

David

[MaSnaka]

Because you don't want a runny yolk? Good thread! Thanks for taking the time out to educate us.

John

[rbray]

David,
This is very interesting as my wife owns a kiln that looks very much like the one in your picture.

Now I'm wondering how I can have some fun heathing up car parts. I have no idea how heating something up would benefit me, but it seems like a waste to let an opportunity like this pass by.

Any ideas, suggestions?

[FIA-ERA]

David, Great post!! I always enjoyed books with pictures. I would think the front axles are matched with the hubs and keeping them together insures they get treated to the same temperatures as not to expand or contract differently? It seems there could be different variations in the metal strength and finished product if done separately? I'm not an engineer but I do like the late night questions. Thanks for your contributions!! Matt.

[BERT]

David,
The front hubs and axles are placed in the oven at the same time to prevent delaying the next batch of chocolate chip cookies at snack time. Did I win?
Robert in Virginia

[David Kirkham]

Matt,

No...good guess, however. Are you sure those axles are "matched" to those hubs???

Look back through my post (including this one) and all the hints are there.

John,

At that temperature the yolk would definitely NOT be runny...

rbray,

The kilns may be VERY similar...we just tweaked ours to work like we needed it to with special thermocouples.

Robert,

900 degrees is a little hot for cookies. As a matter of fact, I think it would hard to be around that temperature as it would precipitate a lot of sweating...

David

[David Kirkham]

Next hint,

After 40 years, things rust...and I HATE rust.

David