NoRotors.com - RX7 Engine Swap Forum
Technical Information => Drivetrain => Topic started by: Demon on January 02, 2011, 09:55:30 PM
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Started pulling the rear end out to freshen it up/check on it after many hard launches this year (30 or so 1.4 60' times)
Found this:
(http://www.mr2turbz.com/images/FD/2010-2011winterupgrades/DSC00496.jpg)
(http://www.mr2turbz.com/images/FD/2010-2011winterupgrades/DSC00499.jpg)
(http://www.mr2turbz.com/images/FD/2010-2011winterupgrades/DSC00504.jpg)
We have a backup rear end, so we'll switch to that and the aluminum hard bushings, instead of the poly bushing that obviously failed and allowed the diff to break.
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Interesting breakage.
I would be installing a pinion snubber, or a loop over the top of the housing, anchored at the same mounting points, to keep the ears from flexing.
What makes you think, that solid mounting the ears, would not cause the same damage?
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And that's why I run the cast iron housings :D
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The shape of the break is exactly the same shape as the break of the poly bushing that's torn, I think it let it give and twist causing it to break where it doesn't have as much surface against the bushing.
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Gotcha. I'll have to keep an eye on mine, but my bushings are red, so hopefully they're better :)
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The shape of the break is exactly the same shape as the break of the poly bushing that's torn, I think it let it give and twist causing it to break where it doesn't have as much surface against the bushing.
The ear breaking could have also caused the bushing to get torn away.
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Iron housing and solid bushings here.
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"The ear breaking could have also caused the bushing to get torn away".
I just wrote the same exact thing, but my post did not go through.
Yes, it appears that the break may have sheared the bushing, then bent the washer, when the housing raised up.
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It's the way it was mounted. The support and structure needs to be ABOVE the nose of the diff, not below it. A couple of washers on top of the bushings won't f$%king cut it. Cobras with factory engineered subframes 1000 pounds heavier making twice the power of your car don't have that problem... guess why.
Don't blame the diff housing, it isn't at fault. If you want a subframe that won't cause that to happen, shoot me a PM.
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You may want to make a brace that goes across the top of the 2 front diff mounts for extra support.
That broke because of the poly bushings. Use solid bushings and you will be less likely to have that problem again.
These diff housings as a rule never break in Cobras.
I have an empty Mark VIII/ Cobra aluminium center section if you want it. Shoot me a PM if you are interested.
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It's the way it was mounted. The support and structure needs to be ABOVE the nose of the diff, not below it. A couple of washers on top of the bushings won't f$%king cut it. Cobras with factory engineered subframes 1000 pounds heavier making twice the power of your car don't have that problem... guess why.
Don't blame the diff housing, it isn't at fault. If you want a subframe that won't cause that to happen, shoot me a PM.
So would Justin's mount be the right way?
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That's a negative ghostrider.
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It's the way it was mounted. The support and structure needs to be ABOVE the nose of the diff, not below it. A couple of washers on top of the bushings won't f$%king cut it. Cobras with factory engineered subframes 1000 pounds heavier making twice the power of your car don't have that problem... guess why.
Don't blame the diff housing, it isn't at fault. If you want a subframe that won't cause that to happen, shoot me a PM.
I knew you were good at flipping things over :).
I may get in contact with you, thanks!
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get back to work!
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It's the way it was mounted. The support and structure needs to be ABOVE the nose of the diff, not below it. A couple of washers on top of the bushings won't f$%king cut it. Cobras with factory engineered subframes 1000 pounds heavier making twice the power of your car don't have that problem... guess why.
Don't blame the diff housing, it isn't at fault. If you want a subframe that won't cause that to happen, shoot me a PM.
Very good point. Take a look at a photo of a 2003-04 Cobra rear setup out of the car, like here;
http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812 (http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812)
Most of the nose weight of the unit maybe carried by the lower mounting bracket, but the twisting motion is controlled by both the lower and upper brackets, which work in tandum to brace the differential case and share in resisting the twisting motion, during both on and off throttle (acceleration and deceleration) loading.
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So why couldn't you just make kind of a U channel out of it so it grabs on both side of the ear?
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So why couldn't you just make kind of a U channel out of it so it grabs on both side of the ear?
You could, but you'd just be band-aiding something that isn't the root cause.
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Damn speaking of all this I forgot to get my subframe from you Tracy. Or are you keeping it now due to the Saturn head ake?
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I might be up to Savannah in a few weeks, we can work something that way if you want.
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Very good point. Take a look at a photo of a 2003-04 Cobra rear setup out of the car, like here;
http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812 (http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812)
Most of the nose weight of the unit maybe carried by the lower mounting bracket, but the twisting motion is controlled by both the lower and upper brackets, which work in tandum to brace the differential case and share in resisting the twisting motion, during both on and off throttle (acceleration and deceleration) loading.
The lower mount is actually an add on piece, and not part of the subframe. It attaches to the lower control arm mounts and is held by the forward LCA bolts. This was added for use in the 2003/2004 Cobras. Earlier 99 and 01 Cobras and 2000 Cobra Rs did not have this lower brace.
(http://www.maximummotorsports.com/content/large_images/rear_susp/M-5030-F_LG.jpg)
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Very good point. Take a look at a photo of a 2003-04 Cobra rear setup out of the car, like here;
http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812 (http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=2812)
Most of the nose weight of the unit maybe carried by the lower mounting bracket, but the twisting motion is controlled by both the lower and upper brackets, which work in tandum to brace the differential case and share in resisting the twisting motion, during both on and off throttle (acceleration and deceleration) loading.
The lower mount is actually an add on piece, and not part of the subframe. It attaches to the lower control arm mounts and is held by the forward LCA bolts. This was added for use in the 2003/2004 Cobras. Earlier 99 and 01 Cobras and 2000 Cobra Rs did not have this lower brace.
(http://www.maximummotorsports.com/content/large_images/rear_susp/M-5030-F_LG.jpg)
So with the higher powered '03-04 Terminators, Ford apparently addressed an issue involving the high magnitude twisting/movement of the 8.8 IRS differential with the addition of this lower brace. It would make perfect sense that with the lower powered car, the brace was not needed, but with 390 ft-lbs of torque it became necessary. I also sent you a PM about this subject.
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I might be up to Savannah in a few weeks, we can work something that way if you want.
Thats fine just let me know. You going to be racing there or something?
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If anyone wants the Maximum motorsports piece we are a dealer. I tore up the poly bushings as well road racing. We made aluminum ones for it.
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If anyone wants the Maximum motorsports piece we are a dealer. I tore up the poly bushings as well road racing. We made aluminum ones for it.
Is that all you did? How is it holding up?
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Whoever is making the FD cradles needs to combine the Cobra case with an Explorer rear cover. That is what I did on the FC cradle that I used to sell. That cradle is being used in Enzo's 8 second rotary FC.
In my opinion the front mount pictured in this thread broke because of twisting forces, not from force of the diff trying to move up. It is the same issue that causes the stock Cobra rears to shatter the rear cover when used in the Mustangs.
Andrew
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Hmm, I'll be checking mine out before getting on it again. I've noticed a little bit of a new noise coming from on off acceleration.
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Whoever is making the FD cradles needs to combine the Cobra case with an Explorer rear cover. That is what I did on the FC cradle that I used to sell. That cradle is being used in Enzo's 8 second rotary FC.
In my opinion the front mount pictured in this thread broke because of twisting forces, not from force of the diff trying to move up. It is the same issue that causes the stock Cobra rears to shatter the rear cover when used in the Mustangs.
Andrew
Andrew, why aren't you selling the old FC cradle any more?
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You may want to make a brace that goes across the top of the 2 front diff mounts for extra support.
That broke because of the poly bushings. Use solid bushings and you will be less likely to have that problem again.
These diff housings as a rule never break in Cobras.
I have an empty Mark VIII/ Cobra aluminium center section if you want it. Shoot me a PM if you are interested.
Like this
(http://i184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/Dsc00972.jpg)
(http://i184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/Dsc00978.jpg)
(http://i184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/Dsc00964.jpg)
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Whoever is making the FD cradles needs to combine the Cobra case with an Explorer rear cover. That is what I did on the FC cradle that I used to sell. That cradle is being used in Enzo's 8 second rotary FC.
In my opinion the front mount pictured in this thread broke because of twisting forces, not from force of the diff trying to move up. It is the same issue that causes the stock Cobra rears to shatter the rear cover when used in the Mustangs.
Andrew
The FD is very tight in the cover area. In fact, the stock cover mount ,is removed for clearance as I recall.
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DeaconBlue,
I started to redesign the cradle to use the Explorer diffs. The Explorer case fits better in the FC and they are much more readily available and less expensive than the Cobra diffs. I never finished the project and I moved and got rid of my FC. Sort of a perfect storm of events. My original design is very strong but it required the customer to send in the rear crossmember for modification.
The builders of FD cradles need to focus on eliminating the twisting forces from breaking the front mounts on the Cobra case. The setup that Grahm posted for his FC takes care of that by distributing the load through the whole casting. The Explorer rear cover does the same thing. The front mounts on the cobra case was not designed to resist twist. Its only purpose is to control the upward motion of the front of the diff.
Andrew
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If anyone wants the Maximum motorsports piece we are a dealer. I tore up the poly bushings as well road racing. We made aluminum ones for it.
Is that all you did? How is it holding up?
It's been fine ever since. We also put a cooler on it from day one. I melted the bearings in 1/2 a race in the stock one. Once they cooled the car wouldn't move. (oops).
Bill
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Cool, we have a cooler we are adding this winter. Thanks!
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And that's why I run the cast iron housings :D
+1 to that! :D
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The setup that Grahm posted for his FC takes care of that by distributing the load through the whole casting.
Andrew
Thanks Andrew - sorry for the newbie question, but who is Graham and where did he post his design? Do you mean the photos that mayhamfx posted in this thread?
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Mayhamfx is Graham. He's got a nice write up in his build thread IIRC
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Pics here: http://s184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/ (http://s184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/)
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Pics here: http://s184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/ (http://s184.photobucket.com/albums/x134/mayhamfx/Lincoln%20IRS/)
SHOW OFF!! :D
Yeah it is a great write up! Read it at least a dozen times on the old forum before I tackled my 8.8 swap. Great write up Graham! and 28 splines isn't all that bad! I can just ripp the tires to the cows come home now lol! Good thing I get mine free! :D