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Old 07-18-2010, 05:54 PM   #1
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Default I want to pound my Miata in the *** - Hardcore

Yes, indeed I do. I think this track car has pounded me in the *** long enough, without even a reacharound. So I think it may be time to be the pounder for awhile.

Here is the thing... I am trying to raise the height of the Ford Explorer 8.8 differential in the car. I have a plan, a spare subframe to modify, and the toolz and skillz to make it work.

But there is a problem... there is always a problem... and my *** is hurting again.

The 8.8 diff housing is a LOT larger than a Miata diff housing. If I had to guess, like 3-4 times the volume, and maybe twice the height. Because of its height, or to be more specific, the distance from the axle centerline to the top of the case, I am having clearance problems with the gas tank. I cannot raise the diff as high as I would like to in the chassis because the bottom of the gas tank is in the way.

I've been crawling around under the car a lot this weekend ***-essing the situation. I've raised the diff into place between the subframe members, I've measured everything twice, carefully, so I know what the issue is. Not enough vertical space. I cannot tilt the front of the diff downward to get more clearance since that will make the pinion angle too severe, and it would partially defeat the purpose of the whole exercise anyway.

So, like I said, I want to pound my Miata in the ***. Not in the harsh, unlubricated, don't-care-about-you way it has been pounding me in the ***. I mean gently, lovingly, carefully pounding it. Specifically I want to take a hammer to the gas tank, the rear, high portion of the tank, and pound it upwards about an inch. I'd like to do this to make a 'tunnel' about 4-5 inches wide that runs from front to rear, shaped like an ***-crack

So, I need some input from the hardcore Miata fabricators on whether this is WIN or FAIL. Though I will do it gently, and empty its *** before I start, I am not sure how much I can pound on it before its unpleasant contents will come gushing forth. Anyone ever done this?

My other option, and it is somewhat appealing, is to ditch the stock tank and go with a fuel cell. I am swapping subframes anyway so it should be pretty easy to remove the stock tank. I could also go with a smaller diff, but this one has nice internals and I have about $700 in it.I could probably recover a lot of that if I sold it and went to a Getrag which I believe is smaller.

OK you hardcore ***-pounders, tell me how it is.

Last edited by ZX-Tex; 07-18-2010 at 06:15 PM.
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Old 07-18-2010, 05:58 PM   #2
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Can't even give you my opinion cause I'm so horny from all the *** references

*edit: fuel cell all the way. or install a smaller tank from some other car (don't know if there are much smaller tanks out there. or try to make your own. but to "pound" the stock tank sounds like a bad Idea and very dangerous.

Last edited by 18psi; 07-18-2010 at 06:37 PM.
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Old 07-18-2010, 06:24 PM   #3
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I would say it's a very bad idea. Go with the fuel cell (you can get custom ones made), or the smaller diff. Just pounding away, even gently, is bound to create a crease and it will leak all over the place. Leaking fuel=very bad things.

And, I think you have some issues that have nothing to do with gas tanks.
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Old 07-18-2010, 06:59 PM   #4
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Why can't you fit the 8.8? Mine fits fine with axle output exactly in the stock locations and clears the gas tank fine. Something's not right.

Many pics in my build thread. It's on jackstands so I can take more if needed.
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Old 07-18-2010, 07:43 PM   #5
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You might try looking into the 90-93 tank it's about 2 gallons smaller. I'm not sure in what dimensions it's smaller since I don't have a 94+ tank to compare mine too.
It's a shot in the dark but it might keep you from whanging on your tank or replacing it with a fuel cell.
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Old 07-18-2010, 07:53 PM   #6
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I would just go with the Fuel Cell option.

If you able, to pound in the extra metal and/or the stock tank. Your opening you self up to dangers situation. If anything to were to break free, like a driveshaft, or you run over something. The extra air/metal gap that is currently there, won't be there to absorb the damage. Allowing much easier for something to break the stock tank.

Now from the sounds of it, you willing to cut and demo anything. Wonder if you able to cut out some of the truck metal and remove the stock tank, if you could put a rectangular fuel cell in roughly the stock tank location but a few inches higher.
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Old 07-18-2010, 08:14 PM   #7
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Quote:
Originally Posted by Stein View Post
Why can't you fit the 8.8? Mine fits fine with axle output exactly in the stock locations and clears the gas tank fine. Something's not right.

Many pics in my build thread. It's on jackstands so I can take more if needed.
I'll check it out. I was thinking the same thing, that is I am not sure why I am having such a clearance problem. I have been looking at the FM conversion pictures, and some other conversions for that reason. I'll go check out your pictures. Which diff housing are you using, the T-Bird/Cobra, or something else?

Well, asking about hammering on the gas tank was the whole basis for the ***-pounding joke, so I had to ask But yes believe me I know it is risky which is why I am asking. If someone else has done it successfully then I might try it. If not, then I will look for other options.

EDIT:
OK Stein I looked at your pictures. I remember your mount system now, the tray setup like the Boss Frog kit. You have the Thunderbird diff housing. You know what though, I believe the Explorer and T-bird diff covers are interchangeable, ergo your diff is about as tall as mine. How close is the top of the cover flange to the underside of the trunk deck? Where the housing slopes down to the pinion bearing carrier area, is there much clearance between that and the underside of the tank? No need for exact measurement, do not want to put you to any trouble, so approximate is OK.

Last edited by ZX-Tex; 07-18-2010 at 08:24 PM.
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Old 07-18-2010, 08:26 PM   #8
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I would also agree that maybe you have a housing with a weird casting. In my little bit of reading I have done for 8.8 rear end swaps into the Miata, I have never heard of anyone having to beat stuff to shape to fit it in. If not that, I'm also voting fuel cell, I wouldn't beat the stock tank.
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Old 07-18-2010, 08:53 PM   #9
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I think it may be that the Explorer housing is significantly taller than the t-bird housing. For one thing there is a decent gap between the ring gear and the top-inside surface of the housing. For another, there are a lot of cooling fins and protrusions on the top of the housing. So the distance from the center of the axle to the top of the housing could be significantly taller on the Explorer housing.

T-Bird diff housing (In a FFR Cobra frame)


Steins t-bird housing (can't see top but notice no fins)


Mine


Notice all the fins and protrusions and what not


I nearly grabbed the grinder this afternoon and cut all of that crap off of the case. But I decided not to be hasty.

Don't mind all of the grime. That case was really clean until the CV boots exploded and coated everything with grease

Last edited by ZX-Tex; 07-18-2010 at 09:13 PM.
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Old 07-18-2010, 09:06 PM   #10
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Actually if those are all solid I don't see why grinding them off would be too bad of an idea.
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Old 07-18-2010, 09:08 PM   #11
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Yeah I am 99% sure they are solid. I am thinking about it...

Here is another picture of a T-Bird/Cobra aluminum IRS. No fins, or at least not huge ones.


Here is another of a T-Bird housing, looks like a cast iron case maybe. Bot notice it is completely smooth on the front. Ignore the red circles.


Here, finally found a good shot of a T-Bird aluminum IRS. Much cleaner on the front top of the case where it slopes down to the pinion carrier area.
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Old 07-18-2010, 09:36 PM   #12
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Doesn't look like those other housings have that sensor either,like yours does.
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Old 07-18-2010, 09:39 PM   #13
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I say try the grinder method. Cheapest option. Should anything go wrong or messed up, swap the housing. Either option would still be better than pounding on the tank or getting a cell.
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Old 07-18-2010, 10:10 PM   #14
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Yes I do not need that temp sensor or whatever it is. There is another one on the bottom anyway.

I may just end up grinding it. My only concern is whether or not the fins are adding significant strength/stiffness to the housing. They are well away from any of the high stress areas so the forces should be well distributed at that point. Plus I can leave a bit there, and even more on the side fins.

I also have another wrinkle going on with the driveshafts that could impact what I do with this housing. I should know more tomorrow. Hopefully I do not get shafted... in the ***...

Last edited by ZX-Tex; 07-18-2010 at 10:25 PM.
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Old 07-18-2010, 11:18 PM   #15
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I'd say get the grinder out and smooth those bitches to a reasonable level. The Miata is going to weigh half of anything else this diff ever came in, I really doubt that even if they were some type of partial load bearing element that it would cause any major issues.. I'm anxious to hear what the Driveshaft Shop has to say about those axles as well. GL with both ventures!
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Old 07-18-2010, 11:31 PM   #16
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Thanks. I hope I can work something out with the Driveshaft shop as well. If I cannot, then the smartest path may be to sell this entire diff assembly and use the funds to get a 28-spline truetrac, a different R&P, and another housing. Then I can get the normal driveshaft setup from the Driveshaft shop.

Or, I take the cheap way out. Get some more Miata outer CVs, rebuild the shafts I already have, grind down the fins on this housing, and make it work.
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Old 07-19-2010, 12:56 AM   #17
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For real. I am off wed and thurs, i would be glad to come help you, and if not, drink beer withyou
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Old 07-19-2010, 12:59 AM   #18
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Would it be possible to modify a set of the factory cobra axles (or insert other 31-spline variant) to be useable in our conversions? Or is that more trouble than it's worth? Just popped in my head, so I thought I'd throw it out there.
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Old 07-19-2010, 10:13 AM   #19
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One of those pics you posted (the smooth one in the middle of post 11) was the weaker 7.?" diff that they use in the non super coupe thunderbirds.
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Old 07-19-2010, 12:37 PM   #20
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Swap to the 7.5 and be done.... you'll walk home with more cash in your pocket and have a diff that fits better.
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