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AT to MT swap

Old 07-23-2008, 06:17 PM
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Wow, congrats on the swap!

Interesting that the driveshafts are exactly the same except material. Does that mean us AT owners could swap to the manual driveshaft and reduce some rotational mass without changing anything else? The connnections, etc all the same?
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Old 07-23-2008, 07:04 PM
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yes, both ends are exactly the same, as is the length. Only the mass/material differs.
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Old 07-23-2008, 08:46 PM
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Wonder why Mazda did the heavier driveshaft on the AT? To save some money, I guess?
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Old 07-23-2008, 08:56 PM
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I imagine steel is a good bit cheaper than carbon with plastic/resin covering. I wonder why mazda went that extra mile to do the shaft on the manual cars...a light driveshaft is one of those 0.1% modifications that you do after everything else has been exhausted, in most cases.
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Old 07-23-2008, 09:03 PM
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Does the weight difference between the two feel substantial? I wonder if this would be a worthwhile, noticeable mod for us AT owners if we can find a relatively cheap used one?

Thanks for posting all this info!
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Old 07-23-2008, 09:07 PM
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I didnt think to weigh them, but the auto is definitely heavier by at least 2-3lb.

Odds are that you could do a before and after test...not knowing which shaft was on during which test...and not be able to tell the difference.
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Old 07-23-2008, 11:34 PM
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i think yours is the first ive ever seen someone pull off.
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Old 07-23-2008, 11:44 PM
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is the diff ratio different on an auto ?
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Old 07-24-2008, 12:58 AM
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I checked mine, it is a 4.44 and LSD. I believe they are all the same, but I am not an rx-8 options expert like I am on rx7s. It is easy to check...jack the back end up in the air and put it in neutral. Mark the differential input/driveshaft with a piece of chalk, facing the ground, and do the same for one wheel. Now rotate the input/driveshaft slowly, counting the number of turns it takes to turn the wheel one complete turn. You should be at about 4 and a half.

During this test, also note if both wheels turn the same direction, opposite directions, or only one wheel turns. This tells you if you have an open diff or a limited slip diff, or a worn out limited slip. IF both wheels turn and seem to be locked together, it is LSD. If one wheel turns forward and one wheel turns backward, it is a standard open differential (peg leg). IF one wheel turns and the other doesn't, it is likely an LSD that is badly worn out.

Speaking of that, I need to verify my mph versus the road markers and a stopwatch, but I see no reason why the speedo would be off given that the diff ratios are the same between the models.
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Old 07-24-2008, 01:36 AM
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Great read. Good job.
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Old 07-24-2008, 01:41 AM
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Needless to say, I almost died when i saw this post, PMMMMMMMMMMM'd!!!!!!!!!!!
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Old 07-24-2008, 02:32 AM
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Thats awesome! One thing though; wouldnt it have just been cheaper to buy a used MT?
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Old 07-24-2008, 02:39 AM
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possibly, but not really. I got this car about a year and a half ago for 10 grand cash. At the time, even medium mileage 04 MT's were still pulling 16-17 most of the time. I didnt have 16-17 to put into one at the time, and I didn't want to finance one. So it was either buy this auto that fell into my lap at the time, or not have an rx-8. I chose to buy it, figuring I could learn about the cars as I went and develop knowledge that I could use as part of my business later.

even now, I think most MT's still pull 14 grand or more in good shape, and I have a rebuilt motor and trans to show for about the same amount of money spent whereas most of those cars have used engines (or questionable mazda remans) and worn transmissions.
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Old 07-24-2008, 06:13 AM
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congrats on the swap. its really interesting because the majority of people wanting to do this swap dont have the skills and knowledge that you do.
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Old 07-24-2008, 09:58 AM
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From what I understand, the base model AT had a different rear end gear ratio, but the sport package on up (or touring, i'm not sure which) had the same 4.44 with LSD as the manual.
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Old 07-24-2008, 09:59 AM
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Originally Posted by RotaryResurrection View Post
I didnt think to weigh them, but the auto is definitely heavier by at least 2-3lb.

Odds are that you could do a before and after test...not knowing which shaft was on during which test...and not be able to tell the difference.
Oh well, I was hoping for more of a difference.
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Old 07-24-2008, 12:57 PM
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What would make it not worthwhile, is the fact that you pretty much have to remove the PPF to get the driveshaft out, and that PPF is heavy as a bitch. You want some weight savings? Get a carbon PPF instead of a metal one.

It probably only weighs 40lb, but when you are under a car on your back trying to bench press that ****** for about 45 seconds to get all the bolt holes lined up, and then you take one hand off to try and start a nut, you realize exactly how heavy it is.

And it's not like most rx8s (even modded) make enough ground thumping torque to crack a PPF anyway, unlike some modded rx7s that have done it.

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Old 07-24-2008, 01:38 PM
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Originally Posted by mdw1000 View Post
From what I understand, the base model AT had a different rear end gear ratio, but the sport package on up (or touring, i'm not sure which) had the same 4.44 with LSD as the manual.
What was the ratio on it?
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Old 07-25-2008, 12:27 AM
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Hey RotaryResurrection, I just want to say you are awesome for making impossible to possible. Support you all the way for doing all kind of experience on AT rx8
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Old 07-25-2008, 02:03 AM
  #45  
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I thought the 'mileage' was stored on a CAN module located near the gauges.
You might be able to swap just that part...

But that could've just been hearsay, I'll have to check.
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Old 07-25-2008, 02:55 AM
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IF the mileage were stored on a module in the car, it would still read the same. The mileage must be stored in the cluster itself, since the new cluster has retained it's old mileage each time, even though it was plugged into my car with all my original modules and boxes (I did this before I ever did the swap).
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Old 07-25-2008, 05:10 PM
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the module could be in the cluster... (i thought i wrote that... oh well)
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Old 07-25-2008, 07:17 PM
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The cluster is one integrated micro board, there are many things soldered to the inside of it but I did not see fit to try and remove the needles and jack up the gauges to get to the inside of the board and see what was in there. Bottom line, the cluster is an integrated, sealed, non serviceable unit, except to those very good with electronic boards and soldering. The solder points are so small and close that I couldn't even tell which functions most of the stuff went to...it is very hard to follow the traces compared to older, less complex boards.
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Old 07-25-2008, 11:50 PM
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Originally Posted by RotaryResurrection View Post
What was the ratio on it?
I think it was a 4.10, but don't quote me on that.
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Old 07-26-2008, 01:42 AM
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****, I wish mine had a 4.10 in it like the rx7s run. I mainly use mine for cruising and I see no reason for it to be turning 3500-4000 at interstate speed. The 3000-3300 that rx7s turn at similar speeds is bad enough for gas mileage.
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