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Index > Engine/Drivetrain > Thread: Just got one, with questions.
Thread: Just got one, with questions.
roaddancer


Hauling
Posts: 127
posted May 07, 2004 08:26 PM

Just got one, with questions.

OK, I'm back in the game! Just picked up a 75 that was converted to AT. Naturally the speedo hasn't a clue. Indicated 70 is about 60. Has anyone worked out a mix n match of speedo drives to adjust the reading? I'm thinking that a drive gear from an appropriate alternate year rear end might get it close. Naturally, it also has a different size tire as well. I will have to sit down and calculate various ratio changes and see what happens. I am acting on the assumption that the speedo itself was always the same. Does anybody know different?
Also, the tachometer appears to be reading at about half true RPM. I can't quite picture how, but will look into that soon. Anybody see that one before? Original type ignition. Might disappear after a tune-up. When I get to it....
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rx2/3/4/cosmo,repu,94 rx7,

       
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Klaus43


Rotorhead
Posts: 1259
posted May 12, 2004 07:48 AM
Edited By: Klaus43 on 12 May 2004 07:49

Congratulations!

Glad you're 'back in the game'! Things to consider: Rearend ratio may or may not have been different from one another for your year, manual vs. automatic... those automatics tended to die around 40-something K miles, probably due to lack of maintenance... Outside wheel/tire diameter has typically been reduced from stock tallness, adversely affecting speedo accuracy... (205/60 15's might be close enough...)
Don't know about your tach; sounds like funky wiring...?
(You want electronic ignition!)

       
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roaddancer


Hauling
Posts: 127
posted May 12, 2004 09:35 AM

It's a '75, and was originally manual. Tire size is off, of course...Who would leave it stock, tall, skinny tires! My previous experience with the '74 I had showed a problem of tire to body contact with wide, larger diameter rubber. I will eventually convert back to manual, as I miss the better power application, and plan to do some autocross. The AT would work locked in second, and the smoother power delivery would reduce the need for posi. There is no crisp throttle response with an old school AT. I expect it would eventually die from the abuse! It was freshly rebuilt by the P.O. so I have some leeway. I will have to find several parts for the conversion. The P.O. disposed of all that..Dumb!
It does have a recent Pineapple rebuilt engine in it. I figured the existence of all the hard to get body parts on it made it worth the effort and cost. This thing is complete! Just cosmetic restoration needed.
As far as the speedo, I wonder if the speedo drive gear from a '77 would put it in the ballpark.
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rx2/3/4/cosmo,repu,94 rx7,

       
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Klaus43


Rotorhead
Posts: 1259
posted May 13, 2004 09:23 AM

I would think

...that the biggest difference in speedo drive gears would be with the '77 model, since it had the tallest rearend ratio...
Why not try a set of 7 or 7.5" wide x 15" rims, shod in 195 to 225 width (depending on manufacturer, and specific tire) 60-series rubber? Certain Mitsubishi steels have the needed offset... Not the ultimate, but functional and economical for fitting under the stock REPU, and getting the approximate correct outside diameter...
You might even be able to go to a 50 series tire and still have 'em be big enough...

       
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roaddancer


Hauling
Posts: 127
posted May 19, 2004 09:52 PM

Went looking for the tach problem, and had no luck. Hooked up a hand held unit and got the readings I expected. So I opened the Dizzy, and found it is already converted to electronic ign. Don't know what source. Stock coils still wired in. The setup wasn't near 75 spec timing, and didn't seem to want to be. It ran worse if I moved that way. I don't think a funny voltage could cause a lower RPM reading on the tach, but who knows. I have a major visit to the dash ahead of me. It may be a bad tach. It's just a pulse counter, and may be messed up.
I shall begin re-constituting all I once knew about electronic instruments, and see if a light comes on. Damn light isn't too awful bright these days!
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brad


Rotorhead
Posts: 1671
posted May 20, 2004 10:29 AM

235/60/14 dunlop


       
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brad


Rotorhead
Posts: 1671
posted May 21, 2004 08:34 AM
Edited By: brad on 21 May 2004 08:38

235/60/14 dunlop

Only rubs on the drivers side fender. very lower front corner edge. only when hitting a pothole. just need to bend the fender a tad out of the way.




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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge

       
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