1970 Mustang Transmission Swap

70grande

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Feb 3, 2009
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I have been having a huge problem with my C-6 Tranny for the past 2 years. Long story short I had a bad experience with a rebuilding shop and now after taking it back to them they are suggesting that I completely swap up to a new tranny. I'm not going to pay them one more dime if they cant even rebuild the thing one time. It got me thinking though, why not switch up to a modern day automatic?

What are some good 4-5 speed tranny swaps that I can do easily and cheaply? I heard the transmissions from 89 5.0s swap well but then again that is what the shop tried to convince me to let them do.

Im open for any suggestions. Thanks in advanced.

B.T.W. its for a 351 Cleveland with electronic ignition, Holley carb, Pertronix electronic ignition, and a performer air-gap intake.
 
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D.Hearne

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Sep 29, 2000
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There are no cheap modern overdrive transmission swaps. You can buy a lot of gas for the difference you'll end up spending. Get the C-6 fixed. Is it a C-6 or an FMX ? Most had an FMX
 

70grande

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Feb 3, 2009
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There are no cheap modern overdrive transmission swaps. You can buy a lot of gas for the difference you'll end up spending. Get the C-6 fixed. Is it a C-6 or an FMX ? Most had an FMX
The 2 tranny shops I have taken it to said that it was a C-6. And it doesn't have to be cheap, I was just wondering what some of the least expensive swaps people have done are, even if they are $2000.
 

2+2GT

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Apr 25, 2009
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Well, a 70 351 would have had an FMX from the factory, but that would have been a long time ago, and anything is possible.

You could just take the C6 to a competent shop. A good shop will either fix it or tell you why it can't be. What is wrong, anyway?
 

70grande

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Feb 3, 2009
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Well, a 70 351 would have had an FMX from the factory, but that would have been a long time ago, and anything is possible.

You could just take the C6 to a competent shop. A good shop will either fix it or tell you why it can't be. What is wrong, anyway?
After taking the car to a shop about 8 times for warranty repairs they are just now claiming that the case is warped due to heat and that the tranny is on its last legs. Two other shops that I have taken the car too opened up the transmission to check out the problem and they found that the car has no second gear whatsoever!

Also, I understand that the C-6 will work fine when I get it professionally rebuilt but I want a transmission that is better than fine. Maybe a 4 or 5 speed.

Feel free to share any transmission tech with me that may shed additional light on the issue. Automatics are something I just cant fully figure out.
 

68RCodeConv

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Oct 2, 2003
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Contact Broader Performance. They will set you up with a new tranny and custom converter for less than $2K. No core required.

I just bought a 500hp rated C6 from them for my FE motor. With custom converter, shift kit and low gear kit it was only $2200.

These guys know their stiff.
 

tx65coupe

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Nov 29, 1999
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My vote also goes for an AOD conversion. Just get an non computer controlled one.
 

streetdemon70

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Apr 4, 2005
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im about to do a 5spd swap on my 70 coupe. there are lots of websites to help out. just do a search in here and you will get lots of advice.
 

70vert

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Dec 31, 2004
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Gear Vendors Overdrive?

Have you thought about getting your C6 fixed and getting a Gear Vendors overdrive? Sure they cost a lot, but I bet fixing your C6 and adding a GV would cost the same or less than an AOD swap and then you can have a manual split between each gear for 6 total gears . . .