FMX transmission swap with C4

[lefty 10]

Hi guys

 

The old FMX has seen better days! have attempted rebuild on 2 seperate occasions now, by 2 different so called 'EXPERTS' and both have failed - same ol' story parts hard to find and product knowlage minimal. Lost faith!

 

Question; Is it a straight forward change over from FMX to C4 or C6 in 1969 mach1 351w. Which transmission is best suited to handle a slightly worked engine,(street use only no drag racing)?

[chrishall1953 11]

I choose a C6 for my FMX replacement. You will need a new rear crossmember which i found used at a swap meet for 25 dollars. In addition there are two bell housing styles for the C6 a tall and short the short will fit the C6. Also the linkage will need to be tweaked slightly. Good luck

[BigDuke6 17]

I have a C6 in my car because that is what the PO put in it. I got all my parts from Broader Performance. I would rather have a C4 because it is lighter and consumes a lot less power. A C4 can be made to handle a decent amount of power (500 hp) for the same price as a 700 hp ready C6 from Broader Performance dot com. The C6 shines behind a 1000 hp big block. Unless you are making insane HP, you can stick with a C4.

[miketyler 15]

I dont know how much freeway driving you do but consider a later model AOD trans? I replaced my FMX with an AOD and was surprised I didnt have to change or alter my driveshaft length.

[stangs-R-me 121]

AOD is based off of the FMX and I aggree with Mike that it would be the BEST choice if you do any highway cruising. They are a bit tricky getting properly set up to run behind a carburated engine and will cost a bit more than a C4 ... this I know from personal experience .. I had to make my own linkage back in the 80's as there was no store-bought kit available back then; and YES I did burn up one AOD due to improperly tweeked linkage !!

 

Cheapest and Easiest route would be a C4 ... a lot more common than a small block C6 which you will only find in Ford Trucks of the 80's. Unlike the C4, the C6 design has an integral bellhousing so the more common big block C6 will not bolt up to a small block engine.

 

Back in the 80's there used to not be much of a performance aftermarket for the C4, but that has changed to where they are building them to handle big-block power as well as special bellhousings to mount to big-blocks.

 

As BigDuke stated, C6's are also quite a bit heavier and consume A LOT more power when compared to a C4.

 

Back in the 80's, I had my tranny guy find a SB C6 for my '67 Fairlane. It took as while and was not cheap, but I had trashed 2 C4's in Mustang's with just plain 302's and the Fairlane C4 was on it's last legs as well. That C6 in that Fairlane was behind what WAS a potent '85 HO 5.0L when it was in my '79 Fairmont with an AOD. In the not much heavier Fairlane and behind that C6 the lost power was very obvious.

 

Just read an article recently that there are now ways to drastically reduce the power consumption of the C6 trans by adding roller or ball bearings to most if not all the power robbing friction points, but this is new technology so it is probably not cheap.

 

Doug

[LindenBruce 27]

Hey Lefty,

 

If you decide to do the AOD I have pics of the TV cable bracketry that I modded for my 69. Just let me know and I will send them to you. Bruce

[BigDuke6 17]

 

Just read an article recently that there are now ways to drastically reduce the power consumption of the C6 trans by adding roller or ball bearings to most if not all the power robbing friction points, but this is new technology so it is probably not cheap.

 

Doug

 

That's what I have on my C6. I don't think it is that expensive. Broader Performance sells a wide ratio gear kit for $325 and a rollerized wide ratio gear kit with needle bearings for $420. A rollerized rear planet gear is another $105. I talked to Jay at Broader Perform. at great length when selecting parts and he told me that I should expect to see my rollerized C6 have the same parasitic loss as a standard C4. He said that a C4 with rollerized front and planet gears could be comparable to a manual tranny depending on other factors such as a tight converter and clutches and bands.

 

I am betting I reduced parasitic loss by a few percentage points, maybe even 5 considering I went all the way on my rebuild, with a tight converter, a 5 clutch direct drum, 2 inch rigid band, R code servo, full manual forward valve body, etc.

Edited April 10, 2012 by BigDuke6

[lefty 10]

Many thanks to all for your replys...lefty