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Community Manager

Ford C6 Transmission upgrade?

After a little research, it appears you can upgrade your Ford C6 3-speed transmission with the quicker 1st and 2nd gears from a later model 4-speed Ford gearbox.  It makes sense considering the C6 was the foundation for the E4OD and 4R100, and it's great to see this is backwards compatible!  


This will really get my 1972 Lincoln Mark IV launching off the line harder. It also has roller/ball bearings (instead of thrust bearings) so it will likely put more power down and add to efficiency: both are always concerns with this monster of a gearbox.


I will probably pull the trigger on this conversion and report back!



CT PowertrainCT Powertrain


I wouldn't call the roller bearing vs. thrust bearing a huge concern unless you are WAY above stock torque and horsepower specs. A simpler alternative to going this route would be to install a touch higher stall speed torque converter. 300-400 higher rpms would get you off the line much smarter than you are currently. 


The reason I say this is that if you aren't experiencing slipping issues from your C6, why go through the trouble of a rebuild unless you are planning a rebuild anyhow. Although the e4OD and 4r100 are loosely based on the C6, I have found them to be wanting by comparison of durability even though they are MUCH better than the AOD that they replaced. With that said, the simple act of installing a constant pressure valve body in place of the stock one really helps as the T.V. cable becomes a kickdown, and the trans then gets a constant feed of pressure. I won't say most, but a LOT of AOD failures are from the T.V. cable being out of adjustment which WILL cause an AOD to grenade. 


It's up to you, but if the trans isn't broken, I wouldn't pull it for a better holeshot. Going with something like an 1800-2000 rpm stall speed torque converter will net you the same results for a LOT less moolah and a lot less work. 

Community Manager

Oh the trans was all kinds of worn out.  The shop's disassembly showed a lot of wear, but to be expected for an almost 50 year old gearbox. 


The upgrades are now in and I am gonna write about them soon.  I can't tell you how much different it is now...throttle response, acceleration, etc is way better. Sure you could get a lot of this with just a proper rebuild, but a 2200-ish stall and that short first gear are a BIG improvement off the line and around town. No way a C6 with stock gear ratios would scoot like this, and accomplish so much with a part throttle downshift. 


Now it has all come together for me. Not al C6 transmissions are geared the same either. 

The 77 LTDII I had had a shorter first gear, and a longer second gear than my wife's '79 Tbird. With the same rear gear, the LtdII would shift out of first at 5,000 rpms at 50mph. Second would take you to 90. My wife's tbird shifts at 4,000 rpm to 55mph in first, but then only winds out to 70 mph. If you wound it out 5,000 rpms (pointless with her 351m as it is out if breath by 4200), first gear would take you to 60, and 2nd would be about the same, maybe a tad lower. All with the same 2.75:1 rear gear. 

So you went with the 2200 stall, eh? That combined with a reworked valve body and a 3.55 rear gear in my Cougar makes for some fun holeshots. VERY fun🤫

Hagerty Fan
Not applicable

Although not a direct answer to your query Sajeev it sparked a memory years ago like in the 80,s I worked at a transmission shop the owner was a drag racer from way back and still raced his 427 Fairlane quite competitive also mostly stateside east coast he had a C6 Auto and I believe at that time ran A stock automatic I always thought what a pile stock was so many restriction till one day he pulled his trans for a freshen up usually did any work to his car in his home shop but this time did it on a Sunday at the main shop and asked if I would come in and give him a hand well a chance to work on a real race car sure,out with the trans and to the bench he opened it up and i stood there in amazement although a stock for the period Ford C 6 transmission it had all C 4 internals he looked at me and smiled but never said a word you could shove a chicken in where the main drum was i never thought it possible but there it was in front of me  and worked quite well I was like Hmmmm A stock i guess hard to detect but rotating mass cut damn near in half that fella new his stuff sorry Sajeev for a slight hijack jus thought U might like the story.Cheers R