TravisTheHuman Posted February 1 Share Posted February 1 I'm starting this thread with the hopes of having a vehicle-agnostic discussion of the 8F35 & 6F35 Transmission, hence my post in this forum vs. a specific model forum. As you might be aware, its used in about 8 (?) different Ford vehicles, so its pretty common. Sadly, its also common for it to die a horrible death as mine is doing in a new-to-me Transit Connect. As a bonus, the price to have it replaced is borderline ludicrous (dealer quoted me $8200, AAMCO quoted $9500). After scouring the internet for information on this, this is what I have come to believe (although hard data is extremely hard to come by): Most (all?) shops that replace this transmission source it from Ford/Ford's authorized rebuilder There is no documented improvement/upgrade for the replacement unit Its common for this trans to see very high temperatures, even on the highway in a single gear Its common for the cooler to clog with clutch material There is no recommended fluid change/service interval on this transmission from Ford If anyone wants to dispute these or add, please chime in. Based on the above info, [Warning: rampant speculation ahead], its my guess that the clutch particulate matter slowly (or quickly??) clogs the cooler or the thermostatic valve, compromising cooling, causing high temperatures, causing increased wear. A vicious cycle that quickly leads to an untimely death. Strategies I see for dealing with this: 1) Install the tow package cooler available for the Escape/Maverick/Bronco Sport(?), bypass/drill out/install a kit to open up the thermostatic valve (full cooling all the time). Combine this with regular (25k ish) fluid changes or fluid flushes. 2) Install a separate cooling loop (not sure where to tap in) that uses an aftermarket trans/diff cooling pump and heat exchanger. Put a spin on oil filter in this loop. Combine this with regular-ish fluid changes. Can also easily change the filter and top up fluid on a regular basis. 3) Install a manual transmission. There is only plausible on certain vehicles. In the case of the Transit Connect, many have attempted, but I see very little evidence of success or how to do it. As I am currently living the apartment life (no garage, no second car), this one is off the table for me unless someone is aware of a shop that can do this (in which case, take my money). Thoughts on the above? Quote Link to comment Share on other sites More sharing options...
jpd80 Posted February 1 Share Posted February 1 This might be completely wrong but on the 6R and 10R transmissions, ther is a thermostat switch on the cooler outlet circuit, it stops oil flowing to the cooler until the temperature reached 95C which has been a point of overheat failure over the years. Might be worth finding out if the 6F and 8F gearboxes have the same sort of cooler thermostat…. Quote Link to comment Share on other sites More sharing options...
Captainp4 Posted February 1 Share Posted February 1 I don't know anything about this specific transmission, but adding more cooling capacity to an automatic is never a bad thing. Waaayyyyy different eras and tech, but I added a cooler with a fan on my '78 bronco with a c6 that was getting so hot it was overheating the engine coolant because the coolers were stacked (higher stall converter in trail riding speeds didn't work out so well lol), but it made a huge difference. I know there's not much room in modern vehicles to add more coolers, but if you can find room I don't see how adding another cooler in line wouldn't help, this was a common thing to do at least up until the e4od in half ton and larger trucks when you added more power or load to extend transmission life. Quote Link to comment Share on other sites More sharing options...
TravisTheHuman Posted February 2 Author Share Posted February 2 (edited) 16 hours ago, jpd80 said: This might be completely wrong but on the 6R and 10R transmissions, ther is a thermostat switch on the cooler outlet circuit, it stops oil flowing to the cooler until the temperature reached 95C which has been a point of overheat failure over the years. Might be worth finding out if the 6F and 8F gearboxes have the same sort of cooler thermostat…. As I mentioned in the first post, there is a thermostatic valve. I suspect it could be the first part to clog. I'm not 100% sure how it works, it appears to be a ball/spring scenario - so I'm not totally sure how to render it full open all the time. If its as simple as removing the ball/spring, awesome. This bypass kit comes up when you search for 6F35 and implies it fits. But is opening the cooler flow full time really this complicated? Edited February 2 by TravisTheHuman 1 Quote Link to comment Share on other sites More sharing options...
TravisTheHuman Posted February 2 Author Share Posted February 2 (edited) 16 hours ago, Captainp4 said: I don't know anything about this specific transmission, but adding more cooling capacity to an automatic is never a bad thing. Waaayyyyy different eras and tech, but I added a cooler with a fan on my '78 bronco with a c6 that was getting so hot it was overheating the engine coolant because the coolers were stacked (higher stall converter in trail riding speeds didn't work out so well lol), but it made a huge difference. I know there's not much room in modern vehicles to add more coolers, but if you can find room I don't see how adding another cooler in line wouldn't help, this was a common thing to do at least up until the e4od in half ton and larger trucks when you added more power or load to extend transmission life. Agreed, however my concern with this transmission isn't necessarily capacity, but flow. My suspicions are even the stock capacity is plenty, but it clogs, hence the desire to get a filter inline, open up the valve, increase fluid change frequency, etc. As I mentioned, there is a larger OEM cooler on tow package models - I have no doubt there is plenty of space for the cooler in most (all?) applications of these transmissions. I'd love to see evidence of which part clogs though. Edited February 2 by TravisTheHuman Quote Link to comment Share on other sites More sharing options...
jpd80 Posted February 2 Share Posted February 2 4 hours ago, TravisTheHuman said: As I mentioned in the first post, there is a thermostatic valve. I suspect it could be the first part to clog. I'm not 100% sure how it works, it appears to be a ball/spring scenario - so I'm not totally sure how to render it full open all the time. If its as simple as removing the ball/spring, awesome. This bypass kit comes up when you search for 6F35 and implies it fits. But is opening the cooler flow full time really this complicated? Yes unfortunately and that kit is the answer, it’s the same rotten thermostat they put in the RWD boxes. They came up with the bypass kit because the oil gets far hotter than intended before the thermo opens. Looks like the problem is repeated in all gearboxes on the list….. Quote Link to comment Share on other sites More sharing options...
GearheadGrrrl Posted February 2 Share Posted February 2 I've got a '22 Transit Connect with the 8 speed auto, in the manual it says 150K miles service interval but lowers that to 30K if you're towing or hauling tall stuff on the roof. There was also a TSB that noted some internal transmission upgrades around December 2021, unfortunately mine was built before that. I'd ask Ford or the previous owner for at least a contribution to the rebuild cost, also I remember someone on the fordtransitconnect.com forum that was able to revive these transmissions by doing some work on the solenoids. Quote Link to comment Share on other sites More sharing options...
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