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68RFE Hard lockup

Practical Diesel Tuning

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Discussion and questions related to the course Practical Diesel Tuning

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Have a 2022 Cummins, had the trans go so installed a built trans, had 3 different tuners tune the transmission (hard to find a good tuner due to the truck being a little lighter then factory) its got a triple disc converter and the lockup is firm which i know is to be expected with a tripple disc but on the 3-4 shift it is absolutly violent from what i researched it says its because its engaging the overdrive clutch, any sugguestions on what i could change myself since, every tuner i ask says its bad tuning from the previous tuner then try theirs and its no better then the last, currently using hp tuners for software just unsure of what to change as the course doesnt talk about alot of trans tuning, also have efi live files if it has better adjustability for trans (from what i hear hp is better then efi for this truck)

Way outside anything I've done, last Time I had an auto'stripped was more'n forty years ago, but from what i do know, excessively high line pressure(s) may be a potential problem.

Many "tuners", and/or "tuner kits", seem to default to cranking up the line pressure to make sure the clutches engage "firmly".

There should be a process for checking this - can't advise the specifics, or the OEM spec' range, but there should be plenty on-line. Depending on the transmission fluid flow characteristics, you may simply need to plumb in a "T" fitting to the output line that goes to the transmission cooler. If it is high, it may be a simple case of removing and replacing a pressure relief spring, and while most may need removal of the sump and, maybe, valve body*, others may be accessable from the side of the transmission casing.

*that would also be an opportunity to check it was put together correctly, and that no spools are sticking, check balls were incorrectly placed, etc.

Oh, IIRC, some control protocols call for a torque reduction on shifts - no idea if this is even possible with your setup, but if all else fails, may be a potential avenue to check up on?

Also, double check it has the correct transmission fluid in it, there are differences between them and the wrong one may be part of the problem?

Taylor,

I think Gord has offered some solid advice. I've got quite a bit of time on the 68rfe and know exactly what you're talking about. I would start by logging line pressure and lockup activity during the aggressive shift. Is it shifting while locked, locking during the shift, or locking just after the shift?

Then, put the trans settings back to stock and log the same data. Is it happy or not? This might give you some insight as to appropriate line pressure for the 3-4 shift and lockup. Many tuners run excessive line pressure, especially on 'built' transmissions which already have aggressive clutches and accumulators.

Revmax told me once that their trans wanted 220psi for and very steep ramp rates so the pressure came up quickly even at light throttle. Tuning the trans to feel showed it much happier with 160-185psi and stockish ramp rates. Test and learn, go slowly and you'll feel any issue before you slip/hurt the trans.

Nick

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