Transmission longevity?
 

Hi all,
I have a 2001 F350 7.3 PSD auto 3.73 gears 4x4. I really want a tuner, and I like what I see at PHP. I have had one concern all along that has kept me from pulling the trigger- how will this tuner effect the lifespan of my transmission? I have 138K on the truck now, the tranny seems fine. I also checked my tranny manufacture date, and do not have the mechanical diode :thumbs up yellow:. So, is it necessary to get a valve body from somebody like BTS in order to preserve my transmission? I'm not looking for anything crazy here, just better fuel economy, more drivability, towing a horse trailer (about 8-9k) and PERHAPS the occasional trip to the track (like once a year, Diesel Nationals :cool:). How will my tranny hold up to a PHP chip, with and without an aftermarket valve body?
Thanks,
Jack

You have some very valid concerns. If I may, I would like to use my personal experience to help you make a decision.

I have an '01 with the "mechanical diode". My truck now has 128K on it and I became the second owner at 62K miles. The first owner chipped it immediately (Western Diesel Performance) and used it to haul a horse trailer, much like I have been doing since I bought it. If it's not the horse trailer, it's something that puts me at a combined weight of at least 15-16K with the occasional 20K tow. I also made a 200 mile trip hauling an M35A2 "deuce and a half" truck grossing 32K.

I don't race it or abuse it. I have run 6 different types of tuning since I bought it and it's still all original.

I also have some thoughts concerning the valve body craze that everyone seems to have. I don't like the thought of firming up shifts and making them quicker when it comes to stock parts...especially high mileage ones. Knowing what goes on inside an automatic transmission has kept me from modifying mine. My concerns have to do with durability and I believe that a stock transmission is not up to the task of shifting as quickly as a "built" or freshly built 'box. Take it for what it's worth. An aftermarket valve body WILL NOT make the transmission stronger.

The risk of breakage exists even with a stock truck. Cognizant operation will ensure a long life with ANY form of tuning.....recognize that certain shifts are more "fragile" than others (1-2 mostly) and that forced downshifts are hard on stuff.

Thanks, Cody. Some good info there. The only thing I am confused about is the shift firmness/quickness. Isn't some of that accomplished through tuning by increasing line pressure anyway? If so, how much would a valve body do anyway? From what I have heard, the quicker the shift, the easier it is on the tranny, because it reduces the amount of time internal clutches are engaged. Is this not true? Oh, and I forgot to mention my mods (not that it effects the tranny specifically) I have 4" exhaust, 6637 air filter, EGT, boost and tranny temp gauges, and 285/75 tires... I that that's everything significant).
Thanks,
Jack

Jack,

Yes, most aftermarket tuning WILL increase shift firmness significantly with a stock valve body. This helps reduce clutch "burn time" while pushing significant amounts of additional power through the transmission. This can be a good thing because as miles get put on vehicles, piston seal bores wear, clutch material and steels begin to glaze, etc. Increasing the holding pressure and shortening shift time help with these problems by giving a good feel.

The main difference between setting up the tuning for increased shift firmness versus using an aftermarket valve body is that with the VB upgrade, the fluid simply flows faster and easier through the orifices. With tuning, the fluid is usually forced through under higher pressure. When thinking about that aspect, it makes sense to go with the valve body upgrade. On the other hand, it's $300 that could be better spent because the increase in shift pressure to firm up the shifts is only momentary DURING the shift.


However, there are other things to consider as well like torque reduction during shifts. A lot of tuners command 100% torque during a shift. The factory runs between about 85-93% of torque during loaded shifts. Just doing this makes the shift feel more firm. I don't do it because I hate firm shifts when hauling a trailer. Don't get me wrong, there is a HUGE difference in a soft, long-burning shift and a "good" shift....the latter is what should happen under all driving conditions. A short "burn time" with a noticeable yet pleasant shift. I usually run 70-80% torque during a shift with the lower output under heavy load shifts.

There are mechanical components ("hard parts") inside the transmission that wear. Typically these are splined shafts and hubs. They also include friction element drive teeth. Under operation, there are many instances where a splined shaft or hub needs to reverse directions almost instantaneously. The more miles that are on the transmission, the greater the free play or "lash" between the spline teeth. At this point, reversing the direction becomes like more of a hammer and wear (to the point of stripping out or breaking) becomes more likely at an increasing rate. Clutch friction teeth suffer the same fate.

Wear is a fact of life, but purposely trying to force something to occur faster than designed is more likely to break it. If you play nice and don't try to abuse your truck, a program with firmer/quicker shifts WILL help extend transmission life. Racing stoplight to stoplight and performing multiple 1-2 upshifts under full load WILL kill your transmission in a hurry though, stock or not.

Cody,

What you said is exactly the reason we have to be very careful how torque reduction is handled. There are programs where the torque reduction is reduced or eliminated to achieve a specific feel, but it should never be removed on towing programs where a significant load is being pulled. It's a quick way to overstress the hard components as well as the clutches.

Installing a modified valve body has a significant advantage because it allows the transmission fluid to flow more easily through the programming orifices and results in faster flow into the clutches and more responsive clutch activation. Also, because the fluid no longer needs to be forced through at higher pressures, there is also a resultant drop in tranny fluid temps... often as much as 25-30 degrees.

Good questions, for sure. :2thumbs:

Well there you go, 74baja. Straight from the horse's mouth. :thumbs up yellow:

I guess I don't see this because I don't understand how cutting transmission input torque momentarily during a shift is bad (GM has been using it on the Duramax/Allison combination since '01, and it's REALLY noticeable). Unless there are other things at work here in addition to slightly reducing engine torque that is happening in the code at the same time that I am not observing, I don't see a downside.

I guess I shouldn't say that I have reduced the values in the torque reduction maps much if any under high load (the upper right corner of the table) but primarily in the low load portion (where stock values are at 100%). This has made for seamless shifting at light acceleration that isn't jerky. I can increase the TV pressure during the shift (hence the shift occurs very quickly and positively) and still have a great shift feel.

Concerning the 2-3 shift, I have found that commanding low torque output during a shift (in the 60% range) makes for an especially harsh upshift and actually increasing the torque output back into the stock range will soften the shift a little. The shift seems to get better the lower you go until the values are lower than about 75%; then the shift feel improvements appear to get counter-productive (on the 2-3 shift).

Here's a question. Why do the 02-03 transmissions have a horrible flare if the torque reduction values aren't increased to 100% while the earlier trucks do not (even when running close to stock power output)? What is changing here that has nothing to do with engine torque output? Is this why the values we are discussing shouldn't be decreased due to side-effects NOT related to engine output?

Well said. There still is ZERO strength addition to the transmission though.

Edit:

Ok, so maybe I was dumb......

It seems the F1 (help) came in handy today after I typed the previous post.

"This is used to limit torque output during shifts. This helps prevent wear on the clutches and also reduces shift flaring."

If I am reading this right, then there IS something going on during the engine torque reduction that has to do with transmission operation. What exactly though? I was thinking "defuel during shifts" as is the case with the Duramax/Allison because setting the torque reduction values around 70% for a low load 1-2 shift creates a dip in the RPM only during the shift and then it recovers and begins accelerating again.

So many questions.....are you sick of me yet?

:D