I'm trying to learn as much as I can about cars and trucks so I can understand them better. When I'm ignorant to all the facts I try to apply what I perceive to be common sense and take things from there.

That said, today's topic brings us to shift kits for auto trannys. From what I've read the purpose of a shift kit is to prevent the transmission from engaging 2 gears at once when shifting between gears. When shifting between gears and overlapping the bands it tends to put the wear on the transmission that will eventually ruin it because you're stressing 2 gears at once and sort of feathering them for a smoother shift. A solution after a rebuild is to install a shift kit which eliminates the overlap of gears. The drawback to this for the operator is the more jerky shift between gears. The overlap of gears provides a smoother ride but stresses the transmission more.

OK, if those facts above are pretty much correct I have a few questions. While I understand the overlap stresses the transmission wouldn't the "bang" feeling of the rougher shift between gears put just as much or more stress on the internals? If not the transmission than certainly the u-joints, axles, transfer case, etc.? In the past those components weren't used to being jerked but rather eased into use. A quick jerk seems like it would add up stress quickly. Same with the trans itself. Maybe the bands wouldn't wear out as quick but wouldn't the gearing inside it be stressed since it's a rougher shift now?

 

Those are some very good questions. I have often wondered about the good/bad effects of a shift kit myself.

When I first got my truck, the previous owner installed a shift kit in the AOD and it "banged" into gear as you described. I personally didn't like it very much, and it did feel like it was harder on the drive train components. When the transmission failed a few years ago, I had it rebuilt without the shift kit. It shifts nice and smooth now; not too soft, yet not too firm. I like it better this way, but everything I seem to read in these forums says that a shift kit helps extend the life of the transmission.

The transmission mechanic who rebuilt my transmission (friend of mine who wouldn't BS me) didn't say anything about installing a shift kit, but he did tell me that installing an auxiliary transmission cooler is good for an automatic transmission, as heat is what usually kills automatic transmissions.

 

i put a shift kit in every truck that i use for pulling and even on my daily driver. my gmc that i drive daily has over 120k on the trans since installing the shift kit and when i mean shift kit i mean it lays 3 foot of rubber posi-marks when ur in the throttle hard ive never had any issues with any other driveline components as well as the transmission

 

I've heard this too. Fortunately my truck rolled out of the factory with the towing package so I have that little cooler in front of the A/C cooler to go along with the radiator cooler. The trans cooler does seem pretty small (it's roughly 4"x12") but it must help some I suppose.

 

Ok, I'm not good at typing out this sort of stuff so bear with me. For starters, the bands in an AOD are for two separate operations. You have the OD band and the Low/Reverse band. The OD band is applied, well, in the od gear (4th). The low/reverse band is applied in low (1st) and reverse.

From the factory an A/T slips the clutches in the clutch packs for a softer shift. The softer shift is NOT for the sake of the trans, but because consumers wanted a smoother shifting trans. The slipping of the clutches causes heat inside the transmission and we all know heat is the #1 enemy of a trans. A shift kit reduces the slippage, which is why the shifts are firmer. With less slippage, there is less heat buildup. This IS better for the trans.

This is all achieved by replacing different springs inside the valve body, replacing certain valve pistons, in some kits changing over to a different separator plate, in others changing the accumulator springs, and in some there is drilling of the valve body involved. This adjusts the line pressure and when the trans shifts by changing spring rates.

Here are two examples of different shift kits.


Transgo C-6 Kit


Transgo AODE Kit - corrects 4-2 downshift problem

Also for more valve body theory try here: http://www.autoshop101.com/forms/AT23.pdf
This is a Toyota Tech article, but well worth the read if you interested in understanding how the valve body works.

Hope this answers some of your questions.

 

Smashclash, how many miles are on your AOD now? There are some members in here that have AODs that have lasted well over 25 years and 150K without a shift kit, so I don't think it is imperative for transmission life.

The original AOD in my truck lasted to a little over 100K miles before it needed to be rebuilt. The previous owner then installed a shift kit with the rebuild and it lasted almost 80K miles. Both times the problem was that the transmission overheated and the clutches welded together. I don't know if the shift kit had anything to do with it or not, but that is my own experience. My truck did not come with the auxiliary cooler, so I got one from the junkyard and the lines for about 20 bucks. When my AOD was rebuilt a few years ago, I installed a new radiator and a Ford AOD auxiliary transmission cooler.

With an AOD, the Throttle Valve cable can be adjusted which affects the line pressure, which in turn will affect the firmness of the shifts. My transmission mechanic/friend adjusted my TV cable for a somewhat firmer shift than factory, but not as stiff as the shift kit I had.

This is a good example of how a lot of people tend to "rawhide" their vehicles when they install shift kits (or other "upgrades" to their motor), so that may or may not explain why my AOD didn't last as long with the shift kit installed and the previous owner still had it.

That makes perfect sense to me. I guess that means two things. If you do not have a shift kit, your automatic transmission will slip the clutches more which in turn generates more heat, therefore an auxiliary transmission cooler will indeed help. If you do have a shift kit, less heat is generated and an auxiliary transmission cooler probably isn't as important.

 

If you are into towing/hauling fairly heavy on a regular basis, the biggest cooler you can find/fit is always a good idea. For the average stock truck that sees DD use and no real work, whatever it left the factory with is most likley sufficent.

 

Thanks for that. I'll read the link when I have more time tonight. Interestingly I read that the valve body could be what plauges my 2005 Mazda6 daily driver. It's not a serious problem and if you drive it you can avoid it but basically it suffers from a shift SHOCK after it's downshifted. For example, let's say I was just accelerating fairly hard and going around 25 MPH and was in 4th (it's a 6 speed auto) and then coasted without applying a ton a brake. Sometimes when I'd go back to the gas the trans would have a hard time finding what gear to be in, drop down low and really BUCK the whole car. I mean, to the point where you're almost certain something in the front end just broke. I saw this effected some Mazda's on the Mazda forum but mine is out of warranty now. Mazda had elected to just replace the entire trans!

Anyway, it's very rare and I have a feel for the car so I can pretty much avoid it but it's a frustrating thing in the back of my mind.
My truck's drivetrain is still all original. Just over 75K on it. It seems to shift fine to me. There's a little jerk between 1st and 2nd on occasion but the rest of the gears shift like butter. I certainly don't beat the truck and hope/expect the drivetrain to last a while but I can't help but want to research what happens if/when the time comes so I"m not caught with my pants down!

 

Out of curiosity, have you checked the snorkel for the air box? I've had cars come in for transmission problems, which ended up being solved by replacing cracked/broken snorkels. Not sure if this applies to your car, but you might want to take a look.

 

I'll check it out... if I even have one? I assume I'd just be looking for a hollow tube coming out from the trans somewhere?



Which is kind of funny because there's a hollow tube on the truck that's vertical with the end facing the ground. I always sort of wondered what this vent was for and how it seemed semi impractical for it to breathe if the front end ever got sunk in some mud/water for a little while.

 

Smash, I too have the stock AOD with just under 130,000 on it and mine seems to be working about like yours does. A little hard out of first, then smooth on the rest. I doesnt really shift into OD at the most opportune times, but it works fine. I was wondering about a shift kit too, but after reading this article, I think im jsut gonna install a trans-cooler whenever i get around to rebuilding. I wonder how difficult it would be to get the tranny to shift at better times... But i guess that all depends on which rear end i switch to, and what size tires ive got. I'll figure all that out later. Anyway, my whole point is, thanks for starting this thread.

 

If I'm ever hauling anything with some real weight, off-roading, towing, or in a place with steep grades (i.e. mountains) I drop the trans down to D. Otherwise I put it in OD. Can't really recall the need to ever drop it into just 1. Then again, I've only owned the truck about 8 months.

 

Your air cleaner box on your '05. It sounds silly, but you might take a look.

 

What does an air cleaner box and snorkel from an '05 have to do with an AOD transmission for a 1986 F150?

 

It has nothing to do with an AOD and everything to do with his '05 Mazda