Manual Shift option wears out transmission

[GeneralMaximus]

I own multiple vehicles with manual transmissions. Whenever I downshift, I always rev match first. During spirited drives, I may even heel/toe when slowing for a curve. Barring necessity(due to a steep downgrade as a few have stated), I would never use the manual mode on an automatic for normal breaking, due to the inability to rev match.

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[BourbonRunner]

Throwing this out there: in all the stress testing of this and other transmissions with manual shift modes, if there was a precaution against downshifting to slow speed like with a clutch and gearbox, it would probably say not to.

Then again, the reality is the use cases for this type of behavior on an automatic transmission are limited. I can see doing this on an especially steep downhill grade to preserve brakes (descending the Mt Washington Auto Road for example), towing, or if your brakes go 10-7.

 

[ShadowsPapa]

I own multiple vehicles with manual transmissions. Whenever I downshift, I always rev match first. During spirited drives, I may even heel/toe when slowing for a curve. Barring necessity(due to a steep downgrade as a few have stated), I would never use the manual mode on an automatic for normal breaking, due to the inability to rev match.

I have no problem with manual mode in Jeep or manually shifting my other automatics but I do watch the road speed vs. engine RPM vs. gear I'm about to hit.
You get to know the car and know what speed you can safely drop back a gear and not make the tach climb too high too fast. I guess it's experience? It varies with every vehicle, gear ratios and so on, but you get a feel for it and when you see the tach jump and the engine wind up and you feel the jerk back - it's too much.

Manually shifting isn't bad, manual mode isn't bad - it's how much RPM jump you cause by the downshift that's the problem. People drive thousands of automatics manually every day, no problems.

Doesn't take much to find out that's true.

There's also another area people may not be thinking of - the differentials - the rear axle, the ring gear and pinion bearings. The ring gear has a weaker side and that's the side you hit when you do a downshift that makes your passenger lurch forward in the seat. using the back side of the ring gear like that isn't a good idea.

It's not the manual mode or manual shifting that's a problem at all - it's downshifting to avoid using the brakes - downshifting to do a quick drop in road speed, with a large increase in engine RPM vs road speed.

 

[chorky]

There's thousands of guys who modify automatics with manual valve bodies and shift completely manually - just without a clutch.
Think of those who have installed paddle steering wheels and the sport shifting of automatics.

All I can think of is you are downshifting too soon and putting a big drag on things.
Iron is going to be from the planetary gears for the most part.



Naw, not unless downshifting too soon at too high a road speed. Thousands of people have used the paddle shifters, or converting older automatics to a full manual valve body.



Only if shifting down too soon, or using it instead of braking.
You'd have to downshift and really feel it pull back to be abusive.
The TF998 has been turned into a racing transmission forever - manual valve bodies, hammering with 500Hp - so unless a person downshifts and really causes a hard drag on things, it shouldn't be a problem.
Iron indicates gears.

The problem comes in downshifting too soon, driving in too low a gear and then you have a sort of back and forth force on the planetaries.

But the transmission people out there even confirmed my belief - it's not bad unless you do it wrong (like I described above)
Using downshifts instead of braking is bad - but manually shifting isn't harmful. It's just when you drag the vehicle back too much by dropping down a gear before you really should.

There's a lot of info out there on it. You can shift if manually all you want - it's when you drop a gear and feel yourself moving forward in the seat - you are stressing things then.

Shift manually all you want - but temper how you do it. Manual shifting will not hurt the transmission.

Yeah but I would like to think that no damage would result even from downshifting at a relatively high speed unless it was done over and over again. I know I have downshifted off highway at least a dozen times with the intent to slow down and control speed. I have done that for years with auto's and never had an issue before. Now on the highway, sure thats a bit of a different story I suppose

 

[GeneralMaximus]

I have no problem with manual mode in Jeep or manually shifting my other automatics but I do watch the road speed vs. engine RPM vs. gear I'm about to hit.
You get to know the car and know what speed you can safely drop back a gear and not make the tach climb too high too fast. I guess it's experience? It varies with every vehicle, gear ratios and so on, but you get a feel for it and when you see the tach jump and the engine wind up and you feel the jerk back - it's too much..

I guess my point is, if I wanted that type of driving experience, then I would have bought an MT. But I paid $2,000 for an 850RE. On my normal day to day drive, I’ll just stick with the Gas and Brake pedals and let the computer decide on all the shift points.

 

[ShadowsPapa]

I have done that for years with auto's and never had an issue before. Now on the highway, sure thats a bit of a different story I suppose

Back to "it depends". If you are tooling along at 70 and in 8th and drop back a gear at a time to 7th then 6th and watch the tach doesn't shoot up too high too fast, it's not a big deal.
Around here, it's hilly - and to keep from gaining speed, I've learned using the brake pedal in a certain way can cause a downshift and applied engine braking - by the TCM itself. I find I'm down 2 gears from where I was, and going down the hill without gaining speed. So - the Jeep itself will do that.
I notice it even more when towing in our home area - it really will apply engine braking and drop sometimes 2 gears at a time. It's actually programmed to do that if you dig up the details on these. They don't always shift down one gear at a time - they'll often drop 2, skipping one of the ratios.

I'm not sure about these, but many transmissions of the past actually ran higher line pressures when manually shifting, meaning less slipping of the clutches and bands.

 

[chorky]

I'm not sure about these, but many transmissions of the past actually ran higher line pressures when manually shifting, meaning less slipping of the clutches and bands.

I was just about to ask if you knew about this. I have a suspicion that these modern transmissions run a fairly static line pressure all the time now. But I could be wrong. I never seem to hear of pressure issues like I did in the early 2000-2005. Then again, I haven't rebuilt an auto trans since 04 anyway.... I vaguely recall reading that maybe only reverse is where there is a higher pressure. That could have been for a different vehicle too who knows.

 

[redriderjf87]

Interesting but makes enough sense I suppose.

If you're not rev matching in the case of a manual, something has got to absorb that extra energy being put on the components.

I'll admit I've driven a few rental cars in manual mode like that, pretending they were manuals ha

 

[Volt0]

Why would anyone do this on the road? I understand certain situations off-road. Does the OP live/drive in mountain passes a lot, or are you doing this to behave like a jake break b/c of hauling something heavy ( and/or undersized breaks for oversized tires )? What’s the scenario?

 

[cranbiz]

I downshift the auto in my motorhome all the time to assist the brakes. Never had an issue. Of course, I'm towing my Jeep on a trailer. I have plenty of braking between the 1 ton brakes on the MH and dual axle trailer braking but it helps keep the brakes from overheating and allows me to come to a nice, gradual stop. You just have to match the speed to the gear.

 

[legacy_etu]

My gut has to call BS on this theory.........although your evidence is interesting. I gotta add that the basic trans. in these is the same as what's in my Supra and let's just say that gets enthusiastic use (both up and down) and I've never had a hiccup nor anybody else on the Supra forums. Trans. is solid even on heavy track duty.

One common denominator in all this (I'm going to assume) is it's the same shop doing the work. Could it be they're doing something wrong on install? Suppose you'd never know........

 

[Mr._Bill]

Isn't the transmission used in the JL/JT the licensed version of the German transmission that is produced in a Stellantis factory?

 

[Maximus Gladius]

Why would anyone do this on the road? I understand certain situations off-road. Does the OP live/drive in mountain passes a lot, or are you doing this to behave like a jake break b/c of hauling something heavy ( and/or undersized breaks for oversized tires )? What’s the scenario?

Good question. I live in a city that’s an hour from rolling hills and the Rocky Mountains. The city has some big hills too, the kind of braking needed would be to either ride them like I see so many do or pump them, which is my style. My tires would be considered closer to 34”.

My vehicles of choice have always been manual shift types so I’ve had great enjoyment in being more “involved” which also included using the gears to assist in slowing down. So now that I have this automatic with the manual shift option, I used it to assist the brakes which, when thinking about the physics of that, the stopping energy is shared and not all on the brakes. My book doesn’t warn against this and it also seems to know when a shift is dangerous to perform, so it won’t. If the transmission was beat to hell, it would throw a code and go into limp mode and non of this happened with my driving style.

This time with this new transmission, I’m not using the manual shift and the analysis report shows the benefit of that.

So let’s all assume I actually know how to drive (bare with me Bill) and that i take great pride in this vehicle and past ones too and I’ve taught my kids how to be responsible to care for what they own, I know that to beat the shit out of this vehicle or take the rpm’s to red line because I just stole it and escaping the cops or I just want to make my wife yell at me or maybe race that sports car cause I think I’m one too or slam those rpm’s to shy of red line to slow down the truck, … this will in fact bring harm to something not built for it and would be abusive.

Let’s also assume, (Bill), that there’s was a manufacturing “Covid” problem as the dealership said and QC went out the window and this component was sub par as was #2 transmission that was made at same time but failed at just 500kms.

I’m going off a theory that any use of the manual shift feature that puts negative force on the clutch packs in this auto transmission (beyond what the computer would naturally do) will bring extra wear to the transmission and cause a shorter life to it than what would be considered expected by the engineers, so it should never be used unless you feel it’s absolutely necessary.

So far, I’m the first to run this test and we will continue to see analysis reports and cross check it with #3 tranny as we move along. So to some degree it’s a controlled study, we just don’t have the internals of #2 or 3 to look at, …we just have a theory and two pages of debate so far.

 

[legacy_etu]

Good question. I live in a city that’s an hour from rolling hills and the Rocky Mountains. The city has some big hills too, the kind of braking needed would be to either ride them like I see so many do or pump them, which is my style. My tires would be considered closer to 34”.

My vehicles of choice have always been manual shift types so I’ve had great enjoyment in being more “involved” which also included using the gears to assist in slowing down. So now that I have this automatic with the manual shift option, I used it to assist the brakes which, when thinking about the physics of that, the stopping energy is shared and not all on the brakes. My book doesn’t warn against this and it also seems to know when a shift is dangerous to perform, so it won’t. If the transmission was beat to hell, it would throw a code and go into limp mode and non of this happened with my driving style.

This time with this new transmission, I’m not using the manual shift and the analysis report shows the benefit of that.

So let’s all assume I actually know how to drive (bare with me Bill) and that i take great pride in this vehicle and past ones too and I’ve taught my kids how to be responsible to care for what they own, I know that to beat the shit out of this vehicle or take the rpm’s to red line because I just stole it and escaping the cops or I just want to make my wife yell at me or maybe race that sports car cause I think I’m one too or slam those rpm’s to shy of red line to slow down the truck, … this will in fact bring harm to something not built for it and would be abusive.

Let’s also assume, (Bill), that there’s was a manufacturing “Covid” problem as the dealership said and QC went out the window and this component was sub par as was #2 transmission that was made at same time but failed at just 500kms.

I’m going off a theory that any use of the manual shift feature that puts negative force on the clutch packs in this auto transmission (beyond what the computer would naturally do) will bring extra wear to the transmission and cause a shorter life to it than what would be considered expected by the engineers, so it should never be used unless you feel it’s absolutely necessary.

So far, I’m the first to run this test and we will continue to see analysis reports and cross check it with #3 tranny as we move along. So to some degree it’s a controlled study, we just don’t have the internals of #2 or 3 to look at, …we just have a theory and two pages of debate so far.

Good luck. I know if I was in your shoes I'd most likely be moving on .....

 

[biplaneguy]

According to the manual, "If a requested downshift would cause the engine to overspeed, that shift will not occur."

I will use the autostick to downshift to maintain speed coming down the mountain road from the cabin, but I'm not using it to regularly slow the vehicle down from a higher speed, that doesn't seem an appropriate use of the feature. Yes, the transmission will refuse the command where appropriate, but still...

If the OP has been through four transmissions, it seems clear that he's using it in a way that most other owners don't, and that the designers never intended.

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