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Transmission failures
2

Transmission failures

Transmission failures

(OP)
I've been studying various websites and video's about the state of Transmission failures. I constantly see the folks complaining about automatic transmissions, and how great manual transmissions are.
Personally I have dealt with some bad manual transmissions in the past, that made automatics look way more desirable.
I would like to hear others experiences with various transmission types, and the reasons for the many reported failures of modern day transmissions used in road vehicles.
Automatic transmissions have been manufactured for what about almost 80 years now, you would think they would be almost trouble free by now.

RE: Transmission failures

Manual transmissions are more vulnerable to operator error.

I bought a 1999 VW Passat TDI with 90,000 km on it, and sold it at 462,000 km still with the original clutch and transmission.
My 2006 Jetta TDI 5-speed manual, which I bought new, was in need of a new clutch at 430,000 km because the dual-mass-flywheel mechanism had seized.

The clutch master cylinder push-rod on the Passat failed at one point, leading to the clutch pedal staying on the floor and not actuating the clutch. I still got home, by shifting to 1st gear when stopped with the engine stopped, using the starter motor to start the engine and start the car moving, and very carefully grabbing whatever higher gear that I could.

My current car, Fiat 500, had a shift cable rod-end break (there's almost 200,000 km on the car). I still got home using 3rd and 4th gear. But, this type of fault is possible with automatics as well. I fixed the rod-end with JB Weld.

I've only ever owned a couple of vehicles with automatic. My van has one, and it has been fault-free, but it only has 85,000 km on it, so that's to be expected.

The Fiat is soon to be traded in on something that doesn't have a transmission. (Chevrolet Bolt, once the battery recall situation gets sorted out - already signed the paperwork and then the recall got expanded to include the one I'm after)

RE: Transmission failures

(OP)
Seems like all I drive is a manual as well. Though prefer the automatics. I have done the same broken clutch linkage deal you mention as well.
Now to reliability, Geo Metro manual transmission ? I know of one that so far has had I think 4 transmissions the car was used as were all the transmissions that have been installed, so not sure how long
one would last with a decent manual transmission driver behind the wheel. It is like many mechanical things these days, yes it works, but just not an impressive design. Another manual transmission that was not very dependable was the basic 3 speed offered in a 74 Duster. The syncro's would not last, just a bad design. Not sure how true this is now, but back in the old days it was faster and easier to fix an automatic than the manual transmissions.
Battery power? They are just huge fire hazards. The floors are filled with lithium battery's, you will never have a new one shipped airmail.

RE: Transmission failures

transmissions fail either through operator faults, lack of maintenance or bad design. it is nearly impossible to design a transmission in such a way that operator mishandling can be fully prevented. bad design may occasionally occur, but usually will be corrected over time. lack of maintenance (or inadequate maintenance instructions given by the manufacturer) are nowadays the main reason for failure. over time the need for oilchanges has been steadily declining, most passenger vehicles do according to manufacturer instructions need no oilchanges at all. that is correct in the sense that most transmissions will function sufficiently well to survive the warranty period in both manual and automatic transmissions. when however you want to last the transmission quite a bit longer regular oil changes can be helpful. in manual transmissions prolonged use of oxidized oil may lead to deposits that may influence the frictional characteristics of the synchromeshes and lead excessive wear on synchromesh rings. in automatics oxidized oil may lead to poor shifting, malfunctioning of the electronic/hydraulic operating system, corrosion and deposits that prevent adequate cooling of the transmission. in the past usually a transmission oil change was required about every third oil change. nowadays that is no longer the case. most transmissions will survive the warranty period, but if you want to use the transmission (much) longer oil changes at regular intervals, suitable for the type of use, will be very useful. some more maintenance will work wonders for both life expectancy and shift comfort. and so will the use of the correct oil type in stead of a "universal" type that more or less does the job. people are often very critical on the type of engine oil they use and not so on their transmission fluids, although the variety in transmission fluids is far higher then in engine oils. there is no such thing as a "universal ATF"!

RE: Transmission failures

The issue of durability/reliability isn't manual vs automatic, it is down to the specific design.
It used to be that manuals were simple and reliable, as long as you watched after the clutch. And automatics were delicate.
But today that isn't always true.
While automatics still have a lot more parts many manuals have been built to a specific light weight with strength a secondary feature.
I have a friend that uses the rule of thumb that if a trans does not have aftermarket performance parts available then he doesn't want it.
The first 4 cars that I owned were manuals, and largely trouble free (just a couple of clutches) to get them to 150,000 mi.
Since then everything has been automatic and other than a minivan with a problematic design they have not had issues either.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Transmission failures

The only actual "gear" related failure in the automotive powertrain world I've heard about in the last decade is that afflicting the Mazda MX5/Miata ND manual transmission. Some owners, particularly those who do weekend amateur racing have experienced a catastrophic failure. Mazda to their credit almost always covers the cost. The gearbox is new to this version and appears to be designed as lightweight as practical. It's a conventional RWD manual layout with a countershaft and the primary reduction taking place at the input end.

My analysis, based on photographs and sectional drawings is that the mainshaft is insufficiency rigid such that excessive centerline spacing occurs during hard acceleration, specifically while in 2nd gear, located about in the middle of the mainshaft span. That loss of spacing of course significantly increases the bending load on engaged teeth. The tooth face wear pattern is visible all the way to the tip, rounding it slightly, pretty much conclusive proof.

The failure continues with a fatigue crack starting at the root of one or more 2nd gear teeth on the mainshaft. Once the crack has propagated about halfway the remaining material yields and the tooth parts company with the wheel. What happens after that is certainly exciting, but immaterial. The photos I've seen were of a unit that had suffered little enough subsequent damage that the evidence was well preserved.

RE: Transmission failures

Had a heck of a time trying to rock my 2015 Tahoe (auto transmission) out of some snow ruts. Seemed like there was an electronic limiter in there that kept it from quickly shifting forward to backward to forward, etc. I was not able to get it out of the ruts. I didn't have any problem with older transmissions (auto) when doing that. Before this vehicle, I was able to get the vehicle rocking fore/aft enough to get out of the ruts most of the time.

It was very frustrating and I pushed it hard. Now the shift points seem a bit harsher. In all fairness, it would not have been good on a clutched manual tranny.

RE: Transmission failures

Since the ecm/computer tunes operational parameters on how the thing is driven, it has learned that it needs to shift harder for you?
How long ago was that? perhaps it will revert to previous behavior after a while?


Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Transmission failures

Also rocking it wrong....

RE: Transmission failures

Quote (enginesrus)

you would think they would be almost trouble free by now.

They are.

RE: Transmission failures

Ford made a few million automatics that were not trouble free even while they knew they were substantially problematic. How many dual clutch automatics did they make?

RE: Transmission failures

I understand Ford's problematic DCT was made by Getrag. Unlike VW's it uses electrically-driven actuators, which in my opinion don't have sufficient bandwidth to operate the dry clutches. But I'd call that a design failure rather than an operating failure that I presume this thread is about.

RE: Transmission failures

I just bought another manual transmission car for my daily driver - a 2018 Mazda 3 to replace a 2012 Mazda 3.

I choose manuals because I know how to rebuild them and because I enjoy having better connection to the car. And it's entirely up to me how much I want that transmission/clutch to last. By contrast my ex-wife had an Escape Hybrid with CVT and on rolling terrain (basically everything around here) it was impossible to hold a consistent speed without staring at the speedo. I felt connected to that transmission because I was constantly reminded how much I hated it.

As for reliability, I once owned a 97 Nissan Maxima M/T. They often had bearing failures on the differential carrier around 60-100k miles. Spalling failure. After learning how to rebuild my own I rebuilt at least a dozen others. Fortunately they were easily rebuildable with bearings and seals if the owner didn't let things go too far. I never could figure out if Nissan simply overloaded those bearings or the housing flexed too much or... but it was very interesting that the adjustment shims on the transmissions I tore down were always the same exact ones. There was a theory that the factory building the transmissions was lazy and didn't actually set endplay - they just used the same adjustment shims each time and didn't actually meet the endplay specs. It would seem they got away with it.

Another reliability shortcoming was the early Nissan 350Z's. From what I understand one of the mainshaft bearings did not get consistent lubrication or cooling. In any case Nissan revised the design but it was out of pocket to the owner. After messing with the Maxima transmissions I considered getting into fixing these but ultimately I did not.

RE: Transmission failures

(OP)
The 2 worse manual transmissions I can think of at this time are, the standard 3 speed offering in a 74 Plymouth duster, with the worse designed syncro system, and the 5 speed Geo Metro transaxle, difficult to work on and don't last. Maybe because of the people that can shift them correctly, don't know.

RE: Transmission failures

Quote (geesaman.d)

By contrast my ex-wife had an Escape Hybrid with CVT and on rolling terrain (basically everything around here) it was impossible to hold a consistent speed without staring at the speedo.
What - no cruise control? wink

Seriously though - that is a good point.

je suis charlie

RE: Transmission failures

Does anyone recall how bad the manual boxes were in 1950's-60's Jaguars?
I helped a neighbor change a few of these before he figured out how to install a ZF.

And Grunt, on the subject of cruise control, I wish that there was an adjustment for how tight it would hold and related to that how it would accelerate. When I am on county or state roads with little traffic (esp the rolling ones) having 'softer' speed control would improve economy and not bother anyone.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Transmission failures

While I prefer a manual, their relative unpopularity in the US market has led mfr's to use some sketchy stuff.

New Venture 1500 5-sp in my '98 S10; described by all the shops I've been to as a "throwaway" unit. Rebuilding requires special jigs the shops don't care to invest in, and parts are non-existent. The NV1500 replaced the excellent Tremec T-5's used in earlier models, that were more robust, had great parts support, and were easily rebuilt by a home mechanic.

I was set on buying a new Mustang with a manual, until I drove one. The V6 models come with a Chinese-made trans that is as rough as a corn cob. No fun to drive. Clearly a choice made by the bean counters. I have seen that the better trans put in the GT's is much better, but not up to the abuse owners give them.

EdStainless, I never drove those Jaguars, but oddly enough some of the nicest trans I ever drove were in MGB's and Austin Healey 3000's.

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