Reverse gear failures

Steve Hoelscher said:
I saw that the 5th slider hub was on upside down. I have't tried to assemble one like that so I am not sure what would cause it to "not go into 5th" but there are a whole list of bad results from that.

Not to mention its full of rust.

Re: the excessive RTV Brandon noted. That seems to foretell a lot of surprises once you get inside. The excessive and incorrect RTV demonstrating the builder's lack of knowledge and skill.

I could do a whole thread on Detent Springs. :)
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It wouldn't go into 5th because the slider was on upside down too so there were no teeth to help it engage with the gear.
 
Sure enough. Didn't catch that. In the first pick you don't know its a single sided slider, some are and some aren't. In the followup pic, you can see its single sided. Yeah, it would have no drive. And if you tried to hold it in it would explode the synchro ring.
 
Thanks for explaining it guys. These examples of improper assembly mistakes reminds me. In the "Wiki" section is the old write-up Steve did on how to go through the trans. It is an excellent step-by-step guide: http://www.seattlex19.org/data/5s101/

What is the possibility of adding some photos to it, making it even better for the 'visual learners' among us (e.g. me)? I know there is another thread (by another member) with some photos, but frankly it isn't as comprehensive as the "Trans 101" article. And there are some points in the '101' guide that are a little difficult to follow if you haven't been inside one of these units before; mostly terminology issues, not knowing what something looks like to identify it from the instructions. For that reason it wasn't too helpful to look at the pics in one thread and read the description in the other source.

Certainly not criticizing at all, just suggesting a little enhancement. It would be really nice to have photos inserted in the existing 101 write-up to go along with the description. Steve has already shown a lot of good photos in related threads to illustrate some findings (reverse gear failures for example). So I'm hoping it might be possible to take pics of each step as you go through the next trans and add them in the 101 please.

Hope this suggestion is taken as a positive note that would definitely benefit us, thanks for considering it.
 
Yeah, I have considered adding photos previously. At the time 5 Speed 101 was written digital photography was in its infancy and embedding photos wasn't supported.

in the last 10+ years I just didn't have the time to take on the project. Way to much on my plate. Presently, I am pulled in too many directions to do this now. Its been easy to snap a few photos while working but to read through the text and setup and take the photos, catalog them and then do the insertion, would be quite a project. Not that I won't do it but right now I simply don't have the bandwidth.

Having given it some thought now, what I might do, instead of taking photos, is to shoot video. Perhaps shooting a series of videos; tear down, inspection, assembly. It would be easier to do and post the videos on Youtube and link them to the 5 speed 101 text.
 
Perhaps someone near your area would be willing help with either photography / videography. Allowing you to work while they do the images would make it much quicker and easier.
 
Steve Hoelscher said:
Yeah, I have considered adding photos previously. At the time 5 Speed 101 was written digital photography was in its infancy and embedding photos wasn't supported.
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Do a search on the title "5 speed transaxle" posted by rupunzel. There are 4 threads stuffed with excellent pictures describing a disassembly, done with Bernice's excellent tooling and superb attention to detail.

Paul Davock
 
Steve Hoelscher said:
More reverse fun. I tore down a core last week that I was told had no issues with reverse. This unit had been rebuilt by a previous owner of the car and was working "reasonably well" as described by the current owner. I honestly never know what I am going to find when I tear a unit down.
Again, this transmission "worked reasonably well". I have no doubt, but it was a time bomb set by the previous rebuilder.
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I'd be curious to see what mine looks like when you eventually get it - it also shifts reasonably well - except for when it doesn't - but that's usually stationary 1st or reverse shift that just doesn't want to go without some juggling :D
 
PaulD said:
Do a search on the title "5 speed transaxle"
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The threads referenced by Paul are what I mentioned previously. They have photos but not the level of rebuilding instruction detail as the "101" article. And trying to match the pics from one source to the description of another source wasn't very helpful for a Fiat transaxle novice like me. That is why I suggested pictures be added to the 101 article. If Steve can use some of pics from other sources to add to his article that's great. But I'd guess he might find it easier to make his own? Anything will help though.
 
Yeah, that's where the time pit comes in. Reading through the text and deciding where there should be photos and of what. I think a video series would be easier because I could narrate. Perhaps this fall I could arrange an opportunity to do it.
 
It would be MUCH appreciated! :cool: Thanks for considering it.

Over on another (non-Fiat) forum someone did this for the transaxle specific to those cars and it has been exceptionally well received.
 
One more note as a follow-up on Greg's transmission:

I was supposed to follow up on this photo:

Reverse Worn B.jpg


Note the wear on the tooth face is so shallow. This is because of two reasons; 1) the gear on the input shaft is badly worn, and 2) the reverse idler shaft is badly bent.

0607181134b.jpg


The bent shaft doesn't correctly position the reverse idler shaft close enough to the other two shafts for it to fully mesh with its mating gears. Thus the shallow mesh will cause excessive wear and eventually strip the teeth entirely. While this much wear doesn't look like that much its probably more than 50% of the way to total failure.
 
I would not have guessed a shaft that size could bend like that. Something I might not even check for it I hadn't been advised. Thanks.
 
Great picture , Steve!
Straight spur gears have a low contact ratio compared to helical gears. Usually 1.2 to maybe 1.5. A ratio of 1.2 means that 100% of the time one tooth is in contact and 20% of the time two teeth are in contact. Even a little increase in center distance (i.e. the bent shaft and worn input) decreases the contact ratio. Add in some wear and pretty soon the contact ratio is below one. This is bad for two reasons: you only have one tooth carrying all the load all the time, and more importantly, you no longer have conjugate motion and the mating gear will slam from tooth to tooth rather than transition smoothly. That gear Steve is showing us has been BEAT into the that shape by the other gear slamming into it.
 
Thanks for the detailed explanation Paul. We see this kind of problem from time to time with straight-cut gearsets in racing cars. It can be caused by all kinds of problems. I have seen cases flex enough to cause this. When they fail it can happen very quickly and usually catastrophically. You start to see wear like that and very soon the gear starts shedding teeth and its instantly trash. Since this is reverse, it could limp along for a while but failure is inevitable. Again, the results of a rebuilder who really didn't know what they were doing.

In racing we call it 'contact overlap'. Its a careful balance of tooth pitch to achieve adequate overlap without compromising the parasitic losses and strength.
 
Dr.Jeff said:
I would not have guessed a shaft that size could bend like that. Something I might not even check for it I hadn't been advised. Thanks.
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This is the 16mm idler shaft. The '84+ cars have an 18mm shaft. I see no difference in the number of bent shafts. In fact, bent shafts are so common that I pretty much exhausted my inventory. And when I buy used shafts I usually order several (or as many as I can get) because I know that half of them will also be bent. :(
 
Thank you Steve for the picture. What is invaluable to us, mere mortals, is seeing how much deflection is too much. If I had looked at this shaft I would have think it was good. Now I know.
 
So much of building any manual, and these in particular, is experience and reasoning. I still learn stuff. I recently bought a number of gasket sets that had the 5th gear extension housings cut improperly causing leaks. Its not obvious because of how the extension housing was added to what had been a 4 speed casting. Now I know to check for it, assuming I am using a gasket on that case. You have to look carefully, take nothing for granted. Ensure every part is correct because so many of these units have been molested by inexperienced rebuilders.

Typically, a bent reverse idler shaft is the result of a catastrophic failure. Roll starting in reverse which broke teeth off a gear, or jumping out repeatedly and taking hunks of reverse teeth with it. In this case there was no catastrophic failure present because the unit had been rebuilt and those parts replaced. But the builder didn't know to check the shaft, thus he reused a part that would guarantee premature failure. Inspection of the worn reverse idler shows shallow engagement which comes from a bent shaft and/or worn mating components.

There are so many similar pitfalls. When I built my first transmission I didn't know any better either. I followed the manual step-by-step and fell right into them.
 
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