How burnt is burnt?

[JayArr]

Hi all

I'm finding it difficult to find a point of reference on how pristine a steel clutch plate needs to be to be re-used.

I'd watched some youtube videos that say if it is just a small blemish then just buff it out. I'm sure once you've seen a burnt clutch you'll always know what it looks like but I've only ever seen one clutch pack, the one I've got open on my bench, so I don't know if it's bad or not.

This is the reverse clutch, I note that the friction discs all still show the lines from manufacturing so it's not like they have been worn down to a point where they were too thin. The steels generally look like they are still shiny and they haven't turned a bronze color that you get when metal gets overheated. They do have small blemishes here and there. It almost looks like a small piece of grit got between the friction plate and the steel and a littl spot was created.

Can I just take a scotchbrite pad to these and clean them up or are they shot and need replaceing?

I'm trying to learn and get smarter here. If as a mechanic I don't know what's burnt and what can be replaced I can always just replace everything every time but that makes me a lesser mechanic than they guy who knows where the line is between reusable and not. The information regarding which clutches are burnt and which are not is also valuable in troubleshooting and knowing when to look closer for other problems, if all I ever do is replace everything I'll miss out on clues and hints as to what to scrutinize.

So... if this was your transmission would you put these steels back into it? (I'll replace the frictions)

 

[Mooseman]

How expensive are they? Is it really worth it to not replace them given the labour involved? Personally, if I were doing something like this, I would replace them just to be sure.

 

[JayArr]

They aren't expensive but this is a question more about knowledge than finance.

A good mechanic should be able to inspect a part and determine if it reusable or if it needs to be replaced. I'm trying to get this knowledge.

 

[JayArr]

Here is the 3/4 clutch pack.

I don't even see any small blemishes on these. The frictions are all still 80 thou just like the new ones in my kit and if I take a brand new disc and wet it down with ATF it's almost as black as the used ones.

There is no burnt smell and no "rainbow" or bluing on the steels.

Would you consider this clutch pack "burnt"?

 

[gmcman]

My honest opinion, may not be the best financial decision, but if I was that far into a trans, I would absolutely change all the clutch packs as well as the band.

Just too much labor to get to that point to not replace them. I would replace the bushings as well.

 

[Mooseman]

The steels don't look good to "me" with those black marks. And by "me", that's as a regular shadetree mechanic, not a specialist. I've watched my fair amount of transmission teardowns and they never say they look good.

 

[Reprise]

As you know, I'm not a pro wrench. But I have had a 4L60E rebuilt.
Anytime I've explored or inquired into what goes into a trans rebuild, without fail I've heard "all new clutches and steels". Never anything like "replace bad steels" -- it's always 'replace all'.

It's probably due to how cheap they are, relative to the full parts / labor cost of what a comeback would cost the shop.

I did look at your pics, and I'd agree that none of the steels look burnt / overheated, at least to my untrained eye. The name of the game for them is smoothness and warpage. The smoother they are, the less resultant clutch wear you'll have. If those black marks have a noticeable difference in roughness, compared to the other areas, I'd replace (or, at least use something to remove the roughness -- steel wool, scotchbrite, roloc wheel, etc.)

If you put micro scratches on them in the process of smoothening them, I'd give them a turn on a polishing wheel to try and remove them. You probably won't remove enough material, but if you have a micrometer handy, it wouldn't hurt to measure afterward. Note that they vary in thickness according to what purpose they're serving in the trans, and there are often 'thick' and 'thin' options, by year. And there are other variations, as well, for different applications. So I'd measure before *and* after, myself, whether you reuse or replace.

Back to smoothness If they feel about the same, before / after cleanup... you could probably use them (your index finger is a good indicator, as human fingers can discern down to 13 nanometers or so; a human hair is roughly 15-180 micrometers, so you can see our fingers make a pretty good RA measuring device

If I were doing it for a customer, I wouldn't even bother with the old ones, myself. And if I were doing it for my own build... I'd probably use new ones there, too. But according to Google, as long as they're not burnt, and not too warped, it's ok to reuse them.

Due to the (lack of) thickness of the steels, it's common to see some warpage in them, even new. Meaning that you'd detect it with a straight edge, not really with your eye alone. If you see waviness, etc., that steel should be replaced. If I had them on a relatively flat surface and couldn't see light as I turned them, I'd probably send them, tbh. I don't know the allowable tolerance figures, though.

TL; DR: They can be reused, but I would probably replace, for peace of mind.

 

[JayArr]

Looking at the pics I posted I realize that it looks like there are black marks on them. This is just a trick of the light or flash.

Take a look at this pic, it shows more clearly what the steel looks like. The light and dark shades are just differences in how shiny the steel is.

I dislike the idea of buying new steels every time because "I don't know" if the ones I have are OK. There has to be some experience level to determine if they really need to be replaced.

I also don't generally like the logic of "always replace" theorys. When I hear "always replace" "just to be sure" I think it has become a substitute for experience and observation, it's a fallback mentality of the inexperienced to ensure a rebuild works. I want to be better than that. Where does that end - do I replace the sunshell just to be sure? Do I buy all new sprags just to be sure? Do I replace the whole transmission just to be sure?

I've watched Brad's Transmissions you tube on the 4L60E and he is a pro with years of experience, he quickly picked up the set of steels and glanced over them on both sides and said these look OK and he re-used them. If you know what you're looking for I think it's possible to determine if a set of steels are OK and not have to "always replace" "just to be sure".

Just so you know, I've already got a new set of steels and I'll use them on this build but if these are OK then the 3/4 clutch didn't burn and I don't have to worry about a bunch of other stuff.