aluminum "paste" in t20

[applejack]

well, here i am again. im in the garage,t20 split,i see gunk in driven side case, wipe it out, it smears on my hand like graphite, but is aluminum color. what could it be? released band, but didnt pull anything out yet. jeesh! the only reson i opened it was because it leaked at joint. aj

[jpswift1]

It seems like this is common for most T-20's that have never been taken apart for a long time. I've noticed the same thing, rebuilt them after a good cleaning, and never had a problem after that.

[applejack]

well at least thats better than the expected BAD NEWS. but whats it from? the only reason i opened it was to put new gaskets in. the bearings seem tight, the input and output seals dont leak, and the plungers dont leak, but since it was open, and the computer is in the garage tonite, i could use nice colored pictures and good description of what to do, thanks to Mike's how to, i decided to look into it further. it says to inspect bands to make sure there are no cracks ANYWHERE, well there are some cracks in the 1st 2 inches from the top. does that mean bad?

one other thing, the 1st time the throttle froze up and i started it, it went WOT and wheelied. one of the last times i drove it before engine lock up i TRIED to wheelie it and it wouldnt. does that mean something is worn out?
aj

[brushcutter]

It probably means you need to be sure your machine is in neutral before you start it. Reminds me of my very first ever start up with an old max I restored-look out MIL's flowerbed thing took off without me...


Yeah, cracks are bad, and I've seen that "paste" in all of the older ones I ever went into. I don't think it's band material- wrong color- but I could find NO place it would have come from and once they were back together the t-20"s worked fine. There was one that some moron had filled with gear oil MAJOR NO NO, but the bands and drums were trash the cast off from that was different from the paste. I think you can get the bands re-lined but I don't have the name of the place that does them, some of the members have had it done and it's a fraction of the RI price.

[kpike52]

What is that paste? and the answer is...

That gray paste bothered me too. I had a sample run through the lab to ID the materials. The scan is attached and shows the majority of the material is iron (Fe). The amount in the sample is proportional to the heights of the peaks on the plot. You can see a little aluminum (Al) and copper (Cu) too.

[mudNmallards]

I’ll tell you where it probably came from and what to be on the look out for to see if you have exceeded normal wear and may have a potential serious problem. This comes from decades of pulling samples and having to analyze them then rebuilding the units.

You see this ( the toothpaste as we used to call it) in grey/silver for gear boxes with alloy housings or worm drives with brass gears routinely. ( in those cases it’s a yellow/gold paste)
It comes from the fact that that you have 2 radically dissimilar metals together where one is substantially harder than the other. (usually hardened gears and steel shafts in a softer housing or the brass gear running against a case hardened worm in those applications- same effect) If the gearbox has bands or backstops that run partially engaged- they contribute to this a little but not very much.

The gear box comes under load and 2 things happen.
1) The housing flexes a bit because its weaker of the two (remember, alloy/aluminum is used because its cheap, lightweight, easier to cast and easier to machine- not because it’s the best and strongest choice)
2) When the flex happens, this causes bearings to slip in the housings and meshes to move out of the proper angle.
The end result of those 2 over time is excessive polishing ( which removes micron sized particles which give the “goo” its color and body) and “minute” housing wear. This is normally easily seen with the naked eye in the form of polishing patterns in the metal around the contact surfaces and comparing them to a normal mesh and load pattern.
Its simply the nature of these types of construction and there really is nothing that can prevent it and over the lifetime of the transmission- its seldom a problem if the transmission is properly lubricated and does not undergo excessive load against its design torque.

What CAN cause a problem is when lubrication is not flushed and changed regularly is when this “stuff” finds its way into bearings. This can cause bearings to “stick” and when they do they will turn and wear the housing ( and the rolling media of the bearing). (this is easily seen with the naked eye to or found with a caliper that has pin attachments on it. The bearing and housing show signs of fretting and polishing). When that happens, you need to either machine the housing and install an insert ( if there is enough base metal to allow it) or replace the unit.

A trick we use during rebuilds is to put a SMALL “touch” of bearing mount (Loctite 680 or similar) (if you use more than 1/100th of a 10th of a drop per bearing- you better bring the torch because that stuff is wicked).

What this will do is prevent the bearing from rotating in the housing so any damage is absorbed by the bearing. This is the best choice because during a rebuild you are already going to replace the bearing anyway but if there is housing wear that can affect load alignment of the shaft and gears then the transmission is crashed anyway.

Don’t worry about the presence of the paste because the sump is where this stuff is designed to accumulate and over time its normal to have some. No flushing/filling operation ever fully cleans a unit out. What you do worry about is the polish/wear pattern of the internals especially in bearing housings.

[jerseybigfoot]

This material is typically from the planetary gear faces rubbing on the drum journal shoulders. The newer t-20's have micarta thrust washers that prevent this. Whipper just posted a mod to install the washers in the older units.