I tested ATF in my gearbox; didn't like it

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MexicoMike

MexicoMike

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As I posted in a different - and basically unrelated post - I drained the gear oil from my tranny a little over a week ago and replaced it with Dexron ATF. This morning I drained the ATF and put gear oil back in.

I found that the shifting with the ATF was noticeably less smooth. With gear oil the shifts were very smooth and it "snicked" through the gears easily and positively.

With the ATF, it felt noticeably less so, losing a good bit of that smoothness, becoming a bit "crunchy." I actually had to "re-nudge" the shifter to get it into the next gear occasionally. I'm sure I could have gotten used to needing a bit more force than I was used to using to change gears but, frankly I didn't see any point to that.

I am not arguing/suggesting that ATF is bad for the transmission, I know a lot of knowledgeable folks on this site use it and like it. I just prefer the feel of the tranny with gear oil.

I don't use any "fancy" gear oils - just basic gear oil. Quaker State 90W is what's been in there for years and is what's in there again as of this morning.
 
I tried the same experiment as Mike. While it shifted "OK" I never liked it as well as with the tranny fluid that I was using. So back to the Harley synthetic gearbox oil that has worked so well for me.
 
A quick search show a only a couple people using ATF in the tranny including @hobot but only on one of his bikes, the one he rides "really fast!". In a modern transmission with high tolerances and well engineered and spec'ed for ATF, sure. For a 70 year old AMC box? Hell no.
 
MexicoMike said:
As I posted in a different - and basically unrelated post - I drained the gear oil from my tranny a little over a week ago and replaced it with Dexron ATF. This morning I drained the ATF and put gear oil back in.

I found that the shifting with the ATF was noticeably less smooth. With gear oil the shifts were very smooth and it "snicked" through the gears easily and positively.

With the ATF, it felt noticeably less so, losing a good bit of that smoothness, becoming a bit "crunchy." I actually had to "re-nudge" the shifter to get it into the next gear occasionally. I'm sure I could have gotten used to needing a bit more force than I was used to using to change gears but, frankly I didn't see any point to that.

I am not arguing/suggesting that ATF is bad for the transmission, I know a lot of knowledgeable folks on this site use it and like it. I just prefer the feel of the tranny with gear oil.

I don't use any "fancy" gear oils - just basic gear oil. Quaker State 90W is what's been in there for years and is what's in there again as of this morning.
Click to expand...

So, in summary, gearbox oil works well... in your gearbox...

There’s a moral in there somewhere !
 
swooshdave said:
A quick search show a only a couple people using ATF in the tranny including @hobot but only on one of his bikes, the one he rides "really fast!". In a modern transmission with high tolerances and well engineered and spec'ed for ATF, sure. For a 70 year old AMC box? Hell no.
Click to expand...

A certain Mr Comstock uses it too I believe, so it must work for him.
 
swooshdave said:
Yeah, but he is putting thousand upon thousands of highway miles on his bike so the gearbox is spinning like crazy in top gear.
Click to expand...

True, but my guess would be it works pretty well at low speeds too. I somehow doubt Jim would be putting up with the symptoms described by Mike.

Personally tho, I’m a fan of gear oil in my gearboxes.
 
Mike, just out of curiosity, if your gearbox was performing so well with gear oil what prompted you to try the ATF?

Maybe the ATF would offer even better shifting than gear oil?
Not criticizing by any means, I’m a big fan of experimental thinking and trying new stuff.

Were you concerned about inadequate lubrication, scoring, too much heat, something seizing up?
 
There were several thought in my mind re this:

1. ATF is the standard fill on a fair number of car manual transmissions

2. It works fine in Automatic transmissions which also have plenty of gears

3. Trusted folks here use it

4. Lower viscosity means less drag

I had no issues at all with gear oil so I guess my big thing was reducing the drag...as if on a street Norton it matters! ;)


Maybe a different ATF than Dexron III works better as far as smoother Norton shifting but I've finished with that experiment.
 
MexicoMike said:
There were several thought in my mind re this:

1. ATF is the standard fill on a fair number of car manual transmissions

2. It works fine in Automatic transmissions which also have plenty of gears

3. Trusted folks here use it

4. Lower viscosity means less drag

I had no issues at all with gear oil so I guess my big thing was reducing the drag...as if on a street Norton it matters! ;)


Maybe a different ATF than Dexron III works better as far as smoother Norton shifting but I've finished with that experiment.
Click to expand...

I've been using ATF for a couple of years now. No issues.
One possible benefit seems that the ATF does not absorb condensation water due to warming and cooling of the gearbox.
I have drained the standard 90w previously and found water in the bottom of the shell and air bubbles in the 90w. Probably from just short trips never getting warm enough to burn it off.
Similar to the engine oil foaming up due to not getting hot enough to burn off.
Draining the ATF the oil seems to be clear, no bubbles.
 
I've toyed with the idea and gone no further because it just doesn't sit right in my mind. However, I shall do the primary with it. Norton transmissions are pretty pricey pieces to experiment with.
 
I'm going to try it this year, I've already put it in.
I had one of those dodgy push rod seal nuts that fouled the diaphragm and screwed up the clutch adjustment. Gone back to the normal nut with ATF in the box
Terry
 
What about wear on the gear teeth - that dreaded line that etches across the tooth near the root and can lead to a broken tooth. No one wants to have to replace their expensive gears. You want oil with film strength that's going to protect - that's what's important. One extreme is AFT 10 wt, the other extreme is Redline shockproof 250 wt. Which do you think is going to protect the gear teeth better when you're torquing around town or on the track through the gears (not just cruising down the highway in top gear which actually bypasses the gears).
 
Ive considered it as it might be a better lube for the sleeve bushes. Maybe it would be better but what about the rest of the box?
 
I just got back from a 10 mile run and the transmission now shifts smooth as silk again. :)
 
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