Dexron? Mercon? Whats The Diference

[logfarmer]

I intend to change the trans fluid in my 2001 HD and have some questions. It has about 76k on it now I belive the previous owner had the dealer change the fluid at 50k what the exact procedure was I dont know.

 

1.Can I use dexron /mercon fluid that is available eveywhere?

Or is it best to use dexron 111 from the dealer. I was thinking maybe since the dexron/mercon can be used in Fords it is not adaquate for the Allison?

2.When I bought the spin on filter at the Allison dealer he told me to just empty the pan and put in new fluid dont worry about replacing all the fluid. Ive also read somewhere that Allison does not want all the fluid changed or replaced all at once.

3.I see here about the hoot method which seems to be most of a complete fluid change, Will it harm the tansmission to change all of the fluid at once.

Thanks,

Martin__________________

[jake111]

1. As long as it's Dexron III then it's good, whether or not it happens to also satisfy the Mercon specification. I think it might be getting hard to find anything labeled Dexron III because it's been superceded by Dexron VI (but I haven't looked lately). I did my '04 last summer with Mobil 1 synthetic ATF which I think said it was appropriate for pre-2006 GM vehicles but I don't think they could say Dexron III, and it wasn't Dexron VI approved. The Mobil 1 was also Mercon approved, but that doesn't matter. I would recommend a synthetic, with Transynd probably the best followed by Mobil 1; some people just love the Amsoil ATF.

 

2. Personally, I don't believe in flushing transmissions so I agree with the idea of just draining what comes out the drain hole, plus the external filter. This is what I did and (IIRC) it seems like it was ~8 qts. Others will swear by flushing, so to each his own.

 

3. Probably not, but is it worth the effort? Some agressive flushes have caused problems in old transmissions, but the Hoot method doesn't appear likely to cause a problem. I wouldn't bother, so to each his own. If the fluid is really contaminated, I would just drain/change once, run around for awhile, then repeat.

[ATMINF]

I believe the new Dexron IV is synthetic. It is supposed to be pretty good stuff.