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Old 01-16-2019, 10:11 PM   #1
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MT643 Fluid Change

Anyone do there own fuild change on there MT643 trans? What do I need to do? How do I do it, I have done plenty of cars, and the school district said they used Dexron III that still a good choice

Does the pan have to be dropped, is there a TQ drain plug, any filters besides the spin on one,
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Old 01-17-2019, 04:14 AM   #2
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Dexron III?
Heck, there are people who still use motor oil.

But once TranSynd was invented, everything else became obsolete.

Kind'a like... you can debate the merits of KodaChrome versus EktaChrome, and various Fuji films -- some of us swore by Fuji Velvia. And it all became moot when digital photography was invented.

TranSynd is expensive, and worth it.

Other brands exist and are acceptable, so long as they meet the TES 295 standard (which you can see on the TranSynd can label). But TranSynd dominates the TES 295 market.

Good luck!
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Old 01-17-2019, 06:44 AM   #3
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Transynd is 50 bucks a gallon. Ive got 5. Should I run it in my 545?
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Old 01-17-2019, 08:12 AM   #4
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Transynd is excellent in a 545. it can withstand higher temperatures without breaking down..



same in an MT-643..



there are internal filters and spin-on on most of the older transmissions.. I cant remember when the external spin-on became standard and fully recommended.. but I believei n the 80s.. the external filter is in the cooling line circuit.. the internal filter requires a pan drop.. which is a good idea anyway as you can clean off the magnet and any sludge out of the pan as well as get a better fluid drain..



from what I have been told transynd is compatiblke with Dexron III.. if your trans has motor oil in it now (yes allison at one time recommended 15W40 rotella in transmissions).. then you will want to do a complete flush-down of the trans, as you dont want a permanent solution of motor oil and trans fluid together..



BEWARE!! if your trans fluid is really dark and dirty, it may be indicitave of imminent transmission failure.. sometimes fresh fluid introduces detergents and cleaning agents into the mix which will finish-off an ailing transmission..



if the fluid is just a bit dark but not black or cloudy you are most likely OK and recommended to change it and all the filters..



-Christopher
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Old 01-17-2019, 09:43 AM   #5
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The fluid looks really good itís bright cherry red and clean. What happened is I was driving in southern Utah and my trans temp was hovering at 220-225 for many miles so I assume I cooked that fluid pretty good.

Anyone have any part numbers or guides on how to do the paper filters inside? Is there a toque converter drain bolt
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Old 01-17-2019, 10:08 AM   #6
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I know on my new MT643 there's no converter drain bolt. im assuming you have the Deep pan.. (dipstick goes into side of pan and pan is like 3-4" deep).. the filters on the AT545 deep pan and MT643 deep pan are the same. if you cant find a number online, I have a spare set at home and can get it's part number.



that temp seems a bit high for an MT643, however if it was hot and you were running high engine temps / pulling heavy it could get there.. might want to install an external cooler just to keep things down.. if you drive in cold weather you'll want your external cooler to be in series with your radiator cooler, which helps to Warm up the trans in cold weather.. or install a thermal valve in your cooler lines which bypasses your cooler until the trans warms up
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Old 01-17-2019, 10:54 AM   #7
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The heat effect is a combination of time & temp. You were on the edge for sure but probably did not do a lot of damage. See the chart below. It is for "standard" fluid. As noted, Transynd will handle significantly more heat for longer without negative effects.



And I will double down on adding some cooling. Maybe the best thing anyone can do for their tranny.
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Old 01-17-2019, 12:11 PM   #8
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Caddykid, I do have the deep pan, with the dip stick out the side it's about 4 3/4"-5" deep from the lip. Ya if could get me a part number of the filter kit when you get home that would be awesome. I am seeing two types of filters besides the spin on one, a flat one that looks like a GM 4T65E filter and then two round paper ones?

Thanks,
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