AT545 question

GreyCoyote · 05-07-2016, 02:52 PM

When I changed the fluid in my AT545, circumstances conspired to make me change it when cool-ish. I got about 15-ish quarts out of it just by pulling the plug, filter, and waiting. That means there was only about 3 quarts up in the converter.

Does this seem right to you AT545 owners? Seems like there should have been a lot less fluid available in the pan and more in the converter.

Supporting data point, when I check the dipstick hot *immediately* after shutdown, the fluid level is in the correct range. Wait six hours and the level is stable at "really REALLY overfull". Anyone else seeing this?

I'm not complaining as it makes converting to Transynd a bit cheaper,

but I want to make sure its not a harbinger of future doom.

opus · 05-07-2016, 03:31 PM

Get an oil sample if in question.

2kool4skool · 05-07-2016, 04:21 PM

Changed mine on Thursday. Cold also, 4 gallons out, 4 gallons in (emptied the spin on filter but did not change it). Upon start up the stick shows cold level OK.

The TC will drain back, then pump up when running. Not unusual.

GreyCoyote · 05-07-2016, 04:48 PM

Quote:

Originally Posted by 2kool4skool

Changed mine on Thursday. Cold also, 4 gallons out, 4 gallons in (emptied the spin on filter but did not change it). Upon start up the stick shows cold level OK.

The TC will drain back, then pump up when running. Not unusual.

Awesome! Thanks for sharing your experience.

turf · 05-07-2016, 11:42 PM

good to know, i am want to change to a synthetic too and the does take the bite out. i was expecting 5 gallons.

im not seeing trysynd at any of the stores but do see other synthetic trans fluids like mobil1 and a few others that list Allison compatibility. seems they're all pricey. especially when the 545 was spec'd dexron.

please post results of your fluid change. im on the fence about the synthetics.

superdave · 05-08-2016, 05:29 AM

remember when they state how much the tranny holds it does not include the cooling system or external filters

somewhereinusa · 05-08-2016, 05:49 AM

Mobile One isn't the same. Mobile Delvac Synthetic ATF is. Do your homework, there are a number of brands that are the same, it has to have been TESTED to meet the Allison spec. (some have not). I found the best price at an oil distributer. I did a lot of research and found the Mobile for $172 for 5 gal.

gbstewart · 05-08-2016, 07:40 AM

Do you really think its worth it going to synthetic oil? how much of a improvement would it really make?, I change mine and the filter every 2 years with dino atf from petro Canada. I'm just not sure about synthetics on these old trannys, and engines, I believe in frequent oil changes. Now if I had shiny new bus, then yes to synthetics gbstewart

somewhereinusa · 05-08-2016, 08:16 AM

I think it is, my temps were getting really close to the "too high" for dino oils. At least with the synthetic I don't have to worry about that. I think my temps are cooler now although, I haven't been in any mountains since I made the change.
I also found out it makes a big difference where the temp is taken. My temp sender is in the location that senses torque converter temp, I didn't thing the cooler was working. I have since added a sending unit to the pan, the cooler drops the temp about 40 degrees. Still, that 300 degrees at the torque converter is getting a bit hot for dino oil.
Do a little internet searching, there are a lot of posts on various sites by the guy who did the research and wrote the specs while he worked at Allison.

gbstewart · 05-08-2016, 08:24 AM

Quote:

Originally Posted by somewhereinusa

I think it is, my temps were getting really close to the "too high" for dino oils. At least with the synthetic I don't have to worry about that. I think my temps are cooler now although, I haven't been in any mountains since I made the change.
I also found out it makes a big difference where the temp is taken. My temp sender is in the location that senses torque converter temp, I didn't thing the cooler was working. I have since added a sending unit to the pan, the cooler drops the temp about 40 degrees. Still, that 300 degrees at the torque converter is getting a bit hot for dino oil.
Do a little internet searching, there are a lot of posts on various sites by the guy who did the research and wrote the specs while he worked at Allison.

Good point about the temps, I never really notice my tranny getting hot, always runs the same, but I haven't run high mountains.
Have you notice any leaks started ? synthetic is so much thinner, I heard of leaks starting in oils seals
tks
gbstewart

turf · 05-08-2016, 09:56 AM

when i got my bus, there was a burnt scent to the atf fluid. the first service home was a change to brand new fluid and filter.

after several trips in to the mountains, lots of funny noises, and a gut wrenching sense that im gonna have to replace that transmission before i get to the bottom of this hill. again the fluid smells burnt @ 12,000 miles post fluid change.

i'd like to hear comments of any that have changed to synthetic.

Tango · 05-08-2016, 10:45 AM

Synthetic can handle heat better than dino, but if you have been running in the 300 range, it is probably too late to do much good. 250 is really max and anything over that wrecks the oil rapidly...then the trans. Any good trans tech will tell you that 90% or more of all transmission failures are due to fluid issues. Most commonly...overheating breakdown.

Once again...check out the chart below. It is about the same as the one Allison puts out for conventional fluids.

Transmission temperature/failure chart.

And if you are up for quite a bit of reading/research, there is a long discussion with "Mr. TranSynd" himself over on the DuraMax forum. Covers lots of ground including effects on seals, temps, proper flushing techniques and much more. Way too much to include here but you can see it below...

Former Allison Transmission Fluids Engineer (Mr. TranSynd) - Chevy and GMC Duramax Diesel Forum

Jolly Roger · 05-08-2016, 12:40 PM

If anyone does decide to change to synthetic. How big of a concern is it to drain all of the old oil from the low points, pockets that don't drain from the pan like the torque converter and bottom of the cooling coil before you start mixing the two different types? I know the two will mix as circulation happens but will the original change need to be changed sooner because it is mixed? Just something in my head?
I have tried a few time and haven't found a drain plug on my torque converter and pulling hoses to drain is not that big of a deal but time consuming and worth it if it matters? Or just spend money and change the fluid earlier?

Tango · 05-08-2016, 12:54 PM

For anyone willing to take on a fairly long read...below is a link to a discussion on the DuraMax forum that goes into a great deal of detail on tranny fluid. It was started by Tom Johnson who was the Transmissions Fluids Engineer at Allison Transmission from 1990 until his retirement in 2009. Very informative and authoritative. Covers heat, flushing, changing and lots more.
Former Allison Transmission Fluids Engineer (Mr. TranSynd) - Chevy and GMC Duramax Diesel Forum

turf · 05-08-2016, 01:37 PM

that was a good read, i got 10-12 pages in and was about all i could take.

by that account, he reccomends a double drain and fill.

drain and fill, change filter,

run the truck 20-30 mins and

drain and fill again.

so that puts us up at about 8 gallons to change.

the other link tango gave has a link to a trans cooler. very reasonable compared to a few gallons of the synthetic.

with out looking, does anyone know it the 545 uses 3/8" cooler lines or 1/2" lines.

somewhereinusa · 05-08-2016, 03:09 PM

Quote:

Have you notice any leaks started ? synthetic is so much thinner, I heard of leaks starting in oils seals

No leaks.Now I need more stupid words to so I can post my answer.

cadillackid · 05-08-2016, 04:38 PM

where and how omn an AT545 are the best places to put sensors?

I figured I'd place on on the pan (standard location).. but where is another port to install a sensor? my bus currently has no trans temp gauge.. though an insert exists for my IHC dashboard cluster.. so I plan to add 1 or 2.. there are plenty of open slots on the cluster to place gauges..
-Christopher

Booyah45828 · 05-09-2016, 09:50 AM

Turf, check that your tv cable is correctly adjusted, that will overheat a transmission in no time. Especially an old mechanical one like the at545.

Synthetics are great. They're more stable, better protecting and last longer. But I'd use only If you need them. My bus moves less then 500 miles a year. So it's not necessary in my situation.

As far as compatibility goes and which fluid to use. You'll have to research. The Allison 295 spec'd fluids are probably some of the best atf fluids on the market. They work awesome in all the newer transmissions. How well it will work in the older ones is anybody's guess. Seal leaks are a pretty valid concern as well. Even though numerous people and manufacturers say it's not a problem. Here's a short story on my experiences.

When GM switched from dex3 to dex6, every pickup that used an Allison that we swapped over developed some sort of leak, or had the pressure switch board go bad. Allison conveniently changed the seal materials in all the transmissions spec'd for dex6, but GM says dex6 is backwards compatible with older trannies. I blame the fluid, but gm says that isn't the problem. And they didn't happen overnight either, all were about 3-6 months after the swap. Most of them, after we fixed them, were swapped back to either dex 3 or Shell Spirax S6 A295. After that fiasco, I use nothing but the Spirax S6 in the newer alllisons, whether spec'd for Dex 6 or not, while the mechanical ones still get dex 3.

Booyah45828 · 05-09-2016, 09:58 AM

Quote:

Originally Posted by cadillackid

where and how omn an AT545 are the best places to put sensors?

I figured I'd place on on the pan (standard location).. but where is another port to install a sensor? my bus currently has no trans temp gauge.. though an insert exists for my IHC dashboard cluster.. so I plan to add 1 or 2.. there are plenty of open slots on the cluster to place gauges..
-Christopher

Like somewhereinusa found out, Trans temps will vary wildly depending on where you measure them. A large number of oem's put it in the valve body along with the rest of the pressure sensors and switches. I've also seen them put in the output line after the pump, right after the cooler, and in the pan. Which one works the best? Hard to say. I'd imagine that being in the pan would give you the most average temp, but being in the valve body would be the most accurate. I wouldn't rely on one right at the torque converter telling you much, because I think that one might swing pretty wildly depending on how you're driving at the time.

cadillackid · 05-09-2016, 10:01 AM

Quote:

Originally Posted by Booyah45828

Turf, check that your tv cable is correctly adjusted, that will overheat a transmission in no time. Especially an old mechanical one like the at545.

Synthetics are great. They're more stable, better protecting and last longer. But I'd use only If you need them. My bus moves less then 500 miles a year. So it's not necessary in my situation.

As far as compatibility goes and which fluid to use. You'll have to research. The Allison 295 spec'd fluids are probably some of the best atf fluids on the market. They work awesome in all the newer transmissions. How well it will work in the older ones is anybody's guess. Seal leaks are a pretty valid concern as well. Even though numerous people and manufacturers say it's not a problem. Here's a short story on my experiences.

When GM switched from dex3 to dex6, every pickup that used an Allison that we swapped over developed some sort of leak, or had the pressure switch board go bad. Allison conveniently changed the seal materials in all the transmissions spec'd for dex6, but GM says dex6 is backwards compatible with older trannies. I blame the fluid, but gm says that isn't the problem. And they didn't happen overnight either, all were about 3-6 months after the swap. Most of them, after we fixed them, were swapped back to either dex 3 or Shell Spirax S6 A295. After that fiasco, I use nothing but the Spirax S6 in the newer alllisons, whether spec'd for Dex 6 or not, while the mechanical ones still get dex 3.

I dont know alot about commercial transmissions.. but every GM transmission I ever used. . fromm 200-4R, 4L60E, etc i always ran Type F.. gave me firmer shifts and the transmission seemed to run cooler.. now maybe thatd ruin an Allison I dont know.. it sure worked in the consumer grade trannies and I beat the &%^%$ out of those transmissions
-Christopher

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