Allison 748 trans fluid change procedure

Scott & Heather · June 05, 2017, 08:59:45 PM

I am considering changing my trans fluid tomorrow as well as my spin on fluid filter. Anything special I should know? Just remove the drain bolt, let it drain, swap new spin filter on, and drain bolt back in, and new fluid? Nothing special? I'd like to put in TranSynd. I know I'll need two fluid changes, so this will be the first of two, and the next one I'll do when we get to Iowa.

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luvrbus · June 05, 2017, 09:31:20 PM

Yep don't start it 2 or 3 gals low and then add bring the level up and try to get it as close as you can then add a couple of quarts to top it off, fill the filter or filters too,if the 748 gets air you will get the dreaded "do not shift".It is your bus,transmission and money,Transyn is a waste of good money on the 700 series transmissions IMO

Lee Bradley · June 06, 2017, 12:47:00 AM

I had a re-manufactured 748 installed recently and requested Transyn. When I picked up the bus, they told me they hadn't used Transyn as the builder said not to use it. Seems to go along with what luvbus said.

Scott & Heather · June 06, 2017, 04:58:21 AM

Ok. I had been reading tons of past posts about the positives of using it and how it dropped trans temps 10 degree for people like Sean (odyssey). I would love to see my trans temps drop 10 degrees. So cliff, basically fill it as close to the "cold" level as possible after filling filter...this will prevent air?

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Scott & Heather · June 06, 2017, 05:25:36 AM

Ok, reading more past posts both on here and busnuts and I'm finding a few friendly arguments pro and against TranSynd use in the older 700 series trans. Mine is an ATEC 748. I have been running slightly elevated trans temps which are causing my engine temps to frequently pop up to 200 and slightly above. My cooling system is in solid shape. I really suspect my trans is running warm. Will the trans run hot if the spin filter is clogged? My fluid looks great. I'm double checking the level today after I get a test run in to warm her up.

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thomasinnv · June 06, 2017, 06:00:14 AM

Scott do you have a silver leaf or scan guage2? You should be able to monitor your trans temp. If the trans temp is causing the engine temperature to rise then the trans temp should be a bit higher than the coolant. Under normal circumstances I would think the temps would be close to the same. That is my experience anyway take it or leave it. But I would want to verify that before I go spending money on something that may not be a problem to begin with.

If you don't have a silver leaf or similar type device you can pick up a scanguage 2 at any auto parts store for around $125 I think I paid for mine.

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Iceni John · June 06, 2017, 07:40:47 AM

While I was replacing my radiator I also replaced my transmission temperature gauge with a Speedhut - the sender is almost impossible to reach when the radiator's in place. (The old Teleflex gauge had a mind of its own - it used to creep up even with the engine off and the batteries disconnected, so after a few days it would be up to 300 degrees! I think it was possessed.) The transmission fluid now runs through the new external cooler, and I keep its thermostatic fan on all the time when driving in warm weather. The fluid is usually either exactly at or a few degrees below coolant temperature, except in stop-and-go driving when it will be a few degrees warmer than the coolant. In other words, most of the time it isn't contributing heat to the coolant.

John

Scott & Heather · June 06, 2017, 09:22:36 AM

Ok, I read all of this too late and I'm already having the fluid/filters changed at SS. From what the Allison tech here said, the trans can easily run consistently 10-20 degrees higher than coolant. And from what I've read, 748 trans with retarder (mine) can reach 300 degree for short stints. I disabled my retarder but yeah.

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Lee Bradley · June 06, 2017, 10:27:29 AM

Of course, the engine shouldn't be adding much heat while using the retarder. I had a set of jakes installed while the engine/transmission was out; one of the best things I have done to the bus. I put all new brakes on during the conversion and they will stop the bus (39,900 plus 3550 toad) in a hurry but I could smell them on a couple of hills on 101 in Oregon and Washington.

Scott & Heather · June 06, 2017, 10:32:23 AM

The engine doesn't add heat when using the retarder, but the trans sure does. And since mine is cooled by my coolant, it heats up my coolant...

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Scott & Heather · June 06, 2017, 11:14:41 AM

FYI, I guess the young man test driving our coach after fluid change mistook it for a race car. I've never ever dumped stuff out of my latched cupboards in 20,000 miles of nationwide driving

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HB of CJ · June 06, 2017, 12:23:23 PM

Abuse of the transmission vehicle speed retarder can lead to absolutely insane transmission oil temps. Enough to destroy the transmission and nearly burn down the heavy vehicle.

Like coming down the Californian Ridge Route North at 75 mph riding the max position of the transmission retarder WITHOUT touching the service brakes. 44,000 pound Type One Fire Apparatus.

The fire engine nearly caught fire. The OTHER fire agency had to respond to save them. Very non professional apparatus driving. Embarrassing. Retarders can kill transmissions.

I do not know what kind of transmission oil they were using. Too long ago.

Scott & Heather · June 06, 2017, 02:34:59 PM

Yep. I've already done a few stints in the mountains out west and northeast. We just drive down them real slow. 40mph slow. I have never used the retarder and when the switch somehow got stuck in the on position, I just disconnected it. Anyway, coach does seem to run a bit cooler now. The shifts are butter smooth compared to before the TranSynd. Wow, I never expected it to change how the coach shifted. No more bang clunk...just real slick. They gave me a $75 credit for my tech making a mess inside. Total bill for filters changed and fluid changed to TranSynd was $750 out the door. I'm happy.

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luvrbus · June 06, 2017, 03:05:29 PM

15/40 would have gotten you the same results,only thing I could ever see a benefit was the oil change intervals using Transyn glad you are happy though.
If you keep the torque converter lock up the transmission won't generate as much heat either

Scott & Heather · June 06, 2017, 04:36:01 PM

Cliff, with your mention of getting the dreaded "do not shift" you scared me into having an Allison tech do the fluid and filter change lol. I do have a question tho, how do I "keep" the torque converter locked? I honestly do wonder if 15/40 would have softened the shifts like TranSynd did. I'm thrilled with how it shifts now...but yeah, I have to wonder if I just put golden juice in there for nothing. It wasn't cheap.

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