Allison 1545 Automatic Transmission Specs

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
I saw this posted in the 1545 failure poll and was surprised to see it wasn't repeated here:

Not exactly the thread for this, but I'm trying to (discretely) spam this info I just found about AT 1545s:

For those 1545s with serial #s GREATER than 321-101-6535 (or retrans GREATER than 9108-0912-20), there is a newer option for the front pump. This newer option involves replacing the front pump and stator. It retains the lockup. Darpco in Dallas (likely among others) can assist with this.

Good luck!
SJ
 

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
I have a 545 and I have changed the transmission fluid and filters ... it seems to be doing fine except if I don't hold the peddle to the floor when speeding up the transmission jerks when going from 3rd to 4th ....any ideas about what could be going on ?
It is my understanding that this is normal behavior for the 545 transmission. My truck and another owner's do the same thing. It just clunks into 4th gear, and the tranny takes its time shifting into third. I almost thought it was going into another gear between where it felt second and third were!

FWIW my experience has only been with the motor oil it came with. I plan on switching to ATF in the spring.
 

rustystud

Well-known member
8,486
185
48
Location
Woodinville, Washington
I have a 545 and I have changed the transmission fluid and filters ... it seems to be doing fine except if I don't hold the peddle to the floor when speeding up the transmission jerks when going from 3rd to 4th ....any ideas about what could be going on ?
To much "governor" pressure. Your using "modulator" pressure to counter-act the high "governor" pressure when you hold the pedal to the floor.
The governor weights could be sticking. Take it apart and clean it real good.
 

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
To much "governor" pressure. Your using "modulator" pressure to counter-act the high "governor" pressure when you hold the pedal to the floor.
The governor weights could be sticking. Take it apart and clean it real good.
I'll have to get this checked out now. Although my jerk may be different from the other guy's jerk. Probably best for me to get it checked out at the local Allison shop and have them do the ATF conversion as well!
 

URSATDX

Member
138
16
18
Location
So Jersey, NJ
I am planning on doing the MO to ATF conversion on my Allison 1545. I will introduce the ATF thru the check/fill tube. In order to insure a complete and thorough flush what would be the best point to disconnect the flow circuit so that the entire trans and cooling system are flushed. I’m assuming the ideal disconnect would be at the return line at the transmission. Thoughts? If this seems to be the best location, I would need to confirm the direction of flow of the MO/ATF in the system. I am ASSuming that the fluid flows from the trans to the top of the radiator out the lower radiator to the trans cooler (top) and from the cooler back to trans. If this is the correct direction of flow then I will proceed to flush until the fluid at the trans return line is all ATF and no MO. I’d then drop the pan, replace filter and gasket. Replace the inline spin on filter, run and adjust fluid level.

Suggestions on ATF types?

Any thoughts from the troops?

Much appreciated.

God Bless our Great Country!
 
Last edited:

rustystud

Well-known member
8,486
185
48
Location
Woodinville, Washington
I am planning on doing the MO to ATF conversion on my Allison 1545. I will introduce the ATF thru the check/fill tube. In order to insure a complete and thorough flush what would be the best point to disconnect the flow circuit so that the entire trans and cooling system are flushed. I’m assuming the ideal disconnect would be at the return line at the transmission. Thoughts? If this seems to be the best location, I would need to confirm the direction of flow of the MO/ATF in the system. I am ASSuming that the fluid flows from the trans to the top of the radiator out the lower radiator to the trans cooler (top) and from the cooler back to trans. If this is the correct direction of flow then I will proceed to flush until the fluid at the trans return line is all ATF and no MO. I’d then drop the pan, replace filter and gasket. Replace the inline spin on filter, run and adjust fluid level.

Suggestions on ATF types?

Any thoughts from the troops?

Much appreciated.

God Bless our Great Country!
The return line is located directly behind the breather vent. This is the procedure we used at the transit agency to flush the bus transmissions. Just be careful ! Don't allow the transmission to run dry ! That would destroy your oil pump in a heart beat !
Since I'm pretty sure you don't have ATF on a pressure system like the transit department does, (we just put the nozzle in the transmission fill tube and pulled the trigger and out poured ATF at 20 gallons a minute) you need to run the engine in short bursts. Then top off the transmission and run it again. Do this until the fluid runs clear ATF.
 

URSATDX

Member
138
16
18
Location
So Jersey, NJ
The return line is located directly behind the breather vent. This is the procedure we used at the transit agency to flush the bus transmissions. Just be careful ! Don't allow the transmission to run dry ! That would destroy your oil pump in a heart beat !
Since I'm pretty sure you don't have ATF on a pressure system like the transit department does, (we just put the nozzle in the transmission fill tube and pulled the trigger and out poured ATF at 20 gallons a minute) you need to run the engine in short bursts. Then top off the transmission and run it again. Do this until the fluid runs clear ATF.
Thanks for the response, Rusty.
Looked thru TMs for answers, but I have a hard time navigating thru them.
I do have an ATF dispenser (gun) fed from a 110 gal tank. (Own/operate a quick lube).
The tank is filled with a multi veh full syn ATF. (Specd for Allison / Allison (C-4 / TES-295 / TES-389) . I will look for a diagram of the 1545 to be sure I pull the correct line. I'll keep you posted on the results.
Thanks again.
God Bless America.

1580153467767.png
 

Sgt Jiggins

Potato Peeler
Steel Soldiers Supporter
396
124
43
Location
Lynchburg, VA
I'd like to make one more add to this thread: after having my 1545 rebuilt the rebuilder suggested using "John Deere Hy-Gard Transmission and Hydraulic Fluid" (not just Hy-Gard Hydraulic Fluid - there apparently is a difference?) in it. I know fluids in these things come up in discussion frequently and don't want to start a battle with this information but maybe put it out there as an alternative in case people are still not happy with other options.

As always, YMMV har har
 

Boatt2082

New member
2
3
3
Location
Jacksonville FL
I'd like to make one more add to this thread: after having my 1545 rebuilt the rebuilder suggested using "John Deere Hy-Gard Transmission and Hydraulic Fluid" (not just Hy-Gard Hydraulic Fluid - there apparently is a difference?) in it. I know fluids in these things come up in discussion frequently and don't want to start a battle with this information but maybe put it out there as an alternative in case people are still not happy with other options.

As always, YMMV har har
As someone who just purchased an M36A3 I found this thread very helpful.

Has no one found a alternative transmission for the A3 (maybe one with an overdrive)

Toby what’s the big difference in a locking converter vs non locking ? I see you say a non locking isn’t preferred for a highway vehicle. Any way to elaborate a little more on this?

I’m not a transmission guy by any stretch of the means.

Thanks in advance
 

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
As someone who just purchased an M36A3 I found this thread very helpful.

Has no one found a alternative transmission for the A3 (maybe one with an overdrive)

Toby what’s the big difference in a locking converter vs non locking ? I see you say a non locking isn’t preferred for a highway vehicle. Any way to elaborate a little more on this?

I’m not a transmission guy by any stretch of the means.

Thanks in advance
Welcome! And you have a pretty rare truck in an M36A3! I think you should start another topic and post pics :cool:

The locking transmissions eliminate losses between the engine and transmission through the fluid coupling (torque converter) in 3rd and 4th gear, increasing fuel efficiency. In function, it's like a clutch in a manual transmission.

As a result of the locking feature, it seems it puts extra stress on transmission components responsible for 4th and reverse gears, causing eventual failure of those components (but maybe this only affects trucks that are regularly loaded with heavy cargo?).

The Army seemed to have realized that this was a problem because they have instructions in one of the support TMs for switching a 1545 with the more-common non-locking 545. The 545 has been used in trucks and school buses for years, so I wonder how much less fuel efficient the A3 would be on-road. The Army didn't think it was a big deal, evidently.

I'd prefer to keep the 1545 on my truck and try to fix it if it broke. From reading around here, the stressed components can be replaced with those found in other flavors of Allison - maybe it's a HMMWV transmission I'm thinking of?

Plus the private bus owners like the 1545 for the torque converter. It seems quite a few of those bought the surplus 1545s when they were still around!

I don't think there are any OD automatics that would fit in the space available under the truck without shifting a lot of stuff around. I think the ESP avoided that to keep costs low.
 
Last edited:

tobyS

Well-known member
4,804
734
113
Location
IN
The A3 is a redesign of the A2 and A1, but eliminate shifting. By the wisdom of the day, they took a good performing commercial Allison 545 and added the feature of the locking TC, calling it the 1545.

Probably the reason there is a different thunk between 3rd and 3-4, is that the 2-3 shift is unlocked while the 3-4 shift is with the converter locked and does not soften the change so much.

Seems someone should make it only go to locked after going in 4 to reduce the 4th gear stress on the gears and fourth clutchs...which is the weak link.

If you missed it before, look up the "direct" clutch in the L480E and consider the race frictions, steels, and vulcanized steel piston to replace the OEM clutches and aluminum piston.
 

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
Probably the reason there is a different thunk between 3rd and 3-4, is that the 2-3 shift is unlocked while the 3-4 shift is with the converter locked and does not soften the change so much.

Seems someone should make it only go to locked after going in 4 to reduce the 4th gear stress on the gears and fourth clutchs...which is the weak link.

If you missed it before, look up the "direct" clutch in the L480E and consider the race frictions, steels, and vulcanized steel piston to replace the OEM clutches and aluminum piston.
The transmission is supposed to unlock between 3rd and 4th gear. And thank you for the 4L80E mention. That's a pretty common transmission outside HMMWV applications, I think, so it shouldn't be hard to get those parts!
 

Redneck of Enon

Member
Steel Soldiers Supporter
44
15
8
Location
Chester , VA
just want to say thank y'all for sharing your knowledge to people like me ...who have sometimes think they know it all and then wake up and know God is the only one that knows it all ...
 

tobyS

Well-known member
4,804
734
113
Location
IN
The transmission is supposed to unlock between 3rd and 4th gear. And thank you for the 4L80E mention. That's a pretty common transmission outside HMMWV applications, I think, so it shouldn't be hard to get those parts!
No, go back in this thread and it gives the shift sequence. Going from 2 to 3 the converter is unlocked. Then the converter locks while in 3 and is locked when going from 3 to 4. That puts a lot of strain on the 4th clutch pack that could be avoided.

The parts I reference are high performance, not just the standard OEM. They are thinner so have a couple more, tougher material and the vulcanized steel piston holds more pressure.

It would be nice if there was an easy change on the shift pattern or making the lock-up entirely manual. I'll ask my Allison man.
 
  • Like
Reactions: HDN

tobyS

Well-known member
4,804
734
113
Location
IN
It would be nice to have the details of the 1545 lock up torque converter control. Does anyone know how the hydraulic pressure is controlled inside of the valve body? I think most Allisons now use electronics, but the 1545 is hydraulic..... Hey Rusty???
 

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
Okay, guys, if anybody is still checking this thread, I found some info (maybe outdated) on these 1545 trannies.

Gear ratios: 3.45, 2.25, 1.41, 1.00 to 1.00 and R 5.02

It shifts 1c, 2c, 3c, 3L, 4L . C = converter, L = locked clutch
Thank you for that @tobyS . I listened to my truck shifting in my sound recording and I thought I heard the 4th gear re-locking.

Here's a sound recording of my truck starting at an intersection and running through the gears:

You can clearly hear the shift into 3rd gear, then 3rd gear locking up. I think it sounds like the transmission does the same thing for 4th, unlocking into 4th then locking into 4th, despite everything I've read saying otherwise.
 

tobyS

Well-known member
4,804
734
113
Location
IN
I have to return this fold out schematic of the 1545. I have it in PDF emailed to me but don't know how attach it with my I pad. Here is an overall shot and one of each end of the schematic.
 

Attachments

HDN

Well-known member
912
1,487
93
Location
Finger Lakes Region, NY
I have to return this fold out schematic of the 1545. I have it in PDF emailed to me but don't know how attach it with my I pad. Here is an overall shot and one of each end of the schematic.
That's in the service manual. I just found the PDF, which I'll post later when I get on that computer.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks