Allison 545 Transmission Review, Specs, and Problems
It just may be getting old. That seems to be the viewpoint of some skoolie owners. The Allison 545 has been around for a very long time and there are different bus owners who think it is time to switch gears and upgrade to a more modern transmission. Old technology is good but newer may be better.
For the most part, you are getting a good transmission for the money. The transmission works best with 235 HP input and 445 torque lb. ft input and it does well in vehicles weighing up to 30,000 pounds. The acceptable full load engine governed speed is 2400 to 4000 RPM for diesel motors.
To learn more about the Allison 545 transmission just continue to read our article. It has the information you want to know about so you can make a good purchase decision. Just remember that if you are buying used, it will have a couple of hundred thousand miles on it and it needs to be treated right.
Allison 545 Transmission 101
What Allison Transmission is in a School Bus?
This would depend on the year your bus was made. Allison has upgraded its transmission to the 2000 PTS and 3000 PTS series models and those seem to be the ones in many school buses currently.
There have been many transitions over the years but earlier models would have had the Allison 545 transmission installed. It has been a workhorse of a transmission transporting millions of school children for years in hundreds of thousands of school buses.
If you are buying used chances are you have the 545 model shifting the gears. There were also the 540 and 543 models but they are exactly the same as the 545 except for the smaller oil pan.
This series of transmissions were fully automatic and were said to need less maintenance than the manual model. This led to less downtime meaning schools got better service out of their buses with the 545 handling the workload.
But you may find different models of Allison transmissions in a school bus as different school districts have ordered different buses made by different companies. One series of buses had the Allison 2500 model.
Is The AT545 Good?
According to what we have found during our research, it is a very good transmission. It has been placed in hundreds of thousands of school buses and driven for tens of millions of miles over the years. Plus, it has been placed in many medium-duty trucks.
To quote one reviewer, ‘you do not get this type of market penetration if you are producing an Edsel.’ That popularity and production as well as longevity say a lot about the reliability and durability of the transmission.
Of course, repair records may say something not as flattering as these transmissions will break down from time to time but if they did it a lot, Allison would not be a respected transmission manufacturer.
The 545 is just getting old and it may be time to replace it with an upgraded model. The trouble is, the newer versions may not be interchangeable with the 545 bell. There has been some discussion on this and the consensus is clear, you need adaption to make newer transmissions work in the old school buses.
Our Allison AT545 Review
This transmission has had its day. It is an older technology that may not be up to the rigors that newer motors and heavier vehicles send to a transmission. The transmission may be best for flat road surfaces or slight inclines but not for pulling a 30,000-pound vehicle up mountain roads and steep passes.
It does have its weaknesses as it does not reach full pressure on the internal bands until the input shaft reaches 2400 RPM. Also, the transmission may slip a little when hauling loads when you drive a little slower than 2400 rpm.
Plus, the transmission is not idiot-proof, meaning that if people do not take care of the transmission, read the update bulletins, and do not learn how to drive with this model, it will break down.
There is no excuse for doing that and you are only putting a good transmission at risk of damage. When you do that, you are looking at paying some high repair bills. Good maintenance habits should keep the 545 running for a lot longer.
Allison AT 545 Transmission Specs
The following information is not original to us. The link to the source is placed at the end of the article.
General Purpose Truck and Motorhome Rating
Net input power 235 hp (175 kW)
Net input torque 445 lb-ft (603 N·m)
Vehicle weight Up to 30,000 lbs (13,608 kg) GVW or GCW
Airport Shuttle Bus Rating
Net input power 180 hp (134 kW)
Net input torque 380 lb-ft (515 N·m)
Vehicle weight Up to 26,500 lbs (12,020 kg) GVW
School Bus, Intercity Bus, and Shuttle Bus Rating
Net input power 235 hp (175 kW)
Net input torque 445 lb-ft (603 N·m)
Vehicle weight Up to 30,000 lbs (13,608 kg) GVW
Refuse Vehicle Rating
Net input power 235 hp (175 kW)
Net input torque 445 lb-ft (603 N·m)
Vehicle weight Up to 22,050 lbs (10,002 kg) GVW
ENGINE INTERFACE
Acceptable full-load engine governed speed 2400-4000 rpm (diesel)
3200-4000 rpm (gasoline)
Minimum engine idle speed
(with the transmission in drive) 500 rpm (#1)
There are a lot more specs at that link. The origination source website does not exist anymore
AT545 Transmission Weight
The actual weight of this transmission is roughly 267 pounds or 121 kg. There is also a dry weight with PTO and that comes in at 275 pounds or 125 kg and finally, there is a dry weight with retarder which reaches 315 pounds or 143 kg. (#1).
We doubled checked those specs and the Allison spec sheet simply says that the transmission weighs 289 pounds (#2). You can use the second source to compare with the first one to see how accurate both spec sheets are.
There may be some weight differences depending on the model of the school bus the transmission is placed in. One answer to this question came back as 293 pounds. There may be some discrepancies as scales may be off or there have been extra parts added like the torque locking mechanism.
But those figures should give you a rough idea of the total weight. It does tell you that you need to be careful when lifting or removing the transmission for repair work.
AT545 Transmission Fluid Type
The transmission fluid type that you will use will depend on the year the motor was made. For example, source #1 says Dexron III, C4 is the type of transmission fluid you should use. However, that information was published in 2014.
Source #2, published in 1992 states that the transmission fluid needed for the Allison 545 is Dexron II, C4. The best advice we can provide you is that you check the owner’s manual of the model you own or want to buy to see exactly which type of transmission fluid you should use.
Upgrading to the current generation of transmission fluid for older 545s is not a bad idea. That way you can give the transmission better protection and help it run better. The failure to make this change can shorten the lifespan of the 545 or cause you to have some troubles down the road.
Keep in mind that the 545 series is an older model and already has a couple of hundred thousand miles on it and it needs the best protection possible.
AT545 Transmission Fluid Capacity
The amount of fluid you would need to operate this transmission effectively and efficiently depends on the type of transmission fluid pan you have on the model. Source number 2 only states that with a standard oil pan and excluding the external circuit, you need 20 US quarts to fill the pan.
Source #1 concurs with that statement for the standard oil pan. But it goes one more as at least in 2014, a shallow pan was available and with the same exclusion, you would only need 15 US quarts.
If you want those figures in liters then the standard pan would need 18.9 and the shallow pan would require 14.2. Check your owner’s manual for the amount your model year will require.
Allison continued to make upgrades to the 545 over the years and may have made some changes to the transmission fluid requirements from time to time.
Allison AT545 Transmission Parts Breakdown
This may be a bit hard to do as, over the years, Allison has continually upgraded and updated their transmission models. While they place a new label on these transmissions, 545, 1000, 2500, 2000, 3000, and so on, finding parts may be confusing.
The rule of thumb to follow is that to find the correct part, you need to know which generation your transmission falls into. For the AT 540, 543, and 545, you are looking at 50 parts that can go wrong on the transmission.
Since these 3 motors are basically the same, the same source will apply to all three. For an official parts breakdown, just go to source #3 at the bottom of the page. It lists all the parts in the transmission plus provides images for each one and where they go.
This is a 4 page PDF file that is very clear and very easy to follow.
Common Allison AT545 Transmission Problems
One common problem will be the shifting aspect. When cold the transmission can shift fine but when warmed up, it may not get into 3rd or 4th very easily. The source of this problem could be obstacles building up in the governor, modulator, or valve body passages.
To repair this problem, you would need to take the transmission apart. Another source would be old cooler fluid. If it is not kept clean, it can cause a shifting problem. Flushing the system is the solution here.
A failed clutch is another common problem. These will fail over time and sometimes it may be the fourth clutch that keeps you from going into reverse gear. The clutch failure is due usually to leaking pressure and you need a kit to fix this issue.
Another problem will be when the mechanic does not do their job properly. Something is not hooked up properly and that results in transmission issues. You need another mechanic to double-check this problem.
AT 545 Allison Transmission Troubleshooting
Understanding how the 545 works are part of fixing any problems that come along. For example, there is no gasket on the plate. You may be surprised to find this out when you pull it off.
You may also be surprised to find a hole in the transmission behind the plate that goes into the torque converter. There is a method to this madness. The hole is there to let leaking fluid escape and the lack of a gasket lets that escaping fluid reach the ground.
This design is done on purpose so that you have a very easy clue that you have a problem somewhere inside the transmission. With the leaking fluid, you could have a front seal leak or a problem in the torque converter.
Check the service manual to see other troubleshooting tips that may help end any confusion you have and lead you to the source of your problems. (#4)
Some Final Words
Allison has been around for over 100 years. They do make top-quality transmissions that are long-lasting and very reliable. The AT545 is just one of those transmissions. However, it is getting old and the technology inside is not up to date anymore.
You may want to consider upgrading to a more modern generation and take advantage of the upgrades this company has made to its transmission models. If not, use current fluids to give the transmission all the help it needs to keep running.
Sources
1. http://www.barthmobile.com/eve/forums/a/tpc/f/3731087061/m/6453935387
2. https://www.dal-trans.com.au/files/AT-545.pdf
4. https://issuu.com/manualtrucks/docs/allison_transmission_at_545_service
