A freshly rebuilt transmission comes back with a no movement. The customer says they were driving around and then suddenly there was a loss of power and then dead on the side of the road, no movement. You verify the no forward or reverse gears. You find out later after the disassembly that the pump gears are broken and welded to the metal plate in the pump.
This is one of the worst situations for you and the customer. The rebuilt transmission did not even make it 100 miles and it’s back at the shop. The last thing you want is the customer second-guessing your workmanship.
There are two main areas to look at for the broken pumps; the pump rebuild and the chassis grounds. Before a comeback happens to you, we’ll show you how to keep the 5R110 transmission front pump working flawlessly.
THE PUMP
The 5R110 transmission normally is seen in shops with over one hundred thousand miles. Usually when they come in for a rebuild they need the coast clutch drum replaced and the direct clutches are burnt. Most of the time, the pump is rebuilt with a solution from the aftermarket for the worn pressure regulator valve.
The new bushing on this transmission many times is too tight on the torque converter. This will cause heat and the bushing will weld itself to the converter hub.
Here is how you prevent this, don’t replace the front pump bushing. Yes, you read that correctly. This sounds cheap or some may say that it’s not proper to not replace the bushing during a rebuild.
The front pump has the bushing installed then they finish the bushing in place for a true center line. It has been proven the bushing alignment is off center in many pump castings and therefore they are finished in place. After the factory bushing is removed and a new bushing is installed, it is not on true center, causing the bushing to ride off to one side.
If you want to or must replace the bushing, then line bore it to true center after installing the bushing into the pump.
One of the other reasons I say not to replace the bushing is that the new bushing is too tight. You can also hone the bushing to make the clearance correct but that still does not make it on true center. Always check the converter hub to bushing clearance, it should be 0.003″ – 0.0045″.
The bushing has a lube slot cut into it. Make sure the lube slot notch is aligned correctly in the pump (figure 1). With the slot alignment correct the bushing gets a full amount of lube.
When you’re installing the pump gears into the pump, first take the inner gear and check the fit onto the torque converter. Make sure the hub contacts the gear on each side equally.
Lube the pump pocket and gears with ATF. The outer gear has a chamfer on the outside edge (figure 2). This chamfer has to go down into the pump pocket first. If the chamfer isn’t down, the outer gear can gouge up the gear and pocket and weld itself together.
It’s a common procedure to use a pump band around the outside of the pump to align it, that’s not the case on this transmission because the bushing may not be true centerline. The best way to align the pump is to align it off the stator support tube. There are aftermarket alignment tools available to help align the pump up to true center line.
To sum up the pump rebuild, make sure you address the worn pressure regulator valve to fix the high-pressure issues. Do not replace the front bushing unless it really needs to be replaced. Lube the gear and make sure the gear is in the correct direction. Use an alignment tool that centers pump off the stator tube.
BATTERY GROUND
The main ground cables will need need to be replaced in many cases, but you can also do a voltage drop test on both cables in a diesel. Doing a voltage drop test to test for bad ground is a must for this transmission. Install one end of meter on the ground post of the battery and the other lead on the component you’re testing. I recommend testing the engine block, frame, cab, transmission case and ground cable.
With the engine running you should have no more than 0.10V DC at those locations. If you do have more voltage, you have a bad ground. You’ll need to clean and/or replace cables or wires.
You also want low voltage while cranking on the ground circuits. I like to see under 0.40V DC while cranking the engine over. Most diesels are around that because the starter draws so many amps.
If you are wondering why you should be so worried about ground circuits, take a look at figure 3. This pump damage was caused by bad grounds. The inner gear welded itself to the pump. Bad grounds normally just affect the inner gear and you will see damage primarily to that gear.
NOTE: Do not forget to clean the engine to transmission mounting surface and clean and lube the crank and converter pilot.
You can have the perfect rebuilt transmission and the best grounds circuits possible and still can have pump problems. That’s right, get your R & R man in on this information too.
The torque converter must be full before installation, three quarts is sufficient. After the transmission is installed and before you start it, you’ll need to add 8 quarts to the transmission. Next, start the engine for about twenty seconds then shut it off. Add 5 more quarts to the transmission and restart and fill the transmission to the proper level.
This pump moves a lot of fluid fast and can run the pump dry quickly if there is not enough fluid in the transmission. If you have a pump with damage and hot spots to both gears that is a sign of a starving pump.
If you rebuild the pump with alignment tools, clean and test the ground circuits and add plenty of oil on the startup, you will keep the 5R110 transmission running strong and the customer happy.
