Installed the new ring gear on the carrier. I put the ring gear in the oven on about 300 and the carrier in the freezer for this one as well. Make sure you have the ring gear bolts on hand so you can line up the bolt holes during install. You will not be able to rotate the ring gear in order to line things up. I did not use the ring bolts to get the ring gear on the carrier. I used a dead blow hammer once I had three bolts in so I knew it was lined up. I have read some that use the ring bolts to pull the ring gear on, I chose not to. Once you get it all lined up, put red thread locker on the ring gear bolts and torque them down to 65 ft lbs in a criss cross pattern.
Now need to press the outer race back into the Housing. I used bearing race drivers and a press.
Press on new bearing on pinion head. Oven and freezer trick here too.
OK – So I’ve got my new bearings installed on my new carrier, new pinion outer bearing race in the Housing, and new inner pinion bearing installed. Time to try setting up some gears.
One thing to note - On the face of your old and new pinion, there will be a marking. My old pinion had a +4 and the new had a 2.551. What these numbers are telling you is the optimum pinion depth location. The number is the distance the face of the pinion should be from the centerline of the axles. That’s somewhat irrelevant to us since we won’t physically be measuring that distance, but it does tell us something. This distance is controlled by the pinion depth shims located between the pinion inner bearing race and the Housing. The standard setting, centerline distance, for an AMC 20 is 2.547 inches. The +4 on my old pinion is telling me that is should be set at an additional 4 thousandths, or 2.551 inches away from the centerline of the axles. Since my new gear also reads 2.551, theoretically they should both be optimum at the same location, so the shim pack that came off will be a good place to start. It could also say +4, but for whatever reason they put the actual distance on there instead of the variance.
Example – If your old pinion read +4 and your new read +2, you would start your shim pack with 2 thousands more shims, in order to move your pinion face .002 closer to the axle centerline. There are charts available that tell you where to start, but the math is pretty simple.
Now when setting up gears, there are several things that must be correct.
Backlash – This is the play between teeth of the ring gear and the pinion gear. This is adjusted using the carrier shims. Moving the ring gear away from the pinion increases backlash and vice versa. Moving the pinion closer/farther from the ring gear also affects backlash.
Pinion Depth – This is the distance the pinion head is from the centerline of the axles. We will actually never measure this distance(though if you could it would save some time). We will read the gear pattern to help determine if we are acceptable. This is adjusted using the pinion depth shim located between the inner pinion race and the housing.
Pinion Bearing Preload – How tight the bearings are pressed into their races. Measured using the inch pound torque wrench.
Carrier Bearing Preload – How tight the carrier sits between the carrier bearing races. To determine shim thickness needed, install the carrier and enough shims on one side until there is no end play in the carrier - Then add about .008 in shim thickness. It should take several good blows from a dead blow hammer to set the carrier, it should not easily go in and out. You will not overload the bearings. Just remember, when you add shims to one side of the carrier to adjust backlash, you must remove the same thickness of shims from the other side. Keep the same total thickness of shims in the carrier.
As I go through the setup process I will be checking pinion preload, backlash, then gear pattern. In that order. Once I get backlash within spec, I will begin adjusting pinion shim depth. As you go through the process, you will get a good feel for what adjustments to make.
Since I am waiting on shims to come in, I have no choice at this point but to start back with what came out. This is a good starting point for me anyway since my old pinion was +4 and so was my new pinion (2.551 = +4).
Pinion Depth Shim = .100
Ring Gear Side Carrier Shim (RGCS) = .09125
Non Ring Gear Side Carrier Shim (NRGCS) = .085
Again, these were the shims that came out during disassembly.
The pinion is installed back in the housing using the inner bearing race setup bearing (with the pinion depth shim between it and the housing) and the outer setup bearings installed. You will need to install the yoke, but not the seal or crush sleeve at this point. I had to use the tool again to turn the pinion nut until I got a preload rotating torque of about 8 in-lbs. This is a rotating torque you are looking for! You will need a beam or dial type inch pound torque wrench in order to read this value. For old bearings on an AMC 20, preload should be 6 to 8 inch pounds. For a new bearing you are looking for 14 to 19 inch pounds according to Yukon and 15-25 according to the FSM. This reading is taken without the carrier installed. Since I am basically using old bearings as setup bearings, I will use the old bearing preload numbers until I go back with the new bearings, at which time I will aim for 15-25 inch pounds.
One thing I noticed here that I wasn’t sure about was when I was reading my rotating torque, the pinion was jumping a little, it was not a smooth rotation. According to some here that’s normal, so I kept going with it.
Anyway, got my preload rotating torque to 8 in lbs. Turned the housing around and began to install the carrier and carrier shims. Got it installed and installed my bearing caps back in their original location and orientation.
So, using my original starting shims, I had NO backlash. I couldn’t even turn the ring gear a complete revolution without binding. So, I need to increase backlash, which means moving the carrier toward the ring gear side of the carrier – Away from the pinion.
Pinion Depth = .100
RGCS = .085
NRGCS = .09125
Still no backlash
Pinion Depth = .100
RGCS = .078
NRGCS = .099
Trial 4 -
Now – Since I am out of shims to use – I just removed all shims from the RGCS, just to see where that would put me with backlash.
Finally – I have Backlash –
Now, when measuring backlash you will need a dial indicator and a magnetic base. Mount the magnetic base to the axle and get the indicator as close to perpendicular to the ring gear as possible. Rotate the ring gear all the way in one direction, ensuring the pinion is not moving. Set the indicator to zero. Rotate the indicator all the way in the other direction until resistance is met from the pinion. Note the reading on your indicator, this is your backlash. In my case here it was a whopping .053. Range for an AMC 20 is 6 to 10 thousandths with .008 preferred. I am at a standstill waiting on my shims at this point.
Upside down backlash reading.
Once my shims come in I’ll be back at it again