As discussed earlier, the gear pin holes in my P160 differential were worn and allowing the pins to slop around. This is bad in a couple of ways. It will cause hard shifting, but also can potentially cause the axle to go out of gear, which is without brakes and therefore very dangerous. Possible solutions are replacement of this part, or rebushing the pin holes. I opted to try to rebush the pin holes. I had a spare, through the generosity of a MFCTA member. I posted a request for advice to the MFTCI forums.
Here is the response I got...
Mount the thrust plate to the 160 housing. Setup in a drill press and clamp the 160 housing using the thrust plate and a 1/2 inch rod to locate the pin holes in line with the drill press spindle axis. Once the pin hole is centered on the drill press, remove the plate and using an end mill, true up the diameter of the hole. I used a 9/16 end mill. You must use an end mill as a drill will follow the old hole. Now using a 5/8 drill, cut the hole to size. Install the bushingsif they are a good press fit. If not a good press fit,use loctite. If they are sloppy, make some oversize bushings.This is a recap of the advice in the Chaffin book of course. The one exception is the use of an End Mill, a term and a tool I have never used before. Having used one now, I will again in the future. Nice tool.
As shown below, I walked this path exactly. But when done, I had 2 holes perfectly on center, and one was still off. Willingly would blame myself, but I rechecked the orientation of the pin 3 times, at least, on each hole. I suspect my clamping device has some side play when vibrated. My drill press is quite old (1940s Delta), but we did check for side play on the chuck and shaft. Otherwise would have sent to a machine shop. I am not sure what happened here, but regardless here are a set of photos of the process. At the end however, I feel that the one is too far out to use versus the other one I have.
Regardless of my results, the process is correct and should be used by others....
1. Image at right shows the existing P89 gear pin chucked into my drill press. You can see the clamp I used to hold the P160
2. 9/16 End Mill with depth marked in tape. Use care not to go too far, to avoid drilling past the pin foot.
3. Depth checked with ruler. I came up with 255 mm as the correct depth.
4. Chuck a 1/2 rod into the drill press and confirm alignment. Here I am doing this first without the plate, then with. I removed the plate, reinstalled it, confirmed alignment a second and third time. It invariably moved due to the tapping to get the plate off. Kept repeating until it was confirmed twice.
5. Installed a 9/16 end mill. Took an intial light pass to look at the cut.
6. Commitment Time. Drilled down to my tape mark with the End Mill
7. I chose to rotate the P160, and do all of the 9/16 holes first. This seems a mistake, but I wanted to reconfirm everything all over again before committing to a larger drill size.
8. Now, continued on to the 5/8 bit. This is where I ran into trouble as my first pass on hole 1 chattered. This is probably where the alignment on one of the holes failed, having vibrated the housing half a bushing width off. I did not see the misalignment of course, troubles ensued. Anyway, here is one hole completed
9. After all holes drilled, I then installed the bushings. As indicated above, they were a press fit - a bit of Loctite and taps with a small ball peen hammer got them seated. You can see one in place, and the alignment thereof. They are now too tight for the pin to be installed; they will have to be reamed to fine tune.
10. I drilled a bit too far into one hole, so the bushing sat a bit proud. A tap in the opposite direction corrected this...
11. Here is the end result; you can plainly see the problem hole - which was the same problem hole before I started...
Point is, despite my issues procedure works if carefully followed.
