rear gear install

rockyracoon

10 Year Member
Nov 23, 2005
874
27
49
margate NJ
in the past I have used the ratech pinion depth tool,however I seem to remember loaning it out and now I dont have it.anyway I decided to use the MHD method which is basically measuring the old pinion head and shim,and then measuring the new frpp pinion head,and coming up with the appropriate shim to get to the same depth.well I did that and the math was telling me to decrease the shim from .036 which was the old shim to .015 on the new pinion,but after doing that and trying a mock up the pattern is kinda high and out towards the heel,so I decided to try a mock up with the old shim,and the pattern looks much better.I dont get it. the thickness of the new head is 2.895 and the thickness of the old head was 2.874 without the shim,so how is it that the old shim is showing an acceptable pattern? could it be because the new 410 pinion head is much smaller in circumference ? I would think that wouldnt matter because the new ring is thicker.
 
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If you look at the set up procedure in the Ford manual (using the special Ford tools), no where does the gear ratio come into play. 4.10's are set up exactly the same way as 3.27's.

The Ford tools works by using a mock up bearing and measuring with a mock up piece to take the place of the pinion. So the actual size of the pinion head is not taking into account and does not matter.

The pinion depth is established from a known distance between the bearing cup to the pinion head (not the end of the pinion).

I suspect that the difference in pinion head thickness is the reason the MHD method calls for a different shim.

At the end of the day, the pattern is what really matters.

The only OBTW I can see regards pinion pre-load. If the bearing cups are not fully seated and pre-loaded, the pinion may shift when installed. The other major function of the Ford special tool does is to pre-load the bearings for an accurate shim measurment.

Sounds like the original shim is a great place to start.
 
they are frpp gears.I am getting what seems like a good pattern with a shim.001 smaller than the original which was .036 thats the biggest I have ever seen BTW.so well see.one thing though I must be getting weaker as I get older because Im just now crushing the sleeve and im starting to wonder if I will be able to do it,its ungodly hard.I had to stop but I will resume later on tonight.god I hope I dialed it in right the first time,at this point only a test drive will tell.