Thread: Narrowing a 9" ford rear end

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To get an alignment that is ideal I would recommend making 4 blanks, two of which will have the outside diameter of your axle bearings with 1 1/4 inside dimension and two of which will have the outside diameter of your ring gear or third member bearings, with an inside dimension of 1 1/4 then you can remove the ring gear, install the 2 blanks where the ring gear bearings go, and install the third member and replace the axle bearings with the other two blanks. Next install a piece of cold rolled steel (cold rolled should be within .002 tolerance)the full length of the housing, going thru the blanks. This will give you a true and straight alignment with less chance of getting off center, causing premature axle bearing failure. After completion of welding you can slide your axle bearing fixtures into the axle housing and measure the gap between the axle bearing fixture (or flat) and the axle housing face. The tolerance should be no more than .005 .

Thanks, chickenlegs. In my first post I said that I borrowed a narrowing jig.

It is exactly what you describe. It is installed already using an empty third member that I had hanging around the shop. Before I installed it in the housing the 1 1/4" alignment bar was checked for straightness using a set of V blocks and a dial indicator. The alignment bar was true within .002". I was not happy with the alignment plugs (you called them blanks), that went in the housing ends (they were pretty sloppy from abuse during past uses), so I made a new one that allows both the bearing bore and the flange to seat on the plug. The new plug runs true on the shaft with less than .001" runout. It is also longer than the old plug(s )so it should not be as prone to cock on the shaft.

I called moser engineering and the phone tech guy did not know the misalignment tolerance dimension. He did say they use a 1 3/4" alignment bar and massive fixturing. He said that enabled them to make 1 quick continuous weld all the way around ,and that seemed to keep things straighter than numerous segmented tacks and welds. I'll be TIG welding mine so I can check it as I go and make adjustments as needed.

I have heard from several other folks that when the axle housing is all welded up if you can turn the bar by hand with all 4 plugs in you are good to go.

I will try to keep things within .015 TIR. I noticed that the bar by itself sags from its own weight about .001, so it will be hard to measure to .005.

I found a tech article, (through the HAMB), on the fordmuscle website that went pretty in depth about the procedure and I contacted the author, who straightens and narrows rear end housings as part of his business. He told me .020 was what he shoots for and has no problems.

Here is a link to the article. http://www.fordmuscle.com/archives/2...Inch/index.php

I had to buy a 1 year 15.00 subscription to read the entire 3 page article, It was worth it to me, as the second 2 pages had alot of pics and some pretty good technical writing.

Thanks for reading this,
Mikey