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I'm rebuilding a Differential out of a '68 for my buddy Brett. He's going to use the car at the track from time to time so he wanted a strong differential. One of the mods I'm doing to it is fitting a Tom's steel cap. I've wrote about these before but this one proved to be a bit of a job and got me thinking about what guys would do if doing this at home. The instructions are very brief and the process is basic. Depending on the cap you get and your housing you may be in for fun. After the last 3 steel caps I fit, I would not recommend doing them without access to a grinder and maybe a mill. Here is what I found with this one.
First this is the cap compared to a stock one. I've posted this before but in case someone new doesn't know about this, here it is.
First the holes for the LH cap in the housing need to be tapped for 1/2-13 bolts- up from the stock 7/16-14's. Now you can step drill like the paperwork says but I was concerned about keeping the holes perpendicular and not oval them out with a hand drill. I set up the housing the Bridgeport and indicated the pads. Drilled the holes out with the tap size drill and tapped them all in one place.
Ok, now the cap should be fit over the new race and the gap under the pads should be set to .001". Here is where the fun started. I put the cap on and like the last 3, the pads had way too much gap to start with. The only thing to do is work on the ID of the radius. In the past I polished the ID little by little to drop the cap down on the race to set the .001 gap. This one I just couldn't get the gap set. Finally it occured to me:lookinup: to check the pad gap without the race in place. It should be flat- metalon metal.The pad gap was .002 to .000" it was not flat and I wasted time trying to fit the cap. I had enough of that cap and put it aside and got another new one out. This time I checked the pads and again the was a gap? So I had to get the pads flat first. I set them up in a vise, indicated them as flat as I could get them and ground them until they were flat across. The cap fit nice on the pads now, .001 feeler couldn't fit in between them. Then I checked the fit with the new race- Ha, the SOB had .020" gap now- No Good. I set up the cap in the mill, swept the ID to center it, then setup a boring bar to sweep the ID. With it centered I moved it up .020", bored the ID to fit and then had to go back and final fit the pads in the grinder again. Don't ask how long this all took:thud:
Here are the pictures as I went along. I have the cap fit now. With it on the race there is a .001 gap under each cap leg and this will allow to crush the race just enought to pinch it from spinning under load. The steel cap is much heavier then the cast cap and I like them but I can see where this would be a real problem in your garage if faced with what I was.
With the first one I decided to toss it out rather then use it in a job. What I did was to set it up and polish it like you might had home. I just wrecked it more but it did prove my point.
I then set it up in the mill and tried to dress the ID back to size by moving it up in the cap. I had to go .120" to get a nearly full radius that would work but then I would have had to set it up and machine the pads down to set the gap. I didn't bother I'll use it for a demo at Carlisle instead.
Here is another job with a fit cap that didn't take me as long to fit.:smack
The same goes for fitting a steel solid sleeve in place of the crush sleeve. The shims in the kit are worthless, the shim is not parallel ground and needs to be fit to be correct. Just something to think about if you are planning this for a garage job. It can be done just be sure to plan it out first.
:thumbsup:
Gary
First this is the cap compared to a stock one. I've posted this before but in case someone new doesn't know about this, here it is.

First the holes for the LH cap in the housing need to be tapped for 1/2-13 bolts- up from the stock 7/16-14's. Now you can step drill like the paperwork says but I was concerned about keeping the holes perpendicular and not oval them out with a hand drill. I set up the housing the Bridgeport and indicated the pads. Drilled the holes out with the tap size drill and tapped them all in one place.


Ok, now the cap should be fit over the new race and the gap under the pads should be set to .001". Here is where the fun started. I put the cap on and like the last 3, the pads had way too much gap to start with. The only thing to do is work on the ID of the radius. In the past I polished the ID little by little to drop the cap down on the race to set the .001 gap. This one I just couldn't get the gap set. Finally it occured to me:lookinup: to check the pad gap without the race in place. It should be flat- metalon metal.The pad gap was .002 to .000" it was not flat and I wasted time trying to fit the cap. I had enough of that cap and put it aside and got another new one out. This time I checked the pads and again the was a gap? So I had to get the pads flat first. I set them up in a vise, indicated them as flat as I could get them and ground them until they were flat across. The cap fit nice on the pads now, .001 feeler couldn't fit in between them. Then I checked the fit with the new race- Ha, the SOB had .020" gap now- No Good. I set up the cap in the mill, swept the ID to center it, then setup a boring bar to sweep the ID. With it centered I moved it up .020", bored the ID to fit and then had to go back and final fit the pads in the grinder again. Don't ask how long this all took:thud:
Here are the pictures as I went along. I have the cap fit now. With it on the race there is a .001 gap under each cap leg and this will allow to crush the race just enought to pinch it from spinning under load. The steel cap is much heavier then the cast cap and I like them but I can see where this would be a real problem in your garage if faced with what I was.






With the first one I decided to toss it out rather then use it in a job. What I did was to set it up and polish it like you might had home. I just wrecked it more but it did prove my point.

I then set it up in the mill and tried to dress the ID back to size by moving it up in the cap. I had to go .120" to get a nearly full radius that would work but then I would have had to set it up and machine the pads down to set the gap. I didn't bother I'll use it for a demo at Carlisle instead.
Here is another job with a fit cap that didn't take me as long to fit.:smack

The same goes for fitting a steel solid sleeve in place of the crush sleeve. The shims in the kit are worthless, the shim is not parallel ground and needs to be fit to be correct. Just something to think about if you are planning this for a garage job. It can be done just be sure to plan it out first.
:thumbsup:
Gary