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Triumph TR6 - Trailing arm studs

I know that the trailing arm studs are a weak spot, and with this in mind, a few years ago, when it was first sold, I bought the Patton jig for drilling and tapping the holes for keen-serts. This was after I had already put the rear of the TR6 together, and figured it was good to have just in case I ever had a problem. I am actually working on my Stag at the moment, but the trailing arms are basically the same. The car has been off the road for 35 years, and as far as I can tell, nothing at the rear has been taken apart since it left the factory. As a result, the threads in the trailing arms are in good condition. I have the parts sitting on my workbench, and I am ready to drill, but I just hate to drill out the perfectly good threads. I have googled and seen a few people show their results, and everyone seems happy. I just wonder if anyone has had any problems with the process, or if you would just do it while the arms are sitting on the bench?

Thanks for any thoughts
Alistair
A Hewitt

The first couple of times I did trailing arm stud holes, I did them with the arm in a vise and used a drill bushing and no jig. That made it relatively easy since I was at a better angle to perform the task, I don't think it would have been nearly as easy to do it on the car with a drill bushing without a jig. Using a jig on the bench would have made the task easier still.

The big advantage of the Patton drill jig is that it would make it much easier to do on the car if that was the only issue and the arm wasn't coming off for some other reason.
SteveP1

Don't know anyone who performed it is unhappy.
The question of doing good studs is a crap shoot and up to you Alistair.

Though, I think he has changed his jig.
You might want to contact him
DNK

Thanks guys

After I typed the above post I wandered to the garage and looked at everything sitting there, and decided to stop messing around and just get to it. With the jig it was easy enough and I got one arm done before turning in for the night. The hardest part was getting the right depth - the drill bit kept getting stuck in the metal and spinning the drill in my wrist. I did notice that there are a couple of small holes between the drilled holes and the inside of the TA (the part where the axle passes through). I don't know if this is down to the Stag having different thickness or if it happens a lot. I went ahead and tapped the holes and inserted the keen-serts, and this seems to have sealed up those holes, but I am wondering about putting a blob of JB Weld or similar on the outside of the hole to keep water out. The area of the threaded insert is so much larger than the original that I suspect it is still stronger, but not really ideal.

Anyway, thanks again for the thoughts.
Cheers
Alistair
A Hewitt

Alistair, do a hole depth check measure on the original hole along with the jig and drill bushing. Check it against the required depth for the threaded insert as well. When you go to drill the hole, use a drill stop set at the depth you determined previously. If you don't have a drill stop, you can use a few winds of heavy strong tape.

A couple of other considerations would be for the drill itself. For aluminum, I like a split point design with a 135° point. I'm not really hard over on finish, I've heard all manner of arguments on bright finish vs black oxide vs TiAlN finishes when drilling aluminum and found coating to be a minor factor. Since you drilling in a blind hole and using a drill bushing with the Patton jig, you should consider a more tightly spiraled drill to aid in chip clearing. Drill material should be either HSS or HSS-Cobalt.

Carbide tipped or carbide drills are rather brittle and I don't like to use them for hand drilling operations in aluminum or your more typical steels. You get into some of the stainless and high strength steels before those are needed.
SteveP1

Hopefully that info will stick in my walnut size brain
DNK

Hi:I have installed Keen-Serts on both trailing arms of my '72 TR6 successfully while the arms are in place,its not that hard.If you modify the Patton jig a bit the PCD will turn out perfect. I used 5/8" steel plate drilled in 3 places to just fit the existing studs. Drill & tap 3 X 1" NC female threads at the correct spacing in the 5/8 plate. Machine 2 threaded steel inserts,1 drilled for the tap size drill for the keen-sert and one drilled & tapped for the tap of the keen-sert. Because the the tap is already engaged, it will start in the trailing arm square. Make sure that you use drilling and tapping fluid specifically made for aluminum. Apply a small amount of 262 Loctite to the OD thread of the keen-sert & buy the drive down tool from the manufacturer. A fine smear of aluminum based anti-sieze in the cleaned locating bore of the arm on installation of the axle and tighten nyloc nuts.

T.Stock
T.S. Stock

Alistair:
Did mine 3 years ago on the car with the Patton jig using Heli-coils. No problems - glad I did it. Well, one problem I may have mentioned here before. One stud had been stripped for so long that by the time I pulled the hub, the hole had been enlarged by the stud rattling around - no threads left whatsoever. So when I tried to drill using the jig and the specified bit (22/64" I think; can't remember now) the hole was already too big for the 5/16 Heli-coil so I finished the other 11 holes and bought a 3/8" coarse TA stud from Richard Good, drilled & tapped the appropriate-size hole and inserted the stud without Heli-coil but with Loctite. I've not had a problem with any of them. I did have to slightly enlarge the holes in the hub and the brake plate to accommodate the larger stud.
Cheers,
Bob
Bob Evans

Bob, I had a similar thing happen. The difference in the technique I used was that I drilled and tapped for a much larger course thread bolt, which I then cut off flush and drilled and tapped the original stud into the new metal of the cut off bolt. This process has all the ease and convenience of using a heli-coil, only without the ease and convenience.

Tony
A. J. Koschinsky

Just to update this in case someone one day searches to find out if the Patton jig can be used with the Stag trailing arms (I know I often search for things and find a similar question with no resolution). I did use the Patton jig on the Stag T/A, and I now have twelve studs installed in the Keen-serts. It looks stronger, and hopefully is stronger - I will have less concerns about the risk of stripping the threads on assembly, and also the possibility of a wheel coming off mid-corner.

The only problem I had was the depth of the hole I drilled. I figured that the depth had to match the existing hole, so I very carefully measured and marked the drill bit accordingly. Even with that depth, and a bottoming tap, the inserts were getting quite tight by the last turn or two - I put this down to the less well defined threads on the tap close to the end, but could be wrong. With the hole drilled to this depth (using the X size drill bit recommended for the inserts) I managed to create holes on the inner part of the arm - the thinner part of the casting behind the flange with the studs, if that makes sense. Once the studs were in place, I cleaned up the area around these holes and filled with JB Weld (which just happens to be the same colour as the TA casting, by the way). If I were doing it again, I would be tempted to drill a shallower hole in the hope of avoiding this. Whether this would allow enough thread to be cut for the insert is not clear - I didn't try the shallower hole.

Anyway, I hope this is of some use to future Stag owners. Thanks to everyone for the help. With this job off the to-do list, I reckon I may only be a decade or so away from driving the car!
Alistair
A Hewitt

This thread was discussed between 21/01/2014 and 27/01/2014

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