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Triumph TR6 - Trailing Arm Section

I find myself in the unenviable position of having to completely replace the left rear trailing arm section of the frame on my '71. I question whether this can be done effectively with the body on, since one clearly wants to be able to weld completely around both ends of a replacement section. Has anyone done this before or is it just wishful thinking on my part? I really don't have the time or the space to go through the process of removing the body, but if I must, it's basically the difference between a one year and two year restoration.

Thanks Guys,

Jim Vandenberg

Hi Jim

Doing it right requires frame off if its real bad? Describe it to me?

The main reason is the center section. Don't know the extent of rust but in most cases the center between cruciform plates is also a victim due to water. When you cut out the rot you have no place to weld to. Been there several times.

If your rot is fairly local on that part usualy starts at bottom back of trailing arm bolts because of the internal supports catching moisture from the stupid forward tilting opening at side. Let me know. I have done cut and replace work that is still very safe after 10 years. Only if its caught early. Do not cap!

If thats the case. The frame is 16 gauge mild steel. The top section will have the least damage and still be strong.

Now if you have a mig and a grinder. With a fair bit of experience measuring, getting real dirty and spatter burnt grinding and welding above your head you can probably save taking the body off. At least for quite a few years.

Let me know

Bill Brayford

Thanks for the quick response Bill. The center section is actually OK, so I'm not TOO bad off. Unfortunately, however, the trailing arm section is almost completely shot. Even the top surface, which is unusual. It was kinda weird actually; I knew there were several silver dollar sized holes here and there, but when I started probing and pounding to get to solid metal, things went south in a hurry. Next thing I knew I was buried in an avalanche of rust. You know the kind. By the time I was done there was virtually nothing left on any of the 4 sides of the section or of the internal supports. After looking at it again I think there is enough solid metal on the center and outside rails to weld to, but getting the right angles and proper access to make a good weld will be a challenge, at best. I think your final comment is accurate. With my trusty MIG and grinder, and full body armor, I should be able to make a go of it that will last for a little while. at least.

My next dilemna ia whether to completely cut out the old sction or replace all four surfaces individually with steel plate rather than a finished section. That way at least I will maintain the proper orientation and not create potential alignment problems for myself. I'm frustrated.

Jim Vandenberg

Jim ,
what is it worth to you? That is a big project.
The external steel box is not that hard to fabricate
but the internal supports of the trailing arm retainers
would give me pause. I supose all they really are is
a re-enforcement of the steel box frame to keep the
trailing arm from twisting off. If you start with three
sides of that box and weld in the internals , then weld on the forth wall with drilled holes to match
with the trailing arm holding bolts you might get away
with it.
Christopher Trace

Hi Jim

I can't see it from here? But if you have a few inches I think from description of both ends. You may be able to do it. Center section can be worked. Chewing it out and getting an edge weld to the top cruciform wedge is great

They sell the sections or you can have 16 gauge formed in 2 pieces and create the supports for the bolts yourself. Way cheaper. The repops 2 sections are already spot welded in your case that causes problems. Joining 2 pieces end to end should not throw out alignment unless you screw up on bolt holes :)

First measure your holes and create permanent marks with a scribe on old metal to measure back on your new material for your bolt center points.

The front piece is a box insert. Now if you think about it. Do you have enough space and good metal to cut the old out in a zig zag form at each end and then weld in the new U section or back. Its hard to explain but if you have the front box insert out you can weld all seams mostly inside. Most of the strength in this type of frame is in the bended corners. The new box should not have a continuous weld. You want to offset and interlock the metal retaining some of the old bend area. Make your replacement from measurement before cutting first and try fit.

Then create the front insert with pipe and supports to finish. Will go into more detail. But just remember and make a note the insert requires spot weld holes at top none on bottom. The main box on bottom edge.

Getting real late here.

So let me know what you find and think and we will go on. As I have mentioned before I am better at doing than writing about it.


Bill Brayford


Good suggestions. I like the idea of the zig-zag cuts. It makes great sense, although I imagine it will be easier to say than to do. I'll try to measure, cut, and fit the front insert, line up the bolt holes, drill, and set aside. Will then fit and weld the bottom, fit, drill and weld the back, and then the top. As you say, I should be able to do inside welds for all of these. Assuming that's successful, it should be easy to cut and fit internal support pieces. Hopefully my pre-fab front insert will still fit at that point.

Conceptually it all makes sense. But we all know the difference between concepts and realities. We'll see how it goes. Any other suggestions are welcome.

Jim Vandenberg

Hi Jim

Get 2 channels formed 16 gauge. One with a 1/2" to slip inside of main at whatever your measures are. Back holes are the important ones measure wise. Cut out the old and fit carefully the new.

If this is what your plan is e-mail me first. We can go on from there. I have been locked up twice after a fair amount of 3 finger typing trying to reply 2 nights in a row. Nope no viruses by 2 checkers.

Bill Brayford

I had a welder do the same job with the body on. He was a very good welder and had worked building stock car frames in the past so he really knew what he was doing. He still managed to accidently set my seats on fire though. The job he did is solid as can be. The alignment news a bit of tweaking but it can (and I think should) be done.

I believe there is, or used to be someone in RI that sells ready made trailing ar frame sections. I'll post the link if I can find them.

I had a minor (if frame rot can ever be "minor") case of rot in one of my TA sections, one blister on the bottom about 7/8 of the way inboard. The ends and walls of the section were intact so we doubled the bottom sections w/ galvanized steel and put a drain hole on the bottom...maybe something the factory should have considered. Got the idea from seeing drain holes in the sub-frame of a BMW.

Good luck!

This thread was discussed between 23/05/2003 and 01/06/2003

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