TR4/4A Advice for grafting TR6 frame front to TR4A frame rear

[Chancybc]

Good day everyone. I am new to the forum and hoping for some advice. I have a solid axle TR4A frame that is in excellent condition for the rear 3/4, but the front 1/4 (starting in front of where the inner and outer rails meet) is a mess, and a 1974 TR6 frame that is in near perfect shape for the entire front 1/2; and I need to figure out how to put them together to go under my solid axle TR4A running gear and body. The front of the 4A is so far gone, in so many ways (towers and mounts were broke and welded in wrong and are broken again, and almost all rails and supports are bent or crimped) that trying to straighten it would leave me chasing one misalignment after another. Accordingly, my thought was to take the entire front and outer frame rails right up to the trailing arms from TR6, and graft them to where they meet the similar parts of the inner frame rails and trailing arms of the 4A frame. That way I get the upgraded front suspension and yet keep the proper transmission and differential mounts and other good frame parts from the 4A frame. I know that in 2011 EpicBryan posted about doing something similar on a thread, but he does not appear to be active on the site since 2013. If anyone has any advice it would be appreciated. For example: 1. has anyone tried it before? 2. Does anyone know a reason this is not going to work? 3. Should I just repair all significantly rusted parts of the TR6 frame? 4. Should I make the cuts/grafting at a different place? 5. Is there a particular jig you have used to keep the alignment while I make the cuts?
Thanks in advance.
Lorne.
p.s. A new frame is unfortunately not a financial option for me, but I have a couple of months of full-time, free labour to put into the frame/chassis repairs.

 

[malbaby]

Am I correct.....you currently have a TR4A [IRS type] chassis with a solid axle and leaf springs, damaged at the front. plus a TR6 IRS chassis that is damaged at the rear [which is unusual]. Or a complete undamaged TR6 chassis.

 

[malbaby]

"all significantly rusted parts of the TR6 frame"...presumably you meant TR4A.
I would use and modify the rear of the TR6 chassis to suit the solid axle by removing the front diff mount/ coil spring bridge.
That way the main chassis rails would remain intact.
I would also strengthen the rear chassis to reduce the inherent twist and flex. Plus modify the cross tube ends that the rear leaf spring hangers attach to.

 

[Chancybc]

Thanks for the recommendation. If I understand you correctly, you are suggesting that I just scrap the TR4A frame and repair the TR6 frame? That is possible, but the TR6 frame is very, very rotten from (and including) almost everywhere from the trailing arms and T-shirt back. However, I guess it is technically possible to repair all of that. Is there a reason not to graft the two frames together?

 

[malbaby]

No reason at all....Sorry, I was assuming you had a good TR6 chassis, and therefore made the comment.
I wonder why only the rear of the TR6 chassis is bad.
Unfortunately, your geographical position probably limits your access to a good secondhand chassis.

 

[Chancybc]

I guess the rest of the tr6 frame was always covered in engine oil. Lol.

 

[glemon]

Yes, the back is where they tend to rot for the reasons stated. I think the engine and radiator mounts are a little different, but you should be able to use the old frame as a reference. I will leave it to better welders/fabricators than me to propose the best way to join together and make it strong and straight.

 

[malbaby]

Also the steering rack location.
I can give you ideas on how I would do the graft and strengthen the chassis.
Need some pics of both chassis on where you are contemplating the joins...best parts of both chassis.
If you do not have access to a frame table, then I would obtain/borrow 2 long lengths of very heavy IRS.[eg. 10x4].
After setting them up perfectly level, you can use G clamps or similar to hold the chassis on whilst welding etc..

 

[Chancybc]

Attached are pics with descriptive titles. All but one are photos of the TR4A with green arrows showing the different bends/breaks. Notably, the photo from the top down shows the significant twist in the right shock tower, and others show visible cracks and old welds. The right side of the frame bends upwards about 1 inch from a few inches in front of the right front body mount plate to the shock tower. The final photo is of the front of the TR6 and shows two different types of tape to indicate where I was thinking of making the cuts. Option 1: narrow green tape, shows only cutting at the two factory welds on each rail. This seems to be the preferred option because it maintains the integrity of both inner and outer frames. Option 2: The wider, ivory tape shows the option of cutting both the inner and outer rails in front of (or possibly behind) the body mounting plates. A third option would be to cut right in front of the body mount plates, but since the bend on the right side of the TR4A frame starts just around there, I would be risking welding onto a bent part (so it safer to cut behind the body mount plate). I can foresee two reasons I might want/have to use Option 2. First, the TR6 outer frames have more rust than the 4A, but the only obvious weak area is where it attaches to the trailing arm (I could just patch that though). If when I cut into that part of the frame I find too much rust to form a proper weld, I will have to start cutting further up toward the front of the car to find good metal, which might take me to the Option 2 location as next reasonable option? One benefit of Option 2 is that the TR4A frame rails have no rust and are straight "up to" the front of the forward body mounts (as noted above), so I would be using the best metal. Any thoughts?

 

[Rut]

I wouldn’t put much faith in that TR6 frame and I think the inside of it is as bad as what we can see. The TR4a frame has some serious damage, but before I cut it up I would take it to a good frame shop for evaluation/repair if possible.
Rut

 

[Djoslyn]

I'd agree with Rut here. My replacement TR4a frame looked great from the outside but once I started cleaning the paint and what looked like lightly rusted exterior off. It revealed a bunch of pinholes that originated from the inside. These frames rust from the inside out. If that TR6 frame is that bad on the outside already, it will only get worse once you start digging into it.

Also, These frames are super thin to begin with. Welding on them must be done very carefully or else you will get quite a bit of warping.... Ask me how I know

 

[malbaby]

Hmmmm......a few options there.
Obviously you need to measure both chassis very carefully before any cutting. Also obtain the factory chassis dimension sheet. And have a frame table or 2 large "I" beams set up.
1... using the TR6 frame, I would initially cut it off just forward of the main front outer body mounts as per your taped line. [This is not the final joining cut].
Remove the inner diagonal rail which is only [very poorly] welded top and bottom from the outer rail.
Cut just the TR4 outer rail on the RHS just rear of the rail crease where the 2 rails meet. Preserve the existing inner diagonal rail [do not cut] for the time being. The extent of the rear of the crease will determine where to cut.
Rather than do the same on the LHS, you could join the rail further forward toward the LHS crease.
The RHS inner diagonal rail is now either fully or partially exposed.
Now accurately cut both TR4 and TR6 outer rails for the joins.
Cut 3mm plates about 150mm long to plug weld them inside the rail outer sections of the joins.
You may also choose to weld a length of 8-10mm plate 65mm wide to the inside "C" section of the inner aspect of the rails.
Now weld the original diagonal rails into the outers. I would also weld a gusset between the 2.
The front of the TR6 chassis has to be altered to TR4 specs.
2...To repair the TR4 frame. Cut the 2 main creases and join in a similar fashion. Either by using "oxy heat" to straighten the creases once cut, or weld in a small length of rail cut off a chassis remnant. But not finally welded until the RHS tower and chassis is straightened.
Remove and later replace with new, the braces for the towers and the lower plate of the main cross member.
Hard to tell from the pics as to other smaller creases and/or cracks.
Partially cut the tower where it is most obviously twisted, straighten it to the factory specs and weld.

There are measures that can be undertaken to strengthen other areas of the chassis.

 

[Chancybc]

Thanks guys. I will take your advice and get the 4A frame checked before I do any more work. Today I did quite a bit of grinding into the TR6 frame and it stood up pretty well, but I take your point about the inside out issue. If I find a better donor frame, which of the two cutting options would you recommend?

Hmmmm......a few options there.
Obviously you need to measure both chassis very carefully before any cutting. Also obtain the factory chassis dimension sheet. And have a frame table or 2 large "I" beams set up.
1... using the TR6 frame, I would initially cut it off just forward of the main front outer body mounts as per your taped line. [This is not the final joining cut].
Remove the inner diagonal rail which is only [very poorly] welded top and bottom from the outer rail.
Cut just the TR4 outer rail on the RHS just rear of the rail crease where the 2 rails meet. Preserve the existing inner diagonal rail [do not cut] for the time being. The extent of the rear of the crease will determine where to cut.
Rather than do the same on the LHS, you could join the rail further forward toward the LHS crease.
The RHS inner diagonal rail is now either fully or partially exposed.
Now accurately cut both TR4 and TR6 outer rails for the joins.
Cut 3mm plates about 150mm long to plug weld them inside the rail outer sections of the joins.
You may also choose to weld a length of 8-10mm plate 65mm wide to the inside "C" section of the inner aspect of the rails.
Now weld the original diagonal rails into the outers. I would also weld a gusset between the 2.
The front of the TR6 chassis has to be altered to TR4 specs.
2...To repair the TR4 frame. Cut the 2 main creases and join in a similar fashion. Either by using "oxy heat" to straighten the creases once cut, or weld in a small length of rail cut off a chassis remnant. But not finally welded until the RHS tower and chassis is straightened.
Remove and later replace with new, the braces for the towers and the lower plate of the main cross member.
Hard to tell from the pics as to other smaller creases and/or cracks.
Partially cut the tower where it is most obviously twisted, straighten it to the factory specs and weld.

There are measures that can be undertaken to strengthen other areas of the chassis.

thanks for the great tips. I am going to get the 4A frame checked first but if I have to cut, the tips will help. Do you agree that if the outer rails on the TR6 are solid then I should only cut at the trailing arms (and inner rail joint)?

 

[malbaby]

"Do you agree that if the outer rails on the TR6 are solid then I should only cut at the trailing arms (and inner rail joint)?"
Yes...although the RHS rail looks a bit rough.
I would remove the TR6 trailing arm rails and see how bad the outer rail ends are first before deciding on where to graft.
Let us know, with pics what you find.

 

[Chancybc]

hello everyone. Thanks for the many comments. Instead of attempting the "surgery", I was able to purchase a complete TR6 frame in excellent condition. I might try the grafting of the other two when I have some time, just to see if we can save one for somebody's future use. If I do, I will post the results in case anyone else decides to give it a try.

 

[erinspinner]

Working with the wonderful British steel in the TR 6's versus the steel in the TR 250 is day and night, With leyland taking over Triumph, all things had to be British including the steel, can you say British steel (think Titantic), very poor brittle steel. The steel in the earlier Triumph's were, as my sources tell me, from a small steel mill in northwest Indiana, on the shores of Lake Michigan, Inland Steel. My TR 250 frame is in good shape and I had to drive her trough 5 winters, tough car. My 76 TR 6 frame sucks, I had to do major repairs on the frame to even make the car road worthy. If I had not purchased the car, it was going to the scrap yard. Had the car for 20 years, currently working on the frame again.
To make my point I had to make entire new sections of frame to make this car work. I also wrapped the existing steel, reinforcing a weak frame into a frame that can handle some real torque. I have buddy's that build and race stock cars.
Why isn't there a weld shop or steel fab shop making frame stiffening kit.
I Love my Triumphs, but I'm going to keep upgrading them to meet my standards.