Hi Philippe,
I agree with Simon, you need to be very careful realigning everything in this area. Just a little off will transfer to the wheel and tire as significant error, effecting suspension and steering geometry whcih can give the car strange handling and steering characteristics and wear out tires rapidly.
The overall construction of the TR4 in this front area is strong, much better than the TR4A was originally. Without actually looking at the area closely, it's a little hard to give good advice. There are various areas that can be strengthened. Bends or flared openings such as were originally in the motor mounting brackets add a lot of rigidity and strength.
Weld quality must be very good and care must be taken not to overheat the frame and cause warping.
Check carefully the steering rack mount welds.
There are a number of places you can strengthen, if you wish.
One is the steering rack mounts (add welded plates to reinforce the existing welds).
Before doing too much more on the frame, be sure to bolt the upper cross brace tube back in place, between the spring towers. This is important to help keep things aligned.
If at all possible, the rest of the frame should be held in a jig to keep it aligned.
Another area of concern is the angular brace behind the spring tower. First check it very carefully near the bottom where it's welded to the main frame rail. This is a common rust area. Water gets trapped inside. It rusts from the inside out. Drill a 1/4" hole on the inside face (toward the engine), as close to the bottom as possible. This will help it drain in the future. Triangular reinforcement gussets can be put in the corners, if you wish. After the welding and painting are done, plan to inject some Waxoyl or similar into this brace.
When you go to reinstall the pieces shown missing in your picture, you might want to use heavier sheet steel as a base, or double up the original 16 gauge, along the top of the main frame rail. If you do, you'll need to allow for the change in dimensions.
While the frame is stripped, there are a number of other areas that can be improved.
I like to weld 3/8" NF nuts inside the upper fulcrum inner mounting holes. It just makes removal and installation much easier.
The four frame rails that angle to the central box, forming a big X, are C-shaped. You can add a lot of rigidity adn strength to the frame by boxing these in completely. Triangular gussets in the corners of the diamond shaped areas can help too.
The most rigid method here is to add a large skid plate nearly completely enclosing the diamond shapes on either side of the central box. You have to work around the parking brake mechanism on the one side. And, it will be more difficult to route brake pipes and fuel lines on their respective sides. Plus significant weight is added and the plate will trap dirt and water. But, it does make for the most rigidity in the frame.
It's possible to add some reinforcement at the rear engine mounting brackets (actually the rear gearbox mount).
The body support outriggers can easily be reinforced by driving a close-fitting pipe inside, then welding it in place. Use some plug welds along the lengths and weld the ends.
Do the same thing to the rear spring shackle tube cross-member. Some like to add triangular gussets here, for even more support.
Optionally the rear-most tube cross-member can have a pipe driven in and welded, as added reinforcement.
Reinforce the rear shock mounting plates attachment to the frame, as needed. There isn't room here to add triangular gussets, but some heavier strips on the inside, that extend down onto the inner face of the frame as far as possible, can help. Some of the vendors sell kits for reinforce these brackets, might make it easier.
The front mounting point of the leaf spring puts a lot of stress on the frame. Flitch plates, which double up the thickness there, can be added as extra reinforcement.
Some years ago there were some articles in Grass Roots Motorsports with a lot of ideas for strengthening TR4 frames. Probably some I've forgotten here. Also, Roger William's "Restoring TR4" book gives a lot of good suggestions and is pretty well illustrated.
Best of luck with your project!
Alan Myers
San Jose, Calif.
'62 TR4 CT17602L
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