Rear Trailing Arm Reinforcements

[iPee]

I'm refreshing the rear end. This is what I've done so far

80A subframe bushings
80A RTAB bushings
80A Diff bushing
eccentric tabs
differential reinforcement tabs
differential stud conversion

Originally I was going to reinforce the rear trailing arms as well with the kit from, however they said if welded improperly the rear trailing arm may bend.

https://store.garagistic.com/e30-performance-parts/e30-rear-trailing-arm-reinforcement-kit

Searching a little more I found this kit from SRS Concept, which seems a lot simpler to weld and lower probability to mess up. Anyone have experience with the kit below.

http://srs-concept.com/product/e30-trailing-arm-reinforcement-kit-weld-on/

Welding will be done by my friend who is experienced but I don't want to put him in a position where he could be at fault. Also the car will be tracked 2-3 times a year, I don't have any plans for power upgrades. Is it necessary to reinforce the rear trailing arms? My arms are in good condition as far as I can tell.



Thanks
Ivan

[gotaloveRWD]

from what I've read under 450whp you dont need to worry about bending the trailing arms

but i look at it like if you're in there for the cheap money why not?

[iPee]

Appreciate the advice, that though has definitely crossed my mind since everything is out already.

Any comments on either of the 2 kits?

[e30davie]

The most concerning part of those kits is welding to cast items. Can be done successfully, but need special rods and some pre heating (i think, im not a welder).

I wouldn't be in a hurry to install any of those kits. I also don't have any suggestion on where to weld, if i was to reinforce i would do some research on how they have failed previously.

Also remember that you don't want to make them too strong. if you have a crash incident you are better off bending a trailing arm then bending a subframe or your chassis cause the trailing arm is too strong...

[badwella]

If you want to be even cheaper, you could do it yourself with metal you can get at any hardware store. Before Garagistic and SRS concepts were around this is how you did it.

I used C channel that cost me something like $15 cut it and welded it on. Absolutely no problem with it pinching the fuel filler hose either (which is why Garagistic designed their kit the way they did).







I welded all sides of this where they meet the trailing arm. Also, the leftover c channel is perfect for reinforcing the sway bar tabs too (I bought the AKG kit and realized that I could have used this as it's exactly the same).

If I recall correctly, I placed the nearest edge to the bushing end right about 7 1/4". This was far enough back that I didn't hit the fuel filler hose even when compressed past where the spring would stop movement.

As for the reinforcement to the cast portion by the bearing, yes, preheating cast iron to above 500 degF is recommended. You can weld without preheat, but the likelihood of cracks forming is much higher. Also, you need to peen the welds after (hit it with a chipping hammer to pre-stress the weld).

I opted not to add the reinforcement to the cast part at that time since all I had was a crappy mig welder. I have a nice TIG machine now so I'll do that later.

[Northern]

The most concerning part of those kits is welding to cast items. Can be done successfully, but need special rods and some pre heating (i think, im not a welder).

They're cast sure, but are they cast iron or steel? Usually people automatically think of cast iron, but steel is much more forgiving.

Also, the rest of the arm is welded to the cast piece, so it's not that much of a faux pas.