Lamont Welding & Fabrication in Antioch, CA (925) 754-7824 has a fixture to modify trailing arms. It holds the trailing arm in the correct stock alignment.

He mounts the trailing arm in the fixture, cuts it in half and welds in a 1/8" rectangular
plate. The 1/8" plate helps to reduce twisting deformation by breaking the twisting length
of the arm into two lengths instead of one long length. The charge is $80.00 per trailing arm.

I just had my trailing arms reinforced. This reinforcing method is better than plating the arms with heavy sheet metal.
Click to view attachment Click to view attachment

There is a much easier way to do that.

That is cheap for $80.

Welding a bulkhead inside the trailing arm box is the most effective stiffening method IMO. Lighter than boxed, and no warpage. Stiffer than drilling and welding tubes thru. An added advantage is the fixturing - assures proper orientation of the T/A.
I've been doing it this way for many years.

And when you get done installing Chris's reinforced trailing arms the car aligns correctly, unless of course you have a bent body.

I dunno........
I built my 914 AXer over a period of 15 years. I started off with a rust free 74 (or as close as it gets) stocker. It ended up with 10 inch slicks and having been gone through from end to end.

It got an alignment check every year as I jumped around for set ups but it was stable for the last few years as far as modifications went....it still got the alignment checked.
The car was light & worked out well.
Other than seam welding, needle bearings, some grinding for lightness & 275 lb rear springs, the trailing arms were untouched and never a problem.
I was never one to leave a real "problem" alone but a believer in "if it ain't broke...."

Seam welding is pretty smart and a great way to get a car stiff.

I never realized how important a stiff car was until after I had the complete cage built and quickly saw the performance difference at a subsequent event.

And of course the difficult part is figuring out, or finally discovering, that seam welding is good after you had the car built!

A cage/sub frame with the shock towers attached came to me later in the build...maybe 10 years into it. It's hard to explain to someone who's never done it, but it was the best move I ever made. The closest thing I could say was the car became a "piece".( which is meaningless to many)Click to view attachment

By the way Thanks! JP for showing us newbies the importance of a complete cage, tied in from front to back.

By the way Thanks! JP for showing us newbies the importance of a complete cage, tied in from front to back.

I haven't tested the tendency of 914 arms to bend - I've just relied on the advice of others, so take my comments (or not) accordingly.

I'd like to add the point that bending of trailing arms like the 914 uses may be hard to detect, especially if it's only flexing and not permanent deformation. Deformation can be detected with an alignment job. You may not know flexing is happening, and thus not know if's an issue that needs addressing.

I believe there is an older thread in which Chris gives some detail about the mod he does, and there was some actual testing of deflection before/after?

Scott

My recollection was that the trailing arm mounting ears were typically responsible for much of the flexing under load, and that reinforcing the arms themselves does not really stop that from happening... Reinforcing the mounting ears though...

-Josh

unfortunately not legal for 99 percent of vintage racing organizations

Everything flexes if you put enough load on it.
Stock arms definitely flex if you have wide sticky tires, as do the outer console brackets and even the inner and outer consoles on the longitudinals.
These cars were not originally engineered to cope with 1+ lateral G force.

I run 315 - 17 Hoosier slicks on my SCCA
track car. These hot sticky tires will torque
stress the trailing arms and cause them to
Flex. The thin walls of my trailing arms
have stressed to the point of
taking a perminent set. Tired of pulling out and putting in shims to correct geometry.

I have always believed it was better to reinforce the
chassis connetions than plate the trailing arms to the extent that if the trailing arm gets hit, it rips out the chassis connections. Used trailing arms are relatively cheap compared to chassis repair.

I found the most Gawd awful welding on the 914 Right at the mounting points area for the trailing arms. lit myself on fire while rewelding/grinding overhead....not my best position when welding, but after grinding most of that mess out of there , the reweld looked pretty good....... a separate issue from torque tube twist. I too would rather replace a torque tube IF something has to fail.

I have no doubts the tubes twist under load. . Mine never twisted enough to take a set, but since I couldn't feel it, it didn't happen. I'm a butt dyno kinda guy.

Pick your own poison.

Brant and Chris,
Since Vintage racing does not allow "cage to suspension pick-up points," what is your opinion on the inner ear reinforcement which goes forward to the lower firewall. Can be welded or bolt-in as small radius rod. I also think the inner ear problems are partially due to the outer ear becoming loose or ?? Please opine for us vintage cars and more vintage drivers!!

WOW!!
I just noticed that I am a "newbie"!! Only joined in 2004. As my memory fades, everything is new the next day...

I depends on the specific rules of each club
my club allows bolt in reinforcements, but not weld in reinforcements

I run bolt in console braces on both of the 914 race cars I've built

I ripped out 2 suspension consoles within about a year, before adding my first bolt in reinforcement

I consider it mandatory

prior to reinforcement the trailing arm shaft lock nuts would be loose each and every day the car was tracked. it was a daily ritual to re-torque these and would lead to a tear if not tightened.

since adding the reinforcements I haven't had a shaft nut come loose in 15 years.

I believe a cage to the suspension points would make the car handle better
but arm bolt in reinforcements make it not tear itself apart

brant

you need more posts to move out of the newbie status

A bit of drift on the trailing arm, but we are still in the area.

I march to the beat of my own drummer. Sure I listen (or read) what other folks are doing to their cars and take interest in how /what they are dealing with problems.
Some times I even say "hay, that is pretty slick"......some times NOT.

News Flash!!!

Failure of the trailing arm mount is a larger problem than the arm itself and effects all, not just racers.

Marching to my drummer....
Click to view attachment
Looks pretty simple, no?. It ain't. There is a 3/16 piece of plate replacing the inner half of the mount. The reinforcement tube goes to the frame and not the skimpy fwd bulkhead for a reason. No, not a perfect fix, but that ain't going anywhere. I think I have detailed pictures of the process if you want em'.....but it will cost you a PM.

I've noticed the same loosening on passenger side shaft at every autocross. Now tightening that is a ritual for me. That side has extensive long repairs so there's probably all kinds of flex going on. I really like JP's fix above That may be something I do this winter. That is... if I'm not too wrapped up in a 924S FP car build.

You will eventually rip the console out

My style is bolt in because my rules require no weld in braces.

Just read the rules for the class you want to run. Email the tech/eligibility person for any class you may go to in the future and print the response

My class ITE in SCCA requires the use of the tub. Everything else is open.

your good
my comment was directed at Han Solo
just that he double check his rules before he decides which style of brace to go with

p.s. I use bolt in styles on 2 different teeners
I especially appreciate the bolt in style on my -4cylinder car, as unbolting and removing the bar aids in engine drops for that car

Do these bolt in stiffeners require studs welded to the outer firewall and/or suspension ear? I can see just drilling holes through the ear and using nuts and bolts but I'm unclear how you would bolt through the firewall (outer only). Perhaps use long bolts and pass through both inner and outer? Any photos or links Brant?

Yes

Th attachment points are welded to the firewall and ear

The brace is an aluminum turnbuckle rod
I believe from hoerr racing
Or similar

There are pictures in my build thread of the 6cylnder version

I have a kit if you don't want to design your own.

I just looked on your website Chris and only saw the reinforcement plates for the suspension console and trailing arms. Do you offer stiffening bars from firewall to console?

Yes, the inner console braces are available separately from the larger kit.

Old thread bump....


So, looking at the mods for the trailing arm with the "bulkhead" plate, any reason one couldn't cut in half like in picture yet move bearing / wheel assembly inboard 19mm as long as trailing arm is reinforced on each side?

I have 15x7 23mm wheels for it and plan on running 205/55s and I'm trying to avoid messing up the rear fenders, not that my car is anything special.

I know the lower shock mount will need to be modified.

This seems easier and better than cutting and rewelding the round tube that the stub axle goes into.

*going to reach out to the weld shop mentioned in rhe 1st post to see if still in business, maybe they can rent me that fixture if available still.

I don't see why a 20mm offset would be a problem to do. I have the fixture here in Walnut Creek. Check with Joe Lamont Welding in Antioch (925) 754-7824.