Cracked Tub (pic)

[daltvater]

Anyone ever see this before?

Car is a 1979, 3.6 with coilovers/935 setup. Trying to give the shop some direction.

[1QuickS]

Well, not my area but... the production car shock upper mount was not designed to take weight of car (spring loadings) plus shock loadings. I suspect fatigue due to stress levels too high. Recommend repair welding & then adding reinforcing sheet metal to distribute the load into the chassis.

I suspect race application RSRs have reinforcement here. When coil-overs are used in the rear there are reinforcing brackets welded to the top of the shock mount that tie into the rear cross member.

[juanbenae]

that's a mess. you may want to consider a set of camber boxes. some are big enough that you can weld them up to fresh areas on the tub and by pass that distress strut tower (ST) completely. ive never had camber boxes but have seen a number of them that have large gussets for supports that travel a ways down the ST. in fact some may even require cutting away portions of the top of the ST which could favor your situation.

[tdw28210]

Might try posting this here: 911 / 930 Turbo & Super Charging Forum - Pelican Parts Forums

[Flojo]

Originally Posted by 1QuickS

... the production car shock upper mount was not designed to take weight of car (spring loadings) plus shock loadings. I suspect fatigue due to stress levels too high. Recommend repair welding & then adding reinforcing sheet metal to distribute the load into the chassis.

+100%

Here's the setup of a ST reinforcement.
the shock mount insert is just to center out the bore properly

[pmax]

That looks like rust on the lower right corner.

[Steve@Rennsport]

Does this car have a complete roll cage that connects & triangulates all of the suspension pickup points?

[175K911]

/\ /\ /\ What Steve said.

When I converted my '86 to coilovers, I had the front shock towers reinforced, the rear shock towers and the crossmember all reinforced, then tied the towers to the cage to triangulate and reinforce everything. So while you're fixing both front towers, best to take a look at the rears and reinforce them too.

[daltvater]

Originally Posted by Steve@Rennsport

Does this car have a complete roll cage that connects & triangulates all of the suspension pickup points?

Thank you all for the help with this. I'll give you a bit more information to see what you suggest going forward.

This car ran successfully in a NZ Porsche Racing Series for years with this homemade 935 suspension setup.

I have gotten the suspension and car past New Zealand's insane certification laws so the car is now street legal. To do it we had to use stock unmodified spindles!

The car will be used for 5-10 track days a year.

The front of the cage was cut out but never connected to the suspension pickup points.

The rear shock towers have some reinforcement.

After the cracked chassis was welded last week the shop is having a hell of time getting the alignment back.

The doors are hard to open so I'm guessing the chassis is twisted. I'm almost out of funds so I'm looking for a lowest cost solution to fix it.

What would you all do?

[daltvater]

A few more pics of the old girl.

[175K911]

Welding broken chassis pieces should probably be done on a chassis jig to ensure everything is to spec. And any cage welding should be done with the car’s tires on the ground at correct ride height, not up on jackstands. I had a previous 911 that the supposed cage builder welded in the cage with the car on jackstands. Couldn’t close either door until several of the cage tubes were cut to relieve the stress. Had to cut the entire cage out and give the car to another shop who did the cage perfectly.

[daltvater]

Originally Posted by 175K911

Welding broken chassis pieces should probably be done on a chassis jig to ensure everything is to spec. And any cage welding should be done with the car’s tires on the ground at correct ride height, not up on jackstands. I had a previous 911 that the supposed cage builder welded in the cage with the car on jackstands. Couldn’t close either door until several of the cage tubes were cut to relieve the stress. Had to cut the entire cage out and give the car to another shop who did the cage perfectly.

I had a feeling that welding that crack could have been the wrong move. I'll let the shop know that the car needs to be on the ground. Thanks!

[tperazzo]

Originally Posted by 175K911

Welding broken chassis pieces should probably be done on a chassis jig to ensure everything is to spec. And any cage welding should be done with the car’s tires on the ground at correct ride height, not up on jackstands. I had a previous 911 that the supposed cage builder welded in the cage with the car on jackstands. Couldn’t close either door until several of the cage tubes were cut to relieve the stress. Had to cut the entire cage out and give the car to another shop who did the cage perfectly.

I agree with the car needs to be flat and unstressed sentiment when doing structural/chassis repairs. These chassis do move and twist a fair amount. There are several tricks to establish a level floor and take measurements to determine what is out of spec.