Weld-in rear strut brace and harness question

Couple of quick questions. Firstly, I want to weld a rear strut brace in the car, so was wondering, what diameter are roll cages normally, and should there be plates on the inner arches to spread the load or just weld the brace straight to the arch.

Also, how do you loop the harness over the strut brace?

 

I'm not sure I would do this without a full rear cage in the car. A lot of load will go through the bar in the event of a front end shunt and your pulling it in the wrong direction !
Regards "a concerned well wisher"

 

Really? Can anyone else confirm this?

 

I don't understand the logic either? The brace will not be pulling on the wheel arches, but bracing them and as for a shunt, front end of not, forces will be transmitted through the entire chassis and the stiffer the chassis the better.

I had a welded in rear strut brace, (I had to grind it out and bolt it in for the race series regs) and it does stiffen the rear significantly.

Rollcages are wall thickness of 3mm and the one that I have fitted has an OD of 40mm and I have used, and would recommend, spreader plates.

 

Excellent, thanks for that

Did you have your harnesses around the strut brace? Still don't know how to do this, I'm hoping I don't have to buy new harnesses.

 

Surely a rear strut-brace without a full cage is just asking for stress-cracks in the rear towers?
Or are the rear towers on Mk2s really really strong?

 

i've owned 2 mk2s with rear strut braces and no cage without any problems. all you are doing is bracing the rear towers in place so stress cracks shouldn't be an issue as i'm sure you know road cars have a fair bit of shell flex where they are only spot welded for the majority so i'm sure moving this relatively small area of flex shouldn't cause any issues.

go for it luke. i really can't see that it'd do any harm to your car.

 

I've been told that I should do this as it will reduce flex in the body and give me a safe mounting place for my harnesses.

Back to the harness question, I have these harnesses (but in black) with the same ends.



So how would I go about fixing them to the brace like this?

 

the above concerns are a pile of pish. id trust a weld in bar as opposed to cheap crap bolt in alu ones i've seen used before. id also trust a weld in bar at a decent angle. search the other seating/belt threads for pictures.

1" 3/4 cds tube 2mm-3mm should do the job. spreader plates of 2/3mm steel will be fine.

harnesses will need those ends removed and you'll need 2 turnbuckles per harness to be able to loop them and lock them. only concern is that they may be too short and not have enough material to reach and loop through.

other alternative is to get some threaded bosses made that can be welded into the bar to take some eyelets or bolts. search for user 'jamesa' post on the subject for an example of his method used in his mk1.

 

for the love of god please use speader plates and also inspect the towers well and seem wel them!!! the towers are not ment to take the laods in a frontal impact, the wose is it will peel like a tin opener or open another seam,

I have just used the stock mounts as this is with in the 45deg and also these are load tested.

if you are going full weld in multipoint cage fair enough, but just a rear bar is iffy, but not as bad as the ones ive seen at shows why have used bolt in strut braces!!!!!!!!!!!

 

Brace bar is welded to cage, cage is bolted to wheelarches using spreader plates (above and below), 3 M10 high tensile bolts c/w nylocs each side.

Has been passed for RACMSA hillclimbs / sprints, HOWEVER may not be race legal

 

Do you mean the ones for the rear seats?

 

yep, like my pic on the 4 point harness post above this.

 

I do plan to fit a full cage in the not so distant future, just thinking of improving my current set up of fixing them them to the original rear seat mounts, which I have been told isn't the best as in a crash it can crush the seat.

 

Had a quick look and it looks like there is enough adjustment to reach, but I'll measure it up properly.

So do I need to unstitch the end of the harness to remove the metal piece?

Could you recommend a place to get the bits I need like the bar and turnbuckles?

 

Its not 45 degrees mate.

The angle between the seat vertical and harness should be no more than 15 degrees ideally.

 

bar and plate just find your local metal supplier. metal supermarket or similar will do the job. your after steel cds tube, t45 will be a pricey.

yup just unstitch the webbing.
for turn buckles contact trs harnesses. they should be able to sort you out with one to match the width of your belt. you may want to have a look about for the correct diagrams for the wrapping of belts. there is only 1 right way to do it. anything else will kill you in a crash.

 

how to wrap!

 

Interesting post, me and my mate are in a similar position with our track car and intend to weld a strut brace into the rear and use that as a harness bar.

We also have harnesses that have metal loops stitched in to attach to standard seatbelt mounts which we'd like to use rather than replace them.

 

Thanks for the info

I'll get measuring this weekend and order the bits.