I've broken another front anti roll bar mounting. Any idea why?

[GrahamFountain]

The question, if I go back to rubber, would be do I do that and nothing else, or do I do that and try to reduce the bending forces on the bend in the bracket as well?

Graham

[xvivalve]

...and they aren't aware of an issue

Are they ever?

The damage doesn't occur to the back plate or the tag at the bottom of the ? as that can act as a sliding joint. The force applied by the bar, particularly upwards, is transmitted by a denser or less elastic material causing the ? to shear at its weakest point, or at the point just before movement is resisted by the bolt.

Only ever change one variable at a time, else the consequences of the change cannot be attributed to a single action.

Of course, aftermarket rubber bushes aren't the same as OE either...

[GrahamFountain]

...and they aren't aware of an issue

Only ever change one variable at a time, else the consequences of the change cannot be attributed to a single action.

I know this so well. But it's knowledge that evaporates in almost any heat of the moment.

Graham

[sprint95m]

The front ARB is designed to have some flex at the mounting points to the subframe, else there'd be a much simpler rigid fixing rather than the somewhat contrived bush carrier we have. If that ability to flex is restrained, the forces have to go somewhere...

Many years ago,
for the Triumph 2500S, Chris Witor developed front ARB solid aluminium alloy clamps.
However these were expensive and were rendered too difficult to sell by Superflex bushes
becoming available for a fraction of the cost.


Ian.

[Carledo]

Like I said, i've never broken a Fitchetts one yet! So I imagine few people have!

Nearly every car made has a similar sort of fitting for the body end of the A R bar, though there are wide ranging differences at the wheel end.

The mods i've done to my subframes to fit the Vauxhall engines preclude fitting the antiroll bar in the conventional place, I've relocated to below the tie bar and the middle brackets now bolt up horizontally underneath the subframe front extension. But it still works in the same fashion and broke a few old used mount brackets before I got the repro ones. I don't think my adaptation has significantly altered the stresses on the bar or it's brackets, if anything, mine is stronger.






But as you can see, I opted for new rubber rather than poly! The pictured car is the Dolomega but the installation on the Carledo is exactly the same, The bar has been fitted to the Carledo since 2011 but the Fitchetts brackets only made it on around 2015/16 along with new rubber bushes.

I share a little of Alun's suspicion of Poly and as I said, use it sparingly, I might go further on a dedicated track only car, but that's a lot different to my road (Dolomega) and road/track (Carledo) Except for the front and rear tie bars (rear, rear end only) and the column bush, the Dolomega is ALL rubber for a quieter and more compliant ride on long journeys.

Steve

[tony g]

Graham , are you using the same washer size as std on the clamps? Just a random thought if a larger washer was being used it may put load further towards the bend (where yours broke) as it tries to flatten the bracket?

Tony

[Carledo]

In my opinion, the bolt hole is just too close to the bend, too much stress is concentrated in too small an area. But there's not much to be done about that, a redesign isn't really practical unless you want to do something as radical as I have (which, I suspect, won't appeal to many, I wouldn't have even thought of it until faced with the need.)

But there is a secondary load nobody seems to have considered. Most of the load on the front mounts is concentrated upwards which is not too bad if the outer mounts on the tie bars allow the bar to move though them that little bit to take up the plunge. If (as they USUALLY are) the outer mounts are effectively fixed in position on the bar, the plunge effect will try and move the front mount fore and aft, introducing a bending moment right where they break.

On my cars I have been careful to clean the bar and lightly grease the bush at the outer ends to maintain that small shift in position. Taken with the horizontal mount position I was forced into with the inners, with the upward (main) load carried by the subframe extension, I'm hopeful I've changed my last clamp brackets! Time will tell!

Steve

[SprintV8]

Is it possible to gusset the sides of the bracket to improve the strength.

[GrahamFountain]

Graham , are you using the same washer size as std on the clamps? Just a random thought if a larger washer was being used it may put load further towards the bend (where yours broke) as it tries to flatten the bracket?

Tony

There're just spring washers under the nuts, nothing under the bolt heads. That's as I found them. I tighten the nuts with a spanner from the back, as I can only get a 1/4" drive on the bolt heads.

Graham

[GrahamFountain]

Is it possible to gusset the sides of the bracket to improve the strength.

That was one of the initial questions. But if it's failing due to fatigue cracking from where the hole comes close to the sharp bend, outwards, then solving it from the sides may not be as simple as it might seem.

Also, that the bit that stayed was bowed across the width of the channel and right along its length suggests to me that increasing the raised edges strengths might not improve the problem. Given that bowing, I'm thinking that a rectangular fillet under both bolts the width of the channel, or even a thick D shaped washer under the head of the lower one, to carry the load from the raised edges to the bolt heads, may be a better solution.

I have been back and had another look though. I have to apologise that I said the bushes were blue and they're actually orange - I got confused remembering the ones I'd seen in adds not the ones under the car I think; the wife says I have a rotten colour memory. She also says I'm going a bit deaf - at least I think that's what she said.

Also, while I can't see any sideways displacement, the scrub mark in the underseal on the bend in the roll bar, where the tire has caught it in full lock, is about twice the size on the left side, which broke, than the right. The left is about 3" and the right less than 2". I'm running 175 60 13s on the front. That's what the car came with, and I've never done a full set replacement, so stayed with that size till now - have 70s on the back now, and will replace the fronts with them when they wear out.

Graham

[GrahamFountain]

This shows the bow across the channel. It's taken from the unbroken end, which would be looking straight down if it were on the car.

Graham

[Carledo]

This shows the bow across the channel. It's taken from the unbroken end, which would be looking straight down if it were on the car.

Graham

Youd get this effect if the wheel end links are stuck on the bars. Under load when cornering the bar will try to move forward against the bolts instead of sliding back through the link as it's meant to.

Steve

[GrahamFountain]

Youd get this effect if the wheel end links are stuck on the bars. Under load when cornering the bar will try to move forward against the bolts instead of sliding back through the link as it's meant to.

Steve

Not sure how I check for that.

Also, are the scrub marks on the bar normal?

Graham

[Carledo]

Youd get this effect if the wheel end links are stuck on the bars. Under load when cornering the bar will try to move forward against the bolts instead of sliding back through the link as it's meant to.

Steve

Not sure how I check for that.

Also, are the scrub marks on the bar normal?

Graham

Look at the bar where it passes through the bush in the drop link, if there ISN'T a wear mark from the bush moving on the bar, (won't be huge maybe 1/4" or so) chances are, the bush has welded itself to the bar! Can't really tell from the pic.

The rub mark on the bar from tyre or wheel contact, I normally associate with an uncentred rack, which will allow more lock on one side than the other (assuming the rub is only on one side) There's very little margin of error built into Dolomites in this respect, a 1/2" can be critical as there are no built in lock stops. If the rub is on both sides it points to a geometry error or possibly bad bushes. Or non standard wheels and tyres with incorrect offset, but I assume you are using original Sprint alloys so that's not a factor. Your use of 60 rather than the stock 70 profle tyres won't make it happen.

Steve

[GrahamFountain]

Look at the bar where it passes through the bush in the drop link, if there ISN'T a wear mark from the bush moving on the bar, (won't be huge maybe 1/4" or so) chances are, the bush has welded itself to the bar! Can't really tell from the pic.

Steve

You mean where the end of the anti roll bar goes through this rubber bush?
I can't see any wear mark, but it don't look like it's supposed to slide, just move on the compliance of the rubber in the eye bolt.
Not sure why this isn't poly like all the rest. Presumably, it's not in the kit of bushes.

Graham