The Triumph Dolomite Club - Discussion Forum

What's the best method for reinforcing the rear trailing arms on a Dolomite?

Some folk have plated across the open top, but it doesn’t add anything to the strength as the folds there are inherently stronger already. Also, those cars with lots of power have shown if they do fail it’s the side walls that fold just in front of the axle mounts, so if you do anything, I’d suggest plating the side walls and bottom…but you’ll likely just move the stress points forwards…

Also, don’t go mad with poly bushes; only do one end if you must. There’s a reason why OE bushes were voided!

Thanks Alun.

I might do some plates there then. I am fitting poly bushes but they are the Superflex ones from Chris Witor, which have different shore ratings according to the location.

Just polybushed a whole car yesterday and the black Superflex are as hard as the originals.

Jeroen

soe8m wrote: ↑Sun Aug 21, 2022 8:11 pm Just polybushed a whole car yesterday and the black Superflex are as hard as the originals.

Jeroen

But will last a lot longer, I guess?

soe8m wrote: ↑Sun Aug 21, 2022 8:11 pm Just polybushed a whole car yesterday and the black Superflex are as hard as the originals.

Jeroen

Even if they ARE exactly as hard (or soft) as the factory rubber bushes, i'd STILL be reluctant to put poly on both ends of the trailing arm, a) because of the increased noise transmission this will generate (shore has no relationship to noise transfer resistance) and b) my 10 years experience of single poly'd arms under extreme stress (you can't make them work much harder than when doing a line locked burnout on a dragstrip) leads me to believe it just plain isn't necessary!

10 years of systemic abuse on road, track and dragstrip and the trailing arms on the Carledo are still the 1973 Toledo originals!

My 2 pennorth,

Steve

Using the normal superflex polybushes will not have you anything cracked etc. My former daily that did 50.000km a year for about 6 years was fit and forget.

When deciding to use original find NOS ones. The current originals aren't original, unknown hardness and doubtfull quality as these wear out very quickly.

Keep using the original ones isn't most of the time an option..

Jeroen

Ive had polybushes in both ends of the trailing arms for over ten years now. No problems, and the ride is as comfortable as ever...
My arms are also powdercoated - so any excessive twisting or stress and the coat would flake off - it has not....
I'm with Jeroen on this. Polybushes are fine.

Running standard shore polybushes in a standard or near standard car probably doesn't incur much more risk than using OE rubber. I reserve judgement on the noise levels, double Poly on my upper arms with red rear bushes (the hardest sort) made necessary by the implications of the line lock, certainly made MY diff a lot louder!

HOWEVER, knowing Glen (the OP) is adding quite a lot of extra horses to his power output (like another 100+ maybe) takes the car into realms it was never designed for, hence his question was posed about stiffening the arms, not so much about the poly itself. My answer was also tailored to these requirements. It's my considered opinion based on my experience and that of other trusted tuners/modders that you CAN over stiffen the trailing arms and their bushing and that this can and should be avoided.

I have seen and experienced trailing arm failures on high performance modified cars and it's a real thing, when you start USING a couple of hundred horsepower, weaknesses will appear! I've also seen one crack on a bog standard 1500 auto, possibly the least stressed of any model, go figure! In that particular case, however, corrosion was probably a bigger factor than stress!

Steve

GlenM wrote: ↑Sun Aug 21, 2022 1:08 pm Thanks Alun.

I might do some plates there then. I am fitting poly bushes but they are the Superflex ones from Chris Witor, which have different shore ratings according to the location.

Maybe so, but they still fill both mounting points whereas the originals at one end (from memory to the front) were deliberately voided to allow a certain amount of movement. If you deny that movement you transfer the loads to the next weakest point...or points. I've seen pictures of trailing arms which have folded up at the back and I've seen cars where the front mounting plates (which actually are a separate panel) have started to tear away from the floor pan.

Thanks for the replies chaps. I didn't mean to start any disagreements here but I guess we'll call it lively debate instead!

Steve is quite right, I should have about 100 BHP more than a standard Sprint. More power would be quite possible but I think that will be enough for the Dolomite chassis.

I will be careful with the bushings then, perhaps try original bushes in the front of the trailing arms first and keep the poly ones in reserve for now. When I had Dolomites 30 odd years ago, I do remember the front bushes being voided but I also remember that a bit of wear in them caused chronic rear end steering. A combination of this and slightly over enthusiastic driving, caused to me to spin my fully loaded 1300 Dolomite 180 degrees on an A road when I was 18. At that time a friend had a Sprint which rear end steered one way when accelerating and the other way when coming off the power. He had rebuilt the car himself and fitted an 1850 radiator (despite me telling him it wasn't up to the job), which eventually cooked the engine. I broke the car for spares and discovered he had fitted void bushes in one trailing arm and solid ones in the other. Back then I remember that you could get harder rubber ST bushes for the trailing arms but I can't recall whether these were supposed to be fitted at both ends of the arms, or just one.

I suppose the other important thing is to get the trailing arms blasted to make absolutely sure that they are not corroded. I have two sets, so hopefully I can get one decent pair out of the four.

Another posibility is that you fabricate your own. It's not that a difficult part to make in the shed. The GP2 Dolomites had tr7 shaped arms. Similar as Dolomite but without the angle at the rear so impossible to fold up.

Jeroen

I don't think I have ever come across voided suspension bushes (i.e. suspension bushes with air-holes). Why would one use such things; possibly to increase the effective softness or compliance!?!

I managed to find some NOS TR7 voided bushes a few years ago, not stupidly priced. I have used them in the front of my training arms, seemed a good idea.
And yes, allows some lateral movement