303 Stainelss steel corrosion resistance for car suspension components

[tigdlo]

Does anyone have any experience of using 303 stainless for components like press in outer bush housings and crush tubes for polyurethane bushes, same design as the the ones pictured below. How does 303 last long term? Does it corrode like OEM stainless exhausts?

 

[premmington]

Stainless does not corrode..

But it "work hardens" - gets brittle and is not the perfect material for the job....

 

[BrokenBiker]

Stainless does not corrode..

providing it hasnt been overheated or contaminated...

But it "work hardens" - gets brittle and is not the perfect material for the job....

id agree with you there, depending on the application, stainless could turn into a nightmare pretty quickly...and sort of cyclic or repetetive stressing could cause issues

 

[BrokenBiker]

You also need to consider if these bushings are going to be fitted to an aluminium housing or in contact with aluminium in any way, the salty winter road grime will breed galvanic corrosion for fun...

 

[tigdlo]

The problem with polyurethane bushes is they aren't bonded so are a bit of a rust trap between the bush and housing/crush tube, then they wear rapidly. Stainless is used by superflex for the cortina bushes pictured above and sold by burton power so I'm sure even with limitations of some grades of stainless in some applications it must be suitable enough, grade depending. I have 0% interest in machining 304, 316 or a duplex grade of stainless for this job, just too much work on a knackered ML7.

I'll look at some other options as the outer bush tube will be pretty thin at about 1.5mm.

 

[hotponyshoes]

303 will be fine for corrosion resistance on a car. The 303 exhausts rot from the inside out due to the chemicals and the heat.

As said above, its the contact with other metals that will be the issue rather than the material itself.
It also picks up external corrosion easily enough so passivate it after you have finished it.

 

[hotponyshoes]

Would it not be easier to cut them from a length of stainless tube?
Or are the an odd size?

 

[tigdlo]

Would it not be easier to cut them from a length of stainless tube?
Or are the an odd size?

The wishbone bore is 29.5mm and the flange of the bush is 39mm. A 1.5" x 1/4" wall tube would be close enough, that is readily available in mild steel.

I think stainless is overcomplicating the job, extra work and potential for other issues. If I do fit polybushes I think I will be better off loctiting in a mild steel top hat and painting it, I could probably do the job twice that way for the same effort.

Scope creep killed the job 15 years ago so have decided to build the car back up as close to standard as I can but the standard bushes I bought years ago are 0.4mm undersize. I don't think a 0.2mm wall sleeve would survive being pressed in with the bush so making something to fit polybushes appears to be the better option than buying more bushes to potentially be in the same position I am in now.

Thanks for the replies.

 

[tom2207]

if they are not big bucks ,,, give them a go , whats to loose ,, they dont look lie work hardening would be an issue

 

[Agroshield]

Why have you gone for 303 over 304? Is it purely the ease of machining?

 

[Morrisman]

The problem with polyurethane bushes is they aren't bonded so are a bit of a rust trap between the bush and housing/crush tube, then they wear rapidly. Stainless is used by superflex for the cortina bushes pictured above and sold by burton power so I'm sure even with limitations of some grades of stainless in some applications it must be suitable enough, grade depending. I have 0% interest in machining 304, 316 or a duplex grade of stainless for this job, just too much work on a knackered ML7.

I'll look at some other options as the outer bush tube will be pretty thin at about 1.5mm.

I’ve always given poly bushes a good smear of silicon grease before assembling them. Helps lube, helps keep water at bay.

 

[indykid]

Stainless does not corrode..

But it "work hardens" - gets brittle and is not the perfect material for the job....

Stainless absolutely corrodes. Not all stainless steel is the same.

Given the environment, austenitic stainless is an ideal material for a polybush crush tube.

The outer housings look like they'd be quite expensive to make as you'll need a fairly hefty bit of bar and there'd be a lot of boring on a Myford, even in 303. Fabricating from 304L tube with a welded flange sounds like a better deal, but again, passivate the weld to retain corrosion resistance.

Coming at the problem from the other end, if a standard bonded rubber bush is available, I'd use that over polybushes. Polybushes are a pain in the **** to live with.

 

[droopsnoot]

The problem with polyurethane bushes is they aren't bonded so are a bit of a rust trap between the bush and housing/crush tube, then they wear rapidly.

And I believe the suspension works differently, too. With a metalastik bush, the movement of the suspension arm is limited by how much "give" is in the rubber, whereas a poly bush will allow it to pivot much more easily. I don't know enough about suspension and handling to know how much difference this makes, but in my head it seems as if it would be significant.

I have Superflex bushes in the rear trailing arms on the Firenza, I believe they have stainless crush tubes in them. I had them out recently to check whether they'd worn down (it's very crash-bang on poor road surfaces, of which there are many locally) but it all seemed fine.

 

[ian f]

look similar to cortina top arm bushes, i changed to these about 20 years ago and checked them during the restoration, they were still good so went back on and are still good seven years later(and having checked the price i hope they last a long time yet) think i paid £40 for the set back then! how much!!

 

[tom2207]

look similar to cortina top arm bushes, i changed to these about 20 years ago and checked them during the restoration, they were still good so went back on and are still good seven years later(and having checked the price i hope they last a long time yet) think i paid £40 for the set back then! how much!!

you could nearly buy a lathe for that price ,,,,

 

[BrokenBiker]

you could nearly buy a lathe for that price ,,,,

i only paid 300 for my model A...and ive already sold 600 quids worth of the tooling i got with it that wasnt actually for the lathe...might start making and selling bushes and give the cranes up, only need to sell a set a day

 

[dave h 2]

And I believe the suspension works differently, too. With a metalastik bush, the movement of the suspension arm is limited by how much "give" is in the rubber, whereas a poly bush will allow it to pivot much more easily. I don't know enough about suspension and handling to know how much difference this makes, but in my head it seems as if it would be significant.

I have Superflex bushes in the rear trailing arms on the Firenza, I believe they have stainless crush tubes in them. I had them out recently to check whether they'd worn down (it's very crash-bang on poor road surfaces, of which there are many locally) but it all seemed fine.

Poly is much less compliant hence the crash and bang. Like rubber band tyres best for track, show and bragging to those who don't know.

 

[droopsnoot]

Poly is much less compliant hence the crash and bang. Like rubber band tyres best for track, show and bragging to those who don't know.

It's interesting, because when I put them on the car in the first place, it didn't seem to make very much difference. One of the winter jobs is to swap them back to rubber and see if it helps.

 

[tigdlo]

Is 303 stainless passivated in the same way as 304 and 316? Is citric acid passivation suitable? After some internet searching this is the only way I can see I could do it at home but can't find a definite answer.

Poly is much less compliant hence the crash and bang. Like rubber band tyres best for track, show and bragging to those who don't know.

Shore 60A Polyurethane is every bit as compliant as shore 60A rubber. Of course most replace rubber with harder poly to get the performance benefit along with increased NVH, noise vibration and harshness. Harshness is increased most from harder bushes that prevent the longitudinal movement of the wheel when it hits a bump, i.e. the wheel moving rearward in the arch. This is because less of the shock is taken up in the bushes and more is transfered up through the shock/spring instead. A RWD car with the spring/shock attached to the lower wishbones could probably have the front upper wishbone bushes replaced with the hardest polyurethane without any noticeable increase in NVH.

Why have you gone for 303 over 304? Is it purely the ease of machining?

Yes, ease of machining makes it a possible material choice, I don't304/316 wouldn't be worth the extra effort over mild steel.

The outer housings look like they'd be quite expensive to make as you'll need a fairly hefty bit of bar and there'd be a lot of boring on a Myford, even in 303. Fabricating from 304L tube with a welded flange sounds like a better deal, but again, passivate the weld to retain corrosion resistance.

Coming at the problem from the other end, if a standard bonded rubber bush is available, I'd use that over polybushes. Polybushes are a pain in the **** to live with.

The outer tubes are only 25mm long so not a massive amount of work, welding is an option but I have no filler wire and would probably have to machine up an aluminium backer to get anything like the finish of a machined part, probably a better option for a more skilled and experienced welder, also I like machining more than welding and this is a hobby.

I find the quality of aftermarket rubber bushes and all car parts in general are very dissapointing, I have no interest in rewarding these companies with my business if there is an alternative. I would prefer to spend a couple of days doing something I enjoy at twice the cost of materials. The issues with polybushes are the implementation and expectations, I'm confident they won't ruin the car, I certainly won't be fitting stiff poly engine mounts and expecting it to go faster.....

look similar to cortina top arm bushes, i changed to these about 20 years ago and checked them during the restoration, they were still good so went back on and are still good seven years later(and having checked the price i hope they last a long time yet) think i paid £40 for the set back then! how much!!

Did you fit the stainless outer tubes same as the ones in the link?

 

[ian f]

Did you fit the stainless outer tubes same as the ones in the link?

yes, if i remember correctly the bushes don't come out of the outer tubes