A little PU bush story

[GTSBoy]

I recently discovered that I could not remove the outer bolt on one of my rear UCAs. Looked like it was seized to the crush tube. It wasn't all that long since I had last had that arm out (I dunno exactly, but certainly <2 yrs), so I was a bit surprised.

I thought I had stock bushes in the rear knuckles, so I ordered some new PU bushes and resigned myself to having to do some dismantlery....and some butchery. It was clear that the seized bush was going to need to have the bolt cut out of it and then possibly some more brutality after that.

Upon getting the 3x arms on each side disconnected from the knuckles (with the exception of the seized one, of course), I discovered that I had in fact put PU bushes into the knuckles when I did the subframe conversion about 12-13 years ago. So, I say "Oh, good, I might not have to swap any of these others out".

We set to work butchering the bolt out of the seized arm. Stainless blade in a big-arse Milwaukee recipro made short work of it, and also damaged the arm, which added a welding and grinding and painting step to the whole exercise. During the butchery it became clear that the bolt was not just seized but bent. Head scratching ensued, as it is hard to understand how that bolt could get bent. I did suffer a broken (stock) toe control arm on that side a few months ago, and drove some miles with some significant rear wheel self steer and lack of control, which probably was the cause. But it's still hard to understand how it would bend that bolt, rather than just bend the arm.

But here's the start of the real discoveries. The crush tube was rusty as all shit. I mean seriously rusty. A little on the inside, contributing to the tube seizing to the bolt (along with the bend). But the outside had at least 2-3mm of compressed flaky iron oxide jammed in between the parent metal and the PU bush. This one was brutalised and still took some effort to get the PU off the crush tube.

So I thought I'd inspect the others more closely. The one on the tension rod adjacent the bent one was first. I had to use a 2-jaw puller to get the crush tube out, and it took some effort. It came out looking like the first one. All 6 of them were the same, except for one that looked not too bad. Had some corrosion on it, but was mostly OK.

There was also a significant amount of corrosion on the inner surfaces of the knuckles. They took some convincing with pointy tools to let go their grip on the inside of the holes they were in. There was no sign of the original (SuperPro) lube anywhere.

I and my bro-in-law have never seen any crush tube end up looking like this. It was seriously like the car has spent time putting boats into the water at the boat ramp.

So, it seems like the PU might have been bonded to the steel on both sides, which would have to make them work more like stock rubber bushes (where arm deflection results in twist inside the rubber). Despite this, I have never had cause to believe that they were so tightly bound up. The suspension moved up and down much as you'd expect. The car never made any noises in those bushes that would have led me to believe there was a problem. Maybe the rusty interfaces actually were "sliding".

Anyway, lesson learnt. Even quiet, non-troublesome PU bushes should be inspected every now and then!

[Duncan]

We need pics of grumpy GTSBoy butchering things

Do you remember what the plating on the crush tube and bolt was? I feel like the old killer cadmium ones work better than the current silver (zinc?) ones

[GTSBoy]

I was only moderately grumpy. I was in fact quiet happy that there weren't still stock bushes in there, because that requires more effort to get them out.

They were SuperPro, so definitely zincish. It is very much like the coating wasn't done properly.

They were almost certainly of the vintage where the supplied lube with such things was that black messy crap. Some lithium based horror. They have since moved onto the silicone&PTFE greases which are much more sticky and water resistant. I shall have to mark my calendar to have a look at these in 5 years' time.

[GTSBoy]

Oh, and only having done this task yesterday, I've now driven the car ~60km since, and while it is hard to avoid placebo effect and confirmation bias, I reckon that some annoyances I had with the way the car has been behaving have improved. Which....kinda makes sense, I guess.

If the bushes were really stiff and resisting rotation, they would have been contributing to the effective wheel rate. And if it was more so on one side (which it was, because one side was worse than the other) then.... you might imagine that the additional rate would be asymmetric, and potentially even different between compression and rebound. And so...

the car has been twitchy at higher speeds - like freeway on ramps. It really shouldn't be. The wheel alignment is good and there are no (other) known problems elsewhere in the suspension. But at 90-100 on a long sweeping ramp, tiny steering wheel motions would make it feel like it wanted to rear steer. Quite nervous. At lower speeds it would heave about in a manner that it didn't use to. Didn't want to put power down, etc etc.

Now...seems to behave better. Am going to have to concentrate on the various corners where it has exhibited weirdness, on the rare occasions when I can get a decent run at them without Methanial getting in the way in his D-Max/Ranger/LDV Van/etc.

[niZmO_Man]

On 12/11/2024 at 1:06 PM, Duncan said:

We need pics of grumpy GTSBoy butchering things

 

I second this motion. GTSBoy you need to start posting vids man.