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.

[GTSBoy]

Following from this in a related by not closely-related sense...

Because I was buying a bunch of other GKTech stuff, I got some rear subframe collars. The history that leads up to this is:

• 25+ years ago the car arrived into the country with stock subframe bushes.
• At some point shortly thereafter I added Whiteline pineapple rings, set up neutral, and it improved the rear end behaviour. Well, it is my vague memory that I was happier with it with them in. Less axle tramp on launches, generally better, etc etc.
• ~2012 it got a new non-HICAS subframe with new stock bushes. No pineapple rings. I reckon that ever since then I've been dissatisfied with the axle tramp.
• Recently I've been f**king around a lot with all aspects of the suspension. One contemplation has been to relocate the rear lower control arm front mount points (and do the other things needed to make that work) to improve longitudinal rear grip by getting rid of some of the stupid anti-squat that Nissan ladled into the R32.
• But.... before doing that I thought I'd put some collars in.

And.... The collars are good. The rear sounds a little bit different, but there has been no significant increase in NVH coming up into the body. In terms of rear behaviour - expansion joints on long sweeping elevated freeway ramps that would sometimes cause the rear to jiggle around a bit, no longer seem to do so. It appears that jamming chunks of metal into the gaps in the rubber so they can't move much is a really good thing. And the launch behaviour and general forward traction situation seems to be greatly improved too. It's impossible to be really sure, because the tyres are completely shagged - they are freakishly willing to let go right now. But as an A-B test with the same tyres it certainly seems to grip up a lot better.

Highly recommended to anyone who still has stock bushes.

[Kinkstaah]

As someone who has pineapples, and horrible axle tramp... should I change these to collars? Is that what you're saying here?

Why did you choose these instead of getting pineapples where you said you had good experiences of?

I'd love to even attempt to get rid of axle tramp, I either get complete bogginess or absolute insane wheelspin, anything even remotely in between results in filling-removal axle tramp, to the point where launching the car is just not something I do.

[GTSBoy]

44 minutes ago, Kinkstaah said:

As someone who has pineapples, and horrible axle tramp... should I change these to collars? Is that what you're saying here?

Why did you choose these instead of getting pineapples where you said you had good experiences of?

I'd suggest the answer to the first question is at least a qualified "yes". I'll come back to that.

Pineapples just don't do a lot to solidify the mounting of the subframe. They do a little bit, and that little bit was clearly helpful to me in the past, but the main thing they are intended to be used for is to tip the orientation of the subframe to try to either dial in more or less anti-squat. You can install them one way to try to increase launch traction, or the other way to try to increase lateral grip (at the notional expense of longitudinal traction). Or, as I did, you install them neutral, which only really offers a little bit of "snugging" up of the subframe.

When I did pineapples, that was the only option. No-one had a machined alloy collar like the GKTech ones. There were some other options, but nothing like the slip in collars. And it is clear from looking at them that they occupy almost all the free space inside the rubber bush, so they will do a lot to stop them moving internally. So I thought, "that's the game for me!".

Obviously the next/adjacent step is poly bushes, but what's the point in doing that with all the work and hassle required to change them over, when jamming (and I mean literally jamming) some alloy into the rubber bushes probably gives an equivalent, or possibly even superior result?

So, to go back to your 1st question, I would suggest, for the investment of <<$100 and a morning spent lying under the car swearing and getting some sore fingers, it is certainly something you should try. Who knows? Maybe your situation is so severe that it doesn't solve it. But it might help a lot.

If your problem is as severe as you say it is, the next thing to look at is what the rest of the bushes in the rear end are made from. Things like the Hardrace arms with hardened rubber bushes might be a good thing (for the purposes of having adjustability AND stiffer bushes). Otherwise, just poly bushes throughout could be a help. Or following in my fever dream footsteps and putting a lot of sphericals into the rear? Eliminate undersired movement to avoid the build up of resonances that cause the tramp.

Also, if you have adjustable uppers in the rear, and you haven't put effort into adjusting the traction arms to minimise bump steer, there might be some advantage in that. If you don't want to go to the effort of doing it yourself (like I am pretty much forced to in Adelaide, owing to a lack of race alignment specialists) then surely there's a place in Melbs that is able to do it. It will cost $$, But that's life.

[The Bogan]

12 minutes ago, Kinkstaah said:

As someone who has pineapples, and horrible axle tramp... should I change these to collars? Is that what you're saying here?

Why did you choose these instead of getting pineapples where you said you had good experiences of?

I'd love to even attempt to get rid of axle tramp, I either get complete bogginess or absolute insane wheelspin, anything even remotely in between results in filling-removal axle tramp, to the point where launching the car is just not something I do.

I put Whiteline pineapples in my old 33, they came in a 6 pack of them, got rid of the axle tramp altogether, cheap, quick and easy install,  they were pretty solid units though...???high durometer???? and NVH was increased a fair bit

How hard are the ones you installed?

[Kinkstaah]

I'm not sure they came in different hardnesses?

Going from memory only - I had set them up in the balanced setup. I also have poly bushes, so I have both poly bushes and pineapples.

This is what my memory tells me at least.

I'll have to take a look under there to be sure. The tramp was so bad that I managed to eject/kill a diff bushing, so those I know are stock.

The tramp is bad enough that you are 200% sure you are doing severe damage to the car. It's not just chirping or vibration, it feels like you're hitting a speed hump/kerb 10 times a second. The issue has persisted between subframes! (I went from Hicas to non hicas subframe and replaced every bush a few years ago now) so I'm entirely lost. Every arm is factory.

[GTSBoy]

1 hour ago, Kinkstaah said:

I'm not sure they came in different hardnesses?

They do. The pale yellow translucent ones from Japan were .... I dunno. Useless? Whiteline and SuperPro are probably fairly similar. There's bound to be a range of different hardnesses amongst the dozens of options on the market.

The simple fact is that the pineapples don't get up inside the bush at all. They just sort of exist in the space between the washer/bracket and the subframe's bush outer tube, and...exert a bit of force between them? Or something like that. I'm sure that with enough provocation, they will simply allow one to move wrt the other.

[silviaz]

On 11/15/2024 at 8:05 PM, niZmO_Man said:

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

I'm keen for this content to 😂