Heavy bottoms and rear suspension question

[New Duke]

I'm out in the car at the moment measuring the rear arch gaps to order snow chains, and passenger/NS gap is visibly higher that the driver side. By about 10mm, maybe a smidge more.

I had a neighbour sit in the passenger seat and that side lowered to match the drivers side. So it's likely down to my drivers side rear just not springing back up fully when I get out of the car.

Given that I rarely have a passenger is that to be expected? Does suspension have that kind of 'memory'? I've had a passenger in it maybe twice since the last time it was up on jack stands. But the suspension is the PZ GB kit and was fitted new in June. I weigh 70kg so have some extra padding, but didn't expect to squish down the suspension permanently

I'm unsure whether this is a good thing (suspension doing it's job to balance the load), or a bad thing because despite being new it looks like it's settled or slumped without the other side matching.

Is that normal when you rarely have a passenger though? Any thoughts?

[Conan]

No it shouldn’t be like that.
When the car is on as level ground as possible measure accurately from center of hub nut to bottom of wheel arch vertically
On both sides and post up in mm please
Pete

[sKenDread]

I had the same thing happen to me. Turned out it was a broken rear spring. I couldn't see it until it was on a ramp and wheel removed. You might want to have a look see dude

[Phil Bate]

Assuming everything is in order, it only takes a slight undulation in the road surface across the diagonal to throw the height out between axle sides. Measure the difference at the front as well, you'll likely see it out too but the other way around. As Pete says you need to find a perfectly flat surface to verify a real difference.

When I adjust the alignment on mine in the garage I have to pad the front nearside wheel with half a magazine as the floor is out by a few mm left to right at the door end, it's that sensitive

[New Duke]

Thanks guys. Good to know it wasn't a silly question.

I measured the gaps on an even slope (if that contradiction makes sense) with the car pointing various directions to attempt to shift the weight of the car, and the slump on the rear OS has been consistent, even with that corner at the highest point of the slope (to put it under the least load). With the car in any orientation the rear was over a cm lower. With the front wheel gaps remaining even and pretty consistent.

I'll try to find a perfectly flat surface tomorrow to measure again. If it doesn't match then I'll pop the wheel off and see if there's anything amiss. Thanks for the advice.

I really hope the PZ kit hasn't broken already, it's only just done 5k miles and was a pricey faff to get the geometry set up just right. Gonna try to avoid getting ahead of myself though.

[Phil Bate]

Hmm, interesting If you don't find anything obvious perhaps it would worth loosening and re-tightening the inboard suspension arm bolts with the car settled, to reset the bushes

[qwakers]

it is in theory possible that one of the springs wasn't tempered properly and no longer has the correct spring rate. if thats so you are likely to have the unenviable privilege of being the first person to have to claim on the warranty.

but there are other options. loosening off all the bush pinch bolts (both sides) giving the car a good bounce and doing them back up when its settled is where id start...

[goodeggbob]

Wouldn't he have to do another alignment if he undid the bush bolts though?

[qwakers]

not as long as he only backs the nuts off and doesnt move the bolts. best to mark their position if you're worried...

[chriskirkham]

Had similar issue with my car, low on rear nearside.

It was the damper unit which had gone soft, and was sagging, no lose of damper fluid though - so rather unusual.

Not bad though for an original unit with 83,000 miles on the chassis.

I did have H&R sports springs fitted approx. 25,000 miles ago and all the damper units were fine then.

Hope you solve your mystery.

Sent from my SM-T550 using Tapatalk

[warpc0il]

I suspect that Phil might be on to something with the pivots bolts being nipped without the full weight of the car on the wheels.

This is easily done, if you just out-of-sequence doing the job and all it takes is to reconnect the anti-roll bar first, with the other side hanging and the forces will uneven.

[New Duke]

Looks like the bets are in! I'll be at it in the morning cold once the 'sun' is up.

The last person to touch the suspension was Fergus who set up the geometry with string after it was fitted by one of our traders. It's not been meddled with since then specifically so as to not ruin the set up. It's a long way to both places from my house so I'd rather not make the trip back so soon!

Given who did the work (ie not me), I'm going to place my bet on a hardware failure. But will investigate all the possibilities. Thanks for all the advice. Will report back.

It was the damper unit which had gone soft, and was sagging, no lose of damper fluid though - so rather unusual.

How did you assess it was the damper without there being a leak Chris? Was it just floppy and movable by hand?

[New Duke]

Been on this today. Have to preface that I haven't undone any bushes yet. Even with the car on my low profile ramps I can only reach the two lower adjustment bolts, for anything else the car sits too low (on my ramps) to reach. I'm hesitant to slacken those bolts myself in case I mess something up even more.

I took the wheels off and both rear dampers and springs look fine. No damage or cracks visible.

I spoke to bigpete and he confirmed my memory of the suspension having been tightened under load when the new PZ kit was fitted. He also thought as I did that anything way out like that would have been apparent when the geometry was done by FW Motorsport about 500 miles later. His suggestion was that something might have shifted the suspension after that.

He suggested looking at the top bolts up in the boot in case they have shifted. I have and they look fine as far as I can tell.

He also reminded me that (ironically), 5 days after having the geometry done last summer, on the way back from track my RX8 was rear ended on that side by a van. The repairers said it was only bodywork (rear bumper) damage but now I'm wondering if that was enough to throw one side out. Despite there not being much visible damage it was a fair old shunt and my car was pushed a couple of metres forward from stationary with the handbrake on.

Measurements of the hub nut to the top of the arch:

Rear drivers: 355mm
Rear passenger: 363mm
Front driver: 365mm
Front passenger: 365mm

I took measurements on a few different flat surfaces and there was a tiny bit of variation within margins of error (1-2mm) but all results remained relatively consistent with the rear driver side 6-9mm lower than the rest every time.

Would resetting the bushes as suggested release tension created from a rear end smack assuming it was all setup correctly beforehand?

If the cause is that the impact knocked out the geometry and I just need that redone then I'd take that over the other possible alternatives.

[ChrisHolmes]

Whoever repaired it should have checked the alignment as there are shock absorbing crumple zones at the rear.
Thus could well be the cause of your issue so you need the alignment checked again

[Conan]

Hi Hayden,
Thanks for the measurements
To shunt 1 1/2 tons of car metres with the brakes on is a reasonably heavy shunt and I would of insisted on the insurance paying for realignment at the previous place.
However can we get someone to measure their car with the new PZ suspension in the same way you have to see where we should be at before assuming anything
Pete

[Conan]

Another afterthought
Peel back the carpet in the boot and look carefully for any buckling of the boot floor etc.
This is a regular thing with rear ending.
Pete

[ChrisHolmes]

Slide both front seats as far back as they will go, then make both seatbacks upright.

The headrests should be perfectly aligned - if not then the floor is buckled.

[chriskirkham]

How did you assess it was the damper without there being a leak Chris? Was it just floppy and movable by hand?[/quote]



Once the damper was removed from car, it was VERY easy to fully compress it - the lack of fluid leakage remains a mystery.

Sounds like you are making progress with potential diagnosis of your sag issue.



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[New Duke]

Thank you gents. I did ask for the alignment to be redone at the time but was told it wasn't necessary by the repairer and given a flat no when I challenged that with my insurer. To take it further I'd have to show proof that the repairer hadn't done enough, which is a tall order since they and the insurer have closed ranks. Needless to say I'm changing insurers at my upcoming renewal. This was the accident where I ended up taking the other driver's insurer to court and won, so it's already been a miserable affair.

Having said that, since then I've had both bigpete and Robert at Krown (who worked in accident repair in a previous life) look over/under/inside the car for signs of crash damage post repair and they both thought it was fine. (To the point of me looking neurotic and having made a fuss of it all)

Thanks for the fun tip about the headrest alignment Dave. Did this yesterday and yep they're aligned.

I'll call FW Motorsport tomorrow and ask if he has any time soon to look at it. That'll be another long day off work.

Haven't decided yet whether to cancel my ski trip yet. The height difference on that wheel makes it more likely that the snow chains will rip the arch liner. I need every mm I can get back there.

[New Duke]

Thanks for the fun tip about the headrest alignment Dave. Did this yesterday and yep they're aligned.

It's so simple to do and reassuring to get the right result.

Spoiler:

A work colleague had his (then new) Sierra Cosworth RS500 rear-ended and it was over two months being repaired.
Had it been any other Sierra it would have been an automatic write-off, but the book value of the Cosworth was more than retail list.

He'd been driving it around for a couple of weeks, still complaining that it didn't feel right, when the insurance company sent their engineer to come and take a look, just as a random quality spot-check.

We all went out to the carpark and the engineer did the trick with the front seats, which showed a significant difference.
The car was collected on a low-loader and we never saw it again, though we heard that it was stripped for parts.

John got a brand new replacement, which his wife was chuffed about as the original car was black (which she hated) and the replacement was moonstone blue (which she loved).

According to a friend that worked closely with Tickford there were actually 504 real RS500s produced, plus many more replicas.

[New Duke]

I don't like unresolved threads so wanted to update this.

Took it to FW Motorsport and even though the ride height difference wasn't as much as I had measured, turns out the steering geometry was all over the place. Only 7 months after it was last done. So it was corrected and all is well now.

Although 'all over the place', it was of course still within Mazda's wiiiiide spec

The main culprit is most likely the rear impact, but could well be partly down to the enormous potholes littering our roads... and a couple of bridges I may have jumped (shhhhhhh).

Anyway seeing how much it can shift in such a short time and 5k miles I've decided to have it re-done properly annually.

It's fun just looking around the other cars in the workshop:

Geometry.jpg