NA Coil-over damper unit lower bush replacement

[Mokesta]

Guys,

I am after information about replacing the lower bush on the NA shocks (coil over damper assemblies)

In the NA the bush is rubber with a steel pin. It looks just like any other bush but I am told it is bonded in place.

The NA ones sag so that the pin is off centre. This lowers the car by more than the sag amount due to the motion ratio of the suspension. I would like to replace the bushes in mine because the shocks are fine and not ready to be replaced.

NBs have a different arrangement with a vulcanised assembly type bush with its own outer ring which is pressed into the shock eye. These don't seem to suffer the sag problem. So, one solution is to replace NA for NB parts.

I have spoken to:
Supplier - What they said (what they meant)
Fulcrum - Nothing on the shelf but the R&D guys may be interested but you'd have to leave the shock with them (don't hold your breath cheap arse, just buy Tiens)
Pedders - Nothing on the shelf, could turn up a urethane bush but can't do it without the shock. Will probably end up with a different diameter pin through it. (I am an arrogant twat and think that all customers are mindless gimps.)
Super Cheap & Repco - Nothing in any catalogue, (what's a bush again? what's a car look like? duh, scratch)
Mazda - We don't sell parts for those but let me look up the price of whole new assemblies. (my screen isn't wide enough to see all the zeros in the price.)
Heasmans - No stock parts, the bush is bonded because it is load bearing. Why can't Fulcrum mould up the right bit? How about machined urethane? Come in and I'd love to help. Oh, you're in Brisbane, bummer, leave bush where it is and machine new spring seat circlip groves at right ride height. (Meant what he said)
Ex racer at work - Mate... Machine in some circlip grooves and put in some spherical bearings. (Harden up hairdresser boy)

Has anyone gone through this and achieved a satisfactory result? Anyone know of a supplier of parts that don't need to be custom made??

M

[Boags]

No idea how to help, but I had a good chuckle at the post.

[grump]

you get 10/10 for sense of humour, you could drillout the old bushes and turn up some new ones out of urathene with a steel , or stainless steel sleeve. Iv'e got an engineering lathe and access to a larger one if needed, have the contacts and expertise to reccomend the urathane, .
Graeme, 39010518. or 0402 075 176 . only too happy to help if i can

[fastfreddygassit]

Hey Mokesta
shoot me an email with a pic of the bush if possible.
My brother has been making his own custom engine mounts for his turbo swift and has been stuffing around with different durometer levels.
Just don't ask me what ASTM D2240 type he uses as I have nfi.
From what I have seen of what he does it seems that the process is the same for you to possible use and it seems fairly straightforward to dyi.
fastfreddygassitAThotmail with pix and I'll pass it on.

[bigdog]

Urethane bushes can be turned up on a lathe - I did all the bushes for my clubman (Lotus 7 not MX5)when I restored (well dad did the machining - its his lathe). We bought a cylindrical block of urethane from Nolathane for the purpose. Its a bugger to turn as it distorts under the pressure of the cutting tool, and if you turn it too fast it will melt, but a little experimenting soon had us sorted. I think the whole cost around $50 (Late 1980s). The steel inserts should be readily available from people like fulcrum or heasmans. That said I would be surprised if the bush size is not common to many other shocks. You can remove the bonded bush with a gas torch, and depending on the original shape and size you may need a lipped split bush to replace the original. So long as the fit is tight the bush is retained by the bolt and housing, so you should have no problems.

[PUR157]

I'll be following this thread closely...

The screen door from hell sounds even worse now...

[Mokesta]

Progress update:

Richard from MX5Plus was kind enough to let me borrow a crash damaged NA Bilstein. I have pressed our the centre (Thanks ORX626) and have the following to report.

The bush eye in the shock body is not a plain cylinder. it is a smaller diameter in the middle;



The bush eye is not bonded to the rubber at all

The central tube that the bolt goes through is bonded to the rubber and the rubber is a waisted shape. Here is it's good side:


Here is where I disected it a bit so confirm it is bonded.


I have measured it all up but haven't done a drawing yet. One thing I can confirm is that if the centre pin is 3.5 mm off centre, then it is metal on metal.

So, I am thinking that a urethane bush may just split in the middle and extrude out each side. It would need to have some large diameter washers either side of the shock eye to keep the urethane in.

[Mokesta]

Oh, and I've been sick all weekend so I just gave up and left the old bushes in. Got the rear kings and whiteline in place but havn't started the front.

M

[bigdog]

3.5mm off centre should not be an issue - the rubber will give that much anyway, so a centred bush should work fine (worst case you would loose 3.5mm of droop or compression). There is no reason to bond the inner tube to the new bush - bonding would serve no useful purpose IMO, and was probably done for manufacturing convenience. The shock eye looks standard to me - pop down to a suspension place and ask them for new bushes - I'm sure you'll find an off-the-shelf item that will fit the bill nicely.

[Mokesta]

3.5 mm gives metal on metal so it is likely to squeak and wear rapidly. 3.5 mm at the shock is probably a drop of 5 mm ride height due to the motion ratio of the suspension.
These bushes take the whole load of the car, unlike a standard shock bush which is basically under no load if the car is not moving over bumps.

A standard bush, under constant load will split in teh middle and extrude out the sides. Bonding the rubber to the pin stops (not enough in this case) the rubber extruding out the side by adding some shear strength.

So, I don't really agree with the above but am happy to be proven wrong. I still can't find anyone who has replaced these bushes.

I will take the assembly to a few suspension places and see what they think.

M

[bigdog]

I'm only going off my experience here - my race car shock bushes are not bonded and support the weight of the car with no issues. They are machined urethane with steel inserts (I don't think you can buy a bonded urethane/steel bush??). Weight is less than your car but I think the principle still applies... nevertheless I am still sure you'll find a replacement bush off the shelf that will solve the problem.

[Mokesta]

Thanks Big Dog, Actual experience like yours is always better than theory.

However, because I've been sick and crazy busy at work I haven't managed to get the bilsteins to a suspension place.

Instead, knowing the outer part of the rubber isn't bonded but the inner is, I decided to just rotate the bushes 180 degrees in the shocks.

To do this I pryed back the rubber around the edge of the outer ring and sprayed INOX in the gap. Then I put a bolt and nut through the hole in the through-tube. With a breaker bar I could turn the whole bush until it was in the right position.

I believe that the through tube is clamped and prevented from turning when installed in the car, so they shouldn't just spin back to their old position.

Just a few more jobs to do while the car is on stands and then we'll find out if my plan was cunning or stoopid.

M

[tbro]

Mark
try this

Bush, poly, MX-5 Bilstein shock absorber mount


At last, we now have in stock replacement poly bushes for the lower mount of Bilstein shocks as fitted to S-Special Eunos Roadsters.

Are you getting annoying squeaks from the front suspension of your S-Special, S-Limited, R-Limited or RS-Limited Roadster? Chances are the rubber bushes have failed in the lower shock mount (see the pictures). Instead of spending hundreds on new shocks you can just replace the old bushes with these quality polyurethane bushings.

Sold individually.

NM00617.



Our Price: £10.46
Price Excludes VAT

boundville.co.uk

[PUR157]

AHAH
Clubman owners rejoice... Thanks for that Terry!

Here's a link for the interested - seems like they cost 17GBP posted
Autolink Online Store - Boundville UK

Looks like these guys wreck all sorts of weird and wonderful japanese oddities...

[tbro]

PUR157
If you do decide or anyone else wants to buy these contact Andrew and mention mx5cartalk.com.

When I did the GB he was willing to give a special code price to forum members.

It all counts $$$$$

Terry.