I had my Mk4 (2015) serviced at Coventry Mazda, as usual in November in order to maintain the dealership service history. I bought the car 2nd hand from the Green 4 Motor Group, Leamington in Nov 2018 with 17250 miles and linked to the Coventry franchise. It had previously passed its MOT at a local family-owned franchised dealer where I take my cars for their MOT only 3 days prior. However, Mazda, Coventry informed me that they would fail the MOT upon detecting slight wear/play in the rear suspension bushes/knuckles and quoted £2096.41 to replace with 2.4 hours labour!! The car has only done 22715 miles!! That can’t be right so will seek an independent assessment in the spring. I only do 1500 miles a year and it is never raced/track or rallied. Seems ridiculous and they are trying to find business in these difficult times as dealerships can’t sell cars due to the present financial situation. Comments/advice, are welcome.
There are some good treads on this. eg Rear bushes - Technical Area / Wheels, Tyres & Brakes - MX-5 Owners Club Forum (mx5oc.co.uk)
Do a search for more.
Welcome to the world ND1 ownership (a 2015 is an ND1, ND2 started 2018/19). It’s highly likely to be right, known failure point on the car is the rear hub carrier bushes and Mazda don’t sell them as a standalone part so you have to replace the entire hub carrier if you do it OEM which cost over £400 per side without labour.
None OEM route is the 27AL blue Polybush set MX5 MK4 (ND) Polyurethane Suspension Bushes & Components - Polybush
Hearing the knocking from the rear going over rutted surfaces like this is a typical symptom REC_5340_cut
Don’t or won’t?
Roddison near Sheffield (@rodders ) offer a polybush replacement service at a reasonable price, tbh I’d trust the service here rather than a dealer for this.
Yes I’ve seen he does this job at a good price, was about to mention also.
The 4 that fail are not bushes but spherical bearings, Andy Leslie is the only one that makes replacement bearings
Hi guys I had the same problem but thanks to Andy Leslie problem solved even got them fitted by someone near me that Andy put me in touch with
Thank you and interesting. Can you give me contact details if near to me in Northants and what was the cost.
I will follow up in the spring.
Hi John I contacted Andy Leslie through Facebook I think he may be on this forum too £475 for the new bearings and mechanic charged me £100 for fitting them much cheaper than the £1600 I was quoted hope this helps
Using the guide linked below then in the context of the ND suspension it would suggest either term could be used.
No it doesn’t Ian. In terms of the rear suspension of the ND the bushes are in simple terms a tube surrounded by rubber or polyurethane contained within a cylinder which provides a small amount of movement and reduces nvh. The spherical bearing in this instance on the other hand is a bearing contained within a cylinder and provides a limited range of movement but no flexibility as there is no rubber other than the rubber end caps which prevents water or dirt entering the bearings. The Mazda bearings have been failing due to the rubber end caps allowing water and dirt to get into the bearing creating excessive movement and premature failure.
The Mazda bearing
Okay first time I have seen a detailed picture of the part, is there any detriment to replace it with a polybush do you think?
Surely it would change the way the suspension moves as the ‘spherical’ nature of the bush allows free radial movement and no longitudinal movement, which presumably is part of the overall geometry and design.
A more solid bush would restrict the radial movement considerably, particularly as it reached it’s extremities. There would also be some longitudinal movement within the bush as well. Exactly how that would change the way the car handled I have no idea, but it would change it for certain.
What we need is someone with lots of time and money to do a back to back comparison and make a ‘podcast’ for us all to muse over.
The spherical bearing only allows a specific range of movement allowing rotation about the bolt axis and across it. I’m sure if Mazda thought a bush would suffice instead of the spherical bearing they would because a bush is cheaper.
Paul Roddison did mine on my ND1 . It still isn’t a cheap job , for the reasons stated above but it’s a helluva sight less than a dealer job . I now have a silent ride over bumps .
Paul is hardly any further from Coventry than he is for me in N Yorks - put a day aside and save some money ?
We can hope 
Assume then this is the polybush replacement and as you state you’re happy with the outcome. It’s good there are choices beyond a complete assembly replacement.
I did see somewhere that there has been a design change to the spherical bearings though don’t know when this applies from in terms of production dates.
When was the spherical bearing change to the rear suspension,my car is a 2019 ND2,at moment 23000 miles and no problems?
Simon
The bearings were revised in production from Feb '22.
Do you know whether they changed the bearing or just made the seals better?