NB Series-2004-MX5 Sport

Whilst removing the engine undershield, I noticed that on the nearside, one of the A/R Bar  mounting plates had a ‘missing’ fastener. To be specific, the ‘missing’ fastener was on the outside face of the ‘chassis’ rail, not one of the two located on the underside. I checked with the off-side and found that all four fasteners were fitted there, two underneath the ‘rail’ and two on the side. On closer inspection, it appeared that the 'missing fastener may have either been sheared off, or other. I have owned the car from new and have never had occasion to either attempt to tighten, or loosen that fastener, so all a bit of a mystery.

So, is this the way it is on the A/R Bar mounts, was the fastener head sheared on the original assembly, or, or, or ?

Answers on a postcard please!  


The anti roll bar mount plates fix to the chassis rail just where the infamous rail corrosion occurs. The two bolt fixings screw in to an inner plate in the rail fitted with welded nuts. It is the proximity of this second skin that creates the problem with corrosion where water gets trapped between the two layers and the rail rots out. Replacement sections have a single layer.

Despite the corrosion issue these mounts normally survive intact so your issue is hopefully rare. Sounds like some stress has built up combined with perhaps some corrosion and the bolt head has snapped off. Assuming the rail is in good order I would drill and tap and fit a new bolt. 

Take a look at the pic a short way down on…

This Thread      

Hello rhino666,
I (think I) greatly appreciate your response to my A/R bar mount post. Having taken a deal of care with my MX5 - limited winter use, copiously washing off any potential salt water, cleaning the inside of the rear wings, at every wash, etc., etc., I was pretty defeated when I spotted the corrosion around the A/R mount on both off and near side. It was one of those moments when you don’t want to dig around too much, for fear of what you might uncover! However, on both rails, ‘sound’ paint and metal could be seen on the lower, external surfaces, so maybe all is not lost? I think I would be pretty devastated if the car was scrapped off, given how much care I have bestowed upon it , coupled with the low mileage - 28,200 mls. As from a previous post, I am saving up the £1000 to professionally replace the off-side front wing, which has a small patch of corrosion around the run out of the inner arch protector; it now looks like I will have to spend that money on chassis rail repair work and the wing will have to wait a little longer!
So, moving forward, would it be possible for you to recommend a supplier of repair sections and/or a company within Northamptonshire, or adjacent county, who might be proficient and trustworthy to undertake such repair work? From the MX5 link images, it would appear that the front bumper/valance has to be removed and obviously the a/r mounts and roll bar. Any idea as to a ball park price for this work? A little late now, but why did Mazda ‘puncture’ the upper surfaces of the rails, thus allowing water ingress?
Many thanks, once again, for your help on this one,

Lets not get too depressed here tyton - you can see from the link I sent you how bad things can get.

If there are no holes and the base and side you can see look true rather than crusty and plimmed, relaxxxx man:-)

The design of this rail is pants but if the car has been treated with kid gloves it will likely last twice as long and more than one that hasn’t but…

get onto it now with injected rust repeller of your choice - fill the chassis legs now.

I would say that some rust has occurred between the two layers exerting terminal pressure on the bolt head. Take the hint:-)

If the worst occurs, repair sections are available from people like MX5 restorer.

The repair is quite involved so will likely cost £800+ for both sides. PaulG did this repair himself on Christmas day IIRC so if you buy him a couple of pints he may be available to do yours in a few months - the things people do to get away from their families:-)    

Thrussington Garage in East Goscote, Leics, recommend that the entire chassis leg is replaced, and have developed their own solution, as opposed to a patch.


I’ve had two MX5s welded up there. They do good work, reasonable price.

This is not to say SAZ that this will be a better job. As yet we have had no structural analysis published or controlled crash analysis done to confim that solution is better than replaceing the box sections in front of suspension tower area. To be honest it will not be done on an old car.

Just an opinion of that garage that may or may not the best thing to do.

I would be interested to see the area from the front of the suspension towers to the bulkhead opened up to find how much loss of metal that has occured in that area.

Pretty filthy day, so catching up on MX5OC posts.
I thank you for your response regarding the front chassis rail problem. It is my intention to call Thrussington on Monday morning to discuss a potential repair. I note concerns from others regarding the structural integrity of any repair work. however, just how structurally sound have thousands of MX5’s been whilst their rails have been gently corroding? I’m fairly new to this rail corrosion saga, but regard the issue as being pretty sordid on behalf of Mazda. I understand fully that an OEM will never admit liability but I wonder, historically, did Mazda ever issue a repair scheme and /or parts? Are you aware if Thrussington use MX5 Repair (Sussex) fabrications, or their own? It is difficult to ascertain from the MX5 Repair web images as to what gauge the plates are - 16swg, or .064" / 1,5mm, I would hope. Following on, is there a consensus of opinion as to the very best, in terms of quality and structural integrity, rail repair fabrications available?
Many thanks, yet again, for your response and assistance,