Premacy rear strut tower stiffeners fitted!

[TheMAN]

So last month, after I fitted the Autoexe chassis braces, I was hungry for more chassis stiffening mods for my car... while I was going through the Mazda parts catalogue, I found out that the Premacy came with stiffener plates on the rear strut towers. Mazda didn't bother fitting them on the BJ to cut costs and I guess they decided the Premacy needed them as it's a much heavier car.

The stiffeners are thick pieces of steel that sits on top of the strut towers to reinforce/stiffen the sheet metal beneath them. This greatly reduces the metal from deforming/flexing under load. Mazda added these to the front strut towers on the BJ2s but not in the rear! These stiffener plates work so well that, all new Mazdas now come with them. They greatly improve handling by not allowing suspension geometry changes like any chassis bracing does, despite the fact that real braces do a whole lot more, these are a cheap alternative.

Well I have a sedan, not a wagon, so there's not really any rear strut bar options. There isn't a need for one to begin with as the rear parcel shelf IS the "strut bar" So in other words, to fit a strut bar specific for the BJ, I would have to cut holes in the metal in order to fit it! No thanks!

So the best thing to do was to get those stiffener plates from the Premacy. Thanks to Phil who was in NZ a few weeks ago, he was able to find them for me from the wreckers.

They're very thick... not flimsy pieces of metal... I couldn't even bend them by hand! They're 5mm thick with rolled edges to make them hard to flex!


A good comparison of all the CP/BJ stiffeners:

The top left one is used in both the CP and BJ, while the golden one at the top right is obviously only used in the CP. The bottom ones are for the LHD OEM strut bar used only in the BJ.


But why not just use the front stiffeners? They're just pieces of metal right?
Well not really...


Why not just make your own? That takes too much time... having to measure, cut a thick piece of metal, drill holes, paint.... too much trouble for $20 pieces of metal!


But making them fit in the BJ sedan wasn't straight forward though... it runs against the gusset frame leading away from the strut towers.
Old pic from 7 years ago which shows the guesset:

So I had to grind down the stiffeners quite a bunch...




Now it fits!





Around town, the car rides noticeably even more solid than before, but only slightly. The car feels a little more tail happy at the limit too, so I guess it's doing its job.

Is it worth it to most people? Probably not. If you happen to race and drive your car to the limit, then you will want them as you'll notice a difference then.

[Rupewrecht]

Any chance of some measurements? Curious to see if they'd fit BA. Stud to stud if possible.

[TheMAN]

I'm pretty sure it'll fit the BA too
there's a plastic anti-noise film that sits on top of the top hats before it is bolted into the car... it's the same between the BA and BJ, so in other words, it has the same bolt pattern

I did scan one of the stiffeners too, in case somebody wants to make one themselves...

[Rupewrecht]

Fair enough. What's the part number for those plastic films - i should have put some in when i put some coilovers in.

[TheMAN]

BC1D-34-013 front (BA only)
BC1D-28-0A1A rear

[Rupewrecht]

Thanks Ed.

[TheMAN]

As with all new things tried, they don't always go perfect
I noticed recently that the "clunk in trunk" noise was back... I wasn't exactly sure if it's the stiffeners shifting slightly against the body while hitting big bumps, or if it was the strut mounts making noise

so since I didn't want to waste time messing with it multiple times, I went ahead and ordered another 2 of those anti-noise plastic film sheets that are supposed to sit below the strut towers, and also serrated self-locking flange nuts meant for the sway bar endlinks... the films are to help prevent any noise caused by the stiffeners rubbing on the body, and the serrated nuts help prevent everything from coming apart


So I placed the film directly over the strut towers, then put the stiffeners back on with the new serrated nuts and over torqued them to 60ft lbs... just for good measure, I also wrapped those extra washers and nut that hold the strut assembly together with electrical tape



Well, what can I say? The noise is basically gone... it's back to what it was before I installed the stiffeners. I think the stiffeners made the rear strut towers so much stiffer that the stiff suspension had no where to go but put more force on the strut mount/top hat bush, which caused the noise... I'm already using the stiffer wagon strut mounts too! I think before without the stiffeners, there was no noise because the sheet metal deformed enough where the strut piston was given enough movement to not cause any noise. In any case, I say the stiffeners had made a good difference... the more I drive the car, the more I notice it! It's subtle to say the least!