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Discussion Starter · #1 ·
Has anyone experience of rust proofing one of these brilliant little cars? I sprayed my Comma Wax Seal under the obvious bits last year but very aware I hadn't the nerve to remove the plastic shield covering the battery, and of course covering some of the critical chassis elements. These parts seem the most rust-prone, as far as I can tell e.g. Jonathon Porterfield's excellent video of a ten year old i-Miev with its really awful rust damage:

So is removing the plastic shield a matter of running it up a ramp and then carefully unbolting the two sections? No need to disconnect the battery etc? Five minute job and then carefully spray waxoyl or the equivalent and an hour later bolt it back on? I can only assume Mitsubishi didn't upgrade their underbody protection since that ten year old i miev hit the road, nor added galvanisation to the treatment etc etc. And if so, the bodywork is the car's most significant weakness, or am I being unduly pessimistic?
 

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The plastic shield can be removed without coming into contact with high voltages - it's basically a stone/water cover to protect the bottom of the battery housing. It's in two parts that overlap and has many bolts to hold it. Here it is removed:

130532


The underside of the battery chassis can get quite rusty, for example:

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If you remove the plastic undertray be prepared to replace some of the bolts - they're 6mm bolts of a couple of different lengths and on mine about half of them snapped below the bolt head. :( It took me a good hour or more to drill out the remainder of the bolts and retap the holes with a 6mm tap so I could fit new bolts - not fun!

The biggest problem with removing the plastic undertray to look for and prevent rust is that you're only looking at the bottom of the battery chassis - which is a steel frame which supports the main battery enclosure which is some kind of high strength ABS plastic.

The real rust will be body rust on the underneath of the floor pan and you cannot access that without dropping the traction battery down - which is a lot of work. So a lot of what you're trying to rust proof will be hidden and inaccessible I'm afraid. Mine certainly had a lot more rust on the underneath of the floor pan towards the front and rear ends near the suspension than it did on the bottom of the battery pack chassis. For example:

130534


Not nearly as bad as the one in the video mind you. :oops:

Not well rust proofed cars unfortunately and I suspect they're all like this when they get to this age. (Mine is a 2011) Without removing the traction battery any rust proofing job is going to be half hearted at best, but I'm not sure that the complication of removing it is worth the effort just to apply rust proofing! (I did it to swap some cells and it was big multi-day job)
 

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Discussion Starter · #3 ·
The plastic shield can be removed without coming into contact with high voltages - it's basically a stone/water cover to protect the bottom of the battery housing. It's in two parts that overlap and has many bolts to hold it. Here it is removed:

View attachment 130532

The underside of the battery chassis can get quite rusty, for example:

View attachment 130533

If you remove the plastic undertray be prepared to replace some of the bolts - they're 6mm bolts of a couple of different lengths and on mine about half of them snapped below the bolt head. :( It took me a good hour or more to drill out the remainder of the bolts and retap the holes with a 6mm tap so I could fit new bolts - not fun!

The biggest problem with removing the plastic undertray to look for and prevent rust is that you're only looking at the bottom of the battery chassis - which is a steel frame which supports the main battery enclosure which is some kind of high strength ABS plastic.

The real rust will be body rust on the underneath of the floor pan and you cannot access that without dropping the traction battery down - which is a lot of work. So a lot of what you're trying to rust proof will be hidden and inaccessible I'm afraid. Mine certainly had a lot more rust on the underneath of the floor pan towards the front and rear ends near the suspension than it did on the bottom of the battery pack chassis. For example:

View attachment 130534

Not nearly as bad as the one in the video mind you. :oops:

Not well rust proofed cars unfortunately and I suspect they're all like this when they get to this age. (Mine is a 2011) Without removing the traction battery any rust proofing job is going to be half hearted at best, but I'm not sure that the complication of removing it is worth the effort just to apply rust proofing! (I did it to swap some cells and it was big multi-day job)
Thank you so much, Mandrake, for such a comprehensive answer along with such useful photos. You are right that dropping the battery seems a huge task for what I could achieve, and certainly way outside my comfort zone. I was quite happy squirting Waxoyl at my mum's Mini in the 1970s, but didn't expect such poor corrosion protection on a car 45 years later. And even removing the shield seems to be less straightforward, as from what you say, it won't really solve the problem at source, which is what I was hoping, as I hate to see preventable deterioration on such a smart car. Anyway, I guess yours isn't that far gone, and most people here would think the battery is the weak link rather than the bodywork. If only Mitsubishi had made the car in aluminium, as one prototype seemed to suggest, and then we wouldn't be worried (but we'd probably be worried about something else!). Thank you again - it's really appreciated.
 

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You could add front and rear aerodynamic shields and these will prevent stone chipping, mud accumulation and directed winter salt/grit. Should reduce corrosion by a vast amount.
 

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...didn't expect such poor corrosion protection on a car 45 years later
This is typical for a JDM Kei car as they only have an expected lifespan of about 6-7 years (until the first big Shakken) - they SHOULD have been getting much more stringent protection on export models and certainly the USA-destined models do in "how it's built" videos

Looking at these photos I'm now worried about my 9yo recent acquisition I was intending to keep 4-5 years. I think it's going to be time to break out the zinc spray

(Battery is at 60% for 55k miles, no individual weak cells, but it's clear the drivetrain and brakes need TLC, front rotors are quite rusty and badly lipped)
 

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This is typical for a JDM Kei car as they only have an expected lifespan of about 6-7 years (until the first big Shakken) - they SHOULD have been getting much more stringent protection on export models and certainly the USA-destined models do in "how it's built" videos

Looking at these photos I'm now worried about my 9yo recent acquisition I was intending to keep 4-5 years. I think it's going to be time to break out the zinc spray
Yeah, the rust proofing just isn't adequate for salted UK roads, and the lack of under trays under either the front or the rear bays was a mistake.
(Battery is at 60% for 55k miles, no individual weak cells, but it's clear the drivetrain and brakes need TLC, front rotors are quite rusty and badly lipped)
Mine was at 70% at 62k miles when I moved it on, however that was after replacing 4 cells a year earlier that had accelerated degradation relative to others. If I hadn't replaced them I'd say it probably would have been down to 60% by then. Unlike yours there was quite a large variance between cells which I put down to regular deep discharges on the winter commute. If the cells are heavily degraded but well balanced it probably means the car hasn't suffered a lot of deep discharges.

In the 3 years I had mine I had to replace the front discs and pads twice - the first set of discs was a cheaper brand, but within 6 months they had rusted badly to the point that they were grinding and pitted and after a year I finally replaced them a 2nd time with some better quality discs and those did seem to last a bit better.

A tip if I may with the front brakes - they have what I consider a significant design flaw. The bottom caliper slide pin has a rubber bush over a recessed section of the pin - probably as some sort of anti rattle device, however this rubber bush swells up and goes mushy with age especially if anyone previously working on the car has used mineral grease on the pin. (which was the case on my car) When it swells up it starts slipping out of its recessed groove and jams the movement of the slide pin as it gets wedged between the larger diameter section of the pin and the hole.

This leads to one or both front brakes partially sticking on, and also prevents them applying full braking force. Mine was so bad on one side that I had a hell of a time getting the caliper pin out as it was completely jammed. If you try to replace the rubber bush on a worn pin it jams again very quickly, (as I found the hard way) so I ended up replacing upper and lower pins on both sides (as there was also a significant rattle due to the worn pins) and dutifully fitting a new rubber bush with the correct Mitubishi supplied silicone grease.

Guess what - within a year it was jamming again and the rubber bush was the cause once again. :mad: This time I ordered two new top slide pins and fitted them to the bottom. It turns out the top slide pins, which are metal only without a recess or rubber bush are a perfect fit in the bottom slide pin hole. So you can fit four identical pins without any bushes without any problems.

So I did exactly that and 2 years later when I moved the car on the front brakes were still working perfectly and I consider this a significant improvement to the functioning of the brakes. What's more it doesn't rattle with four all metal pins whereas it did still rattle a little with the two pins with rubber bushes despite them being new pins with new bushes! :rolleyes:

None of the cars I've owned before have used slide pins with integrated rubber bushes so I don't see the point and on this car they seem counter productive. Get rid of them and just fit the bushless version of the pins in their place, and if the car had previously been exhibiting any caliper rattle over potholes (as mine was) just replace all 4 pins with new all metal ones and this will fix the rattle at the same time. The pins are not that expensive.
 

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Great advice re the brakes etc, thanks DBMandrake, really appreciated , Ive MOT due and will check caliper pins etc, so thanks. @JimChantal, personally I wouldn't remove the battery for effort invoved and benefit , I did mine a couple of years ago with battery in situ , there is a thread on here from a couple of years ago . I agree not designed for salted UK roads. Main area of concern is rear of battery structure, arches, chassis box sections. I carefully power washed back end structure, jacked up, wire brushed and prepped , remove plastic arch guards, and sprayed a few litres of thinned White ( white body) Hamerite, followed by a few litres of Tetrosyl stone guard (white) , finally Tetrosyl waxoyl equivalent. If you jack up enough you can get around the back of the battery with care. Also carefully cleaned and prepped brake lines as they go above battery. Seems to have been good so far I check it over every year at MOT time, also check / re touching up and greasing brake lines, easy access through rear boot hatch .
 
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