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MX-5 Gearbox fill plug removal
chris68 - 12/7/14 at 02:40 PM

Hi Guys,

Had a minor triumph today - managed at last to remove the fill plug on the side of the gearbox (NOT the drain plug which is a conventional, but shallow, hex head). Having read many horror stories on various MX-5 websites around the world I was begining to wonder if it would ever come off!

So I thought I would share my method just in case anyone else out there is having the same problems.

The fill plug on my MK2 1800 has a 14mm square head and a tapered thread, there are many reports of siezure etc. and I was struggling to remove it. For the record the gearbox is out of the car upright on a workbench with the rear of the gearbox (prop. shaft) at about eye level. In the end I used the following method:

250mm pipe wrench (Stilson type) and a 4 foot length of scaffold pole. The design of the pipe wrench means it grips more as you turn so having got it placed on the square head not quite across the corners but close and keeping it under tension slip over the hollow bar. Then holding the rear end of the gearbox with one hand start putting on the pressure. Came out fairly easily in the end. Will apply anti-seizure paste and/or PTFE tape when putting it back in permanently.

I appreciate that this method is no good with the gearbox still in the car but thought I would share it with you all. Got me out of a hole!!

Slimy38 - 12/7/14 at 04:11 PM

What are the horror stories? Is it something I need to pay attention to? Is it just that they seize up?

chris68 - 12/7/14 at 04:44 PM

It appears that some people have managed to destroy the threaded area in the gearbox leaving a useless hole (and gearbox), the plug must have been badly corroded up to do this.

I think having a steel plug in an ally casing where you can apply enormous torque to the fill socket may have been the cause. If the plug is badly corroded it will of course have swollen so this may also have been a factor.

Most of the info. I found seems to say don't drain the fluid out until you are sure you can remove the fill plug.

Slimy38 - 12/7/14 at 04:57 PM

Why do I get the impression it'll be easier to turn the engine over and fill it back up from the drain hole...

Thanks for the pointers though, I'll be careful when it comes to fluid replacement. What gearbox oil did you use?

prawnabie - 12/7/14 at 05:00 PM

I think the main problem is that people forget to slacken off the plug before they put the box in the car, forcing them to use whatever they can to undo it, mullering it in the process!!

skov - 12/7/14 at 05:20 PM

Well done!
Mine was a b!tch to remove too. Ended up welding a 3 foot length of tube to it to get enough leverage to undo it (the heat probably helped too).
Obviously had to buy a new replacement plug though!

Smoking Frog - 12/7/14 at 06:10 PM

quote:
Originally posted by prawnabie
I think the main problem is that people forget to slacken off the plug before they put the box in the car, forcing them to use whatever they can to undo it, mullering it in the process!!

Yes, I slacked mine before installing. So little room had to drill a hole in the side of the tunnel in line with the filler so I could fill it from the foot well.
quote:

What gearbox oil did you use?

Although I can't say it's correct I used 75W90 gear oil and engine oil in the turret.

chris68 - 12/7/14 at 08:03 PM

Thats interesting about using different oil in the turret haven't heard of that before. I assumed that as the gearbox only has one drain plug and one fill plug that when you filled it up with new gearbox oil it was filled up all the way through including the turret area.

Whilst on the subject of gearbox turrets I will need to obtain a new rubber boot at the bottom of the gearlever as mine was well perished.

Slimy38 - 12/7/14 at 08:35 PM

quote:
Originally posted by chris68
Thats interesting about using different oil in the turret haven't heard of that before. I assumed that as the gearbox only has one drain plug and one fill plug that when you filled it up with new gearbox oil it was filled up all the way through including the turret area.

Whilst on the subject of gearbox turrets I will need to obtain a new rubber boot at the bottom of the gearlever as mine was well perished.


Yup, refilling it up to the refill plug wouldn't reach the turret (if I remember rightly) so you top up the turret separately. It's one of the first things to check if gear shifts get a bit rough. Obviously it doesn't undergo as much abuse as the gearbox though. That rubber boot is also quite a common failure, on the MX5 it lets a whole load of heat into the car. Not quite sure what it would do in a seven?

Mr Whippy - 13/7/14 at 12:17 AM

how about replacing the plug with a brass one? I have heaps of oil fill plugs on my landy (even on the chassis) and all are brass, they always come out very easily

ashg - 13/7/14 at 01:31 AM

Took me about 3 seconds on my mx5 box in the exocet. 14 mm impact socket on the end of the impact gun. Bang out job done.