NA Gearboxes

Purfler · Postby **Purfler** » Sat Sep 25, 2010 8:29 pm

I have a recently acquired '93 NA (an LE, but that's irrelevant here) which has gearbox noise in 3 and 4 at 2,250 to 2,750 - both accelerating and in overrun. I have read all the stuff on the net about the noises and possible sources. This is a gearbox noise - believe me. OK, no great disaster - the gearbox is noisy, big deal. However, the rest of the car is so good it bugs me. So I bought an allegedly 42K km gearbox off ebay (I have no reason to believe it is not as described and my dealing with the sellers has been without problem so I am in no way critical of them) for $200 which seems ridiculously cheap to me. While I have not fitted the 'box yet - this will happen when I take it out with the motor and change the cambelt etc and the clutch - I have noticed some slight differences with what is in the car: the gear lever in the car is unpainted steel, the one I bought is painted black; the flange where the lever enters the 'box in smaller in the original - the "new" box has a bigger flange with edges that curve down.

Can anyone explain the differences?

Regards and thanks,

Tim

PS - the "new" box had the slave cylinder, pipe and hose still attached. All look in pretty good nick to me. Bargain!

Steampunk · Postby **Steampunk** » Sat Sep 25, 2010 10:48 pm

Purfler wrote:... the one I bought is painted black; the flange where the lever enters the 'box in smaller in the original - the "new" box has a bigger flange with edges that curve down.

Does the throw of the lever feel stiffer and shorter in the new 'box? If so, you may have scored a Mazdaspeed short shifter as most of them had black shafts.

Purfler · Postby **Purfler** » Sun Sep 26, 2010 7:57 am

1red5 wrote:
Purfler wrote:... the one I bought is painted black; the flange where the lever enters the 'box in smaller in the original - the "new" box has a bigger flange with edges that curve down.

Does the throw of the lever feel stiffer and shorter in the new 'box? If so, you may have scored a Mazdaspeed short shifter as most of them had black shafts.

Yes

Mr Morlock · Postby **Mr Morlock** » Sun Sep 26, 2010 11:28 am

you buy a gearbox for $200 and it is has only done 42000km?? I reckon that the only way you will find out if the box is any good - shot synchro's bearing noises, teeth missing is to disassemble and check and I suspect if one has that ability then repair of the existing box may have been undertaken.

Purfler · Postby **Purfler** » Sun Sep 26, 2010 7:12 pm

Mr Morlock I share your suspicion and I may well take it apart before putting it in the car. I figured for $200 it was worth the risk. I have no idea what the cost of parts for a rebuild are - depends on what's stuffed. I've never taken a gearbox apart before, but there's a first time for everything. The advantage of having a spare 'box is that I have the luxury of time to work on it. The car is my daily transport so being without it while rebuilding a major component would be a pain. I have all the books so if I take my time I probably cannot go too far wrong.

I could also just put it in and see what happens...

Regards,

Tim

Guran · Postby **Guran** » Sun Sep 26, 2010 8:12 pm

That gearbox sounds like it could be a great find. But I have one question: what are you doing driving around in an NA at 2500rpm? Drop a gear (or two) and put your foot down man! :lol:

Purfler · Postby **Purfler** » Sun Sep 26, 2010 9:29 pm

Guran wrote:That gearbox sounds like it could be a great find. But I have one question: what are you doing driving around in an NA at 2500rpm? Drop a gear (or two) and put your foot down man!

crewmans · Postby **crewmans** » Mon Sep 27, 2010 10:24 am

mine has the same sort of problem, I changed the gearbox and still have the same prob. I have since found out that the noise is from the clutch plate in the limslipp diff chattering. Some other areas to look that were suggested to me were, Cluch, tailshaft notchy, cv's. I was convinced that the gearbox was the problem because the noise was coming from the gearbox. What is happening on mine is the diff chatter is resonating through the power frame to the gearbox and that is what I'm hearing. I can fix the problem by putting Anti chatter additive in the diff. I have heard that the additive can cause some unpridictability in the limitted slip of the diff midcorner so I will put up with the noise on the track.
Hope this helps in some way.
Cheers Paul.

manga_blue · Postby **manga_blue** » Mon Sep 27, 2010 1:41 pm

If it's a 93 LE then the gear oil is anything up to 17 years old. I'd whack in some good fresh gear oil to see what it did. You can always drain it out again later and filter it into a new box. NA gearboxes love good oil and hate bad or old oil.

Purfler · Postby **Purfler** » Mon Sep 27, 2010 3:17 pm

manga_blue wrote:If it's a 93 LE then the gear oil is anything up to 17 years old. I'd whack in some good fresh gear oil to see what it did. You can always drain it out again later and filter it into a new box. NA gearboxes love good oil and hate bad or old oil.

That's a good suggestion. When I got the car I thought the gearbox oil had recently been changed (in fact it was the diff) so I added some Nulon gearbox additive. That did help a bit. I should have drained it and started from fresh. I might do that anyway. In the meantime I'll open the spare 'box and see what it looks like inside. There's no rush at the moment, I don't actually need to do anything to the car immediately.

Tim

Purfler · Postby **Purfler** » Mon Oct 11, 2010 3:54 pm

Anyone with experience in dismantling an NA gearbox?

Following Rod's Manual (much better than the Haynes) I got easily to the point where I need to use a puller in the input shaft to remove the bellhousing assembly. I knew I didn't have one as shown in the book (they used a brake hub puller with longer bolts) but tried making one up with hardwood (hey - I'm a woodworker). Guess what

Clearly quite a bit of pressure is needed to separate the parts. I'd be interested to hear of anyone's experience with this step.

Regards,

Tim

Purfler · Postby **Purfler** » Fri Oct 22, 2010 7:06 pm

Finally got to change the gearbox oil. Yes, significant difference. I am not sure if the oil has been changed before, certainly not by the previous owner in the last 5-6 years. New oil (just standard Valvoline 75-90 or whatever the book says) has reduced the noise significantly and dropped the rpm at which it appears by about 200 in 3rd and 4th. Much less noise on the overrun.

Will still continue with the other 'box I bought but is now lower on the priority list. I was going to change the gearbox, clutch, timing belt, seals etc in one go in January. It will now wait and I'll try to spend some time on the Datsun 2000 and a copy of a Carlo Bergonzi of 1736

(See the OT thread if you wonder what the hell I'm on about).

Regards,

Tim

Purfler · Postby **Purfler** » Mon Oct 25, 2010 7:36 pm

Continued dismantling the $200 gearbox. These photos:

http://picasaweb.google.com/timrobinson22/MX5Gearbox#

show the innards after a bit of a clean. I am far from experienced with the insides of gearboxes, but this looks pretty good to me. There are no broken or chipped teeth, synchro all seem to show little signs of wear and the bearings all turn smoothly. I'd be really pleased if those with experience in these things could offer an opinion from what they can see.

Thanks in advance,

Tim