NA6 5 spd rebuild or swap?

[gslender]

Hi,

Does anyone know what the best option would be to fix worn synchros on a NA6 5 spd ? My 1st-> 2nd and 4th-> 5th crunch (I've replaced the oil, but it still is pretty bad).

a) Swap with a Mania or MX5 Plus unit - which I assume are 2nd hand and potentially could be also soon to wear out.

b) Have the existing unit reconditioned by someone - if so, whom?

thanks,
G

[jerrah]

I have a spare NA6 gearbox. Worked fine when it came out, make me an offer and you can have it?

[gslender]

*bump*

...was hoping that folks that have replaced their gearbox would be able to tell their stories.

Like.... where you bought the replacement, was it 2nd hand, has it worked out, was it what you thought etc ?????

[NMX516]

Did you change the oil in the gearshift turret? Don't write your gearbox off just yet

When was the clutch fluid last changed? Are there any leaks in the clutch slave or master cylinders? Does it 'crunch' changing from 3rd to 2nd? Why would the syncros on the least used ratio - 5th - be worn if all the lower ones aren't?? I don't think you have a badly worn gearbox.

[muzza2]

+1
NMX5 is right, most people have problems between 2-3 syncro, and honestly never heard of anyone with a problem on the 5th unless they've done something completely stupid.

id also agree with NMX5 re checking the master, slave & clutch before looking at a new gearbox imo
also, if the oil hasnt been changed in the last 40-50k then change it, bad oil can cause lots of problems

[gslender]

Like you, I was surprised to the find the gearbox that way, but strangely that is its behaviour... ??

Did you change the oil in the gearshift turret?

Yes, I've done that.

When was the clutch fluid last changed?

About 100 klms ago when I changed the clutch slave, I flushed the fluid too. I also did the gearbox oil too.

Are there any leaks in the clutch slave or master cylinders?

No leaks any more, and was hoping this would improve it... it didn't.

Does it 'crunch' changing from 3rd to 2nd?

Nope, generally a smooth change into 2nd - assuming you are not trying to do something stupid (like 4th or 5th to 2nd).

Why would the syncros on the least used ratio - 5th - be worn if all the lower ones aren't??

It is common that the synchros are shared - ie there isn't 5 in the box... and if you wear out 1, it would impact other gear. This was my guess (I don't know this about MX5 boxes, but other gearboxes on other cars work that way).

I don't think you have a badly worn gearbox.

I'd like to think so.

also, if the oil hasnt been changed in the last 40-50k then change it, bad oil can cause lots of problems

Yeah, just recently changed the gear oil, and lots of metal filings were found in the old oil... so the crunching must have been going on for a while by the previous owner. Perhaps I need to change the oil again ??

Thanks again for the comments/thoughts.

g

[NMX516]

It would only hurt your wallet to change the oil again to flush out any more metal filings... In another car of mine I use an additive made by Nulon to help improve the shift, generally in high mileage vehicles - this car of mine has done 330,00kms with the gearbox never having been opened up. Might be worth a try.

Clutch master cylinder could also be the problem if it's worn/corroded inside.

MX5Plus sell these gearboxes for $350, which should be much less than a rebuild.

[gslender]

I use an additive made by Nulon to help improve the shift, generally in high mileage vehicles

Is this it? http://www.nulon.com.au/products/Manual_Gearbox_and_Diff_Treatment/

[NMX516]

Yep, that's the one. Makes a noticeable difference.

[jerrah]

I bought a 2nd hand 6 speed from MX5plus. It worked out. A bit stiff shifting when cold but warmed up it's beautiful. I replaced my working NA6 gearbox because I wanted closer ratios to help acceleration at the track. I found with the 5 speed there was too big a gap between 2-3-4 to keep the engine on the boil and the 6 speed fixed that.

My 5 speed is just sitting around and I don't think they're worth much. I've heard the NA6 5th gear can be damaged if a car has excessive torque i.e. turbo. Maybe in a previous owner the car was forced induction?

[ShadyDeals]

i recently had to do this exercise also. My 5 speed was pretty clunky and then after reversing it into the garage it got stuck in reverse. I tried to free it up with with all the detailed instructions on you tube and the forum but decided to get a proper fix rather than a band-aid. I rang arount to find a quote for a rebuild... Turns out that auto transmission shops traditionally don’t to rebuilds on manual box’s.. you’ll have more luck going to a diff shop and if you want to sound like you know what you’re talking about ask for a “re-race”.. I rang about 5 shops and the cheapest I could get was 800 bucks. I ended up getting a 2nd hand box with low k’s out of a car that got written off from hail damage.. cost me 280 bucks.. no brainer really..

I’ll post once it is installed and let you know if I got a lemon..

[Benny]

If you've ever seen a gearbox pulled apart and all the parts lined up, you'll know why it costs so much to get them re-synchro'd.

Obviously, when you pull a gearbox down, you'll want to change not only the synchros, but the bearings as well, and then there's the clutch and the........................

Just get a used box.
It'll save you time, money and grief!

A well looked after box should be good for around 250,000 k's.