6-speed - 5th gear grinding on track

madjak · Postby **madjak** » Tue Mar 01, 2016 7:04 pm

I've had this 6 speed for 18 months. Initially I missed lots of gears and found it hard to get into reverse. I added a MR short shifter and Amsoil MTG oil and it fixed my woes. Shifting was good.

Last weekend I found it hard to get it cleanly into 5th (from 4th) during fast gear changes. I figure the synchro is a little worn and I'm probably shifting faster than before.

Before I pull it to bits and replace synchros has anyone tried running the lighter Amsoil MTF Synchromesh oil on a track car? I thought I'd try it and see what happens.

Waz man · Postby **Waz man** » Tue Mar 01, 2016 10:50 pm

Hey Rick. I have always used the Redline in my 5 boxes after using it in my old WRX.
The Subaru people said the box was stuffed (hard to change down into 2nd without it grinding) by just changing the oil fixed that.
Redline is not cheap but it is cheaper than fixing a gearbox, might be worth a try???

madjak · Postby **madjak** » Wed Mar 02, 2016 1:06 am

Yeah thanks for the suggestion. From what I've read to Amsoil MTG is very similar to Redline being a fully synthetic 75-90w? oil. The MTF is much lighter so it won't lubricate the synchros as much which should help them grip. Thats the theory... but the box might get a bit hotter which I'll monitor when I first install it. Maybe I should try Redline first.

The box was much much better with the Amsoil and the shift is nice if done slowly. I put the Amsoil is because the shifts were nasty before as this box must have been hammered before I bought it. On the track I'm hammering the poor thing so I'm not surprised if it doesn't like it. Its only 5th thats the issue which tells be that sychro isn't healthy.

I'm not afraid to pull the box apart. I'm itching for an excuse to see inside and play with all the cool gears.

Magpie · Postby **Magpie** » Wed Mar 02, 2016 7:27 am

With the 6 speed make sure you remove the correct oil plug or you will be pulling it apart

zossy1 · Postby **zossy1** » Wed Mar 02, 2016 12:42 pm

I also run Amsoil. Mine struggles:

1. When conditions are cooler (ie. Below 10C), until the box gets nice and warm.
2. When it gets really hot.

I've tried lighter oil. It makes it better when it's cold, but only until it warms up... And then it is worse once it gets really hot.

6 speed boxes have a limited lifespan in a race car. Consider it a wear item and either rebuild, or replace.

BTW, yet another shout out (on my own behalf) for anyone out there with a good, low mileage 6 speed. My problem is 3rd gear (not 5th). If you have one, please send me a PM

Regie · Postby **Regie** » Wed Mar 02, 2016 12:59 pm

how are you engine mounts?

the NC 6 speed sometimes has trouble getting into 3rd and 5th when the mounts are a bit worn, just the torque/ twisting of the motor will do it

madjak · Postby **madjak** » Wed Mar 02, 2016 1:02 pm

zossy1 wrote:I also run Amsoil. Mine struggles:

1. When conditions are cooler (ie. Below 10C), until the box gets nice and warm.
2. When it gets really hot.

I've tried lighter oil. It makes it better when it's cold, but only until it warms up... And then it is worse once it gets really hot.

6 speed boxes have a limited lifespan in a race car. Consider it a wear item and either rebuild, or replace

I figured this was the case. I was hoping the lighter oil might help a bit... but maybe not. Mine gets pretty hot on the track... I wonder if installing a small oil cooler would help keep the oil in the target range. How often do you change the oil? I've probably done over 12 events on it now so maybe it's cooked.

The synchros are cheap, plus I would need a few seals, bearings maybe. I figure I can pull it down, replace 5th and refresh some seals and see if it helps. I've printed out the manual, and the instructions all look fairly easy... the only concern is when I pull it apart that the parts aren't available quickly.

5th gear synchro is only $24 from Amayama... add some seals, etc and it will probably cost me less than $100 to replace plus maybe a day in the workshop doing it. (maybe that is very optimistic!)

madjak · Postby **madjak** » Wed Mar 02, 2016 1:04 pm

Regie wrote:how are you engine mounts?

the NC 6 speed sometimes has trouble getting into 3rd and 5th when the mounts are a bit worn, just the torque/ twisting of the motor will do it

I'm running hard urethane engine mounts. I found with engine mounts it's more miss shifting that was the issue no grinding. I would often go from 2nd to 5th as the engine unloaded twisting the box.

zossy1 · Postby **zossy1** » Wed Mar 02, 2016 4:14 pm

If you're going to the trouble of pulling it down, don't just replace 5th synchro. Sure as heck, 3rd isn't great either.

FWIW, I run AWR engine mounts (80 Douro from memory). They aren't the problem (at least in my case). I also run poly diff mounts, which can also create some flop in the drivetrain. I previously ran solid engine mounts (aluminium). They were good but dulled steering feel. AWR is a nice compromise for the race car.

madjak · Postby **madjak** » Wed Mar 02, 2016 4:26 pm

All other gears are awesome (currently)... except reverse. The 5th gear shaft is the easiest one to remove and has only a few snap rings and bearings to get off to get to the synchro. To replace 3rd & 4th I'd need to pull the much longer and complex shaft out and pull off the 20 or so bits to get to them. I think for now I'll just do the one item that I'm having issues with, plus it will give me some idea how to work on a gearbox and whats involved without having a trillion bits in bags. There are some special service tools that are required to perform the works... Whether or not I need them isn't very clear but I can probably make up some if required. I'm fairly creative when it comes to pulling things apart.

hks_kansei · Postby **hks_kansei** » Wed Mar 02, 2016 5:29 pm

The making of tools for boxes isn't that difficult.

My GF is the gearbox rebuilder at her work, and there's a few of the special tools they dont have, so she's made her own. Most of the special tools are more to prevent springs and needle rollers from flying around the place from what she's told me. (and to keep them in place while inserting the shafts etc)

The biggest thing she said with gearboxes is to make sure all your tolerances are correct, and that things go back in in the correct order.

In saying that, she doesnt do MX5 boxes, hers are a bit older (MG 4 speeds and overdrive units)

madjak · Postby **madjak** » Tue Mar 15, 2016 5:37 pm

it looks like my Amsoil isn't going to rock up on time. What do you think about running Penrite Synth Pro Gear 75w-90, 75w-85 or 70w-75?

The specs look pretty decent, but then I can't find any reviews online given it's an Australian only product. I suppose I'll give it a shot and see how it compares to Amsoil MTG

zossy1 · Postby **zossy1** » Tue Mar 15, 2016 8:20 pm

I wouldn't hesitate to use it. Every Penrite product I've used has come up trumps.

Disclaimer - I haven't tried this one.

For future reference, I get my Amsoil from Harold at Performance Lub, he usually gets it to me overnight.

madjak · Postby **madjak** » Tue Mar 15, 2016 9:16 pm

I picked up the 75w-90 penrite. I'll report back once I've run it. Im also currently running the 15w-50 ten 10ths engine oil and so far it's been excellent.