Manual Transmission Grinding Occasionally Shifting Into Fifth

Question

I have a 99 Nissan Almera which occasionally grinds / doesn't engage when I try and put it into fifth gear.  Not often, but maybe once or twice a day.

I'm not sure if the problem is operator related, or a potentially clutch problem since it only happens occasionally and only when going into fifth.

Do manual clutches need oil and filter changes occasionally like automatics?  Would you ever use something like Lucas Transmission Fix or a similar type product on a manual?

EDIT 12/1/2016

I haven't dealt with this issue yet, but I was talking to someone about changing the gear oil since I'm going to replace the cv boots.  The Hayens manual says my tranny takes Hypoid gear oil, viscosity SAE 80W to API GL4.  This person recommended that I use Valvoline 75w-90 Limited Slip to help with the problem I'm having shifting into fifth gear.

According to the product information sheet on Valvolines website it meets GL4,GL5 and MT1 ( whatever those are ).

What is this "limited slip" thing they are talking about and might it help my problem, as opposed to refilling with some cheaper oil like regular 75w-90 or 80w?

Got some interesting responses to this on BobIsTheOilGuy.

From what the Bob's guys are saying and the Amazon reviews it looks like I'm going to try the Red Line (50304) MT-90 75W-90 GL-4.

Crap, the Red Line site says MTL, MT-85 & MT-90 are not for use in differentials with hypoid gears

I've gotta check the workshop manual to see if what's said in the Haynes is correct...

amphibient · Answer

I have the same problem with my Tacoma when shifting from the 2nd into the 3rd. The reason in my, and more than likely your case as well are bad syncro rings and the only fix pretty much is to take the gearbox out and either replace the whole thing or rebuild the syncros.

Answered by amphibient on February 14, 2021

Pᴀᴜʟsᴛᴇʀ2 · Answer

I can think of three scenarios which may be causing your issue:

As @amphibient stated, the synchro may be going bad
This could also be due to poor shifting technique. If you don't press the clutch down all the way, you may find yourself grinding gears. If you release the clutch too soon during the shift, you are going to see the same.
If you have a weak master/slave or have air in the clutch lines (assuming this is has a hydraulic system on it)

There is a fourth, less likely scenario, but would be easily discounted. I had an issue with my fire wall getting a stress fracture in it. It started splitting where the clutch master cylinder was mounted at. It would flex outward as I pressed on the clutch. This would not allow the clutch to disengage fully and I would have to slam gears into place to get it to shift. This was the last thing I thought of would have been the problem, but once I put some backing on it, it shifted smooth as silk.

A reasonable assumption would put it in the synchro ball park. I think the other problem areas would see you have problems in all of the gears and not just the one shift.

Manual Transmission Grinding Occasionally Shifting Into Fifth

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