After changing out the transmission fluid on my 1997 Nissan D21 4x4, the transmission started shifting really rough. My first piece of troubleshooting was to adjust the clutch pedal as specified in the factory service manual, but it made no real difference. The stick grinds and resists going into every single gear.
I have a clutch kit on hand (I was admittedly a little trigger happy on that), and I'm planning to do the necessary work in a couple of weeks. I'm just looking for guidance or advice from the community on what the problem likely is, and/or what you'd recommend I do to resolve the issue.
Is it a bad clutch?
- The clutch doesn't slip
- Though adjusted to OEM spec (distance from floor to pedal) the clutch "grabs" quite high.
- When releasing the clutch the truck "jumps" a bit. I've been driving manual transmissions for around 15 years, and I'm definitely not "popping" the clutch, but it still happens.
- The pedal travel is pretty linear, and offers a good amount of resistance such that I don't suspect an air bubble in the system.
Is it a bad transmission?
- Significant grind and resistance on every shift.
- If I leave it in neutral for a few seconds between shifts to allow the engine to spin down, there is still some resistance before it finally clunks into place.
- I'm positive that the shifter bushing is shot, new one is on order.
- It shifts significantly better when in 4WD (both 4-high and 4-low)
- For the transmission oil swap I used 1L LucasOil TRANSMISSION FIX & 3L LucasOil HEAVY DUTY APL GL-5 SAE 80W-90 GEAR OIL. The owner's manual calls for 75W90 or 80W90 APL GL-4.
There are no visible leaks, no obvious noises (beyond the grinding) or symptoms (like jumping out of gear) and the truck is in otherwise great condition (no collisions, rebuilds, etc.).
What made this confusing to troubleshoot is that it was a combination of three problems:
Problem 1: The transmission oil was definitely not suitable for this transmission. A week after changing my transmission fluid to GL-4 MT-90, the shifting had improved by about 80%.
Problem 2: I noticed that my clutch master cylinder reservoir was pretty gross looking, so I cleaned the reservoir and entirely flushed my system. I found that the master cylinder was half full of air, so I removed it and thoroughly bled it before reinstalling the line and bleeding the system again at the slave cylinder.
Problem 3: My shifter bushing was gone. I disassembled my shifter assembly to find that the control lever had no bushing, so it was operating as a ball with no socket. I replaced the shifter bushing and inner boot, and this improved the feel at the shifter - it's much easier to find the gears now.
After making these three changes, the truck is shifting smoothly and consistently... Very satisfying!