300ZX Manual Transmission Repairs

By Mark Gittelman in Auto Repair Information

This story is about my 300ZX manual transmission. Specifically about how my ignorance completely destroyed it to the point that it could not be repaired. First some background information about the car and where it came from so the rest of the story makes some sense.

I was always attracted to the 300ZX sports car. When these vehicles first came out, I could not afford to get one. But in 1998 I decided that I could afford a 10-year-old one as a hobby car or investment. I found a 1988 300ZX 2+2 in pristine condition that was garage kept by the original owner.

I was living in New Jersey at the time and the Z was located in South Carolina. After talking with the owner and seeing pictures online I decided to take a road trip with a friend and go see the vehicle. It was everything that I hoped for and I negotiated a cash sale with the owner. I then had the vehicle shipped back to New Jersey.

I drove the vehicle for several months with absolutely no problems. This car was going to be a hobby car but wound up being my everyday transportation due to circumstances beyond my control. In Jersey We had a brutally cold winter in 1998. And as we got into late December my manual transmission on the Z began to make some noise while driving in any forward gear.

I checked the fluid level in the manual transmission and it was filled properly. But what I didn’t realize was that it was filled with 75W90 gear Oil. I continued to drive the vehicle out of necessity and the noise quickly got worse. The 300ZX came with the original owners manual from 1988. I checked the manual transmission fluid recommendations in the owners manual.

300ZX manual transmission facts

To my surprise the 75W90 gear oil is recommended only for conditions above 40° the manual stated in colder conditions below 40° that automatic transmission fluid should be used. The gear oil worked fine while the vehicle was living in South Carolina. But the extreme cold of New Jersey thickened the lubricant to the point where it was not flowing properly through the transmission.

This lack of internal lubrication did an extreme amount of damage inside the transmission. I disassembled the unit and was extremely disappointed to find a lot of metal inside. But the problem was most of the metal was aluminum.

The case of a 300ZX manual transmission is all aluminum. The lack of lubrication caused case damage that made the five-speed FS5W71C unit unrepairable. Most of the steel gears, shafts, bearings and even the brass synchronizers were in good condition.

Used 300ZX five speed transmission

300Z manual transmission image — 300Z manual transmission

When I started looking around for a replacement transmission there was not too many options. I had to get one from the junkyard and fix it up. When I replaced the transmission I also installed a new clutch kit and had the flywheel resurfaced.

The total bill for the repair was around $2000. And remember I did all of the work myself so there was no labor charges. And the moral of the story is, it was my own stupidity that destroyed the five-speed transmission. If I would’ve broken out my owners manual and read through it when I first bought the vehicle I could have avoided this expensive repair.

Also when this transmission first started to make noise I had a second chance at saving the day and reading the owner’s manual. I would have seen a temperature chart and recommended fluid application that would indicate automatic transmission fluid was needed.