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The FS5W71C is a Nissan five-speed used behind the KA24 in the 240SX and across several Nissan truck applications. The turbo SR20DET versions in Japanese-market Silvias and 180SXs use a closely related box with the right bellhousing for the SR, which is why so many swaps end up with one.
For a stock or lightly modified car it is a good transmission. It shifts well when fresh and tolerates abuse better than its reputation suggests. The problem is age. Most of these boxes have more than 150,000 miles and at least one previous owner who learned to drift on it.
What Goes Wrong
Grinding into 2nd and 3rd
Worn synchro rings on 2nd and 3rd are the classic FS5W71C complaint. It grinds on a fast shift, gets worse when the oil is cold, and eventually grinds on every shift. Before you condemn the synchros, rule out the clutch. A worn clutch that does not fully release, air in the hydraulics, or a tired slave cylinder will keep the input shaft spinning and produce exactly the same grind. Bleed the clutch first. Our hydraulic clutch bleeding guide walks through it.
Popping out of gear
Jumping out of 3rd, 4th or 5th under load or on deceleration is usually worn dog teeth on the gear and sleeve, worn detent springs, or a worn shift fork. Worn engine and transmission mounts make it worse, because the whole drivetrain moves and pulls the shifter. Check mounts first; they are cheap. If it still pops out, the box is coming apart. More detail in our popping out of gear guide.
Whine and bearing noise
A whine in every gear except 4th points to the countershaft or input bearings, because 4th is direct drive and unloads the countershaft. Noise in neutral with the clutch out that goes away when you press the pedal is the input bearing. A growl that only shows up in one gear is that gear's needle bearing or tooth contact.
Sloppy shifter
Most of the slop in an old 240SX shifter is the shifter bushings and the shift rod bushings, not the transmission. Replace the bushings before blaming the box. Our shifter bushing guide covers what to look for.
Leaks
The rear output seal, shifter seal and the front input seal all weep with age. A low oil level accelerates synchro and bearing wear, so fix leaks early and keep the box topped up.
How Much Power Will It Take?
There is no official rating that means much on a 30-year-old box. A healthy FS5W71C lives on the street behind a stock or mildly built SR20DET. Big power combined with clutch-kick drifting and sticky tires is what breaks it, usually 3rd or 4th gear first, or the case cracks near the shifter. If you are building more than a moderate street car, budget for a stronger transmission swap instead of rebuilding the stock box.
Rebuild vs Swap
A bearing and synchro rebuild fixes grinding and noise on a box with healthy gears. It does not fix chipped teeth, rounded dogs on the hubs and gears, or a worn fork. Inspect everything on the bench before you order parts. Our manual transmission rebuild kit guide explains what a good kit should include.
Do the clutch while it is out. For a stock or lightly modified car, a quality organic disc is the right answer. For a built SR, a stronger kit like the Competition Clutch 240SX Stage 2 holds more torque and still drives on the street. A lightweight steel flywheel makes the engine rev quicker, at the cost of a little more chatter and a less forgiving launch. Pull the pilot bushing with a pilot bearing puller and center the new disc with a clutch alignment kit.
Gear oil
Nissan specified a 75W-90 GL-4 gear oil for these boxes. Red Line MT-90 is a common choice and is friendly to brass synchros. Avoid straight GL-5 hypoid oil. The GL-4 vs GL-5 guide explains why.
Clutch and Flywheel While It Is Out
We stock 240SX clutch kits, flywheels, and the gear oil the FS5W71C wants. Doing the clutch at the same time saves paying for the labor twice.
Shop 240SX Clutch Kits →What It Costs
| Job | Parts | Shop |
|---|---|---|
| Gear oil change | $40-$80 | $100-$175 |
| Shifter and shift rod bushings | $30-$100 | $150-$300 |
| DIY bearing, seal and synchro rebuild | $300-$700 | — |
| Shop rebuild, gears reusable | Included | $1,200-$2,200 |
| Used FS5W71C, untested | $400-$1,200 depending on version | — |
| Clutch kit and flywheel while it is out | $300-$900 | $500-$900 labor if done separately |
Ballpark figures. SR-version boxes with the correct bellhousing command more money than KA boxes. For hard parts and more transmission inventory, see our sister store CoreTransmissionParts.com.
Buying a Used FS5W71C
If you are shopping for a replacement box, ask for the original engine and chassis, and look at the bellhousing and tailhousing in photos. Spin the input shaft by hand with the box in neutral: it should turn smoothly with no gritty feel. Shift through every gear on the bench. Each one should click in cleanly and the output shaft should lock against the input. Check the drain plug magnet. A fuzzy coating of fine metal is normal wear; chunks or chips mean broken teeth inside. Look for cracks around the shifter housing and the case near the mounting points. A cheap box that needs a full rebuild is not a deal once you add parts and labor.
FAQ
Why does my 240SX grind going into 2nd?
Usually worn 2nd gear synchro rings. Rule out clutch release first, because air in the hydraulics or a weak slave cylinder causes the same grind.
Will a KA24 FS5W71C bolt to an SR20DET?
Not without the correct bellhousing and, depending on the box, the right input shaft and release components. SR-version boxes are the easier path for an SR swap.
What gear oil does the FS5W71C use?
A 75W-90 GL-4 manual transmission gear oil. Avoid straight GL-5 hypoid oil with brass synchros.
How much power can the FS5W71C handle?
A healthy box survives a stock or mildly built SR20DET on the street. Heavy power with clutch-kick drifting or sticky tires usually breaks 3rd or 4th gear first.
Is it worth rebuilding?
Yes, if the gears and hubs are healthy. A bearing and synchro rebuild cures most grinding and noise. If you are adding a lot of power, a stronger transmission swap is the better use of money.