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Ford put the ZF S5-42 behind F-250 and F-350 pickups from the late 1980s through the end of the old-body trucks, behind everything from the 300 six and 460 to the 7.3 IDI and early 7.3 Power Stroke. The S5-47 is the heavier-rated version that shows up in chassis cabs, some Super Duty applications and higher GVW trucks. Shops just call either one a ZF5.
It is a good transmission. Cast iron where it matters, a direct 4th, a tall overdrive 5th, and gears that rarely break outright. What kills them is age, hauling heavy in 5th, the wrong fluid, and shifter parts that wear until the driver cannot find a gear cleanly. Most of what we see is fixable without condemning the case.
Identify What You Have
Look on the driver side of the case for the ZF tag. It shows the model (S5-42 or S5-47), a ZF part number and a serial. The ZF number tells a rebuilder which ratios, input shaft and output you have, and that matters because diesel and gas units do not always share parts. Write it down before you call anyone for a quote.
Also note whether the truck is 2WD or 4WD. On 4x4 trucks the transfer case bolts to an adapter on the back of the ZF, and that changes the output shaft and how the transmission comes out.
What Actually Fails
| Symptom | Usual cause | Notes |
|---|---|---|
| Grind going into 2nd or 3rd | Worn synchro rings | Worst when cold or on fast shifts. Rule out clutch drag first. |
| Pops out of 5th or noise only in 5th | 5th gear, synchro or fork wear | Common on trucks that towed heavy in overdrive for years. |
| Shifter loose, vague, hard to find gears | Shift tower bushings, stick, or rail detents | Often the cheapest fix on the truck. Check it before blaming internals. |
| Whine in every gear but 4th | Countershaft bearings or gear wear | 4th is direct, so the cluster is lightly loaded there. |
| Growl at idle in neutral, clutch out | Input bearing | If it changes when you touch the pedal, suspect the throwout bearing. |
| Oil at the bellhousing or tail | Input seal, rear seal, or top cover | A low ZF runs hot and eats synchros. Fix leaks early. |
Synchro wear and clutch drag
Before you pull a ZF5 for a grind, make sure the clutch is fully releasing. A tired hydraulic system, a sticking slave or a worn pedal bushing will leave the disc dragging, and a dragging disc makes healthy synchros grind. If it grinds going into every gear and reverse crunches, start with the hydraulics. Our clutch bleeding guide and pedal to the floor guide walk through it. If only one or two gears grind with a good release, it is synchros. See our synchro wear guide.
5th gear and towing
5th in a ZF5 is a tall overdrive. Pull a heavy trailer in 5th up grades and the engine lugs, the 5th gear set takes a lot of load, and heat builds in a small amount of fluid. The first signs are a whine that only shows in 5th, then 5th wanting to walk out on decel. Drop to 4th when towing heavy in hills and the ZF lives a lot longer.
The shifter tower
A lot of "the transmission is worn out" complaints on these trucks turn out to be the shift tower. The bushings and the stick pivot wear, the lever gets sloppy, and the driver ends up between gates. A shifter rebuild is a driveway job. If you are replacing the stick, we carry a ZF S5-47 shifter stick kit for Super Duty applications.
Parts for the ZF5 Truck
Shifter parts and clutch hydraulics are where most ZF5 drivability complaints get fixed. Match the part to your year and engine before ordering.
ZF S5-47 Shifter Stick → F-250 Clutch HydraulicsFluid Matters More Than People Think
Ford filled the ZF5 with automatic transmission fluid, not gear oil, and that is what the synchros are designed around. Over the years plenty of these trucks have had 80W-90 poured in by someone who assumed "manual transmission means gear oil." Thick oil slows the synchros, makes cold shifts notchy, and can be harder on the brass rings. Check what is in it. If it is thick and smells like hypoid oil, drain it and refill with the ATF your owner manual or the case tag calls for, to the bottom of the fill hole with the truck level.
Our manual transmission fluid guide explains why the spec matters. We stock ATF and manual transmission fluids in our fluids category.
What It Costs
| Job | Parts | Shop, installed |
|---|---|---|
| Shifter rebuild or stick | $40-$150 | $150-$350 |
| Clutch master and slave | $75-$200 | $250-$700 |
| Fluid correction and leak repair | $30-$120 | $150-$500 |
| Bearing and synchro rebuild | $350-$800 | $1,800-$3,000 |
| Rebuild with gears | $800-$1,800 | $2,500-$4,000 |
| Remanufactured ZF5, exchange | $1,800-$3,000 | $2,600-$4,200 |
Ballpark numbers. Removal on a 4x4 means the transfer case comes out too, so labor runs higher than a 2WD. If the transmission is coming out, do the clutch at the same time; the labor is already paid for. Our clutch replacement cost guide breaks that part down. For bench parts, browse our hard parts, or our sister store CoreTransmissionParts.com.
Our Take: Fix, Rebuild, or Replace
- Fix the cheap stuff first. Correct fluid, a tight shifter and a clutch that fully releases cure more ZF5 complaints than any rebuild.
- Rebuild when you have synchro grind on a good release, bearing noise, or 5th pop-out, and the case and shafts are healthy. These are worth rebuilding.
- Buy a reman if the gears are chipped, the case is damaged, or downtime matters more than the last few hundred dollars.
- Change how you tow. Heavy loads in hilly country belong in 4th, not 5th.
FAQ
What is the difference between a ZF S5-42 and S5-47?
Both are ZF 5-speeds built for Ford heavy-duty trucks. The S5-47 is the heavier-rated unit used in higher GVW and some chassis cab and Super Duty applications. They look alike from the outside, but many internal parts and part numbers differ, so go by the tag on the case.
What fluid goes in a ZF5 transmission?
Ford specified automatic transmission fluid, not gear oil. Many have been filled with 80W-90 over the years, which makes shifting notchy, especially cold. Drain it and refill with the ATF your manual or tag calls for, to the bottom of the fill hole with the truck level.
Why does my ZF5 grind going into 2nd?
Most often worn 2nd gear synchro rings. Before replacing them, confirm the clutch fully releases. A weak hydraulic system or worn pedal parts make the disc drag, and that causes grinding even with good synchros.
Can I tow in 5th gear with a ZF5?
Light loads on flat ground are fine. Heavy trailers on grades should go in 4th. Lugging in overdrive loads the 5th gear set and builds heat, and that is one of the most common reasons these transmissions wear 5th.
Is a ZF5 worth rebuilding?
Usually, yes. The case and main gears are strong, and most failures are synchros, bearings and 5th gear parts. If gears are chipped or the case is damaged, a remanufactured unit often makes more sense.