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Spider gears live inside the differential carrier: two side gears splined to the axle shafts and two (sometimes four) pinion gears on a cross shaft between them. Driving straight, the pack turns as one block. In a turn the outside wheel travels farther, so the pinion gears spin on the shaft. That is the only time spiders work, which is why their failures show up in turns and when one wheel spins.
Symptoms of Failing Spider Gears
- Clunk taking up slack in a turn. Worn thrust washers and gear faces open up backlash inside the carrier. You feel a bang getting on the throttle mid-turn.
- Clicking or ratcheting at low speed. A tight parking lot turn at walking pace with a click every wheel revolution or two usually means a chipped tooth on a spider or side gear, or a cross shaft worn with a step in it.
- Noise only in turns. Ring and pinion whine follows speed and load in a straight line. Spider noise mostly goes away straight ahead. Our guide on telling transmission from differential noise helps separate the two.
- Metal on the magnet. Fine grey paste is normal wear. Slivers, flakes of bronze or steel washer material, or a chunk of tooth are not.
On a clutch-type limited slip like the Ford Traction-Lok, chatter in turns is usually dry clutches, not spiders. Start with the Ford 8.8 Traction-Lok chatter fix before tearing it down.
Why Spider Gears Break
One-wheel peel and wheel hop
When one tire breaks loose on an open diff, it spins at twice carrier speed and the spiders turn flat out on a dry shaft. When that tire grabs pavement, the shock load cracks spiders and snaps cross shafts. Burnouts, launches and spinning on ice then hooking a dry patch all do it.
Thrust washer wear
Each side gear rides on a flat thrust washer against the case, and each pinion gear rides on a dished washer. As they wear thin, lash grows and the teeth hammer instead of roll. Old, broken-down gear oil speeds it up. See the differential fluid change interval guide.
The cross shaft bolt backs out
This is the big one on C-clip axles like the GM 8.5 and 8.6 10-bolt, the GM 7.5 and 7.625, the 12-bolt and the Ford 8.8. The cross shaft is held by one small lock bolt. When that bolt loosens, shears or was never torqued after a previous axle job, the shaft walks out and hits the pinion gear head or housing as the carrier turns. The result is a cracked housing, broken spiders, and C-clips that fall out so an axle shaft slides out of the tube.
A sheared bolt is common. Drill it out with a left-hand bit, chase the threads, and install a new bolt with thread locker torqued to the factory spec. For the 8.2 GM and posi cases there is the Yukon positraction cross pin bolt for 8.2 GM ($62.89). On older Ford 8.8s the notched 0.750 inch shaft is the Yukon 8.8 notched cross pin shaft, 85 and older ($94.89). Measure the old shaft first.
How to Inspect Spider Gears
- Check the cross shaft bolt first. Make sure it is there, tight and not sheared. Look at the shaft for a polished step where the pinion gears ride. If you can catch it with a fingernail, the shaft is done.
- Feel for lash. With one wheel off the ground, hold the opposite tire and rock the raised one. A lot of slop means worn washers or gears.
- Rotate and look. Turn the wheel slowly and watch every tooth on the spiders and side gears come by. Chips, cracks and pitting at the tooth roots mean replacement.
Check the case bores and the case itself around the cross shaft holes. A cracked or egged-out bore means a new case or a loaded GM 8.5 and 8.6 open carrier ($255.99), not just gears.
Replacing Spider Gears
On an open diff the spiders, side gears, washers and cross shaft come out without removing the carrier from the housing. The ring gear, pinion and carrier bearings stay set up, so backlash and pinion depth are untouched. Roll the new pinion gears and washers in together, line up the shaft, install the lock bolt and refill.
On a Ford 8.8 Traction-Lok, replace the clutches while the case is apart; the Ford 8.8 spider gear and clutch pack kit ($215.99) covers both. Kits for the GM 8.6, GM 12-bolt and Dana 50 are in the table below.
Match spline count and axle size. A 28-spline 10-bolt kit will not fit a 30-spline axle, and the GM 8.5 and 8.6 share a case style but not every year. See the GM 8.5 10-bolt and Ford 8.8 guides.
Spider Kit vs Locker
If the spiders died from age, dirty oil or a loose bolt, a new kit is the right fix. If they died because the truck gets launched, wheeled or spun, the same parts will break again. A locker replaces the whole spider set.
The Eaton Detroit Locker for the GM 8.5 and 8.6, 30-spline ($1,099.99) is a full case: the ring gear moves to it, new carrier bearings go on, and backlash gets reset. It drives both wheels until one overruns in a turn, then unlocks with a click. That click and some push in tight turns are normal for a Detroit. On a tow or trail truck it is close to unbreakable. See our open vs limited slip vs locker guide.
What It Costs: DIY vs Shop
| Repair | DIY | Shop (rough) |
|---|---|---|
| New cross shaft lock bolt and fluid | About $40-$100 | About $150-$300 |
| Cross shaft, bolt and fluid | About $110-$200 | About $250-$450 |
| Spider gear kit, open diff | About $165-$260 | About $450-$900 |
| Traction-Lok spiders and clutches | About $215-$300 | About $550-$1,000 |
| New loaded open carrier | About $300-$450 | About $800-$1,400 |
| Detroit Locker install | Parts about $1,200-$1,400 | About $1,700-$2,400 |
| Cracked housing from walked-out shaft | Used or new axle, varies | About $1,500-$3,500 |
A locker or carrier swap needs a dial indicator, bearing puller and press. Refill with the correct gear oil, plus friction modifier on a clutch-type limited slip; gear oil is in our fluids section. If the axle needs bearings too, read the master overhaul kit buyer's guide before buying parts twice.
Parts for the Job
| Need | What We Carry |
|---|---|
| GM 8.6 10-bolt spiders | Yukon 8.6 open spider gear set, 30-spline ($216.89) |
| Ford 8.8 Traction-Lok spiders | Ford 8.8 spider gear and clutch pack kit ($215.99) |
| GM 12-bolt spiders | USA Standard GM 12-bolt spider kit ($167.89) |
| Dana 50 spiders | Dana 50 spider gear set, 30-spline ($198.99) |
| Ford 8.8 cross shaft | Yukon 0.750 inch notched cross pin shaft ($94.89) |
| GM 8.2 cross pin bolt | Yukon positraction cross pin bolt ($62.89) |
| GM 8.5 and 8.6 locker | Eaton Detroit Locker, 30-spline ($1,099.99) |
If the clunk is the transfer case or transmission, CoreTransmissionParts.com carries rebuild parts for those.
Fix the Clunk Before the Case Cracks
Spiders and a lock bolt are cheap. A cracked housing is not.
Shop Spider Gear Kits → Gear Oil and FluidsFAQ
What does a bad spider gear sound like?
Usually a clunk or bang when you take up slack in a turn, a click or ratchet at walking speed in a tight parking lot turn, or a clunk when you go from drive to reverse. Noise that shows up only in turns points at the spiders, not the ring and pinion.
Can I drive with broken spider gears?
Not for long. A cracked spider can throw pieces through the ring gear. A walked-out cross shaft is worse: on a C-clip axle like the GM 10-bolt or Ford 8.8 it can crack the housing and let an axle shaft slide out. Park it and pull the cover.
How much does it cost to replace spider gears?
A DIY spider gear kit runs about $165-$220 in parts plus gear oil and a gasket. A shop typically charges about $450-$900 if the ring and pinion and carrier bearings stay put. If the cross shaft cracked the case, you are pricing a housing or a complete axle.
Should I replace spider gears or install a locker?
If the truck is a daily driver and the spiders failed from age or a backed-out bolt, replace them with a kit and a new bolt. If they failed because the truck gets launched, spun or wheeled hard, spiders will break again; a Detroit Locker or a gear-type limited slip replaces the whole spider set with stronger parts. A locker costs four to five times more.