C4 Transmission
Ford's lightweight 3-speed automatic transmission, the most common automatic in 1964–1981 Mustangs. Reliable, rebuildable, shift-kit-friendly, and perfectly adequate for street use—unless you're making serious power, in which case it's an explosion waiting to happen.
What 'C4 Transmission' Actually Means
The C4 (also called "SelectShift Automatic") is Ford's small-case automatic transmission designed for lighter vehicles with small-block engines.
Key specs:
- Speeds: 3-speed automatic
- Gear ratios: 2.46:1 (1st), 1.46:1 (2nd), 1.00:1 (3rd)
- Years in Mustangs: 1964–1981 (various versions)
- Torque capacity: 300–325 lb-ft stock, 400+ lb-ft with upgrades
- Weight: ~130 lbs (lighter than C6)
- Identification: Small aluminum case, pan has 11 bolts
Why it matters:
The C4 was designed for the 260/289/302 engines. It's compact, shifts well, and parts are everywhere. For stock or mildly modified street Mustangs, it's perfectly adequate.
The problem:
The C4 has a weak direct drum and clutches that slip under hard use. If you're making more than 350 lb-ft of torque (performance 302, any 351W), the stock C4 is living on borrowed time.
I ran a stock C4 behind my mildly built 302 (about 280 hp, 320 lb-ft). It lasted exactly 18 months before the direct clutches started slipping in third gear. Rebuild cost: $1,800. Should've upgraded it preemptively.
Why It Matters for Your Mustang
The C4 is relevant because:
For stock/mild Mustangs:
- Perfectly adequate transmission
- Cheap to rebuild ($1,200–$2,500)
- Parts readily available
- Easy to find shops that work on them
- Decent fuel economy (for a 3-speed auto)
For performance builds:
- Needs upgrades before handling power
- Upgraded C4 handles 450+ lb-ft: $2,500–$4,000
- Alternative: Swap to C6 (stronger but heavier)
- Alternative: AOD/4R70W (overdrive, better highway economy)
Common in:
- 1964½–1973 Mustangs with 260/289/302 engines
- Some 351W cars (C6 was more common)
- 1974–1981 Mustang II models
Not common in:
- 390/428 big-block cars (used C6)
- 429/Boss cars (used C6)
C4 vs C6 vs Manual:
| **Transmission** | **Weight** | **Torque Rating** | **Shift Quality** | **Best For** |
|---|---|---|---|---|
| C4 | ~130 lbs | 300–450 lb-ft (upgraded) | Good | Street 289/302 |
| C6 | ~200 lbs | 450–600 lb-ft (stock) | Firm | 351W+, towing |
| Toploader 4-speed | ~85 lbs | 400+ lb-ft | Driver-controlled | Performance |
| T5 5-speed | ~75 lbs | 300 lb-ft max | Driver-controlled | Street/economy |
The C4 is the "goldilocks" automatic for street Mustangs—lighter than a C6, stronger than you need for stock power, rebuildable for reasonable cost.
Cost Impact
| Repair Type | Typical Cost (LA) | Labor Hours |
|---|---|---|
| Basic rebuild (stock specs) | $1,200–$2,000 | 8–16 hours (300–325 lb-ft capacity) |
| Performance rebuild (upgraded clutches) | $1,800–$3,000 | 12–24 hours (400–450 lb-ft capacity) |
| Race-spec C4 | $2,800–$4,500 | 20–35 hours (500–600 lb-ft capacity) |
| Used C4 (gamble) | $200–$600 | Condition unknown |
| Reman C4 | $1,000–$1,800 | Exchange unit (300–325 lb-ft capacity) |
| Installation labor (if not DIY) | $400–$800 | 4–8 hours |
*LA labor rates: $110–$140/hour for transmission work. For street performance (350–400 lb-ft): Upgraded clutches/steels ($300–$500), Shift kit ($150–$250), Billet servo ($80–$150), Deep aluminum pan ($120–$200) = Total upgrade cost $650–$1,100 plus rebuild labor. For serious performance (450+ lb-ft): Add billet intermediate shaft ($200–$350), billet forward drum ($250–$400), heavy-duty planetary gears ($200–$350) = Total upgrade cost $1,300–$2,200 plus rebuild labor.
Ask me how I know these numbers.
Common Issues
Slipping in 3rd Gear
Direct clutches worn (most common failure)
No 1st Gear
Forward clutches failed
Delayed Engagement
Seals hardened, pump worn
Harsh Shifts
Shift timing issues or bands too tight
Fluid Leaks
Pan gasket, front pump seal, rear seal
Burned Fluid
Clutches slipping, overheating (hard use symptom)
See This in Action
- Mustang Transmission Rebuild Cost Guide
Detailed C4 rebuild costs, upgrade options, and shop selection guidance
Want to Learn More?
Download the Mustang Restoration Starter Kit (LA Edition) for:
- Complete terminology reference guide
- Cost estimation worksheets
- Pre-purchase inspection checklist
- Shop interview questions
- Project timeline planning tools
No upsells. No bait-and-switch. Just the information Dorian wishes he'd had before he bought his first project car.