According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 1986 Porsche 911 has 2 documented known issues. No issues are rated critical, indicating generally reliable ownership. Across all issues with published estimates, repair costs range from $300 to $4,500. DIY maintenance guides at au7o.io.
On the 1972-1986 Porsche 911, the 915 transmission (1972-86, replacing the earlier 901) is the air-cooled 911's known shifting weak point. Its Porsche-style synchros wear, and second gear in particular suffers — the synchro ring loses its bite and the engagement 'dog teeth' get rounded off (or snapped if someone missed a power shift). The result is the classic notchy, baulky 1st-to-2nd shift and a grind/crunch into 2nd, especially when cold. Owners abuse this further by speed-shifting, which bypasses the synchro and accelerates dog-tooth wear, leaving a short-lived gearbox.
Common Symptoms
notchy or baulky 1st-to-2nd shift
grinding/crunching going into 2nd gear, worse when cold
gear lever pops out or won't engage under power
improves slightly as the transmission warms up
How to Fix
Rebuild the 915 with new/updated synchro rings and replace the worn 2nd-gear (and often 1st) gear sets with good dog teeth, set the correct shift-rod and shifter adjustment, and fill with a quality GL-4/GL-5 gear oil (many specialists add Swepco or a friction modifier that noticeably improves synchro feel). Restorers commonly fit updated late-style synchro components and a short-shift kit, and rebush the worn shift linkage and coupler. A properly rebuilt and correctly adjusted 915 with fresh synchros shifts cleanly — the bulletproofing is doing the rebuild right plus disciplined, non-speed-shifting driving.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
Rauch & Spiegel 91530230114/04 1st/2nd synchronizer ring
Confirm any prior asymmetric conversion before using it for 1st gear.
SWEPCO 201 80W-90 mineral GL-5 gear lubricant, one gallon
1972-1986 Porsche 911 type 915 transaxles after confirming gearbox and differential requirements. Do not use as a cure for damaged synchros, and confirm limited-slip additive requirements before adding anything.
On the 1965-1989 Porsche 911, air-cooled 911s carry oil all around the car through an external dry-sump system, and after decades the seals and hoses leak everywhere. The classic offenders are the two short rubber crimp hoses joining the hard lines to the front-fender oil cooler (they crack and weep), the oil thermostat's internal O-ring (it sees high pressure and seeps around the housing), the thin paper timing-chain-housing cover gaskets (often re-glued without gaskets and then leak), and the cam tower / valve cover seams. A leaky air-cooled 911 also runs hotter because oil IS its cooling system, so leaks are more than a nuisance.
Common Symptoms
oil drips under the front of the car (cooler line area)
oil film around the oil thermostat housing
seepage at the timing chain covers and cam tower joints
burning-oil smell and higher-than-normal oil temps
low oil level between changes
How to Fix
During restoration, reseal the whole oil system as a system rather than chasing one drip: replace the crimped front-cooler rubber hoses with new (ideally braided/AN-style) lines, renew the thermostat O-ring, and properly re-gasket the chain housing covers and cam towers with correct gaskets and sealant. Many restorers upgrade to a larger front cooler and braided cooler lines while everything is apart, improving both sealing and cooling margin. Doing all the seals at once — and torquing covers to spec — is the proven way to end the chronic seep for good.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
DPH 99970731440 engine oil-thermostat O-ring
1965-1989 Porsche 911 engine oil thermostat, 39.2 x 3 mm, cross-reference 99970731440.
FUEL SYSTEM, GASOLINE:DELIVERY:HOSES, LINES/PIPING, AND FITTINGS
DUE TO ROUTING OF FUEL LINE FROM THE FUEL TANK TO REAR FUEL PUMP, THE FUEL LINE MAY BE DAMAGED UNDER CERTAIN DRIVING CONDITIONS. ON FULL TRAVEL OF LEFT REAR SUSPENSION (JOUNCE), THE BRACKET FOR THE BRAKE PAD WEAR INDICATOR WIRE ON LEFT REAR CONTROL ARM COULD CONTACT AND DAMAGE FUEL LINE.
Campaign #91V10300017/06/1991
ELECTRICAL SYSTEM:WIRING:FUSES AND CIRCUIT BREAKERS
AFTER THE ENGINE HAS BEEN TURNED OFF, THE REAR HEATER WILL AUTOMATICALLY OPERATE IN ORDER TO DISSIPATE HEAT IN THE ENGINE HEATING SYSTEM. DURING THIS OPERATION, THE RESISTOR FOR THE REAR HEATER BLOWER CAN BECOME OVERLOADED DUE TO A BINDING OR SEIZED REAR HEATER BLOWER.
Campaign #93V20400007/12/1993
STEERING: STEERING WHEEL/HANDLE BAR
A PART OF THE STEERING COLUMN UPPER UNIVERSAL JOINT CRACKED DURING THE MANUFACTURING PROCESS.
Campaign #96V14700008/08/1996
VEHICLE SPEED CONTROL
THE BALL SOCKETS ON THE CRUISE CONTROL LINKAGE CAN BREAK, ALLOWING THE CRUISE CONTROL LINKAGE TO BECOME DETACHED ON ONE END AND JAM ON NEARBY COMPONENTS, WHICH COULD IMPAIR THROTTLE PLATE OPERATION.
Campaign #92V14200005/10/1992
LATCHES/LOCKS/LINKAGES:HOOD:LATCH
LUGGAGE IN THE LUGGAGE COMPARTMENT AND OR PLASTIC TRIM SURROUNDING THE SAFETY LATCH MAY PREVENT THE LATCH ON THE FRONT HOOD FROM PROPERLY LOCKING.
According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 1986 Porsche 911 has 2 documented issues. The most frequently reported are: 915 gearbox worn 2nd-gear synchros and rounded dog teeth, Chronic oil leaks from cooler lines, thermostat seal and chain housings. None are rated critical, but regular maintenance is recommended.
Is the Porsche 911 reliable?
The 1986 Porsche 911 has 2 known issues compiled from NHTSA recalls, manufacturer TSBs, and owner forum reports. No issues are rated critical, suggesting generally good reliability. Regular maintenance following the manufacturer's schedule helps prevent many common problems.
How much does it cost to fix common Porsche 911 problems?
Repair costs for known Porsche 911 issues range from $300 to $4,500, depending on the specific problem and whether you choose DIY or professional repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 1972-1986 Porsche 911 915 gearbox worn 2nd-gear synchros and rounded dog teeth?
The 915 transmission (1972-86, replacing the earlier 901) is the air-cooled 911's known shifting weak point. Its Porsche-style synchros wear, and second gear in particular suffers — the synchro ring loses its bite and the engagement 'dog teeth' get rounded off (or snapped if some… Repairs typically run $1,500-$4,500. Severity: medium.
What is the 1965-1989 Porsche 911 Chronic oil leaks from cooler lines, thermostat seal and chain housings?
Air-cooled 911s carry oil all around the car through an external dry-sump system, and after decades the seals and hoses leak everywhere. The classic offenders are the two short rubber crimp hoses joining the hard lines to the front-fender oil cooler (they crack and weep), the oil… Repairs typically run $300-$2,500. Severity: medium.
Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.
