Section 10
How-To & Repairs
Task-focused guides for the jobs Stag owners actually do — from an annual coolant flush to a full cooling-system overhaul. Each guide is written in plain English, answer-first, and points to the official Triumph workshop manual for safety-critical figures.
These guides are original editorial. They do not reproduce text, step sequences or torque tables from any workshop manual. For the specific figures your engine number and market require, consult the official Triumph Repair Operation Manual or an equivalent authoritative source — see the Resources page.
- CoolingIntermediate · A weekend
Cooling system overhaul and upgrade
A full refresh of the Stag V8's cooling system — radiator, water pump, fan, hoses, thermostat and a second temperature sender — carried out as a single package. This is the single most important job on the car and the foundation of long-term reliability for the alloy heads and iron block.
- CoolingBeginner · Half a day
Coolant flush and corrosion protection
The annual service job that keeps a Stag alive: draining tired coolant, flushing the system and refilling with fresh inhibited coolant. Do this every year, without exception. Fresh inhibitors are what stop the iron block corroding the alloy heads through galvanic action.
- EngineSpecialist · A full workshop job — allow several days
Replacing the timing chains (overview)
An overview of renewing the Stag V8's two single-row timing chains, tensioners and guides — a service item on this interference engine. Written as a scope-of-work briefing so an owner can understand what is involved before booking a specialist, not as a step-by-step DIY procedure.
- IgnitionIntermediate · One to two hours
Setting the ignition timing
How to check and set the ignition timing on the Triumph V8 with a strobe. The Stag is timed on the No. 2 cylinder — an important detail that catches out owners used to timing British engines on No. 1. Correct timing protects the engine from detonation and preserves running.
- Fuel/CarburettorsIntermediate · Half a day
Balancing and tuning the twin Strombergs
How to balance and tune the twin Zenith-Stromberg CD-series carburettors fitted to the Stag: setting a synchronised idle, matching airflow between the two carbs, and adjusting mixture. A well-balanced pair transforms low-speed running, throttle response and fuel economy.
- BodyworkBeginner · One to two hours
Rust inspection walkthrough
A systematic walk around the car to assess where rust hides on a Triumph Stag: sills, floors, front and rear valances, inner wings, boot floor and hood-well area. Suitable for a first-time buyer's inspection and for annual health checks on a car you already own.
- DrivelineAdvanced · A weekend (UJs) up to a full weekend for the CV conversion
Curing the "Triumph twitch" — rear driveshafts, UJs and the CV upgrade
How to diagnose and cure the Stag's notorious rear-end "twitch": a lurch or momentary lock at the back under power or on the overrun, often with a transmission clonk. The job covers greasing the driveshaft splines, renewing worn UJs and — as the definitive fix — fitting modern CV-jointed halfshafts.
- TransmissionIntermediate · An afternoon for the electrical checks
Overdrive won't engage — Laycock A/J-type troubleshooting
How to diagnose a Laycock overdrive that won't engage or drops out on a Stag. Overdrive is available in 3rd and 4th only. The vast majority of failures are electrical or a low gearbox oil level — check both before ever suspecting the internal hydraulics or a rebuild.
- Fuel/CarburettorsBeginner · Half a day
Hot-starting and vapour lock
How to fix the classic Stag hot-start problem: the car starts perfectly cold or warm, refuses to restart after a short stop in hot weather, then frees up after 15–30 minutes' cooling. The cause is fuel vaporising in heat-soaked lines and carburettors, and the fixes are all about heat management — not more fuel pressure.
- EngineSpecialist · A specialist workshop job — plan on the car being off the road for weeks
Head gasket failure and freeing seized head studs (overview)
An overview of what is involved when a Stag V8 head gasket fails and the head studs have seized into the alloy heads. Written as a scope-of-work briefing so an owner understands the size of the job, the risks, and the strong case for handing head work to a Stag engine specialist.
- BrakesIntermediate · A weekend, more if calipers or cylinders need overhauling
Freeing seized brakes and brake overhaul
A safety-critical overhaul of the Stag's servo-assisted front discs and rear drums. Covers freeing seized calipers and wheel cylinders after the car has stood, renewing flexible hoses, flushing to fresh DOT fluid, checking the servo and bleeding the system thoroughly.
- ElectricalBeginner · An afternoon for the basics, a full day for a thorough sweep
Lucas electrics — earths, connectors, charging and gauges
A methodical clean-up of the Stag's Lucas electrics: main earths, bullet and spade connectors, charging output, and the gauge voltage stabiliser and senders. Upgrading earths and connectors alone cures a surprising number of "mystery" electrical faults on this car.
- TransmissionSpecialist · A full workshop job — allow a week or more
Converting a Stag from automatic to manual
A scope-of-work briefing on swapping the Borg-Warner 35 automatic in a Triumph Stag for a 4-speed manual with Laycock overdrive. Covers the parts required, the trim and pedal-box changes, propshaft and driveshaft implications, and the impact on originality and market value.