The Triumph Stag: History, Design and Variants

At a glance

The manual with Laycock overdrive

The standard box is a 4-speed manual. Overdrive was a popular factory option and operates on 3rd and 4th via a column or dash switch, giving an effective six ratios and materially lowering motorway revs. The engagement should be crisp; hesitation, drop-out or a refusal to engage typically points to the solenoid, its wiring, or the isolator switch rather than the overdrive unit itself.

On a test drive, engage and disengage overdrive several times in both 3rd and 4th, at temperature. Check for clean synchro on 2nd under a firm downshift, and listen for bearing whine that changes with clutch position.

The Borg-Warner 35 automatic

The Type 35 is a conventional 3-speed torque-converter automatic used across many British cars of the era. It is well suited to the Stag's torquey V8 and is generally the less troublesome transmission choice. Shifts should be smooth but positive; look for delayed engagement into Drive or Reverse, slurred or slipping upshifts, and any red or brown staining under the sump or around the cooler lines to the radiator.

Fluid should be bright red and not smell burnt. A neglected auto that is otherwise working can often be recovered with a fluid and filter service; a slipping or noisy box is a full rebuild.

Buying checks specific to an automatic Stag

Everything in the archive's buying guide still applies, rust, cooling and the V8's service history come first. These are the extra checks that only matter on an automatic.

• Cold engagement. From cold, select Drive and then Reverse with the brake held. Engagement should follow within about a second and without a heavy clunk. A long delay before drive takes up is the classic warning sign.
• Fluid condition. Check the dipstick with the engine warm and idling in Park, on level ground. The fluid should be bright red and smell clean. Dark brown fluid, or a burnt smell, means clutch material in the oil.
• Shift quality under load. Accelerate gently to third and then again firmly. Shifts should be distinct but not harsh. Flaring, engine revs rising between gears, indicates slip.
• Kickdown. At a steady 40mph, press the throttle fully. The box should drop a gear promptly. A lazy or absent kickdown is often the cable or its adjustment rather than the gearbox itself, so it is worth investigating before assuming the worst.
• Cooler lines and leaks. The Type 35 is cooled through lines running to the radiator. Look for red staining at the unions, along the lines, and around the gearbox sump. A weeping cooler line on a car already prone to running warm deserves attention.
• Selector and inhibitor switch. The car must only start in Park or Neutral. If it starts in gear, the inhibitor switch is misadjusted or faulty, a safety item, not a quirk.

Fluid and servicing

An automatic Stag asks for very little, but what it asks for is non-negotiable: clean fluid at the correct level. Most Type 35 failures on a classic are the end of a long period of neglect rather than a sudden mechanical event.

Check the level with the engine at operating temperature, idling, in Park, on level ground, a cold check reads low and tempts an overfill, which causes foaming and its own set of problems. Use the fluid specification given in the Triumph workshop manual for your car; several grades of automatic transmission fluid have been recommended for the Type 35 over the years, so confirm the exact specification and quantity against the manual or with a Stag specialist rather than assuming a modern universal fluid is appropriate.

On a car of unknown history, a fluid and filter change is the single most worthwhile job you can do to an otherwise healthy automatic. It is inexpensive, it tells you the condition of the fluid you drain, and on a slightly lazy box it often improves shift quality on its own. It will not save a gearbox that is already slipping.

Because the transmission is cooled through the radiator, the automatic has a direct stake in the health of the Stag's cooling system, see cooling and overheating. A radiator that is marginal for the V8 is also marginal for the gearbox behind it.

What the transmission does to values

In the UK enthusiast market the manual with overdrive is the most-wanted specification and generally sits at the top of the price band for a given condition; the automatic typically trades a little below it. That gap is a buying opportunity as much as a penalty: for the same money, an automatic will usually be a better car, better history, better paint, better mechanicals, than the manual you could otherwise afford.

Two things matter more than the gearbox itself. Originality: a car that still has the transmission it left Canley with is worth more than one converted either way, and a poorly executed conversion is a genuine liability. And condition: rust and a tired V8 will cost you far more than the manual-versus-automatic premium ever will. Current bands are set out in the market report.

Which should you buy?

• Buy manual/overdrive if you value driver involvement and long-term resale. Budget for the overdrive electrics to need attention at some point.
• Buy the automatic if you want a relaxed touring car, lower purchase price, and one fewer thing to fault-find. The Borg-Warner is a known quantity.
• Availability. Do not assume the automatic is the easier car to find. In the UK the manual, usually with overdrive, is the more common survivor; automatics were the more popular choice in export markets, above all the United States, so UK buyers often wait longer for a good one.
• Do not plan a conversion. Manual conversions are involved and rarely add value beyond the cost. Buy the specification you want.

When you have settled on a specification, see where to find one for sale and work through the buying guide before you view anything.

Frequently asked questions