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Triumph TR4/TR4a

Published: 10th Dec 2012 - 0 Comments - Be the first, contribute now!

Triumph TR4/TR4a
Triumph TR4/TR4a
Triumph TR4/TR4a
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A TR5 without all the hang ups – that’s the TR4. Mechanically, the TR4 and 4A are as tough as a pair of regulation army boots and can be made to outperform their bigger-lunged brothers, while the lighter four pot certainly aids handling. This Triumph sports car is easy to maintain and improve at home and you couldn't wish for better back up and support from both the many owners clubs and an army of specialists.

1: Engine Output

The trusty tractor-derived four pot can see around 130bhp for reliable, tractable road use which will see off many TR6s. A good, cheap mod is a simple session on the rolling road, paying attention to optimum mixture and ignition settings, with better air cleaners, then think about a sports exhaust. The ultimate mod is modern fuel injection set up with suitable ‘mapping’, but this is too exotic for road use.

Engine ideally needs unleaded additive or converting with hardened guides, as many reckon TRs were somewhat under-cooled when new, leading to head gasket woes. An uprated radiator, with perhaps an electric fan for good measure, is a wise step, certainly if you intend to increase the horsepower or take on some long hot touring drives next year.

2: Bottom End

The wet liner, tractor-derived engine can be stretched to 2.2-litres and provide TR6-levels of torque. For racing you’re looking at a lot of work and expense if you want more than 160bhp. At this level, the standard crank is not up to the job, so ideally needs a steel crank, conrods etc. Performance engines start from £3500-£5000 depending upon spec and rebuilder.

The wet liner design means that the bores can be re-sleeved ad infi nitum, which allows almost open ended engine life, provided these power units haven’t been horribly abused. Keep it around 60-70lb oil pressure and watch for oil leaks at rear of crank scroll seal which happens only when running.

3: Brakes

DBA discs with Mintex pads, are good fi rst step mods, at around £130. Wilwood callipers next, but these cost £500 alone. A cheaper alternative is to fi nd Toyota Hilux pick-up ones (1979-83). At the rear, discs can be grafted on, or you can use finned alloy Alfi n drums – both not needed for normal road use.

Bear in mind that TR4 disc brakes are in fact larger than later 5/6 type, so don’t assume it’s a good swap! Rest of the brakes pose no particular problems apart from routine service work. If wire wheels are fi tted, then check the spokes for looseness – a tap with a pencil is the usual policy. Conversion from rims to wires is very simple – but we like hub caps…


Uprated dampers and springs are a must for all fast driving; Neil Revington (01823 698437/ has a long history with TR4 and says great improvement can be made by just changing to polyurethane bushes. Revington TR, sells various upgrades, with a full suspension rebuild (including new poly bushes, springs, dampers and anti-roll bar etc.) costing around £1700. A TR6 anti-roll bar is a good cheap mod. Power steering from 2000/2500 can be adapted, apparently.

Front trunnions need periodic lubrication or you run the risk of seizure; ideally they should be fed with EP90 gear oil, not grease, but the latter is easier to handle with a gun and so usually used. The lower suspension wishbone mounting brackets can fall off so check them regularly.


Best ‘handling’ mod can be to fi t a new chassis (around £2500) to stiffen things up. D&G used to make even stiffer replacements; but is not around now. Some thought it actually made handling worse, plus generated more noise and creaks.

A TR that hasn’t been patched up over the decades is ultra rare. Most repairs centre around front and rear axles; if too bad consider a new chassis frame. Trailing arm areas are real rust traps. Body locating chassis outriggers – a common rot point, and often badly repaired – and the chassis arms located under the boot floor can also give trouble.

6: Differential

As with the Stag, the trend now is to install a tailored BMW diff that’s a bolt on kit for the As, even mating with existing hubs, but it costs almost £2000. But, apart from better ratios, there’s greater durability for the outlay.

Rust around the rear diff is common on As and can if bad lead to the unit tearing itself away from chassis, especially on hard driven cars! Infamous ‘Triumph IRS twitch’ can be reduced, if not cured, by ensuring that all U/Js are sound and poly bushing the rear suspension.

7: Transmission

Fed up with overdrive? Then the Rover LT77, Sierra or a Toyota Supra ‘box can be installed with modification kits. For those with overdrives, Revington advises a Logic Overdrive Device (costing £84), which replaces the existing on/off switch. Rather than keeping overdrive constantly in use, once selected, this is a ‘momentary’ device which disengages overdrive when you shift-up a gear.

Biggest problem is the usual Triumph thrust bearing wear – watch crank pulley move as aid works the clutch – if excessive the block is probably scrap. Layshaft problems not unknown and overdrive units can suffer oil leaks and electrical solenoid problems.

8: Body and Trim

The beauty of a TR is that virtually everything you’re ever going to need, either for routine repair work or a complete restoration, is available off the shelf from a wide range of sources. Best of all, trim quality is invariably better than when brand new! Talking of brand new, bodyshells are not technically available but TR Bitz has US-made RHD TR6 shells if you fancy making a hybrid as a project, but these cost around £5000.

Parts availability is excellent, with a wide range of items remanufactured or refurbished. As an example TR Bits can supply a front wing for around £425, and a vinyl hood for £170. A wood veneer fascia will set you back around the same. Keep that Surrey sound, as these tops are becoming hard to locate. If cabin ventilation isn’t good, it’s usually due to the air vent flap not opening properly.

9: Rear End

Conversion to telescopic dampers good mod but involved and dear. If keeping levers, ensure they are good quality recons. Converting a 4A to normal rear end – and vice-versa – possible but extremely difficult. Poly bushing trailing arms should be mandatory but will worsen refinement.

Clutch backlash and clonking could be worn drive shaft splines, although equally these could relate to worn universal joints. The drive train has six of them, and the only way to get at the propshaft is to remove either the differential or the gearbox.

10: Details

Keep on top of the cooling system and fit an electronic ignition to do away of fiddly c.b.points. You may need an Octane booster as some engines demanded five-star brews to prevent pinking (convert to unleaded head asap is our advice). Triumph used to recommend checking and adjusting the front hubs every 12,000 miles plus repack with grease if car is used in competition. Likewise over maintain those front trunnions to reduce wear.

Top Tips

The TR4 is catching up with its six cylinder brothers. An immaculate car can fetch £12,000 or more, while a decent, usable 4A should set you back about £6000 (you can knock about £500 from that for the TR4). If properly looked after these popular roadsters are one of the classic car world’s safest fi nancial bets. US expat cars are good choices, but most of the LHD cars in UK will have suffered R/H ‘swipe’ damage it’s reckoned.

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