Triumph · 1970–1977The Stag Archive

How-To & Repairs / Driveline

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.

Tools needed

  • Trolley jack and a pair of axle stands
  • Standard metric and imperial spanner and socket sets
  • Grease gun with clean, good-quality grease
  • Bench vice and a UJ press (or a suitable puller kit)
  • Torque wrench for the driveshaft and diff-flange fasteners
  • Circlip pliers and a soft drift

Parts needed

  • Universal joints (renew as a pair, both sides)
  • Fresh grease suited to driveline splines
  • Optional: complete CV-jointed halfshaft kit from a recognised Stag specialist
  • New self-locking nuts or lock-tabs as specified by the manual

Warnings

  • When dropping the rear suspension with CV-jointed halfshafts fitted, do NOT let the shafts overextend — disconnect at the differential flange rather than dropping the shocks, or the CV balls can dislodge.
  • Always support the car on axle stands, never on a jack alone.

Steps

  1. 01. Confirm the symptom, and rule out the wrong culprit

    Take the car for a careful drive and reproduce the twitch — a lurch or brief lock at the rear when cornering under power or on the overrun, sometimes with a clonk from the transmission. This is NOT caused by worn semi-trailing arm bushes, a common misconception; the source is the driveshaft sliding splines locking under load and releasing, worsened by worn universal joints.

    Warning:Do not throw new trailing-arm bushes at the twitch — they are not the cause.

  2. 02. Support the car safely and inspect the rear driveshafts

    Chock the front wheels, raise the back of the car and place it securely on axle stands. Rotate each rear wheel by hand and check each UJ for roughness, notchiness or free play. Check the driveshaft sliding splines for dry, dirty or seized movement.

  3. Owner-uploaded photo slot
    Rear driveshaft in place. The rear driveshaft on your car, showing the UJs and sliding-spline section.

  4. 03. Check the differential input-flange bolts for a metallic ping

    A metallic ping from the back on take-up can be loose differential input-flange bolts rather than a UJ or spline problem. Inspect the flange fasteners and re-torque or renew them to the workshop manual's specification before condemning anything more expensive.

  5. 04. Grease the driveshaft splines as scheduled maintenance

    As routine maintenance, dismantle the sliding splines, clean the old grease off and repack with fresh grease. Neglected splines are the underlying cause of the twitch — this alone often transforms the car until the UJs give up.

  6. 05. Renew worn universal joints

    Where the UJs are worn, press the old joints out in a bench vice using a UJ press or suitable puller kit. Fit new joints as a pair (both sides) and refit the driveshafts, torquing the flange fasteners to the workshop manual's figure.

    Warning:UJ removal takes a press — do not hammer the caps out of the yokes or you will distort them.

  7. Owner-uploaded photo slot
    Old vs new UJ. The worn UJ removed from the shaft, alongside the new joint ready to press in.

  8. 06. Consider the definitive cure: CV-jointed halfshafts

    For a permanent fix, fit modern CV-jointed halfshafts from a recognised Stag specialist. These remove the sliding-spline mechanism entirely and, in doing so, remove both the twitch and the transmission clonk. Follow the specialist's fitting instructions in full.

  9. Owner-uploaded photo slot
    CV-jointed halfshaft fitted. A specialist CV-jointed halfshaft fitted in place of the original.

  10. 07. Road-test progressively

    After any driveline work, road-test progressively — gentle cornering first, then progressively harder power and overrun tests — and re-check every fastener you disturbed at the end.

Related faults

Further reading

Figures and procedures should be confirmed against the official Triumph workshop manual; for safety-critical or specialist work, consult a specialist.

More guides