Keeping it on the straight and narrow – Aspects that affect TA/TB/TC steering (Part 5)

Eric Worpe delivered a superb presentation at the MGCC ‘T’ Register’s ‘Rebuild’ seminar in March 2013. Eric used flip charts to aid his presentation and I have been working with him to ‘flesh out’ the flip chart notes to produce a series of articles for inclusion in TTT 2.

Eric divided up his presentation into seven headings which he termed as “Seven Deadly Sins”. We have so far covered the first four ‘Deadly Sins’ i.e.

CHASSIS – is it true? – Issue 19 (August 2013).
FRONT AXLE GEOMETRY – Issue 20 (October2013)
FRONT SPRINGS – Issue 21 (December 2013)
KING PINS – Issue 22 (February 2914)

In this issue we’ll look in depth at the fifth ‘Deadly Sin’:

TRACK ROD AND DRAG LINK ENDS

Over to Eric…

It’s with some trepidation that I’m writing this section, not so much because the subject has already been covered by an excellent article from Doug Pelton – (Totally T-Type 2, issue 5, April 2011) – but by what Jeremy Clarkson of Top Gear fame has to say, and I quote:

“To me a track rod end is probably the dullest thing in the world, but to MG man it is a steel deity, an almost religious icon, an auto-motive Fabergé egg. MG man can talk about a track rod end for two hours without repetition or hesitation”.

I’m not sure whether to carry on now!

One significant point made in Doug’s article was “do not trust the assembly order from the previous owner”. This was illustrated by the experience of an acquaintance, who had paid a hefty sum to a well known dealer for his TC. Whilst examining the steering I discovered that the drag link end connected to the drop arm (and hangs upside down) could “pop out” when forced with just one finger.

The previous owner must have been aware of this as a split sleeve made from brass shim covered the aperture in the drag link end to help retain the ball. A good look revealed that the end plug could not be screwed “home” due to dirty threads and most significantly the neck of the aperture in the drag link end was enlarged sufficiently to allow the ball to pass through.

As can be seen from Fig. 1, the slot should be narrower than the diameter of the ball necessitating assembly of the ball and its stud fixture through the open end of the drag link end. However, due to poor adjustment, the neck of the ball’s stud had worn away one side of the aperture of the drag link end. The drag link ends need to be positioned relative to each other such that the connecting link is free to rock from side to side as determined by the clearances around the neck of the ball’s stud fixture. This also applies to the track rod, so check that both are free to swivel at least 25 degrees.

The Pitman arms or drop arms seem to have a variety of bends altering the vertical position of the drag link end attached to the drop arm. As clearance does not seem to be an issue, the possibility arises that the arms were modified to position the drag link to help minimise “bump steering” It’s for this reason that the drag link is made as long as possible by attaching it to the near side’s stub- axle’s steering arm.

The main contribution to “bump steering” comes from the vertical deflection of the near side wheel altering the horizontal angle of the drag link. The geometry of the beam axle and drag link is such that in not sharing the same pivot point, a differential movement is generated between the stub axle and drag link end attached to the steering arm as the wheel moves vertically. Any such differential movement results in the forced deflection of the front wheels. To minimise “bump steering” the drag link should be positioned in the same horizontal plane as the beam axle, hence the need to position the drag link end attached to the drop arm correctly.

To what extent “bump steering” is an issue is hard to say given the limited deflection of the front suspension’s springs. However, the stiff suspension transfers significant deflection to the chassis, which in turn contributes to the “bump steering” effect anyway.

Both track rod ends are spring loaded, such that the front wheels can splay outwards slightly by compressing their internal springs by an amount equal to how far the end plugs have been “backed off” during adjustment. Most advice suggests that after the plugs have been screwed fully home, they should be unscrewed by 1⁄4 to 1⁄2 turn to the nearest split pin slot.

The pitch of the thread form is 20 TPI, so both springs can be compressed up to 25 thou. each, which is amplified up to about 100 thou. total movement of the wheel rims, resulting in a tracking offset of 200 thou. (front of rims compared with rear of rims). This would seem to make up the bulk of the toe-in compensation needed due to the splaying out forces on the front wheels as mentioned in the section on front axle geometry.

Both drag link ends are also spring loaded, but in such a way that small deviations of the wheels in either direction are absorbed by the springs, thus reducing wear in the Bishops cam box but also contributing to some vagueness in the steering.

Both track rod ends together with the drag link end attached to the nearside wheel’s steering arm are of the type shown in Fig. 2 and sit on top of the ball, making it more secure. These have an alternative design consisting of a flange on the ball’s stud fixture and a 1⁄2” dia. parallel shank to fit into the steering arms. The ends have a figure 8 aperture composed of a small and larger diameter hole. The ball end should not be able to pass through the smaller diameter hole, which is where the neck of the ball’s stud resides if correctly assembled.

The open nature of the ends allows abrasives and water to contaminate the grease, so frequent greasing is needed to purge any old grease. An occasional dismantling, inspection and clean up should be considered with a look out for wear on the ball ends and cups.

Serious wear on the balls can sometimes be revealed by a stiffening of the steering towards either lock, when both wheels are jacked up and free to swivel. Such an assessment is only meaningful if the ends have been adjusted correctly. Alternatively, the balls can be measured with a micrometer to check for ovality.

Fortunately, the balls are obtainable individually, unlike the cups and springs which seem to be only available as part of a complete replacement end.

Whilst dismantled, check that the hollow track rod and drag link have end plugs fitted, otherwise most of the grease pumped in will simply fill up the hollow tubes.

Combine all the influences from road undulations on steering due to free movement in the track rod and drag link ends, bump steering, unequal camber and wheel offset forces, play in the steering box and less than rigid shackles or worn trunnions, and one is left wondering how well over 50% of the TA/B/Cs have survived.

You might like to consider fitting butyl rubber sleeves made from a bicycle inner tube (type meant for 1.5 to 2.1 inch tyres) over the track rod or drag link ends. A 2 inch length with a 1⁄2 inch dia. hole punched in it for the neck of the ball might help keep the grease free from beastliness.

Ed’s note: I’ve published the following before (in TTT 2, Issue 14) but make no apology for publishing it again:

Nothing could have illustrated better the value of a proper steering check than the experience of one of our readers, who might well have been left with no steering due to the wear in the casing of the drag link end. To quote from his experience:

Whilst turning the steering wheel backwards and forwards the MoT Examiner noticed that the drag link end was moving vertically up and down before moving the road wheels. A ‘fail’ certificate was issued and the owner drove the car home slowly.

Upon disassembly it was found that the inner shoulder in the “tube” that supported the cup had worn away allowing the cup to tilt, which in turn moved the tapered peg over at an angle. This caused the slot in the casing to wear away, allowing the ball to protrude through the slot which would have eventually popped out.

A proper steering check is available when the car is presented for a MoT test where the operation of the steering is thoroughly examined from below, or via a safety check by a competent motor engineer.

One thought on “Keeping it on the straight and narrow – Aspects that affect TA/TB/TC steering (Part 5)

  1. Duncan MacKellar says:

    It could be of interest to note one error in this otherwise steller article. Perhaps it had been edited out. Author notes the threads on the end links and rods is 20 tpi. Actually, I can speak only for the TC, original rods and ends were .656″ x 19 tpi, and at some point replacement parts began coming out with 5/8″ x 20 tpi. This concurs with moss motors description.

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