Keeping it on the straight and narrow – Aspects that affect steering

Eric Worpe delivered a superb presentation at the MGCC ‘T’ Register’s ‘Rebuild’ seminar earlier this year. 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”. Here they are:

1. CHASSIS – is it true?
2. FRONT AXLE – Geometry – castor, camber, kingpin inclination angles.
3. FRONT SPRINGS – saggy, un-lubricated, floppy shackles, worn spring eyes.
4. KINGPINS – worn bushes, axle eyes & loose cotter pins.
5. TRACK ROD & drag link ends, worn balls and cups, poorly set up.
6. TRACKING set up, tyre tread & pressure.
7. ‘THE BISHOP’ – BC steering box.

In this issue we will deal with heading 1 (Chassis).

First, it is worth recording Eric’s introduction to his presentation as follows:

“Anyone looking at the Tabc Forever or T-Register forum internet sites would soon pick up that any discussions on the steering are likely to end up in internecine war.

One side will state that:

A TC needs to be driven with a gentle touch on the wheel and wants to be allowed to find its own path with only an occasional mild hint from the driver as to direction.

Whilst the other side will write,

Thanks to everyone who contributed to the steering debate. I’m afraid to say that I’ve been so frustrated by the steering issue that I’ve sold the car; one too many frights out on the road and nothing seemed to make any significant difference and I’ve reached the conclusion that the steering was not for me. I’ve now bought a nice TF”.

Most Tabc drivers’ experiences lie between these two views, some might not even realise the level of steering vagaries until they come across a hazardous situation. It’s unlikely that just one problem exists and so the whole steering system needs to be examined, akin to a holistic approach.

Gestalt theory states that the whole is greater than the sum of its parts and this may apply to the Tabc steering where the interaction between worn, badly adjusted or distorted components can produce an effect greater than anticipated.

I hope to look at seven aspects of the steering set up, which could be described as the seven deadly sins.”

This first part looks at the chassis and how the absence of any cross bracing can lead to lozenging of the two chassis rails. The diagonal measurements (Fig 1) are crucial in assessing any problems whether these are due to lozenging, bent front arches or bent side rails. The diagonal measurements should be within 1/8″ of each other.

Figure 1: the diagonal measurements should be within 1/8” of each other.

Hydraulic or screw jacks can be used to correct the diagonals or straighten the chassis; don’t be too surprised at how springy the chassis is, necessitating an over-correction which then relaxes back to the true shape.

Photo 1 shows a jig used to straighten chassis distortions. The screw jack is supported by a robust RSJ from which some moveable clamps are used to control the area over which the chassis needs to be corrected. Wooden blocks help spread the load and preserve paintwork.

Photo 1 – example of a jig used to straighten chassis distortions.

Inspection of the chassis prior to a rebuild cannot be over-stressed; various points that need reinforcing are detailed in Mike Sherrell’s TCs Forever! One particular weak point is just behind the cross-brace (Fig 2) that supports the radiator. The chassis is fully boxed up to about a couple of inches from the cross brace to chassis flange. The abrupt termination of the 4th chassis side sets up a stress concentration which needs to be reduced by welding in a “fish tail” section.

The underside chassis section of the dumb iron extension which runs forward of the cross-brace is also stressed, look for cracks or nicks in its edge which will propagate. Consider welding in a reinforcing strip along the edge.

Figure 2 showing the weak points just behind the cross brace which supports the radiator.

If the car has been shunted at the front, the dumb iron sweep might be distorted; this can often be detected by a dimple on the underside of the chassis rail just forward of the cross-brace. Look for the front spring shackle that doesn’t hang vertically.

Correcting a bent dumb iron sweep is difficult as the chassis is quite robust and considerable force is needed to unbuckle any distortions. My first attempt used a hydraulic ram and a supporting jig (Photo 2) but was unable to achieve a complete correction. This convinced me that a final correction may even necessitate sawing off the dumb iron section from a point two inches behind the cross-brace flange and then using a hydraulic press to iron out the bulge in the side rail.

Welding back the chassis needs a skilled approach using a strip of 1.5mm thick steel behind the chamfered joint area. The first weld pass should be with a TIG welder and should incorporate the steel strip in the root weld. After the initial TIG weld, the remaining void can be MIG welded and then reinforced with a fish tail section on the underneath running back from the flange supporting the bump-stop rubber.

Photo 2: Correcting a bent dumb iron sweep.
Photo 3 – TIG welding the chassis together.

Welding up the dumb iron accurately needs a jig as shown in photo 4 – this supports the front spring eye housing with reference to the tube in the chassis for the shackle rubbers and the underside of the straight chassis section.

Photo 4 shows a jig for use in conjunction with welding up the dumb iron.
Figure 3 shows a diagram of the jig attached to the chassis to enable the front dumb irons to be checked out and to set up the correct alignment for local welding repairs to the chassis, Although this jig is meant for a TC it can be adapted for the trunnion based TA and TB.

Ed’s note: In the next issue we’ll look at deadly sin Number 2 (the front axle).

And finally… rumour has it that one TC owner was heard to say to another “Steering a TC is a bit like riding a horse”, to which the other replied “Well at least the horse knows where it’s going!”

2 thoughts on “Keeping it on the straight and narrow – Aspects that affect steering

  1. George Cheney says:

    A comment about the importance of a “tight’ rear end might be in order. In my case, not until Bob Seymour of Abingdon Spares pointed out a loose right rear hub on TC5489, leading to new rear wheels, axels and hubs, did all my good work at the front result in superb steering.

  2. Brian Tyler says:

    After 18 months of driving my TC with it’s original Bishops Cam steering box installed, I have to confess to having gone over to the dark side. I needed more pleasure and less pain to me, and potentially my wallet so I took Mike Sherrell’s advice to heart and fitted a Datsun conversion steering box. There’s no going back! Bishops Cam will stay in residence in my garage rafters, while I drive around with heel of hand steering, convinced that I’ve just fitted power steering. My whole driving experience has been lifted from great, but! to ecstatic. I now have fingertip superb steering, way beyond any expectation, and a totally transformed driving experience.

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