Recently I took my TA in for its annual MoT test, using a local garage that is sympathetic to classic and vintage cars. I was fairly confident it would pass OK, having greased all the suspension, adjusted the brakes and checked all the usual things prior to taking it to the garage. The mechanic, who knows my car well, gave it his usual thorough check over. He had the front axle up on a beam jack and checked all the front suspension for wear and seemed quite happy. He then asked me how much vertical clearance should there be on the kingpins; 4 to 6 thou came my swift reply. You better have a look at this then he said, and using a long lever under the front tyre he raised the wheel. To my amazement there was what looked like a tenth of an inch movement between the stub axle and the front axle eye. I won’t fail it on that, but make sure it’s not the same next year when you bring it here was his response!
The MoT test took place only a week before we were due to go away in the TA to attend the “T Register Autumn Weekend” up in the Yorkshire Dales. I anticipated covering about 600 miles that weekend, so I thought I ought to correct the thrust clearance before departing on that journey.
The next morning I was out in the garage early, and had the front end of the TA up on axle stands and set about stripping down the offside front suspension. To remove the kingpin thrust washer requires the kingpin to be drifted out of the stub axle. The easiest way to do this is to remove the front wheel, remove the front hub complete, then remove the 4 bolts that hold the brake back plate to the stub axle and steering arm. Once you have removed the 4 bolts, tie the brake back plate out of the way with a large tie-wrap, making sure there is no strain on the rubber flexible brake pipe. Once you have done this it is possible with a set of feeler gauges to measure the clearance gap between the thrust washer and the front axle eye. In my case it was not as much as I thought, it was 39 thou, but was still way outside the 4 to 6 thou that is acceptable, so I made a note of the clearance. Now I could undo the cotter pin that locates the kingpin and carefully drift it out. I removed the small nut that holds the kingpin top hat and felt washer in place and removed them. I could now drift the kingpin downwards until I could remove the stub axle and old thrust washer from the front axle. It was now time to wash the stub axle, kingpin and thrust washer with Jizer ready for re-assembly. The old thrust washer thickness was measured using a pair of callipers and was found to be 120 thou thick, so the thrust gap was 159 thou (120 + 39). I had a new spare kingpin set, so I was able to measure the thickness of a brand new thrust washer, it was 124 thou. It was obvious that I needed a much thicker thrust washer, but where do you get those from without making your own?
My solution was to use a Torrington bearing as the thrust washer. This is a small flat roller bearing that is 78 thou thick. You need to put an hardened washer either side of the Torrington bearing, and these are available in 3 sizes, being 32, 63 and 95 thousands of an inch thick. I used the Torrington bearing with two of the 32 thou washers, this measured 142 thou thick. I was still 17 thou under size, so I used a 10 thou shim from an MGB wheel bearing shim kit. This gave me a clearance of 6 thou once everything was greased and assembled back together. I put the 10 thou shim at the bottom between the lower Torrington shim and the stub axle. One thing to make sure of is when you replace the 4 bolts that hold the brake back plate, stub axle and steering arm together, clean the threads and use Loctite on assembly. Repack the grease in the front wheel bearings and reassemble using a new split pin in the castellated hub lock nut. Pump the kingpins full of grease before using the car. I had hoped that the Torrington bearings would make the steering a bit lighter, they may have done but I am damned if I can notice it. The TA has the highest steering ratio of all the T types, and is heavy!
The photograph shows the Torrington bearing plus two hardened washers along with the old bronze thrust washer, plus a selection of MGB wheel bearing shims. I have listed the part numbers of the Torrington bearings and washers below, along with the prices I paid for them at my local bearing supplier in September 2011 to give you a guide to the cost.
Torrington needle thrust bearing for ¾ inch shaft, NTA1220, £2-80 each inc vat
Torrington thrust washer 32 thou thick, TRA1220, £1-94 each inc vat
Torrington thrust washer 63 thou thick, TRB1220, £2-76 each inc vat
Torrington thrust washer 95 thou thick, TRC1220, £2-82 each inc vat.
You can purchase a mixed pack of MGB front wheel bearing shims from Moss, part number ATB4242K (7 pieces) for £2-55. The shims come in 3, 5, 10 and 30 thou thickness.
Finally, if like me you also own an MGB in your stable, the MG Owners Club have for several years been supplying exchange MGB stub axles using Torrington thrust bearings in place of the old thrust washer/shims. They supply them ready pre-set and set-up, and you have the choice of needle roller thrust bearings or conventional shims.