Shop Talk: Installing a New Burman Worm and Nut Steering Box in a Vintage XK120 Race Car

Written by on March 13, 2013 in Jaguar, Shop Talk, Upgrades with 6 Comments
1951 Jaguar XK120 racing at Thunderhill in California.

1951 Jaguar XK120 racing at Thunderhill in California.

Guy Broad Parts in England, the world’s best supplier of XK parts, has just this month made available to XK 120 owners the last “unobtainable” part. The Burman worm and nut steering box is now over sixty-years-old and in most cases is catastrophically worn. The only option in the past for shops like ours to repair loose balky steering has been to continually tighten the adjusting nut on the top of the box. This was at best a temporary fix as it increased the wear rate, actually in some cases chipping metal out of the worm gear and the nut.

The drop-arm is free from the track rod pin and the last bolt holding the steering box to the chassis is being removed.

The drop-arm is free from the track rod pin and the last bolt holding the steering box to the chassis is being removed.

Guy Broad has apparently found someone to machine, at a rate that makes them sale-able, both the incredibly complex worm gear and the forged nut that rides on top of the gear. One of our customers purchased the first one to come to this country and asked us to put it in. The installation of the post and box, with a length of nearly seven feet, appears to be a daunting task. In fact it is rather simple with, as usual, the right tools. First, the car must be put on jack stands. The steering wheel and center horn button must be removed. Two locating brackets, one in the cockpit underneath the dashboard, and the other on the firewall in the engine bay, need to be slackened. The most difficult job, in an otherwise rather easy task, is freeing the pin that holds the track rod to the Pittman arm (“Drop Arm” in England). My dad, Peter Jurgens taught me a great and simple way to do this job without using a splitting fork that always destroys the rubber boot that holds grease around the joint. Underneath the steering box is a single long bolt (it secures both the upper A arm and the steering box and post to the chassis). It must be removed. The entire steering post will now slide forward and out of the car underneath the front fender.

Track rod pin just freed from the steering box drop arm.

Track rod pin just freed from the steering box drop arm.

To the customer’s orders, the new post had been painted the original gloss black. We transferred the old Pittman/Drop arm to the new Guy Broad post and box, and to make sure there was no slack in the steering system, we made sure that the arm was incredibly tight on the splines. We then did the reverse of the removal process. When it was in, we filled the new box with Penrite steering box grease, a product that is a pour-able but an extremely heavy and protective grease. The box needs to be topped up periodically and there is a filler bolt on top of the box for this purpose. Indeed, a dry steering box is the most important reason for the destruction of the original worm and nut.

Steering box about to be rotated into position.

Steering box about to be rotated into position.

Final tightening of drop-arm nut.

The owner had asked me to drive the car to our shop. He wanted me to make a comparison between the sixty-year-old box and post and Guy Broad’s new product. The car was utterly transformed from a heavy truck-like feel to a modern light and agile steering. If you’re interested in making an extraordinary change in your 120, contact Guy Broad.

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