Don't buy top plate shims for bishop cam steering from Moss

[Duncan M]

Recently have been going through my front end of MG TC with very low miles. Got to the dreaded Bishop Cam steering box and found all to be in good condition. These units require adjustment now and then to the front plate end play and the top plate. The top plate adjustment is done with the steering in the dead-ahead position, as the sector shaft lifts slightly in that position; which helps in straight ahead driving. Every quality source of information on adjustment of these boxes agree that metal shims are a must. We are talking about very precise tolerances here, and shims must not expand and contract; so either steel or brass shims are used. I ordered some top plate shims and end plate shims from Moss when I installed a new peg on the sector shaft. The top plate shims are not cheap, $4.65 each for .003" and .005" and .010," while the end plate shims run about $3.30 for the .003" and .005" and $14 for the .010". Abingdon Spares LLC was in the process of moving to their new location, and I noticed their top plate shims (same sizes) were .35 cents to .95 cents, while their end plate shims were more evenly priced for about the same sizes, running around an average of $7.50. I figured their top plate shims were likely not metal at Abingdon, so did not wait and ordered from Moss. The end plate shims were accurate dimension steel shims. Their top plate shims were a huge disappointment. The .003" came in a floppy rubber type plastic. The .010 were paper gasket (cheap) material. To add insult to injury the .003" were closer to .002" and the .005" must have gotten scrambled on the phone as I received some odd MGA shim with a similar number. While waiting for the shims I had already done a preliminary top plate adjustment using different thicknesses of paper gasket material, along with the metal ones I had. Now I know exactly why all sources say to use metal shims; as that temporary adjustment lasted about 3 days before the paper had swelled and the preliminary adjustment was no longer any good. And that was after sealing the gasket material shims I had made. So what gives, Moss Motors. USA? Anything besides metal top plate shims are just plain dangerous. $4.65 for useless paper shims?

 

[Brinkerhoff]

Duncan , I am also running the stock Bishop Cam box in my TC . Don't fool with the standard plate and shim setup , use the Tompkins kit that has an adjustable pin built in to set the adjustment. Its one of the many perfectly acceptable modifications to a TC. The way to go ultimately is to change to a VW steering box ,for safety and ease. Kevin

 

[Duncan M]

People assume the sector shaft rotates in a circle when they put on one of those Tompkins kits. It does not. This article should be read by anyone with a Tompkins kit. https://ttypes.org/ttt2/?s=bishop+cam&submit=Search Read the whole thing, but especially above and below pic 3 of broken shaft. It gives you what to look for as a warning sign for impending breakage. My parts are in excellent condition, and I don't want to upgrade everything so I can run a Tompkins kit. I would rather spend the money on a non peter edney vw convert. I don't mind doing a little adjustment from time to time, as it allows me to inspect the box each time I do. I think those Tompkins kits have accelerated the need for Datsun and VW kits dramatically over the years. They are based on a flawed theory of operation for the BC box. But, if a new, hardened steel sector shaft fell in my lap, then I would consider using a Tompkins kit.

 

[Brinkerhoff]

You could be correct. It looks like the sector shaft broke because the adjustment was overtightened , which would have been the tendency to do.

 

[JPSmit]

as an aside, make sure Moss knows, a few months ago we had a moss employee or two on the forum and they seemed genuinely interested in feedback on their products.

 

[Duncan M]

You could be correct. It looks like the sector shaft broke because the adjustment was overtightened , which would have been the tendency to do.

I think the article was saying to only use modern, hardened steel sector shafts with the Tompkins type adjuster. Also, if you are using a Tompkins kit and you notice any increase in the frequency of needed adjustment, you could well be in for trouble.