The Lotus Grand Tourers

Don't need to add much more. How is it checked?
Workshop manuals great at describing how to change it and that 4 deg +/- 0.5 deg is the aim, but no info at all on how to check.

Edit : Oh and my understanding is positive castor is when top of upright leans towards rear of car. Am I right?
Tony

To check it you really need a dedicated gauge. The principal is that it's measured the same way as camber, but for castor you turn the wheels one way by a defined amount (the actual angle of turn can vary but the point is for it to be a known angle and be the same when you come to a later stage), you measure the angle of he wheel relative to vertical, then turn your steering the other way by the same amount as before, measure the angle relative to vertical. Then it's just maths to work out the difference and more maths to take account of how far the steering moved, to come up with the angle of castor.

I have one of these.

https://www.ebay.co.uk/itm/231965586702 ... R5jCiZOXYQ




..... they are a bit pricey, but you can get nearly the same for around a tenner on eBay (Search "Camber Castor Gauge")

I've got the same gauge. The trickiest part is getting it to fasten on - magnetic!

Pete

Anyone got a cheap 'n' cheerful gauge and can comment on performance?
Do these gauges need the car on level ground or are all measurements relative to your starting point ? My drive is on a slope with front wheels high, then it's currently jacked up at front even higher.

Tony

Definitely needs to be level, if wheels are high at front then the reading would be artificially high because it would indicate a lot of lean when doing the reading at the front of the wheel turn but then read low when doing the reading at the back of the wheel (by front I mean the RH wheel when on LH down steer, and so forth).

I have some turntables for the front if you want to borrow them. Just a matter of then getting the back at the same height with bit of plywood.

Pete

I bought a camber bar to use on the rims. Had to adapt the bar to accept the magnetic camber/castor gauge. The round plate is a spacer from a top strut mount off a Nissan micra IIRC.

The rim lugs are set for 13 inch rims (Clan) in these shots so the bar is not sitting on the Excel rim correctly in the last shot. To rotate the wheels for castor, I would sit the tyres on NEWSPAPER or CARD. This, along with the painted ramp surface, is sufficient for easy turning. You would need an assistant to turn the steering whilst you note the readings!

Time to share why I was (am) interested in Castor angle measurement.

I've changed the rubber lower link bush to Poly during the rebuild of my suspension. When dismantling, the whole area was very rusty and seized up, hence although I measured total shims fore and aft as best I could, I had to drill through them to get apart and the rust made measurements questionable. In summary though, I recon I had about 16mm on the O/S and 17mm on N/S.
Then there is the complication of whether the dimensions of the poly bush are identical to the rubber and also if it should have the same compression ?
Finally, the parts list and service notes I have are rather vague regards the combination of ARB and required total shims, even to the extent that Section CA shows a ½”UNF thread variant of ARB, that does not appear on the parts sheet. Is there a later version of service notes than CA?

In simple terms though, it seems the later the car was manufactured, the larger the build up of shims required. I presume the land on the ARB was lengthened so the extra shims give more castor adjustment, but it could also be that there was a desire to increase the compression on the bush. Many car’s have roll bar B089C0183F, which it seems should have 4 x 2.5mm shims per side, but from around 1990, roll bar changes to C089C0183F, using 4 x 4mm shims. There is a note to “See S/B 1990/03”. A Service Bulletin ? Anyone got a copy ? Presumably this last change only affects the latter half of the MY 89 production. – Which is where my car sits.

Supplier of the Poly bush recommended about 3 -4 mm of compression. I would have needed 10mm of shims to just nip the bush, so about 14mm of total shim , which is less than the 16mm from the parts list. As best I could, I put the same thickness at the leading side as I had with the old rubber bush, but it’s quite possible I’ve altered the Castor slightly. It’s rebuilt now so I’ll see how it drives and get checked at some point in the future.

Anyone got any experience with required compression between rubber and Poly bushes?

Tony