Increasing caster

[Nero]

I would like to increase caster on my car to around 5 and possibly 6 degrees total. I am running wider radial tyres (185/60/14) and telescopic dampers, but I get little self centering effect.
I have difficulty with some of the basics: I cannot simply angle the eye bolt as the torsion bar is fixing the KPI to some extent. I had wondered if the lower arm could be pulled forward, but I am also concerned that the swivel pin and trunnions may not take kindly to any bending load (I should also add that the suspension is in a Rochdale Olympic and not a MM).
Does anyone have any advice?

[Kevin]

You need to contact one of the modification specialists to find out exactly what can be done.

[bmcecosse]

As long as you have rubber bushes you will be able to increase the caster by simply shortening the tie-rod. As standard these came on a Minor with a square 'spacer' which sits between the locating fork and the lower arms. Removing this will improve the caster slightly. You may be able to make (or modify original) a slightly shorter fork - but more likely you will need to cut the tie-rod - shortening it slightly - and thread the cut ends, and make a joining piece threaded through so you can adjust the length - lock nuts on each end would be good too! Ideally it should be left and right threads - like a turn buckle - but that's going to be v difficult.
Have you tried a bit of negative camber - by simply spacing the eye-bolt outwards by say 1/4"? This will help handling quite a bit - and automatically increases the caster slightly too!

[Nero]

Thanks for the responses.
I am using poly bushes and currently have 1 deg of neg camber, which required 11mm of spacer (Rochdale quality control was less than the Morris factory!). The Rochdale Olympic did away with the tie rod and instead used a sway bar to fulfill the same purpose.
My car does get used mostly on the road so I do not want to investigate too radical a modification e.g. spherical bearings top and bottom etc.
One thought was that I could mill down the rear of the lever arm damper on an angle to move the top back, but I still have concerns with the trunnions.
I did notice that the marina had/has a top ball joint, yet a trunnion on the bottom, which would alleviate some of my concerns...is there any interchangeability between the MM and Marina swivel pins?

[MoggyTech]

This could be tricky as you risk wearing the trunnion and KP threads, if too much lateral force is applied due to modified suspension geometry.

Not sure why you are not getting enough self centering. My traveller is running 185/60R14 boots with minilite alloys, 1 degree neg camber 2.5mm toe in, and the steering is very light. and centres fine.

What wheels are you using? and is the offset the same (or close to) the standard Minor wheel?

Perhaps too obvious, but have you jacked the car up at the front, and checked that the steering rack is easy to turn?

[bmcecosse]

I think you will either need to move the 'sway bar' (i'm guessing anti-roll bar) forward slightly - or somehow shorten it's fixing to the lower arms. I think fiddling with the damper arm will be difficult.
I wouldn't worry too much about the trunnions - you are only considering slight radial modification - just grease them with Moly grease. Anything is possible of course - but Marina parts won't be a straight swop. That 11mm of spacer would worry me - depends how the eyebolt is located in the chassis - but special 'longer' eyebolts would be a better bet. I suppose you could heat and bend the two halves of the lower arms forwards slightly - bit of a radical mod - but should work ok.

[Nero]

Oh yes I have checked the complete front end. The car has not had a wheel alignment which it badly needs and the steering is light and feel-free. I have put rack stops to limit rack travel, as MM racks have a reputation of breaking locally.
The wheels are custom made with a 22mm offset.
bmcecosse my car will be used for motorsport and should easily reach the long side of 120mph...in such circumstances you mind focus very much on the parts of the car that worry you!
The 11mm eyebolt spacer is welded to the steel subframe so that the end of the eye bolt is supported.
I did not mean modifying the arm itself but did mean modifying the rear mounting face of the damper.
Heating the arm and bending it is illegal here in Australia.
I might get my hands on a marina swivel pin and see how the top ball joint is attached.

[sii803]

When changing castor angles you need to give consideration as to how this will effect the camber angles when the wheels are turned. The castor can account for half of the camber during cornering.

[bmcecosse]

Which is exactly why you would want plenty of castor - in fact all you can handle! More castor = more -ve camber on lock and helps cornering no end. Looka t any modern car parked on full lock - the 'outer' wheel will have very considerable -ve camber. Of course - it has power steering to handle the load. The arm 'bending' would only be slight - I still think best method will be to move the 'sway bar' location on the chassis forward slightly - thus hauling the suspension into more castor. I understand your plan for the top suspension (damper) arm - it will work ok and may be best way forward - just wondered if there was an easier way! Not ever heard of Minor racks breaking - where do they break ?

[RogerRust]

(I should also add that the suspension is in a Rochdale Olympic and not a MM).

I didn't know what a Rochdale was so found this link
Rochdale OC

very nice too!!

[Nero]

Thank you...I like them....apart from the poor access to certain parts of the car!
The racks have a reputation for breaking in 'specials' as there are no rack stops and I have been told that the pinions break...I have no personal experience, but bear in mind that Australian Roads are considerably rougher in parts than what you would see in the UK.
I will have another very close look at the front suspension this weekend.

[Nero]

Has anyone ever gently heated the forged suspension arm and then twisted it? I wonder if this and the subsequent heat treatment is the answer for an additional 2-3 deg of caster.

[jonathon]

Not too sure that I'd attempt this, two reasons I don't like the idea of heating cast steel on a suspension item plus two it will change the orientation of the botton trunnion pin hole.
Can you not fit an adjustable tie rod, or modify the eyebolt pin and retaining cup to allow the thick arm to be spaced further forward equally along its length.

[Nero]

is it really cast steel...for some reason I thought it was forged?
I actually want to alter the trunnion angle to reduce static loads if I increase caster to 5-6 degrees.

[jonathon]

"Heating the arm and bending it is illegal here in Australia."

Think this gives you the answer to this specific question.
You will need to modify both arms if you wish to alter the trunnion angle. I'd still go for moving the whole arm forward with an eye to good engineering

[Nero]

Ha!..yes it is still true, however I can get the modification certified as safe...I would not be doing it myself in any case.
I understand what you are saying WRT moving the lower arm forward. It would be easier for me to move the top arm rearwards. Once again I am concerns at the increase in load on the trunnions.

[bmcecosse]

Don't worry about the trunnions - just grease them regularly and keep an eye on them - you are only changing the angle very slightly.