OTish: Turning circles

they didn't unscrew. the pin rusted and the rust wore the brass away very quickly and then there wasn't enough thread to keep it together and they separated.

I think they did.

What 'pin'?

Sort of. If you have a tension joint where one part swivels on another via a thread, that thread (therefore) *will* screw and unscrew slightly, each time the steering is turned, then the chances are it will eventually let go when the last remaining thread (or remains of the threads) are *unscrewed* away from (therefore) what would be the least worn thread (e.g. the tightening end of the movement) and then would let go. Just the same way as would happen if you were undoing say a rigging bottle screw under tension and the end most likely to give (possibly strip threads) will be the end with the least number of threads engaged. QED.

This same process wouldn't happen to say a king pin because there is no 'thread' holding the two parts together, or even a ball-joint at the bottom of a strut.

Cheers, T i m

This was in 1965 or thereabouts, I don't think Escorts were even in existence then. Fiestas certainly weren't, I worked at the factory in Spain where they were first produced, and that was a lot later.

I recall changing one, where I could have sworn the play was the same after as before.

The secret was then in using a thick a grease you could lay hands on to take up any perceptible play!

It was a half hour job to replace the plastic bushes in them which I did about every 6 months

According to the Isle of Wight online newspaper sites, there are a very large number of single-vehicle accidents in which a car has rolled onto its side/roof, on narrow roads or at junctions where the car can't have been going more than about 20. I'm sure IoW cars are specially modified to raise the centre of gravity or else IoW drivers drive like a bat out of hell in town centres.

There was a model of small Mercedes that failed the 'elk test', possibly an 'A' type. I rented one, and it was terrible.

A class, yes, and it was tweaked very quickly so it passed. The one you rented would almost certainly have been post-tweak and have passed.

The axle went trough the bit of metal with the thread on so at most it could unscrew by about 70 degrees and then you wound it back the other way as you steered.

The male thread that screwed into the trunion.

If it didn't have the axle for the wheel on it maybe but you can't keep turning it in one direction with the wheel attached.

Correct - it was the Anglia 105E as the small Ford.

Axle? We are talking about the front steering / suspension on a Morris Minor? All you had on the front axlewise was the 'stub axle' as part of the front leg?

Correct, so it screwed in and out as you steered.

Ah, yes, that 'pin'. ;-) So, that was like a bolt rusting inside a nut and so the threads would slowly diminish.

Correct, so yes, you can't ever *fully* unscrew it in normal use but it does screw and unscrew in normal use because it is 'pivoting' on a thread.

So, the top trunion is taking the (mostly) vertical shock loads as a result of the dashpot damper and some of the side loads as generated by cornering and braking.

The lower trunion is typically taking 50% of total weight of the front of the car (vertically) and more with side loads when you braked and cornered.

That was why it was the bottom one that pulled out, dropping the car / wheel arch onto the wheel, generally as you turned, rather than braked.

So, like pulling the plastic handle off a wheelbarrow, it's easier to do as you twist it. ;-)

Cheers, T i m

Yes a axle that stops you turning the pin enough to unscrew it.

Not slowly, the brass would wear pretty quickly once the seal went and the grease went away. Rust is harder than brass.

Like I said it doesn't unscrew it fails due to wear

it isn't (just) the (stub) axle that (typically) stops you completely rotating the pin (but not sure why you feel that is pertinent. No one has ever suggested the pin would 'unscrew' (as in completely) in any normal use).

You can't really use time as the car could be laid up. It's use that would accelerate any wear (be it just poorly /un-lubricated (the typical cause)) or 'rust').

Yes and like I said, 'of course' it fails once it is worn out but / typically *and* turned (or people would come out and find them collapsed on their drives or them collapsing under braking and they generally didn't).

They finally fail when the load exceeds the abilities of the remains of the thread *and* the vehicle is turning ... and that's exactly how, when and why mine went. Given a gentle turn, it's more likely the joint will fail when being unscrewed as there will be less thread in contact with the least used (lest bad) section of thread. ;-)

Cheers, T i m

Is that the same as a moose test? Some of this looks fun:

The extra weight (assuming fully loaded) changes the geometry of the suspension.

CV joints for higher torque have reduced angles. A 4wd car only needs

RWD CV joints don't have to allow for 30-40 degree steering angles, just a few (10-15) degrees for suspension movement.

Many 4wd vehicles have smaller front differentials compared to the rear as they have to fit in the sump. These fail if abused. This limits the amount of tuning that can be done as they are hard to uprate.

My RWD Nissan 200SX hatchback has 9.5m turning circle (kerb to kerb, not wall to wall). The rear axle has been proven good for over 500bhp. The only FWD cars with comparable turning circle have less than 60bhp. The turning circle also translates into Yaw angle, more yaw = more style points.

Toyota GT86 has 10.8m turning circle so will need substantial mods to get a good yaw angle for winning style points. But there are two cylinder heads that define where the inner wheel arch is, which limits the wheel turning angle. So the front track has to be made much wider.

Ah. Good point about a 4WD car being able to share its torque among four rather than two wheels. Not sure it applies in our case because (as I understand it) the Honda CR-V is normally 2WD and only sends power to the rear wheels if it detects that the front wheels are losing traction, rather than being permanent 4WD.

My Peugeot 308 has a much better turning circle than my wife's Honda, and when we were looking to get the Honda we were worried about whether it would be a problem reversing onto our drive if anyone parks directly opposite our drive (*), limiting the space for lining up the back end and swinging the front end round. Luckily it's not been a problem, though we've had to go onto the grass verge a couple of times when there's been insufficient room.

(*) The houses on our side of the road have drives. Those on the other side don't - they have a communal parking area a hundred yards up the road. People have a habit of parking directly opposite our drive, outside the gate to their garden path, which is frustrating when they could park a car length either way so as to be *between* our drive and either of our neighbours' drives. I suspect envy and bloody-mindedness: firstly that we have drives and secondly that we own our house (it used to be a council house but the previous owners bought in in the 1980s right to buy) whereas their house is still owned by the housing association.

No, they don't. They just have to be bigger.

Are you sure about that?

It certainly isn't the case on mine. Or any other Land Rover I have seen.

I cant remember seeing a gearbox in the sump since the Austin Maxi actually..

someone else remembers...

.."the last engine to be in-sump was the BL O Series as used in Princess, Ambassador, Sherpa, Marina, and Montego, ending production some time in the mid 90s"....

Its simply not done. The gearbox is either off the side of a transverse, or behind it, or in front of it.

Fora fore and aft engine, its behind it, with any FWD going forward to a front diff and drive shafts under the engine.

Apart from cars like the Renault 6 and maybe the early first series Renault