McPherson top mount questions.

A proper macpherson strut set-up has a bearing above the top spring mount to allow for free rotation of the spring.

If it didn't the vehicle would be pretty much undriveable.

Ok ..

That must be many vehicles then Moray as this Escort certainly never had such a bearing (since 1978 and it's not 'missing' as there is no place for it) ?

I just watched the top of the damper rod on my mates Mondeo and that didn't move as the steering was moved left to right (not lock to lock mind you but quite a bit).

A reason I know there is no top bearing on the Escort and the road spring does in fact wind and unwind as you steer is when changing the springs previously I didn't 'centre' the damper rod in the top mount as I re-fitted the to the car and it then the car pulled to one side? I released the top nut, let the spring turn it into it's correct alignment and when I re-tightened (locking the top spring cup to the top mount) the car drove straight again?

I'm not suggesting the system it good, just that's how it seems to be on some vehicles (and therefore going to cause me a problem unless I also convert the top mount to a bearing type).

All the best ..

T i m

p.s. The top item on the following link looks like a modified version of what is in my car.

?CCode=PC210 The third item down is a cheaper alternative to the modified rubber type. I assume the bearing is 'self aligning' to allow angular movement?

No, you won't see it move from the top - the bearing is under that bit. There is a plate with the three mounting studs, under which is the bearing which allows movement. Below that is the top spring cup.

A picture paints a thousand words - so have a look at this which is prettery clear:

Ah, thanks, so that's how it works for those vehicles that employ a bearing etc.

Yup, again that makes good sense but *not* how it appears it's done on the old Escort. :-(

The exploded view of the leg (in the HBOL) looks similar to yours other than you have the top spring cup resting directly underneath the rubber top mount (or a steel bush running through the rubber) and bolted tightly to it by the top nut.

In the book it describes the top end as: "The upper end of each strut is secured to the top of the wing valance under the bonnet by rubber mountings". Also "The upper mounting assembly consists of a steel sleeve with a rubber bush bonded to it".

The top of the damper rod has a 'D' profile and that aligns with a similar shape in the top spring cup. Sitting above the top rubber mount is a winged 'U' shaped thing [1] that has a tab on it that matches a groove cut into the threaded part of the damper rod where it protrudes through the top rubber mount. If you were to leave the top nut slightly lose and were to rotate the top spring cup with your hand you would see this 'U' shaped thing rotating in harmony (because they are directly linked via the D cutout on the damper shaft and the tounge / grove on the top U bracket thingy.

And this is important and why you are offered the option of the 'D' shaped spring cup ...

Please see the 6th item down.

So, if I use item 6 which positively registers the damper shaft to the top of the road spring and the vehicle, what happens when the bottom of the spring tries to rotate compared with the top when you steer?

All the best ..

T i m

[1] I think this top winged U shape thingy is to stop the leg falling out of the top mount should the rubber bush fail.

Coilover simply refers to the fact the coil fits over the damper, it doesn't necessarily mean it's a machpherson strut set-up.

I'm not familiar with mk2 escorts (well before my time!), but going by the pictures in that link, coil wind-up won't affect the steering, as it's not a machpherson strut system. A macpherson strut is where the hub carrier is mounted directly to the bottom of the damper/spring assembly, and the whole spring/damper assembly turns with the hub. Some the entire damper is mounted below a thrust bearing, so the entire damper turns, whereas other the thrust bearing is mounted between the end of the damper rod and the top spring mount, so the damper rod remains stationary, and the coil turns. If you remove the bearing from either set-up, the steering can be hard to turn, might not self centre, and/or be subject to bump steer, due to the spring wind-up causing the lower part of the strut to react/rotate against the top mount.

The set-up shown in the pictures for the mk2 conversions at the above link, is a basic coil over strut. Spring wind-up won't affect the steering, so there is no need for a thrust bearing.

Mine has a bearing at the top. Without the free movement allowed by the bearing, the steering would be always trying to pull itself back to the pre set position.

Understood.

This link you mean?

Correct, there will be no coil wind up because of the top bearing.

Ok ..

As per the above link etc?

Understood. Removing the bearing from a bearing system is probably a bad thing.

Hmm. I'm not sure what we are looking at here but *my* 1978 1300 MKII Escort based kit car has no bearing, the top spring cup is held to the vehicle and the lower spring cup to the lower leg / stub axle.

So, when you steer the bottom spring cup *will* (attempt to) turn the bottom of the spring whilst the top of the spring is held stationary. Well, assuming the spring doesn't slip against it's mount (top or bottom) and if it did I'm not sure how long the mount would last?

So the question remains, what do I do in this case? The question arises because I am indirectly modifying in a fairly subtle way the way this vehicle works. The modification in itself isn't unusual on many rally Escorts / Capris and potentially why they sell such conversion accessories? Why would they offer a bearing top mount alongside the coilover conversion if it wasn't needed or potentially essential in some circumstances?

All the best ..

T i m

And that's another thing that concerns me Harry. *If* I remove the spring steering centering by fitting a top bearing, how well will the steering on this particular vehicle self-centre (I assume it's ONLY the steering geometry that makes most modern vehicles self-centre)?

Some facts for the pot:

"We built this kit over 18 years ago using mainly unmodified components from MKII saloon.

The steering has been light, positive and self centering (the only time it wasn't self centering was when I didn't lock one of the springs central).

I have stripped these struts down several times over the period we have had the kitcar (broken spring, new damper inserts etc) and I can guarantee there is no bearing in this setup, as confirmed by both the Haynes manuals (MKI and II FWIW) here.

There are key ways locking the top spring cup to the damper shaft and similar to the 'bonded' steel spacer tube that goes through the rubber bush."

The issue for me isn't seeing how the existing setup is configured, but how alternative components would react if I change things?

All the best ..

T i m

p.s. The top nut should be torqued to ~30 ft/lb so I guess the joint was not expected to 'slip'? Beside the torque setting there is ** and that says "These need to be tightened with the wheels in a straight ahead position and weight of the car resting on it's wheels ... "

... as one might typically do with any torque related joint?

Could be that they rely on the fact a long slender spring isn't going to cause much problem with wind-up? And for those applications where it does, they offer the bearing to prevent it.

I do have books somewhere that might give the answer, but I'd need to dig them out.

Really? Seems to have worked fine on MK1/2 Escorts and M1 to MK3 Ford Capris.

There is no bearings in MK1/2 essie and MK1-3 Capper strut tops.

on 22/04/2008, Conor supposed :

It's a wind up. lol

I know. ;-)

The issue I would like help with then please Conor is if I fit an alternative spring solution (ie, a typical 'coilover' spring, adjuster tube and caps etc) and presuming that won't function steering wise as the stock setup, would you consider it a pre-requisite that I fit some sort of top bearing (be it the modified rubber bush / bearing, the central steel bearing conversion plate or the eccentric bearing plate (in case I want to go Ranger racing ).

Also would I be right in thinking the bearing on the steel mounts is 'self centering' to accommodate the suspension angle changes (as the rubber would)?

All the best ..

T i m

It depends on how stiff the spring is, XR3is erc used to get roller bearings, poevrty spec escort IIIs didn't. Given you're trying to buy light springs it seems unlikely to be an issue. Try ringing Peter LLoyd and asking. They'll probably sell you the springs as well.

It's normally a spherical joint.

Hmm, I'm not sure I'm going to be able to get light enough Duncan. Burton have 100 lb springs [1] and I intend getting the front end on the local weigh bridge soon so I can start my calculations. The std saloon springs were very 'wirey' and quite open. I can't see the

2-1/4" springs being to be so willing to wind in and out and on top of that there is no positive location for the spring-coil-end as with the stock option?

I'll give em a call (thanks) .. although the 'old boys' who knew this stuff inside out seem to be long gone these days .. :-(

All the best ..

T i m

[1] I *think* the stock 1300 saloon springs were ~80 lb / in?

Ok ta.

All the best ..

T i m

Not there they aren't, they just drive M3s nowadays

Sounds about right.

;-)

Sooo, 100 lb'ers should be about right .. shame I lose the offset spring and gain a bit of damper stiction ..:-(

Once I know the load on the front wheels I can offset a bit for the un-sprung weight and the spring angle and position along the TCA. Then calculate what spring length I lose for preload > full compression (full damper travel) then I should get to the spring length (to avoid coil binding). Then I should know where to weld on the threaded collar .. ;-)

All the best ..

T i m