Front Suspension Settings

[ysmalkie]

I have finanly managed to set my suspension.

Tyre pressures (Cintuarto Radial):
F 2.1 bar
R 2.2 bar

Setting links on.




Would these be good enough?

I was aiming for:
FRONT:
Castor: 1.5-2.5 deg positive
Camber: 1/4-1 deg negative, if possible
toe in 1/16" - 1/8" toe in (1.6-3.1mm)

REAR:
Camber: 1/2-1 deg negative

My rear toe-in (I would guess it should be 0?) seems a little off, but I guess there is nothing I can do to correct
I managed to get my front Camber negative by shaving the mounting blocks lightly.


Tadek

[bitsobrits]

It depends on how sensitive you are and how much you intend to drive the car. Those settings are good enough for most. Personally, I would work on getting the L/R caster settings within .1 degree, and on the high side of the standard spec. The standard upper fulcrum bar should allow this. Of course other settings will change with caster changes, so a certain amount of ‘chasing your tail’ will be required.

On the rear, the E type feels much more planted in medium/higher speed corners if there is slight and equal toe in on each side. No toe out. With your current settings, is may be possible to get to zero toe in/out by changing the shims at the front (only) of the IRS upper mounts. Adjusting the toe at the lower inner fulcrum shaft is also possible, but is a bit involved and not recommended to the novice as it’s easiest (IMHO) to do this only with the IRS removed.

[ysmalkie]

Many thanks Steve for commenting - could you explain how to shim the mounts for the rear suspension to obtain equal toe-in?
Or how to do it lower inner fulcrum shaft?

Tadek

[mgcjag]

Shimming the irs mounts is only used to get the irs central...you cannot alter one side without affecting the other...so if you shim the irs mounts you can increase the toe one side as you decrease the toe on the other side. ..individual rear toe is however affected by the shims between the diff and diff mount brackets....which should be set on diff Install to fit the inner fulcrum shaft correctly...Steve

[ysmalkie]

I thought the shims are only used to centre the diff brackets to align them with the cradle in order to mount the fulcrum pins.
Is there enough play to play with the toe?

Also, if I have a toe-out of 1/3 deg on LHS, I guess I would have to shim the diff mounts on the rear on the left side. Do you have an idea how much?

Tadek

[mgcjag]

I'm only saying how the diff and mount brackets are set up per the Jag service manual....if you want to get creative then altering the diff mount shims can alter the rear toe but you then have to sort out fitting the inner fulcrum....I would set it as per the service manual..irs mounted evenly to the chassis....drive the car...if you have problems then look for ways to fix them...Steve

[bitsobrits]

My earlier comment on changing the front IRS shims are based on the OPs measurements wherein on side is toed in and the other toed out. ‘Pointing’ the entire IRS in the correct direction by the correct amount will result in even L/R toe. I should note I’ve never done this and shims would likely need to be made to thickness as required.

What I have done is set up equal and negative rear toe on the E type by re-shimming the inner lower fulcrum shaft mount relative to the differential case. Both times I have done this the IRS was out of the car so careful and replicatable measurements could be taken. I used 16” lengths of precision steel bar through the outer fulcrum holes in the A arm (hubs obviously removed). Diff was installed in the cage for the final time and the inner fulcrum shaft brackets, fulcrum shafts, and A arms installed. Measuring from the inner fulcrum shafts to the 16” bars, and between the 16” bars will indicate the amount and direction each fulcrum bracket will need to be shimmed.

Note that the holes in the IRS cage need to be opened up by a few thousands of an inch in advance to allow the inner shafts to be inserted without force through the cage.

This is obviously a very involved process that took me the better part of a day to hit my desired toe in target. Later verification was done by an independent shop with laser alignment equipment after the car was complete.

In my opinion, rear toe should be checked and corrected, if required, on all E types. Certainly it should be done during an IRS rebuild. The toe was set by the factory to correct specs decades ago, and the odds of the car being in spec at this point are virtually zero unless a more recent alignment has been done. Rear toe is as important to tire life and stability as front toe. Perhaps more so as there is no natural self centering that occurs in the rear.

[abowie]

There's nothing about rear toe in being adjustable in the Service Manual.

As above, altering the shims on the frame mounts can only cock the IRS one way or the other.

The shims on the inner fulcrum shaft bracket are there to ensure that the 2 holes in the bracket are concentric with the 2 holes in the IRS cross member, so that the fulcrum shaft is easy to insert and doesn't bind.

Shimming is achieved by inserting the shaft through the crossmember and the bracket, with the bracket loose on the diff centre, then putting shims between the bracket and the diff centre so that the bracket remains in the correct concentric position. This doesn't change toe in.

I have heard of attempts to alter toe in by bending the lower wishbone. I have no experience with this.

[Allrand]

You can't do much about the rear toe, but it does suggest that the whole cage should be turned slightly to equalize them. Can probably be done at the slotted mount holes in the cage. But first check that there's no rear wheel bearing play that could affect the toe-in readings.

[ysmalkie]

Let me see if I get it right.
I have toe-out on the LHS of 21'
I need to shim the REAR mounting point of the LH bracket.

So assuming the distance between the mounting points is 'd',
the shim thickness is = d* tan(21/60) = 0.0061*d.

I am not sure what's the distance, assuming it's 100mm, it's 0.6mm
Am I correct?

[mgcjag]

Hi Tadek...your now getting into "non standard modifications"...and not as per the Jag service manual.....have you driven this car yet and set the ride height.....Trying to calculate shims to modify the rear toe will probably not work its very much a set up and trial as you go...I have done this on my C type build to give me toe in at the rear wheels.....Steve..
PS...I would also remove the setting links and take measurements of the car as you would actually drive it

[ysmalkie]

You are absolutely correct Steve,

All these values I would assume are not too bad (none of them were actually set except the front toe-in and the castor) and they are good enough to drive the car and recheck after few hundred km.
I have set the ride height within few mm, again the car probably needs to 'settle' and then I will recheck it.

So my thoughts here were more speculative, if my engineering math was right :-)

Why the toe-in on the rear wheels?

Tadek

[mgcjag]

Everything you need to know about suspension settings..Steve https://suspensionsecrets.co.uk/adjust-tune-toe/

[ysmalkie]

Oh that _is_ a very interesting page - thanks!

[rfs1957]

There was post on the Forum about 10 years ago that was the only convincing account I’ve ever read of adjusting the toe in, someone who is smarter than I am might be able to find it.

It recounted how CLK Engineering heated the wishbone with a blue-tipped universal-adjuster (AKA an oxy-acetylene flame) whilst watching the effect - live - on the wheel-alignment tracking system.

Counter-intuitively, this involved applying intense localised heat at points along the FRONT edge of the lower wishbone, where the distortion initially pushed the toe OUT, but upon cooling the area contracts beyond it’s starting position and pulls the toe IN.

I actually spoke to Keith Lucas about this, in case it was an April Fool, but he was well convincing.

I subsequently heard that in the States it’s recognised practice in some quarters, where running a bead of MIG has the same effect.

Nobody could tell me how many wishbones you got through before you became an expert, mind.

[mgcjag]

Hi Rory...yes iv read about it and a google search will find it.....but its not a diy option in my opinion...however shimming between the diff and mount brackets is easily doable and more importantly reversible....Steve

[ysmalkie]

Rory,
You can watch it all day long, but unless you know how much you need the toe to go out (that you can watch ) the toe coming in is out of your control....
Experience probably is the key.

Steve, do you know if shimming the the diff & bracket can be one in situ??

Tadek

[mgcjag]

Your problem will be pulling out the inner fulcrum shaft and undoing the diff mount brackets from the diff..
I would look carefully at how your irs cage is shimmed and centered to the chassis and drive the car....would you really notice a problem actually driving it... if there is then look at a fix....Steve