408: rear suspension adjustment. What is the procedure?

[dwomby]

Thanks, Kevin. Very interesting. My old XJ6 had large flat rings in the front spring pans too. They were used to adjust ride height but were plain, flat rings. Nothing like the complex shapes shown in the thread you reference.

I'll update when I get to examine the car. Hopefully tomorrow.

David

[dwomby]

Is there anything specifies how to measure ride height on a 408, etc.. For example, On a Jaguar XJ6 the factory manual gives the measurement when fully laden from the ground to the center of the main headlight.

Thanks
David

[Kevin H]

Originally Posted by dwomby

Is there anything specifies how to measure ride height on a 408, etc.. For example, On a Jaguar XJ6 the factory manual gives the measurement when fully laden from the ground to the center of the main headlight.

On the 408Mk1(up to chassis 408/7200) the unladen ground clearance was specified as 6.5 inches.

When I previously discussed ground clearance of a 411 with Brian Marelli at Bristol Car Services, he said it was measured between the bottom of the front crossmember and the road. I can only assume the measurement on a 408 would be the same. However, no matter where it is measured from, wheel diameter, tyre size and tyre inflation will affect that measurement.

David, what you really need to know initially is whether the body of the car is at the same height at each wheel. I was thinking perhaps you could measure the distance from the upper chrome side trim to the ground at each end of the strip on each side of the car.


Kevin

[dwomby]

Thanks, Kevin. I'll check to bottom of the crossbar today. Meanwhile a quick run out to the car with a measuring stick came up with the following:

Front: ground to bottom of lower chrome strip passing through center of hub cap - right side is 3/8" lower than left.

Rear: ground to bottom of chrome strip passing through center of hub cap - right side is 1/4" lower than left.

I'll recheck later today.

David

[dwomby]

Originally Posted by Kevin H

On the 408Mk1(up to chassis 408/7200) the unladen ground clearance was specified as 6.5 inches.

When I previously discussed ground clearance of a 411 with Brian Marelli at Bristol Car Services, he said it was measured between the bottom of the front crossmember and the road. I can only assume the measurement on a 408 would be the same.
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Kevin

I finally measured this today when I found I was having trouble getting the car jack under the front crossbeam: 5.125". I didn't have trouble getting the car jack under there last time but the tyres were then at 40psi and are now at 32psi. In the end today, I had to jack up each side separately at the front putting the jack under the spring pan. I then managed to get a stand under each side of the crossbeam.

I am a bit troubled that I am 1.375" below specified height yet the car doesn't look nose down. The tyres show completely in the openings - none hidden by the top of the wheel arch but I suppose that just means things haven't sagged as much as they might :-( .

David

[PEU186F]

I very much endorse the other recommendations to look at the front end before adjusting the back, particularly as your front sounds to be lower than it should be.

Having got the front ride height right and level it is relatively straightforward to adjust the back - all that you’re aiming for at that point is to keep the main fore and aft chassis rails parallel with the floor. To answer your specific question about the rear torsion bar adjustment point, it is indeed at the front of the bar at the point you’ve identified, all you need to do hopefully is to loosen the lock nut (which is likely to be extremely tight and you’ll need the correct size ?Whitworth? Spanner) on the bolt that acts on the arm that is splined on to the front of the torsion bar and screw the bolt in or out to suit the rear ride height that you want to achieve. I’d advise a good soak with penetrating oil before you start.

You may find that the torsion bars have sagged beyond the range of adjustment available, if so you’ll need to have the car on a lift on the chassis and a friend with a large Stilson wrench. First screw the bolt right out so that there is little or no tension on the torsion bar. You might need to remove the axle rebound retaining strap to achieve this happy state of affairs. You then need to dismantle the torsion bar mounting, which will allow the torsion bar to drop to the point where the adjustment arm can be taken off and moved by one spline. You’ll then need the friend with the stilson to pretension the torsion bar slightly so that you can reassemble the mounting. That needs some strength on the part of your friend but by no means a great deal of brute force. This might all sound rather alarming but in my experience it is all very well made and comes apart and goes back together again easily - given a good previous dose of penetrating oil.

Roger

[dwomby]

Thanks, Roger.

I assume the only thing that will raise the front end to specification is new springs?

David

[Kevin H]

Originally Posted by dwomby

Thanks, Roger.

I assume the only thing that will raise the front end to specification is new springs?

David, that's not necessarily the case. Some of it maybe down to modern tyres which don't have the same side wall height as the original tyres and it's possible the "distance pieces" as Bristol refer to them have disintegrated, which they do eventually. I mentioned these earlier in this thread and supplied links to more detail. The two combined could add up to 1.375". I would certainly check that before you start getting springs made. Either way you are going to have to dismantle the front suspension.

While you are at it I would consider replacing the wishbone bushes if they haven't been done already.