Exhaust grounding

[Sjmmarsh]

I have just got back from a short break in my V12 - it didn't miss a beat, used some oil (320 miles), but the biggest problem was the exhaust grounding on bumpy roads. I can't see any damage, but it does raise the anxiety factor whilst driving!

Are there things I should do to minimise this, like tyre pressures, rotating thec clamps so the bolts are horizontal rather than vertical etc?

All advice appreciated.

Steve

[christopher storey]

It is often the tips of the clamps which ground, so rotating them to the horizontal will afford perhaps another 1/2 to 3/4 inch of clearance which may be all you need

[PeterCrespin]

Yes of course orientate the clamps to minimise grounding, but the real problem, which is very common on V12s, is tired rear springs - assuming the spring damper units are correct and not shorter ones from a six.

The other factor is tyre section. What tyres do you have fitted?

New springs and/or packing pieces (fitted to some SWB and many 2+2s) and/or new adjustable spring mount dampers are the solution. If your dampers already use packing pieces at the bottom of the spring you can put some at the top as well but it's a slight bodge. New springs are best. Running slightly higher tyre pressures will give you a millimetre or two.

[Sjmmarsh]

The tyres are 205/70 R15s on wire wheels.

According to the service history I have the rear suspension was removed and serviced in 1983 at 101,000 miles - there is no note of the springs being replaced. It has now done 114,000 miles.

Is there an easy test for tired springs, or do they need to be removed first?

Steve

[MarekH]

The is an easy test. You look in the manual for the correct ride height and measure it. If you are too low, you replace the springs.

Pete suggests a cheap fix which is to put spacers in between the perches. This will simply raise the rear of the car.

He also suggests a more expensive fix which is to make the perches adjustable via new (adjustable) dampers AND new springs.

kind regads
Marek

[PeterCrespin]

The tyres are 205/70 R15s on wire wheels.

According to the service history I have the rear suspension was removed and serviced in 1983 at 101,000 miles - there is no note of the springs being replaced. It has now done 114,000 miles.

If I asked you to hold 3000lbs in the air for thirty years, would it cheer you up that you didn't have to travel very far while doing so? Three decades is a long time and the V12 shocks are at a more acute angle due to being splayed wider at the base for the wider track IIRC. Hence any foreshortening is going to have a more pronounced effect on ride height. Your car when new sat fractionally tail-high. Stand back from it today and I bet it is a tail-dragger with the rear rims up inside the wheel arch an inch or more deeper than the brochure photos.

Spring are cheaper than a new exhaust and yes, for the wire thickness of the same grade and number of turns, the free spring length will indicate if your new springs are going to fix the problem when you take the first one off and compare it to the new one.

The final test is only when all four are fitted of course, which is why adjustable dampers are nice because even if the old or new springs are somewhat off-spec, you can compensate by winding the spring platform up or down.

I'd be checking the front ride height too. Scraping an exhaust is bad enough but holing your sump on a stone near Goodwood is a whole lot worse - ask Philippe Picavet, the owner of the car on the cover of my V12 Buyers Guide. That REALLY put a crimp in his visit from Belgium for XK60.

Pete

[Sjmmarsh]

Thanks for the pointers. It sounds like I will be in at the deep end with my new car then....

Are the springs still under compression when the wheels are unloaded?

Steve

[MarekH]

Yes they are. They are under compression even when you take the damper/spring assembly out of the IRS.

kind regards
Marek

[Sjmmarsh]

Peter - you were spot on. The rear height is. 17cm (should be 20) and the front is 13cm (should be 16). 3cm additional clearance should be all I need (as well as presumably improving the ride).

Rear springs are on order - is it likely that I will need front torsion bars as well, or should there be enough adjustment to raise the front by 3 cm?

Steve

[vee12eman]

Hi Steve,

After recently rebuilding my car, I had similar issues to you regarding height. The front suspension was easy enough, the snail cam adjustments brought it in and even if it hadn't, the torsion bars can be removed and re-fitted in a different position - the vernier adjustment is somewhat similar to earlier cars, but they don't get the cam adjustments. You need to refer to the original workshop manual - if you haven't got one, I stongly recommend you do.

As to the rear, I kept the original springs but used Gaz Adjustable height shock absorbers, which brought the ride height into limits. Some fool (ME!) had fitted the upper bolts the wrong way around, so I had to remove the whole rear cage to remove the shock/spring units, but I rectified this and could now change thing without going to such lengths. The car is now the correct ride height front and rear and things are better, but I still get the odd grounding on heavy compressions at reasonably high speeds, I suspect the springs may still be a litle soft so I will look into replacement. I also think the car may have settled since fitting the new components, so I need to check that too. The Gaz Shock absorbers did definitely improve things and I feel I can recommend them, but as you have ordered the springs only, try them and please let us know the results - I for one will be very interested.

Incidentally, a lot of controversy on this forum recently about the best way to change springs from Shock absorbers. I simply used a couple of good quality spring compressors, did it outside with lots of space, made sure I was never in the line of the spring if it should release and was careful to release/compress each spring compressor evenly. Using adjustable shock absorbers has the advantage you can refit the springs without compressing them, using the height adjustment on the shocks to adjust. I have never had problems changing springs when using the correct gear carefully and I was amazed at the variety of different ways people had come up with, not to mention the lack of agreement over which were safe. My recommendation is a pair of the correct size spring compressors, care and common sense - if you have doubts, ask a specialist! Oh yes, my spring compressors were made by Draper and are easily the best I have used.

Regards,

Simon

[abowie]

The other thing to check is how much clearance you have with the exhausts underneath the IRS and adjust it to be minimal.

[Sjmmarsh]

Time for an update on my rear shocks. I ordered complete units from SNG Barratt and took them to my local garage for fitting (I can't get under the car in my lockup garage).

1st attempt was aborted after the garage asked 'Did you get any bushes for the top of the shocks?" My reply "Can't you use the old ones", to which the reply was "there aren't any!" . That explains some of the noises I have been hearing on cornering!

Bushes obtained, the new shocks went in fine and the rear ride height is better, but it will need to wait for the better weather, particularly as I found the engine really doesn't like running in cold weather and stop-start traffic , and the rear heated screen doesn't work!

Steve