Alloy Diff Spacer Block

[Straight Six]

Sounds like a daft question, but does the thickness of a diff spacer block directly correspond to the amount a car is lowered? i.e. Does a half inch block lower the car by half an inch, or does suspension geometry mean that the car is lowered by more than that?

The car in question is a 1978 Spitfire 1500.  

Thanks.

[Steve AKA vitessesteve]

The blocks add negative camber to the rear wheels by fitting between the diff and spring.  The effect will therefore depend on the shape/strength of the spring.  0.5 inch spacer will have less effect than a 1 inch spacer.

[esxefi]

the drop will not be linear due to the changing arc of the driveshafts,the drop to plate thickness ratio will be less effective the thicker the plate gets,if you see what I mean?

if you could fit a theoretical spacer of 1ft thick in theory it will not be as effective as a 1inch one.ie, the car would not drop 1ft but with the 1inch plate it would be getting close to an inch drop,...I think!
it's all about the trigonometry from what I remember at skool

[Straight Six]

Yep! I get exactly what you mean. I was following the car in question this evening and it really is sitting very high at the back with lots of positive camber. The spring looks practically brand new (we're not sure as the current owner's only had the car a few days) so I'm guessing it'll need a 1" block to sort things out.

We also noticed this evening that there is a larger gap between the tyre and the wheel arch on the rear near side than there is between the tyre and the wheel arch on the off side, so something odd is going on there, especially as the front appears to be level.  

The plan is to check dampers, trunnions & drive shaft lengths then see what we can do about the height.

[Straight Six]

Thanks Iain.

Just an additional thought: If I fit a 1" spacer block, will I need to change the studs in the top of the diff for longer ones?

[Richard B]

Quoted from Straight Six

Just an additional thought: If I fit a 1" spacer block, will I need to change the studs in the top of the diff for longer ones?

Yes. 4 pot engine head studs work.

I would try a 1/2" or 3/4" block first, 1" is for race use or the really "slammed" look.

[Straight Six]

Thanks Richard, the slammed look is not what we're after! The car is 61k from new and amazingly standard, and we want to keep it looking that way. I also have some old head studs lying around, so thanks for the tip!

[Chris_68]

Hi!

I had a similar problem with my rear suspension that it leaned to one side.

I haven't put everything back yet so I am not entirely sure what was the problem but I noticed two things:
One of the dampers was really shot and I guess it couldn't extend properly again after a compression, the other thing was the rubber pad that is placed between the spring and the box, had ended up a bit to the side of the spring so putting pressure on one side of the spring. You're having a new spring so less likely but could be worth checking.

If I by lifting one side of the rear levelled out the difference and went for a ride then or me it was fairly alright until I had a few bumps in the road so the shocks compressed.

Also measure the length if the axles so they are the same.

/Chris