Cortina GT - setting the shocks - advice needed

[Andy Bacon]

Originally Posted by LC driver

Pom pom pom call burton for some new springs 500 pound at least And do something with the rake of the car first....it looks like a hotrod

The OP is getting the best of advice here.
Get new rear springs or get them reset to lower the rear and it will also stop picking up rear wheels. Don't use lowering blocks.

[esper]

Originally Posted by zefarelly

espers always wanted to get into drag . . . is that what your saying Terry ?

straight lines? ever seen a healey doing straight lines. proper set up cortina will do that.

[Leo Landman]

Originally Posted by Andy Bacon

The OP is getting the best of advice here.
Get new rear springs or get them reset to lower the rear and it will also stop picking up rear wheels. Don't use lowering blocks.

This OP is happy with any advice, and wil certainly look into getting better springs.

What is the disadvantage of lowering blocks? This is new to me, I thought it was quite common to lower a Cortina using blocks.

[Al Weyman]

According to our old friend Fred Puhn lowering blocks are good.

[terence]

Apart from increased fore and aft movement,far better to have just the springs.

[GORDON STREETER]

I have found lowering blocks can cause axle tramp. If you taper them down at the front to make the diff nose lower that normally cures it.

[Al Weyman]

According to our Fred, blocks can be useful for dialing out built in manufacture rear steer was the reason from memory.

[terence]

Originally Posted by GORDON STREETER

I have found lowering blocks can cause axle tramp. If you taper them down at the front to make the diff nose lower that normally cures it.

Yes exactly Gordon,in effect they give more leverage because of the extra distance from the designed mounting faces.Bit like a short lever against a longer one.

[Andy Bacon]

Originally Posted by Leo Landman

This OP is happy with any advice, and wil certainly look into getting better springs.

What is the disadvantage of lowering blocks? This is new to me, I thought it was quite common to lower a Cortina using blocks.

Lowering blocks, as others have said, promote axle tramp.

As I also think your rear wheel lifting may be caused the shockers lacking travel in droop. resetting the springs will improve this but a lowering block leaves the lower shocker mount in the same place. Try not to run the axle on or close to the bump stops unless they are really progressive.

[jonners]

Originally Posted by GORDON STREETER

I have found lowering blocks can cause axle tramp. If you taper them down at the front to make the diff nose lower that normally cures it.

Sorry to re open an almost dead thread but can anyone explain this??

I would have thought increasing the distance between the driveshaft and the spring increases the torque required to wind the spring up, making tramp marginally less likely

Is Gordon saying the tapering of the lowering block helps because the angles of any tramp bars change??

Have been grappling with this one for years...

As for front spring rates 450-500 lbs/inch offends all the theory but am convinced that people go this way in order to reduce movement as much as possible as lowering the car has a huge detrimental effect on geometry that you cannot rectify unless the regs permit relocating tca mountings and just about everything else

[zefarelly]

interesting that some of the quicker cars don't look as 'slammed' others

my car has actually been raised since I built it!

[terence]

Originally Posted by jonners

Sorry to re open an almost dead thread but can anyone explain this??

I would have thought increasing the distance between the driveshaft and the spring increases the torque required to wind the spring up, making tramp marginally less likely

Is Gordon saying the tapering of the lowering block helps because the angles of any tramp bars change??

Have been grappling with this one for years...

As for front spring rates 450-500 lbs/inch offends all the theory but am convinced that people go this way in order to reduce movement as much as possible as lowering the car has a huge detrimental effect on geometry that you cannot rectify unless the regs permit relocating tca mountings and just about everything else

Just lowers the diff nose.If you think about the wind up,you do have the torque at a greater distance away,hence the problem.

[GORDON STREETER]

Terry is correct. As you drop the clutch to make your amazing getaway the diff pinion tries to wind its way up and round the crown wheel. The leaf spring adapts an S shape and when it cries enough it shoves the diff back down promoting axle tramp.
Lowering blocks magnify this because the leverage is more as the axle unit is further from the spring.
If you angle the diff nose down either by repositioning the spring saddles or tapering the lowering blocks although it still tries to wind the pinion up the crown wheel it will cure most of the problem.
I thought this thread was about shock absorbers !!!!!

[terence]

And Springs/Diff Nose Angles/how to make a Ford Handle,or was that four?

[jonners]

yeah but no but yeah but no but yeah but....

Still a bit confused but thanks for the comments and sorry about the hijack

I can see that what I said earlier was wrong - the increased distance from the axle to the spring means the leverage is greater so more spring wind up...BUT...

...on a GT Cortina fitted with standard radius arms the gap between the top radius arm and the lower one (the spring) increases if you fit a lowering block and this will resist spring wind up so perhaps the problem isn't so big

Still confused about the diff nose thing - the torque reaction will make the diff nose go up by the same amount whatever its starting position - or am I missing something???

Am genuinely looking for help on this for our car so any pearls of wisdom much appreciated

[GORDON STREETER]

Originally Posted by jonners

Still confused about the diff nose thing - the torque reaction will make the diff nose go up by the same amount whatever its starting position - or am I missing something???

Its all to do with the leverage point going past the straight ahead position.
As it starts before (like anti dive)

[jonners]

Originally Posted by GORDON STREETER

Its all to do with the leverage point going past the straight ahead position.
As it starts before (like anti dive)

Gordon - thanks for that - could you elaborate a bit - still confused...

[Keith Graham]

I always understood the radius arms or anti-tramps bars stopped the spring wind-up. The fixed point in the centre of the spring cannot move forwards or aftwards because of the tramp bar thus avoiding wind-up and axle tramp. So therefore lowering blocks should not affect this. Admitted if you did not have anti-tramp bars it would increase the leverage because the distance is greater, but don`t most performance cars have radius or anti-tramp bars? Shorter springs is more a professional way of lowering but surely the outcome is the same. I stand to be corrected.

[Leo Landman]

Time for some feedback. Following your (and other's) kind advice, we uprated the front springs to 500 lbs. We fitted a proper GT rear axle with the proper trailing arms and mounting points. The LSD was softened by 30%. The lowering blocks were tossed out, the leaf springs straightened by a blacksmith to lower the car to the required height. I'm probably forgetting a few improvements but let's just say is was a busy summer.

The result is a transformed car. This weekend at Assen I could finally toss the old Cortina into a corner, and come out safely at the other end, steering with the throttle and correcting with the wheel (or the other way around). It doesn't turn me into Jim Clark, but at least I now see how it can be done. I can hardly describe the sensation of sliding through a corner at 140 kph feeling in control, and not feeling like risking my life!

For the first time I fully enjoyed driving the car. Now I have to develop my driving so as to exploit the newfound 'sideways speed' of the Cortina. That will take longer than a summer, but at least I now have a car that works with me rather than fight me. Thanks for your help.

[terence]

Excellent result but dont forget that sideways is slower than smooth!!

[esper]

Originally Posted by terence bower

Excellent result but dont forget that sideways is slower than smooth!!

so you did race formula cars then it was wet in assen last weekend to explain something .

[Leo Landman]

Esper, I only drove two of the dry sessions (free practrice and race 1) at Assen. Only race 2 was wet, and it was my co-driver's turn then

I know sideways isn't quicker, but we're on Dunlop vintage racings and they seem to work best at a higher slip angle than recommended for modern tyres. Which is nice because, as one of the boys here once said, sliding is part of the Cortina fun.

We'll be at Zandvoort next weekend, don't hesitate to drop by. It's the Cortina with the chequered roof.

[terence]

Absolutely agree it IS fun but----------