Rear suspension droop/Travel/shock length?

[Al Weyman]

I have been have a look around my 2nd gen race car in an effort to get it handling a bit better and was surprised to notice on the passenger side with Koni shocks the shock only has about 1.25" travel before its fully extended, on the drivers side it has about 2.25"s. As we race on predominately right hand corners and with my bulk on the left hand side I am wondering if the shocker is lifting a rear wheel through real heavy cornering as I have spun the thing out a few times recently having a big expensive one at Lydden Hill Race track. It breaks without warning and yet seems OK through the left hand bends.

The car has cart springs on the rear with staggered shocks i.e. the passenger side is infront of the axle the drivers side to the rear which may account for less travel on one side.

My question is how much travel should I have on the shocker before it runs out of travel and lifts the axle?

[JamesH]

Sounds like it might be the culprit - I would have thought that a sudden breakaway would be caused by hitting the end of the shock.

Anyway - silly question time:

Are the shocks the right ones for the car?
Are they supposed to have different travels, or is one duff/incorrect?
Are they they on the correct side of the car?
Can you swap them round to see if that makes a difference?
Can you get someone to video you going round in a circle to see what the wheel is doing?

[Al Weyman]

The shocks are indeed for the car they are these here http://www.rickscamaros.com/camaro-r...1970-1981.html

The reason one is probably a bit different than the other is that they are mounted staggered and the one with less travel is already extended more to reach the forward mounting on the passenger side (LHD vehicle). I kid you not I have had some frightening experiences in this car in the past and I am just wondering now if this has been the problem all along as it has loads of power and just should be going better than this but as soon as I push it harder I am off the island. I smashed it Lydden a couple of monthes ago then the same thing back snapping round at the Walter Hayes in 08, spun on the chichane at Thruxton and Donington and numerous other times and it hits you bang, no warning and too late to catch. One of the reason for my hate hairpins thread as I nearly had to slow down to walking pace at Oulton the other weekend going through the hairpin and had it off a couple of times.

[JamesH]

Originally Posted by Al Weyman

The shocks are indeed for the car they are these here http://www.rickscamaros.com/camaro-r...1970-1981.html

The reason one is probably a bit different than the other is that they are mounted staggered and the one with less travel is already extended more to reach the forward mounting on the passenger side (LHD vehicle). I kid you not I have had some frightening experiences in this car in the past and I am just wondering now if this has been the problem all along as it has loads of power and just should be going better than this but as soon as I push it harder I am off the island. I smashed it Lydden a couple of monthes ago then the same thing back snapping round at the Walter Hayes in 08, spun on the chichane at Thruxton and Donington and numerous other times and it hits you bang, no warning and too late to catch. One of the reason for my hate hairpins thread as I nearly had to slow down to walking pace at Oulton the other weekend going through the hairpin and had it off a couple of times.

Are they on the right side? From what you write, the one with the biggest stretch is on the wrong side. Are the shocks for a RHD car perhaps? If that changes the rear suspension?

Perhaps the phrase "had it off a couple of times" might encourage more people to visit the Oulton hairpin though.

[Chris Y]

Originally Posted by Al Weyman

The car has cart springs on the rear with staggered shocks i.e. the passenger side is infront of the axle the drivers side to the rear which may account for less travel on one side.

This sounds to me like the car is set up for left-hand bends - i.e. an oval set up.

If that's the case, it's no wonder you struggle with right-hand hairpins!

[snailpace85]

I guess there are loads of set-up possibilities and reasons. Usually for the driven end of a car I would say you need the suspension to not have any pre-load or very little - so in this case (live axle on leaf springs) you should be able to jack the rear of the car up and the axle hang on the springs without being restrained by the dampers or any other form of constraint (up and down anyway). My suggestion FWIW is

Undo dampers at the axle
Jack rear of car up so both wheels are clear of the ground
Axle stands under chassis (not axle!) and make sure the car's secure
Take wheels off
Check by heaving on it that the axle can move up and down on the springs showing that nothing is constraining it from that movement except the springs
See if you can attach the bottom of the dampers

My bet is that the right hand damper won't reach but left hand one will or nearly will - that confirms the prob. Don't know why it's arranged like you say - presumably for anti-clockwise ovals as said above. Is it possible to mount right hand damper like the left hand one or is stuff in the way? Whatever, you need the suspension to be able to travel from no load to bump stops without the dampers preventing it.

BTW There can be reasons to pre-load the suspension but usually at the non-driven end on cars that have a lot of weight over the driving wheels.

Hope that's some help. Was at Lydden when it mis-behaved. Certainly I would have thought that your description of the problem would produce the handling you describe.

Scott

[Al Weyman]

No its not an oval car i originally prepared it from a road car. The shockers will be equal I cannot see Koni making a left and a right but I will check. I have disconnected them and the axle will drop away below the shock so the shock is restraining it as the axle will drop several inches lower. As I cannot source any shocks intime I think I will make up a spacer block and bolt the shocker to that plus space the lower pin fixing I recon I will get about 70 mm by doing that so its a start.

[Chris Wilson]

1 1/4 inch droop on the rear of something that size and weight on cart springs sounds far too little to me. Ideally I'd like to try and get shock extension continuing until the spring is unloaded. You can't be short of room under there, surely? Haven't you got any photos of it round corners taken from the rear? For some reason these track photographers have a fixation on side and front aspects, when technically you might be more interested in what the rear end is doing weight transfer wise.

[Chris Wilson]

Oh, Caroll Smith had a dedicated chapter to big saloon / coupe suspension in one of his books, I am sure he was banging on about damper travel as well as bump / rebound settings on the back of live axle cars.

[Moosehead]

Staggered dampers was a set up used on many Yank 'performance' cars to try to stop wheel hop or axle tramp as we know it. Great for drag racing but not always good for cornering.

[GORDON STREETER]

Originally Posted by Al Weyman

. As I cannot source any shocks intime I think I will make up a spacer block and bolt the shocker to that plus space the lower pin fixing I recon I will get about 70 mm by doing that so its a start.

Make sure you have enough travel the other way Al, as that could be worse !

[Chris Wilson]

Is the axle solely located by the leaf springs, or are there radius rods or maybe a Panhard rod or Watts linkage? Could you legally add these?

[Al Weyman]

Yes I know all about that Gordon, when we first built the IROC my mate modified some adjustable Spax's on the back and they wer bottoming out, dont think Mark Hales was that impressed when he tested the car for CC&C!!

Nothing else locating the axle Chris and yes I can add.

I think I have sussed out what has been the problem all along after visiting a yank site and posting the problem. Apparently there is a phenomena known as the 'Nova Curve' amoungst Camaro owners and its basically the rear aftermarket springs for the Nova and the Camaro look identical and are the same poundage but the Nova has a slight more arch. What happens then the Camaro sits too high if you get supplied the Nova ones. When I fitted the 'competition' springs years ago it was way high which was disappointing as they cost a fortune imported from the US so I used lowering blocks and took out a short leaf at the top which was doing nothing. Only problem is the plate that holds the springs together and too the axle also mounts the shocker so what happens the car is lowered but the plate stays in the same higher or (further away from the shocker) position! I am now fabricating an extention from 2" Angle iron and will weld this to the plate and then mount the shocker off of this, this should give me a full 3" droop which hopefully will be enough. The gutting thing is I have used this since 89 and always suspected there was a problem but couldnt put my finger on it overlooking the obvious.

[GORDON STREETER]

Also don't forget that with long travel rear suspension on a beam axle you will get rear wheel steering.

[Al Weyman]

The cart springs won't let it go that far I wouldnt have thought

[phoenix]

Originally Posted by Al Weyman

I am now fabricating an extention from 2" Angle iron and will weld this to the plate and then mount the shocker off of this, this should give me a full 3" droop which hopefully will be enough. The gutting thing is I have used this since 89 and always suspected there was a problem but couldnt put my finger on it overlooking the obvious.

Whilst this may cure some problems, I would suggest you consider this mod only as a stop-gap and plan a serious revision of the rear end as it is far from ideal as it stands. There are 3 stages of upgrade I would consider:

As a minimum I would suggest getting the current springs de-cambered or getting replacement springs - anything to get rid of the lowering blocks as, without radius arms, you will get loads of axle tramp. Lowering blocks increase the leverage the axle has over the springs and so increases spring wind-up and therefore tramp. This can make even a 1600cc Escort rear end horrible - with the amount or torque you have available tramp must be a big issue.

Using opposed damper angles to reduce tramp, as a number of manufacturers used to do, is not very effective and far from ideal even for a road car and really shouldn't be considered good enough for a race car. Add a pair of radius arms as a minimum and arrange pickps on the axle to get both dampers operating on the same sides of the axle, from symmetrically located body top mounts.

Ideally go for a five link setup - two upper and two lower parallel radius rods and a Panhard rod for lateral location. Besides locating the axle, the benefit of a Panhard rod is that you can lower the roll centre height somewhat if you wish. These mods will bring huge improvements to how your car puts the power down as well as how it handles in corners, so you will find them well worth the time and cost. Can't promise to keep you out of the tyre walls though - that's down to the nut that holds the steering wheel!

[Chris Wilson]

I strongly agree with phoenix. If the regulations allow you to modify the rear suspension you'd be mad not to. The current set up is pre-historic! You should be able to transform both handling and traction with some fairly straightforward mods.

[Al Weyman]

Unfortunately I race in a Pre-Historic championship but hey thats half the fun isnt it? Definitely cannot five link thats out, can add a watts linkage, panard rod, and radius rods but suspect with radius rods and retaining the cart springs as I have to, I will get bind and a lot of it so probably counter productive. Oddly enough I get no axle trap at all but the lowering blocks are only about 15mm as I got the axle lower by moving the tiny first spring leaf that was doing nothing also I have to run with 4" ground clearance. I doubt I would be able to alter the centre line of the shock position either.

[Chris Wilson]

I'd do as much as you possibly can to make the springs just spring and properly orientated locators locate

[Al Weyman]

There is some good footage here of William Jenkins hunting me down in his CSL, you can see its very odd on the back end seems a tad high as well, all that grunt I should have finished the Bimmer no problem if the thing didnt corner like threepenny bit!

[phoenix]

Originally Posted by Chris Wilson

I'd do as much as you possibly can to make the springs just spring and properly orientated locators locate

I agree - and the dampers just damp.....

[GORDON STREETER]

Originally Posted by Al Weyman

The cart springs won't let it go that far I wouldnt have thought

Accurately measure the wheel base then jack the car up on one side by the body. I think you will notice a difference !

[phoenix]

What did Frank Gardner and Yogi Muir do with their rear axles, back in the day? Surely you are allowed the same mods they ran?

These might help (with a Panhard rod too):

http://projectautos.com/69-camaro/4-racing_project.html

[Al Weyman]

No not allowed at all the mods they did, they were Group 2 ours are Group 1 based or Group N. What happened to my link? Here it is again. http://www.youtube.com/watch?v=XC4p74p65YA Caltracs are for drag racing and IMHO would hurt the cornering even more. As I said it doesnt tramp off the line anyhow.

[Al Weyman]

BTW the Ranco Springs were set up to reduce axle tramp off the line so this is probably why there is no problem in that direction.