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robinj66
10-06-05, 06:48 PM
I'm posting this on behalf of a friend who has recently completed and SVA'd a Classic Replica Viper 4 MarkII. It has Sierra running gear which was fitted to the chassis when he bought it part built. The paperwork says that the kit was purchased new in August 1997 and that a Sierra based kit was introduced in January 1996.

The problem is that the car drives like a pig. It's very alarming at sppeeds of over 25mph. the steering does not self-centre and it feels as if you are skating on ice when you try to brake firmly.

You will see from the pictures below that the steering rack (Mk V Escort) is at the rear of the front wheels and that the track rod ends have an opposing angle to the lower wishbones. This has been provisionally diagnosed as causing bump-steer.

Another thing that is that the brake calipers are at the front of the wheels - all other cars i have seen (kit & production) have their calipers at the rear (have the hubs been put on the wrong sides?).

Any comments as to the position of the steering rack (we think it needs moving so that the track rod ends move through the same angle as the wishbones) and the calipers (do they need to be at the rear of the wheel?).

Does anyone have any pictures of suspension on Vipers of a similar vintage?

All assistance from knowledgeable engineers gratefully received.

osgood
10-06-05, 08:20 PM
Robin, yes I have a Viper but Jaguar base: Which wont be of much help. The non return of the steering wheel is not enough caster which is the top of the suspension post must lay back rather like front Falk's of a bike. Have you had it tracked up?? Go to Iain Jones site www.fake-snake.com (http://www.fake-snake.com) there may be some one on the members list who can assist re Sierra suspension. The rack and ends look pretty well parallel so I doubt if it's bump steer!! The rack on most Viper lays too the rear with the exception of Granada based cars. Most calipers are at the rear but I am not sure re Sierra based Osgood:thumb:

kevchard
10-06-05, 09:25 PM
We have a cortina based viper, and the steering rack is at the front of the car and the calipers are at the rear.
If you want a word with me about a cortina based version, please pm me and i will give you my mobile number.
I think ceejay has sierra on the back but cortina on the front. Are you sure your frinds is not cortina at the front?
Look in my VB garage for frame pics of pure corty based viper.
Good luck, as ever vipers are right awkward devils.
Does anyone have pics of what asierra should look like in the orig car?
Failing that try www.interford.co.uk forums, very helpful on there as people are on here.

kevchard
10-06-05, 09:30 PM
After looking at pics it is not a cortina based kit. Are you sure it is not a simple thing like tracking, castor or camber.
Our Audi was dreadfull barrelling aorund roundabouts (whrrl squeal, understeer, not sure footed) when tracking was out. Traccking done, all is ok now.
Just a thought.

dave
11-06-05, 06:51 AM
Here is why there is a problem.

Because the steering arm (In this case) it not following the line of the lower wishbone what will happen is that under braking the front suspension will droop (Nothing new there) but as it droops the lower wishbone will travel through an ark whick initially push the bottom ball joint outwards, but because the steering arm is already past ist maximum arc length that will start pulling inwards which on this car will cause the front wheels to toe out.....And judguing by how severely different these two things are the car will be all over the place.
It looks like the track rod ends should be in from the other end at a glance but that doesn't gurantee that all will be perfect, just maybe somewhat better.
There is a book called "How to make your car handle" that will explaind in laymans terms what' how and why etc. aboyut suspension geometry etc.:thumb:



http://www.cobraclub.com/forum/attachment.php?attachmentid=2969.jpg





http://images-eu.amazon.com/images/P/0912656468.01.LZZZZZZZ.jpg

Purple AK
11-06-05, 07:20 AM
I would say that there is something HORRIBLY wrong with the bottom swivels for starters. The one in Dave's photo appears to only be mounted using the two inner bolt holes, and at an angle of 45 degrees to the plane of the bottom wishbone. In fact it looks loose or bent. Surely it should be mounted using all four holes, as the whole weight of the front of the car is bearing on it!!! And it looks extremely likely to snap around the mounting bolts!!! It maybe that someone has modified the front wishbone in an attempt to lower the front end, doing away with the outer mounting holes. But it dosn't look good at all to me :mad:

grandadboats
11-06-05, 07:23 AM
Should the track rod not be parrallel to the wishbone?. ie the steering arm needs to be lowered or the rack mounting needs to be higher?Mine is Jag based with the steering arm in front of the wishbone and the track rod more or less parrallel to the lower (and upper) wishbone so that the angle should not change much with suspension movement. I hope this is right, but will no doubt find out if I ever get the thing on the road!!
I also agree about the lower swivel joint it looks as if it has reached its limit of movement.

Tony

dave
11-06-05, 07:38 AM
Hi Tony.
That's about the size of it.
The top and bottom wishbones are usually on slightly different angles and the angle of the steering arms should be proportional in relation to the two wishbones. And the pivot points of the steering arm should also somewhat line up with the pivots on wishbones.
I hadn't noticed the lower ball joint, that looks scary............i dare not comment further as I might get insulted by the manufacturer........It has happened before, hasn't it Chris!!!!!

robinj66
11-06-05, 09:55 AM
Having seen the car in the flesh I agree that the bottom ball joint does not look right.

It appears to be a Cortina/Granada item which should mount to the bottom wishbone using 4 bolts as Chris says. In addition to the angle you can actually see the shaft showing through above the boot which is an indication as to the strain it is under (it may have worked its way loose).

I posted this thread as a number of us have already given our opinions but thought the owner could benefit from other experience (in case we were in completely the wrong ball park) and to see if this layout was as designed.

Our advice has been to swop the hubs round and to move the rack forward (probably for a wider [Sierra?] rack which would place the coupling to the steering column in a better place) and to ensure that the angles of the track rod ends are approx the same as the lower wishbones. Is this the right way forward?

gareth08
11-06-05, 04:29 PM
On the point of Sierra running gear the caliper should be at the rear of the wheel.
I,ve never seen a Sierra with the caliper at the front.Are you sure it's standard Sierra and not modified in any way as something definatly does not look right there,
regards
Gareth

robinj66
12-06-05, 07:02 AM
Gareth


Definitely Sierra hubs but they have been switched side to side.

steamyrotter
15-06-05, 03:37 PM
Just a quicky.

How did it pass SVA if it didn't self centre??

I thought someones failed on that?

kevchard
17-06-05, 09:45 PM
They don't actually drive the car on a road for the SVA do they?

Purple AK
17-06-05, 09:49 PM
No. But they do drive it round the test centre to check the self centreing ;)

kevchard
17-06-05, 09:52 PM
In that case, as Dean says, how did it pass SVA?
There was me thinking SVA was a worthy cause to make cars safe, as apposed to a pen pushers justification for their job (that said, i have no chance of ever passing SVA now).