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Murray
16-12-12, 01:23 PM
Hi, has anyone got a photo of a Jag suspension based Cobretti steering rack in situ?
I have a power steering rack which is too low, causing horrible bump steer. I may just return to a "manual"
and would like to see how it fits in. Also what rack has anyone used and did it need modifying?
Thanks,

Deck
23-03-13, 12:51 AM
HI Murray
I had an engineer in to check my steering because the bump steer was terrible. He told me to offset the trackrod interface with the hub until the bumpsteer was mostly gone. I haven't put the car through IVA yet but it got through an MOT so it may have some merit. Its a manual sierra rack on sierra hubs apparently in the factory configuration for this model, muppets completely botched it!?

Basically, I swapped out the Track rod end for a rose joint. I had a 14mm track arm and i tapped the hub 14mm and got a 120mm high tensile 14mm bolt with a, wait for it, 14mm rose joint. I then took out the shock and spaced off the rose joint with a tube and some washers until when I jacked up the hub from full droop to full bump there was negligible change of direction in it for most of the travel. This has left the joint at the hub 93mm above its original point. I then got a plate made and welded to the hub to support this as it was so far offset. There's a pic attached of the finished article. I'd welcome any comment on this from anyone on the forum who has tried something like this.

Maybe you could see how far you need to offset the joint to reduce the bump-steer before changing the rack and any other linkages that may be affected. Not to mention the steering pump etc!
Is it possible to offset the rack at its mounting point to the chassis to see it that will help?
From my limited understanding, the distance between the inner joints of the track arm to control arm joints should roughly be the same ratio as the outside joint ratios. This gives an idea of which way to move it.

HTH
Cheers
DEclan

neil50
23-03-13, 10:08 AM
I see then that its not only the Sumo that gets bump steer problems.

Murray
23-03-13, 12:21 PM
Thanks Declan for your comments, that looks like a real good job you have done there. As all my suspension is Jag based I don't know if your solution applies in my case, however I may have sorted it. I have managed to raise the steering rack another inch or so, as far as it's possible to go in fact. I had to relieve the chassis members a bit so nothing fouled. The angles and dangles look very good now with the steering rack outer joints in line with the lower wishbone bushes and the steering arms at a much better angle. I have to get the tracking done again and we shall see how it feels on a test run.

Deck
23-03-13, 01:21 PM
Good luck with the test run. hopefully that will be enough.
The quickest check, and how i noticed my problem, is to set up some reference points at the front and back of the front wheel and jack up the car. The top of the wheel should move in as the car goes up but the lead and rear edges of the tyre should stay fairly stable. Mine were moving through about 15mm before the mod!! there's not much movement now except at the very extremes of the travel.
I have to do this test again after changing the castor angle by 8 degrees but I haven;t been able to face it yet after all the work done already, in case i need to change it...

Let us know how you get on after testing.
cheers,

Murray
10-05-13, 08:53 PM
Just an update on the steering. After the run out it still did not seem too good however the front felt soft and still not right so after a few turns on the shocks it seems to be a lot better. Not driven much over about 60/70 yet and I might get the whole suspension set up, cost is the factor with that but I may not need it.