Bump Steer on TR7 Mc Pherson Strut

[Jolyon39]

Hi, I am trying to get my head around this and wondered if you folks coud shed some light and make it east to understand in relation to the TR7 and TR8 front suspension.

The issue has arrisen because I have been discussing swapping a LHD power steering rack to RHD. Apparently this is classed as modified steering under New Zealand law and suddenly requires testing to prove zero bump steer.

Can any of you draw the bump steer meaturements onto a drawing of our suspension adn explain how you would adjust TR7 or TR8 steering to achieve zero bump steer??

Jolyon

[Troy ODoherty]

Seriously[?] NZ transport actually thinks there are road cars with zero bump steer?

To make it simple for you Jolyon. The easy way to get a feel for the bump steer is to place a gauge against a front wheel now raise the car up and see if the toe changes as the car is raised. This is obviosly a droop setting , but will give you a bit of an idea what is going on.
The gauge we use is 2 pieces of ply about 400mm square joined together with a length of piano hinge. Place the ply on the floor next to the wheel approx 1" away at the bottom. put something heavy on it like a car battery or couple of bricks.Now hinge up the other side so it is leaning against the tyre. Locate where the front and rear edges of the wheel are and put a couple of screws or nails into the ply. Make sure they are the same hieght above the ply. I like screws as they are easier to adjust. Set the gauge up so that they are both touching the wheel at ride hieght. Now if you raise the car the wheel will move away from one screw. This is the tow change per side. To check the actual bumps setting you must note the standard ride hieght then remove the front springs and reassemble the front suspesion. now raise the car to ride hieght and set the gauge . now lower the car and measure the toe change.

When we do this for the rally cars we raise and lower the car in 10mm steps and then measure the change. This allows us to draw a simple X-Y graph of what is happening.
You have 2 choices to fix the bumps steer. 1 raise or lower the rack. 2 raise or lower the outer tie rod end.
Niether are very easy to do on a road car.
The new Audis actually have an adjustment in them to alter the S curve as they call it. Why anyone would want anything other than zero is beyond me.
Haveing said all that, if the inner rack end hieghts are the same on both racks and the steering arms are the same, then there should be no change to the bump steer.

The main point is to have a parrallelogram between the tie rod and the lower control arm.
When I first built the rally car using SD1 strut legs it had 3" of toe change . I cant remember if it was in droop or bump.The other way only had 3/4". To cure it I replace the outer tierod ends with spherical rod ends and put bolts up thru the steering arms. I used hardened washer to space the rod end up and down. The car now has zero toe change right thru it suspension travel. It is possible to change the ride hieght down 1" and not reset the toe. Only the camber increases.
Hope that helps.[:)]

Cheers Troy

[Marko]

no car has absolute zero bump steer. There is only low enough bump steer. On the other hand. Bump steer is not that bad if used properly.



As for the measurement. Troy said it all.

Mark the static position of suspension travel and measure toe. Remove springs , move the wheel trough suspension travel and measure toe.

Depending on how much the car has been lowered bump steer can be modified by changing the location of the steering rack. That is changing the vertical position by stacking shims below the rack mounting points, or lowering the rack by grinding down the moutnting points. But since youre using stock parts there shouldnt be need for that, just so you know that there is a remedy.

[Vegas_M]

Don't know if this can help, but you might try fitting a steering damper and telling them this eliminates any bump steer. The British V8 site has an interesting article about fitting one from a Mercedes that should work for our cars also:





http://forum.britishv8.org/read.php?7,17819

It is the stock damper used on most Mercedes models (e.g. C220) from about 1977 through about 2004. Will need to make custom brackets to clamp to the rack tube and tie rod. The unit is 21" Ext. 13" Compr. SACHS Part # SG203004.

Martin

[bmcecosse]

" fitting a steering damper and telling them this eliminates any bump steer " - Do you really think they will swallow that?? [:0]

[Hasbeen]

Fitting that steering damper as suggested by Martin would overcome our notorious wheel wobble, & it looks like an easier fit than the VW one.

Jolyon, get out of there now, do not pass go, just get out while you can. If their nanny state has gone so far, it won't be long before they will ban all knives, & only allow precut food. Only to protect you dills who live there, of course, who can't think for yourselves.

From your post I assume you will end up with a stock TR7 steering set up. Surely they have approved that all ready.

Hasbeen

[Jolyon39]

Actually, 3300 left NZ permanently for Australia just last month.... highest loss on record. NZ Popn 4,100,000 and popn on NZ born people in Australia is 370,000...... what does that tell you

Luckily I have the correct passport so i will bejust returning home..... one day to QLD I think.

yes manual, already approved steering I think..... unless i get a specialist to do it for about 5K

Jolyon

[dycecooper]

Back in the eighties we had moddified steering arms that were straight and I think shorter (I will try and find out exactly) and this vastly reduced the bumpsteer on the TR7V8 rally car

[Cobber]

<font size="2"><font face="Comic Sans MS">Joylon why don't you just fit the Pwr steering without telling them?
With so few of these cars about, I very much doubt that anyone in authority would know what these cars are let alone what spec is standard!
And that would go for any nosey coppers or mechanics doing annual road worthy checks too!
The golden rule is: what they don't know wont worry their pointy heads!</font id="Comic Sans MS"></font id="size2">

80'Triumph TR7, , 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
85'Alfa 90, 69'Ford F250.
76' Ford F100

[Jolyon39]

I agree Cobber, will have to convert it with a manual rack and then swap to power after inspections. (inspectors will still require proof of a new or fully rebuilt manual rack)

Jolyon

[Hasbeen]

3300 in a month, & we're worried about 2 or 300 illegals being brought in by boat a month. I'm glad it will be my kids paying for all this, not me.

Still, up north about a quarter of the population appeared to be Kiwis, & almost half the workforce in the tourist industry too.

I had to re-compliance the 8, when the boy let the Victorian registration laps, while it was at the painters. Could have simply transferred a current Vic rego to Queensland, but as it was unregistered it had to have new Queensland compliance. We are getting almost as bad as over your way.

As you know, there's not much original Triumph left in the 8, but a local bloke did it for $1000. Took him the car one morning, got it back registered with a new plate the next day. Didn't even have to sign the application papers. I don't know how that works, & won't be inquiring too closely either.

It sounds as if it's not only the government getting into you over there mate. $5000 sounds a bit high to me, but then you rich equestrian people can probably afford it.

Hasbeen