Bump Steer Spec's

[m_fry]

G'day You'all,
I have just installed a RHD rack & pinion unit in my 69 vert. I now have to have the compliance engineer do a bump steer plot to check that the bump steer is no worse than the original measurement.
Does anyone know what the original bump steer measurement was for a 69 sb vette and at what radius it was measured from the front axle center?

Mark

 

[Bob Heine]

I lived in Manly from 1989-91 and realized what a giant pain the RTA could be. Just because I'm missing a left elbow they made me put a spinner knob on the steering wheel and told me my new Toyota had to have the hand brake moved from the center console to the right side of the driver seat. Local Spastic Center sold me a spinner and recommended a mechanic who had a 1958 Holden hand brake he'd install for $800 -- I didn't even make an appointment. When I received my license it didn't mention either restriction so I just installed the $84 spinner (apparently the cheap ones are illegal so the usual auto supply stores can't sell them). Met a cab driver who was similarly inconvenienced and asked about it -- he asked "Did you take your driving test at the Manly Station?" and my "Yes" explained it all to him. Seems to depend on the people you work with as to how hard a time you get.

I looked for bump steer specs in my 1972 Service Manual and in my 1976 Chevrolet Power book. Couldn't find any specifics for bump steer in either one. Did you install an engineered kit or make up your own? If it's a kit, the supplier should have the information you need, especially if the goal is to prove it's no worse than stock.

I'm not an expert in any way but I believe the two measurements your compliance engineer should be interested in are the mounting position of the inner tierod end and the length of the tierod. If it's close to he stock location and length, that might be enough. Good luck with the RTA! Oh, for the stateside folks, the RTA is Roads and Traffic Authority in Australia. They make the California Air Resources Board people look friendly.

 

[m_fry]

G'day Bob,
Since posting this, I have found out the original bump steer measurement, which is 26mm at the outside of the tire. A bloke called Martin Waddingham from the Corvette Conversion Centre in Adelaide SA, who has developed a RHD r&p unit for C3's helped me out.
Just out of interest, I adapted an 84 Holden Commodore rack and it looks pretty good. I had to shorten the rack slightly to suit. I can now get the compliance engineer to do the bump steer plot.

Mark

 

[Bob Heine]

G'Day Mark,

Glad it worked out for you. Bob's your uncle with the engineer now! Hope he doesn't give you grief over anything else.

 

[JohnZ]

GM never published any bump-steer numbers, either in the Engineering Specifications or in the detailed AMA specifications submissions; doing so would admit that the front suspension geometry was less than optimal. The only meaningful comparison would be a bump-steer plot of an original car vs. the plot of the conversion.

 

[m_fry]

Regardless, I have engineering approval.

Mark

 

[Bob Heine]

Regardless, I have engineering approval.

Mark

Brilliant!

Any chance you can post some pictures of the conversion? Here in the States we don't have to worry about converting RHD cars but I seem to recall New South Wales having a rule that LHD cars had to have a foot-high sign on the back warning that the car was Left Hand Drive.

I sort of understand the RTA getting involved in the conversions. I'm pretty sure bicycle chains and sprockets were involved in the some of the older steering conversions I saw at local car shows.

The C3 Corvette has the engine offset to the right by some amount so there isn't room for a stock steering gearbox even if you wanted it. Even your R&P setup must be tight.

Did you have to put a heater/defroster setup on the left side of the firewall? How about A/C -- or is the Gold Coast a convertible paradise?

 

[m_fry]

G'day Bob,
I'll post some photo's in the next few days, working hard at the moment to put the front suspension back in (what a bitch). Mines a non air car. The original mirrored conversion was done by 4steer conversions (what a f***up) of Anahiem in California, see this link AMERICAN VEHICLES CONVERTED TO RIGHT HAND DRIVE

Mark

 

[Bob Heine]

Mark,

That's a fright. I can see the steering wheel is offset a little extra to the right (barely room for your hand to clear the door panel). You might consider a 14-inch steering wheel from a later model if the column can't be moved. Also seems like the wiper door canister dictated the position of the brake booster. You'd think it would be the other way around. Is it their pickie or is the rack mounted to sheet metal brackets? Looks like the engine or oil pan would hit the universal every time you downshift. Scary looking!

Interstate highways and most local roads in America have 12 foot wide lanes. Only the motorways in Australia have lanes that wide. The first time I drove to work behind an Aussie big rig I realized the lanes are quite a bit narrower (three meters wide but lane markers make them look more like eight feet wide -- same as the big rigs). For me there was no such thing as 'acceptable' play in the steering system when driving in Australia. The typical stock Corvette C3 steering would be a nightmare Down Under so a rack & pinion flapping in the breeze would turn the car into garage art. It's good to hear that you got some local expertise to reverse the abortion.

 

[m_fry]

G'day Bob,
The major problems were that the flaming river r&p unit that they used, was to short, so they offset it and that meant that the tie rods were of unequal lengths - the left side was approx. 100mm (4") longer than the right, which would create horrendous bump steer. These blokes do rh conversions for the Australian market all the time, they should have known better. The support bracket was made from 2"x1" rhs and the end plates were 6mm plate, plenty strong enough. As for the interior there's plenty of clearance room between the steering wheel and the door.
As for the engine, the useless p***ks cut the rh engine mount from the chassis and relocated it higher to give them bearly a 1mm of clearance past the engine pipe for the new intermediate steering shafts. They also mounted the rack to high, the rack should be in a straight line with the tie rod ends so that you have even travel up & down thus reducing the probability of bump steer, you can see in their photo's how much angle there is from the rack to the tie rod ends, this would pull the wheels dramatically on the downward travel of the suspension and probably push them out on the upward travel.
I've had my roadworthy certificate done so all that's left is for me to go into the transport dept. and get my rego completed. I'm not entirley happy with the Holden commodore rack that I have used, as it gives a rather poor turning circle, but the steering is very light when driving, no need for power assist.
I'll try and get some photo's today and post them.

Mark

 

[Bob Heine]

G'Day Mark,
I went to the Flaming River site and now I can see how the original rack was mounted. I also see the horrendous angle of the right side steering link -- I thought it hadn't been attached and was just hanging down at that angle. Your setup looks really nice and I like the end takeoff configuration. I have the Steeroids system -- it's the only one that offers a big block version but it's a center takeoff. Seems to function just fine but it looks home made. It does offer a better steering link angle so I understand the tradeoff.

I think all the rack & pinion setups sacrifice some turning radius. However, it looks like you have the tie-rods in the manual steering locations so that might aggravate the problem. You could try the other location -- it would increase steering effort but might be a worthwhile tradeoff -- making a huey on a divided carriageway without having to reverse (or break the rearend loose) is handy.