Bump steer

[Paul Deslandes]

Although it didn't appear in LF, I did change the measurement method slightly which made it easier to do.

http://www.fastgrandad.co.uk/documents/Measuring%20and%20Correcting%20Bump%20Steer%20on%20a%20Caterham%207.pdf

9mm seems to work for nearly everyone, irrespective of standard or wide track, the older combined spring top and shock mount or the later separate mounting points.

Also make sure that your rack has both top and bottom mounts as mine didn't have the lower one, making the situation even worse.

It really is worth the effort.

Paul

[SM25T]

Just make sure holes in side skins are big (high) enough to clear gaiters. Mine needed enlarging with a deburring scraper.

[p.mole1]

Thanks, 

It hasn't quite gone to plan,after finally getting the track rod end off, (it was stuck fast on the taper) I found my tie rods were longer than anticipated almost bottoming out in the track ends. I could not use a male rose joint with a threaded spacer unless I cut the tie rods down and I don't fancy doing that.

So now I am looking at using 1/2 unf female rose joints these are 15mm shorter but due to the length of the tie rods this still leaves 20mm of thread inside the the joint but these are not available with a 3/8 bore so I will need some 3/8 to 1/2 adaptors.

[SM25T]

Why not try raising the rack by 9mm first ?

[p.mole1]

I am not keen on enlarging the hole in the body work

[Jonathan Kay]

So now I am looking at using 1/2 unf female rose joints these are 15mm shorter but due to the length of the tie rods this still leaves 20mm of thread inside the the joint but these are not available with a 3/8 bore so I will need some 3/8 to 1/2 adaptors.

I'm confused... what would be the ideal thread and length for the Rose joint?

Jonathan

[SM25T]

I used a deburring tool on mine ... only took a few shaves to get the required clearance. Certainly not the 9mm the rack was raised.

[elie boone]

Rather than having made 3/8 taper pins you could have drilled the steering arm with a 1/2" and use a bolt and spacers.

BTW rule of thumb is that u need the length of the dia of a bolt to be safe.

[p.mole1]

It would seem never take anything for granted. I fitted my rose joints and taper pins and I was pleased with my results. I lowered the rose joints 5mm and measured the results worse! It would seem in my case the rack would require lowering and don't just guess what spacers you need as a few MM makes a significant difference. 

Unfortunately my taper pins are not long enough to raise the rose joints the required height as I assumed that all the racks required lifting not lowering. back to the drawing board

[p.mole1]

I am having some longer taper pins made, as this is my only option. My car is a 1995 vintage has anyone else with a car of this age checked for bump steer

[Paul Deslandes]

My car, referred to in the article, is a 1995 deDion Vx 2 litre​. So yes.

Indications are that cars of that era with standard steering rack clamps need the rack raised by 9 or 10mm to eliminate bump steer. 

The increase in the panel hole size is nothing compared to the holes if bump steer throws you into a ditch 

Paul

 

[Markiebabes]

Just found this might be usefull for info 

http://www.longacreracing.com/technical-articles.aspx?item=8162 

[p.mole1]

Bump steer cured, I ended up effectively lowering the rack by lifting the track rod ends. I used a 20mm spacer with a spherical rod bearing. I have no idea how this equates to the standard track rod end but the difference it's made is like night and day.

[paul_w]

great that it's sorted, but odd that it seems to be the opposite way to everyone else! I wonder if the rack has been changed for a different length one at some point, maybe from a later or earlier car? Not that it matters really...

I have all this to look forward to on my S1, that has the rack (an upside down LHD Triumph Herald unit!) mounted behind the wishbones, so god knows how close I'll get to eradicating bump steer once I get it all up and running. They'd only just moved on from split beam axles when they designed the S1, so I'm not expecting it to be geometrically perfect :-D

[Richard Price]

P.mole1,

I agree with paul_w, it does seem odd that you've lifted your tracked ends!

Have you measured your bump steer characteritics since fitting your spacers?

 

[p.mole1]

Hi Richard, as standard my car had about 1.5 degrees of movement through its full travel! I just followed every ones advice and assumed it would need the rack  lifting however this made the situation much worse. I have now got the bump steer down to about 0.3 degrees I could possibly get it lower but that seems close enough. To my knowledge it's an original rack,I had to remove it when I purchased the car as it had not been installed correctly It needed centering and moving on its splines and  there was no pre-load on the rack damper.

[Ivaan]

Do you have the correct mounting blocks for the rack?

 

Sounds as if yours is raised higher than usual?

[p.mole1]

You could be right as it looks like a may have been able to machine a few mm off the bottom of the clamps, however I don't think the rack had ever been touched till I bought the car.