Help Support Bigcoupe.com

High Speed - Steering is Very Loose

Post in this forum for topics relating to suspension, steering, and brakes

Moderators: bfons, GRNSHRK, ron

Post Reply
User avatar
Bostn635csi
Posts: 40
Joined: Thu Jun 19, 2014 11:40 pm
Location: Boston

High Speed - Steering is Very Loose

Post by Bostn635csi » Tue Mar 20, 2018 9:30 pm

Hello, during the past summer, I was going about 100MPH and I noticed the steering got very very loose. There was a lot of play in the steering at high speeds. I tried it a few times and noticed it when I got over 80MPH. Anything under 80PMG the steering is tight. Anyone have any ideas? Thanks.
Kevin
1988 BMW 635csi, 5-speed
Lachsilber

User avatar
Brucey
6 Series Guru
Posts: 9716
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: High Speed - Steering is Very Loose

Post by Brucey » Tue Mar 20, 2018 11:09 pm

tell us what you have checked and/or replaced in the steering. Also what offset, width etc tyres you are running.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
Bostn635csi
Posts: 40
Joined: Thu Jun 19, 2014 11:40 pm
Location: Boston

Re: High Speed - Steering is Very Loose

Post by Bostn635csi » Tue Mar 20, 2018 11:51 pm

Hi Brucey, the car is still in winter storage for another month. I know the front suspension is newer including the sway bar. The upper and lower control arms are old as well as the bushings. Old steering pump as well with no leaks.
Kevin
1988 BMW 635csi, 5-speed
Lachsilber

User avatar
Brucey
6 Series Guru
Posts: 9716
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: High Speed - Steering is Very Loose

Post by Brucey » Wed Mar 21, 2018 7:52 am

FWIW there can be all kinds of things that are not quite right with the steering, and wheels with the wrong offset exacerbate any troubles that you might be having. The steering box in an E24 (when new) is only play-free in the centre position. Over time, the steering box wears and the steering may not be play-free in the exact centre any more. You can adjust the play in the steering box (there is an adjuster for this purpose) but if you overdo it on a worn steering box you will find two tight spots either side of centre. If the steering box is at all tight, probably it is doing the gubbins inside no good at all. Even with two tight spots, a worn steering box may not be 100% play free in the centre position. Some folk adjust the track rods unevenly so that the worn spot isn't quite in the straight ahead position any more; this is OK but obviously the steering geometry isn't perfect any more and if you do enough tight turns the tyres will wear oddly.

If you have wheels with the wrong offset fitted, the effect of the scrub radius is to impose a thrust load into the steering linkage all the time. This thrust load is essentially balanced, on a smooth road, but on one that isn't smooth, it isn't balanced. You can feel if this is happening because the car will tend to follow ruts in the road, follow cambers, and the steering will be heavier than normal (you will be pushing harder to keep the line) when in a long corner. The exact same things that cause tramlining also impose higher than normal reaction loads through the steering box and will cause it to wear more quickly. With wheels that have the correct offset (and that are not too wide) these forces are very much lower and the steering box has a much easier life. [a Brucey top tip; if you have not done so already, install a magnet in the PAS reservoir (eg on the lower screen); you will pull all kinds of shrapnel (from the pump and from the steering box) out of the fluid, which gives you an indication of the state of wear/wearing, if you continue to find fresh deposits on the magnet.]

Also the aerodynamic forces at speed can be very large. In addition the rear suspension tends to 'squat' slightly under load. Your car looks like it might have a slightly lower static ride height at the rear; if you plan to drive fast, this is basically a terrible idea, aerodynamically speaking; at speed, the car is squatting under power, the rear spoiler is pushing the suspension down too, the air that gets into the engine bay through the grille is vented downwards etc and the net result can be that air gets under the car and lifts the front, unweighting the front suspension and making it feel light. [early E24s without the front spoiler were even worse for this BTW, and yes, it is actually dangerous].

There could be all kinds of things that are not right that could be helping the steering feel weird, but regardless of this, basically it is best (IME) if you set the static rear ride height to be about 3/4" higher than the rear if you want the car to handle at speed. If you have mismatched springs (stiffer at the front, still soft at the rear) it might be better to go a bit more than this.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

masonjones
Posts: 26
Joined: Sun Mar 02, 2014 1:29 am
Location: Austin, Texas

Re: High Speed - Steering is Very Loose

Post by masonjones » Mon Apr 02, 2018 3:53 am

Brucey wrote:
Wed Mar 21, 2018 7:52 am
Also the aerodynamic forces at speed can be very large.
You can see a real life demo of how much lift is generated on the front of the car at speed if you ever forget to latch the hood and then get on the highway. At about 75-80 mph the hood starts to raise up. Gives you a shot of adrenalin if you're not expecting it. Not sure how much the hood weighs but the lift must be taking quite a few pounds off the weight of the front end at that speed.
1985 635CSi

User avatar
603racing
Bigcoupe supporter
Posts: 439
Joined: Mon Dec 20, 2010 5:11 pm
Location: Barry, IL

Re: High Speed - Steering is Very Loose

Post by 603racing » Wed Apr 04, 2018 1:17 pm

As always, Brucey with great info!

I will add that incorrect camber and toe can add to instability, probably throw caster in there too, but not sure how much caster plays into loose steering at high speeds. Also, worn suspension parts can lead to incorrect caster, camber, toe, and several of the situations Brucey described.
'85 635csi - Dark Shark
'13 Jeep Wrangler
'13 Subaru BRZ

User avatar
Bostn635csi
Posts: 40
Joined: Thu Jun 19, 2014 11:40 pm
Location: Boston

Re: High Speed - Steering is Very Loose

Post by Bostn635csi » Sun May 13, 2018 3:53 pm

Update - suspension is being checked out by Turner Motorsports. Should have an update any day now. Thanks Brucey for the full in depth response.
Kevin
1988 BMW 635csi, 5-speed
Lachsilber

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest