Steering.

RobDorey · #1 3rd June 2009, 17:42

Does anyone know what the Marlin steering rack is off?

I've got a sneaking suspicion it's different from a road car rack as is only has about 3 turns, lock to lock.
The upshot being that you get a lot of unneeded feedback on bumpy roads.

I'm thinking about fitting a road rack and a steering damper from a VW beetle to make the ride a little bit smoother.

Any thoughts anyone?

MartinClan · #2 3rd June 2009, 20:04

I seem to remember it's from a P100 - that was the old Ford pickup based on a Mk4? Cortina.

Don't know why I remember that - perhaps someone else can correct me?

Robin

peterux · #3 3rd June 2009, 22:24

I had that number in my mind but like Robin can't remember why?

Looking at this picture I found with google, it sure could be....

http://media.photobucket.com/image/f...Picture033.jpg

I get a lot of feedback through my steering wheel as well. If you hit a pot hole or drain cover badly my steering wheel will jump out of my grip. I still have the old rubber bushes fitted and wonder if it will be better with polybushes?

Not sure if changing the rack will help?

MartinClan · #4 4th June 2009, 07:35

Quote:

Originally Posted by peterux

I get a lot of feedback through my steering wheel as well. If you hit a pot hole or drain cover badly my steering wheel will jump out of my grip. I still have the old rubber bushes fitted and wonder if it will be better with polybushes?

Hmm... I haven't had that problem - but then I have avoided as many pot holes as I can in case the front wings fall off....

Robin

RobDorey · #5 4th June 2009, 09:20

I've converted my top wishbone joints to rose joints and have fitted fairly hard poly bushes to the bottom wishbones (I have a new set of these in my garage if anyone wants them), but this didn't really make a big difference to the ride quality.
I'll do a bit more digging about about the rack info.

MartinClan · #6 4th June 2009, 10:18

Quote:

Originally Posted by RobDorey

I've converted my top wishbone joints to rose joints and have fitted fairly hard poly bushes to the bottom wishbones (I have a new set of these in my garage if anyone wants them), but this didn't really make a big difference to the ride quality.
I'll do a bit more digging about about the rack info.

That's interesting. Any chance of some pictures?

Just one thought. What size tyres are you running. Very low profile/wide tyres are bound to increase the feedback through the steering.

Robin

Patrick · #7 4th June 2009, 16:45

my steering vibrates a bit too but it doesn't bother me. I've got polyflex bushes at the bottom and rally design hard bushes at the top. I've got 205/60/R15 tyres

alackofspeed · #8 4th June 2009, 17:13

3 turns lock to lock isn't particularly quick - many sporty hatchbacks are in the region of 2.5 to 3 turns.

Are you sure you're not suffering bumpsteer, and it's this that tugs the steering wheel when only one front wheel hits an pothole? Presumably there's no tugging at the wheel if you go over a speed bump or some other road defect that induces a equal amount of bump across the axle?

Mike · #9 4th June 2009, 18:55

Quote:

Originally Posted by RobDorey

Does anyone know what the Marlin steering rack is off?

Any thoughts anyone?

Rob

The Cabrio certainly uses the Sierra P100 rack. It looks just the same as you guys have on your Sportsters.
I've also noticed a few other parts which Marlin supply which look like they come out of the Ford pattern stock bin.
Rgds
Mike

Chris Cussen · #10 5th June 2009, 07:20

My Cabrio uses a standard Sierria rack striaght off the donor car.

Mike · #11 5th June 2009, 08:48

Quote:

Originally Posted by Chris Cussen

My Cabrio uses a standard Sierria rack striaght off the donor car.

Chris
How many turns lock to lock has your rack. I've just checked mine at 4.25
Mike

Patrick · #12 5th June 2009, 09:36

I phoned marlin about this years ago as our rack was 4 turn IIRC, they just said "yes that's right"

Chris Cussen · #13 5th June 2009, 17:45

Disappears into garage (again) - grunt!
4.3 (ish) well just a bit over 4 1/4

peterux · #14 5th June 2009, 22:04

Quote:

Originally Posted by alackofspeed

Are you sure you're not suffering bumpsteer, and it's this that tugs the steering wheel when only one front wheel hits an pothole?

Not sure, but it sounds like it could be on mine?

I found this interesting article about measuring bumpsteer....

http://how-to-build-a-pilgrim-sumo.w...ing-bump-steer

peterux · #15 9th June 2009, 12:21

Quote:

Originally Posted by RobDorey

Does anyone know what the Marlin steering rack is off?

I've got a sneaking suspicion it's different from a road car rack as is only has about 3 turns, lock to lock.
The upshot being that you get a lot of unneeded feedback on bumpy roads.

I'm thinking about fitting a road rack and a steering damper from a VW beetle to make the ride a little bit smoother.

Any thoughts anyone?

Hi Rob,
I rechecked the tracking on my car and reset the height at the front and now my car feels completely different.
I've lowered the front of the car almost to the lower limit taking care to get each side at the same height. On mine that is about 3 threads showing on the Gaz dampers. I've reset the the tracking to zero degrees toe (as best I can?) and i'm running 5 clicks on the dampers.

It made a tremendous difference to the feel of the car at speed and it has lost all the skittishness that I had before. Reaction through the steering is now non-existant. Steering at parking speeds is now heavier but that is the only downside.

Just for reference, i'm running with the standard non-adjustable BMW dampers on the back, maximum caster and 18psi all round.

I'd try adjusting your suspension before making any other changes,

cheers

Peter

alackofspeed · #16 9th June 2009, 16:14

Interesting to note that when you lowered the car, the problem is less noticeable.

"krazyken" as he's known on this forum, has a 5exi which is running the standard Marlin suspension, and I understand the only way he could get the front end to perform properly (roll centre, and bumpsteer I believe) was to set the ride height very low (circa 100mm I believe) at the front.

Another 5exi owner has been trying to resolve the bumpster on his 5exi, but within the limits of sensible rack relocation, he is unable to dial all the bumpsteer out when running a "sensible" ride height.

It seems fairly plausibe given all the suspension systems are Marlin's design (using OEM parts in places of course), that there might be similarities in the dynamic geometry of the Sportster and 5exi.

I spent a good few hours last Thursday resetting the bumpsteer on my 5exi (heavily modified from the factory set-up), and when you do get the bumpsteer nailed, the car drives in a far more confidence inspiring way. With bumpsteer, it is simply horrid!

The article linked to above is interesting, however the method employed seems a bit complicated for what is a very easy measurement to make. The gauge I made is a bit like that shown in the picture linked to below - I bought a sheet of mdf, 2 hinges, and a dial gauge. It cost about £15 all in, and with it I've managed to dial the bumpsteer down to below 1 minute of toe change, when moving the wheels through 80mm of travel.

Allan Staniforth (I think that's the correct name) has written a good book on suspension, which I've found very helpful when trying to understand what's happening with my car.

peterux · #17 9th June 2009, 22:35

Quote:

Originally Posted by alackofspeed

Interesting to note that when you lowered the car, the problem is less noticeable.

"krazyken" as he's known on this forum, has a 5exi which is running the standard Marlin suspension, and I understand the only way he could get the front end to perform properly (roll centre, and bumpsteer I believe) was to set the ride height very low (circa 100mm I believe) at the front.

Another 5exi owner has been trying to resolve the bumpster on his 5exi, but within the limits of sensible rack relocation, he is unable to dial all the bumpsteer out when running a "sensible" ride height.

It seems fairly plausibe given all the suspension systems are Marlin's design (using OEM parts in places of course), that there might be similarities in the dynamic geometry of the Sportster and 5exi.

I spent a good few hours last Thursday resetting the bumpsteer on my 5exi (heavily modified from the factory set-up), and when you do get the bumpsteer nailed, the car drives in a far more confidence inspiring way. With bumpsteer, it is simply horrid!

The article linked to above is interesting, however the method employed seems a bit complicated for what is a very easy measurement to make. The gauge I made is a bit like that shown in the picture linked to below - I bought a sheet of mdf, 2 hinges, and a dial gauge. It cost about £15 all in, and with it I've managed to dial the bumpsteer down to below 1 minute of toe change, when moving the wheels through 80mm of travel.

Allan Staniforth (I think that's the correct name) has written a good book on suspension, which I've found very helpful when trying to understand what's happening with my car.

Thanks, John, I think your theory is plausable and I expect Mark designed both cars to run low to the ground.
I think i've got that book somehere but this is the first car i've owned where you can change so much, so it's all new to me.
I also recently read an article that made me realize how important it is to get the suspension height equal from side to side. I've done my front but still need to check/adjust the back .

...peter