Sams Polo 3.0

[sambb]

here's a shot of one on an early golf. Good pic as it shows it with a rear ARB fitted too. Seems like a lot of unsprung weight to add when the only real gain over shims is the ability to adjust rear toe easily BUT toe adjustment is a biggn

1976 VolksWagen Golf Mk1 Track Car Build Project - YouTube

[HaydEn]

How much toe adjustment would there really be?

After all you’re just loading up a fairly solid structure (rear beam) If I recall those types of toe arms on MK1’s were to increase rigidity rather than adjustment


Sent from my iPhone using Tapatalk

[sambb]

Dunno. I was watching a vid where a common setup on rally mk2 ford escort (solid live axle RWD) that use the Atlas rear end uses links that tie back to the front of the diff casing to adjust toe by pulling on the live axle assembly. So I reckon a twisty twist beam would be plenty pliable enough to pull or push a couple of mm each side for adjustment in comparison to that. I've emailed SCCH to see if they did it just to lock in their toe or actually be able to adjust it.
On the Polo you'd have to make plates that would fit onto the bottom of the spring platforms to get the link low enough to clear the spare wheel well. They'd look like upside down strut brace mounts basically. If the additional weight was going to become an issue then I'd probably pull my finger out and go to an 'inside the beam' RARB to get the weight back to where it was.

[HaydEn]

If you could get close to where you want to be with washers or shims, then use the bars to force the beam to get the last 1mm or so, that would be awesome.

I just don’t think you’d be able to adjust the beam that much. Only my thoughts, no evidence to back up what I’m saying.


Sent from my iPhone using Tapatalk

[sambb]

me neither ha ha. It would be very cool to have the car on the ground on slide plates and just turn the rods and see an easy toe change. That'd be great but things never come that easy.
Still waiting to get my wishbones welded to take wishbone mounted drop links. Having to go into northern beaches ISO has sort of slowed things. I'm no welder so i'll leave that for a pro but the toe rods I can definitely wrangle now that i'll be back in a workshop and have a spare beam at home to build on.

[Sydneykid]

So because the base adjusters were different lengths all my old measurements for positioning them for correct droop etc were null and void. I spent today fitting them up.
My MCA's have 100mm of shaft travel before bump stop contact. The bump stop itself is 17.5mm thick.
At my guard to ground ride height of 630mm I set the base adjusters up for 38mm shaft droop and 62mm shaft bump travel. That 38mm of shaft droop equated to approx 40mm wheel droop.
But there's a problem i'll need to sort. At ride height and the springs lined up so that the beginning of their free coils are in plain view I was able to measure what the spring travel until coil bind would be. If I measured and added up the air gaps, or measured and added up the coil thicknesses minus the total available length that the spring could travel, I get a measurement of 67mm.
That means the spring will be binding 67-62= only 5mm into the bump stop.
I know this means I need to increase the droop to limit shaft travel in bump but I'm not sure by how much.
What I'm thinking of doing is taking the 17.5mm bump stop and taking a 2/3rd measurement of that assuming that by the time its 2/3rds through its travel it is pretty much arrested anyway. That'd give approx 12mm. If I add this likely max of 12mm of bump stop travel to my 62mm of shaft travel then I could potentially travel 74mm in bump yes?
So if the spring coils will bind at 67mm of travel then I need to add 74-67 = 7mm of additional droop travel on the shaft to make sure that its 2/3rd into the bump stop before coil bind.
That'd give me 45mm shaft droop and 55mm shaft bump before bump stop contact. That seems to be the best compromise between not running excessive droop/limited bump travel, yet still giving a good safety margin RE protecting against coil bind.
I know I need to go to better thin wire springs that sag less at resting height. These ones are 11.68mm di wire and are preloaded to get the desired ride height which hurts things even more. At the moment I just need to get operational until I do that though.
What do you think viewers............Gary!!!....

Sorry for the delay in responding, been doing some physical stuff for a change, rather than computer work. Stuff like rewiring the engine fan, fitting the brake ducting, new sphericals for the rear swaybar and best of all I cleaned all the junk off my garage work bench

As we have discussed previously on the front of a FWD car I allow around 2/3rds of the available shock travel (before bump stop contact) for bump (compression) and 1/3rd for rebound (extension, droop). With 100 mm of travel I would aim for around 65 mm of bump and 35 mm of rebound.

On the rear of a FWD car droop limitation is not a bad thing, so around 75B/25R is OK, even 80B/20R often works OK.

I don't know what bump stops Murray uses on yours, I run between 1,500 to 2,000 lbs/inch, in the trimmable V8Supercar style, commonly between 50 mm and 75 mm in length. Around 15 mm into that bump stop feels like a doubling of the spring rate, can't miss it. Your 17.5mm seems like a very short bump stop, I can't say as I have ever seen one that short.

To achieve more travel to coil bind is why we run the thinner wire less coils combination (eg; Eibach), the spring rate is the same (as the thicker wire more coils combination) but it places more load on the base spring steel material. The reason why the "less expensive" coil winders use thicker wire more coils is because they don't have to use as expensive (higher quality) spring steel as is the case with thinner wire less coils. Commonly with Eibach I can use the same rate spring with say 10 coils of 12 mm wire, 8 coils of 11.5 mm wire or 7 coils of 11 mm wire. Obviously the 7/11 has 43 mm more bump travel than the 10/12.

Happy to talk on the phone if you feel the need.
Cheers
Gary

[Sydneykid]

here's a shot of one on an early golf. Good pic as it shows it with a rear ARB fitted too. Seems like a lot of unsprung weight to add when the only real gain over shims is the ability to adjust rear toe easily BUT toe adjustment is a biggn

1976 VolksWagen Golf Mk1 Track Car Build Project - YouTube

Due to the motion and leverage ratios the change to the unsprung rate wouldn't be as much as you think.

Keep in mind that with the V links you would be moving the entire hub inwards or outwards ie; a lot more movement for less effect. Not just the front of hub outwards as with shims for toe out.

Happy New Year to All
Cheers
Gary

[Sydneykid]

so after finally getting the MCA fronts corrected so that I could fit them up, I moved onto the back MCA's. They were untouched in the accident and had just been waiting to go back in once the front was stiffened up to match.
This time I thought I'd check everything properly. After adding up the fully compressed heights of all the platforms, shims, helper springs etc and the working spring I calculated the fully spring bound length between bottom adjustment collar and the chassis. I then fitted up the dampers without the springs and jacked the beam to check that the damper length/bump stop position was correct. It turned out it wasn't. The springs would have been coil bound and the bump stop was only starting to be active. So I had to wind the base adjuster down to lengthen the damper body. This increases droop and pushes the top of the damper body closer to the bump stop. Once I got it so that the bump stop was fully compressed and the spring was a safe distance away from being coil bound I fit it all up.
Thats where the problems appear.

Basically to get the damper body length correct to prevent coil bind, you end up introducing so much droop that the main spring whilst still connected to the helper is not captive over the adjuster. Now I could spin up a cone shaped aluminium guide to fit into the end of that adjuster cup to get around this, but the other fundamental thing wrong is seen on the damper shaft. The cable tie on the shaft shows how much shaft is taken up in droop and how much is available for bump. After taking it out for a test drive the insufficient bump travel can be seen here:


the tell tale cable tie has been pushed to just below the bump stop. While it wasnt going to coil bind and throw me off the road it was only a smidgen off really hardening up in a nasty way. Once out on a circuit pulling much bigger cornering G's and then riding up an outside kerb, this would definitely be going well into the stop.
SSSSssooooo whats the solution. It seems that the keeper arrangement coupled with a low ride height really restricts travel. I could increase ride height to gain travel but then the springs would fall clean out at full droop, and I need it to operate at that ride height.
advice needed!!!

Try relocating the helper/tender spring to the top and see if that helps with locating the main spring over the adjuster.

As per the post above, on the rear of a FWD car droop limitation is not a bad thing, so around 75B/25R is OK, even 80B/20R often works OK and I have used 90B/10R on production cars where we weren't allowed to change the rear swaybar. It may well be that, even with the shock length adjustment, there is is too much (droop) travel on the shocks. This is a common problem with "track cars" and easily fixed (by Murray) in using taller droop stops internally in the shock. They sit between the top of the piston and the top of shock body. Al you have to do is to tell them how much droop you want removed.

Cheers
Gary

[sambb]

thanks Gary. I'll have a good read over your replies tonight. I found this vid put out by MCA which should start at the bump stop bit. The footage where the strut is fully compressed into the stop are the same bump stops as whats on my car. When I was doing the checks on the rear they would compress to within 4mm remaining and be able to lift the car off the stand but are initially very compliant. They are 17.5mm free height and dont look trimmable.

The truth about Suspension - YouTube


RE the toe V links I've gotten in contact with Peter Jones who ran that Kamei inspired Golf Mk 1 to see what he says about them.

[Sydneykid]

thanks Gary. I'll have a good read over your replies tonight. I found this vid put out by MCA which should start at the bump stop bit. The footage where the strut is fully compressed into the stop are the same bump stops as whats on my car. When I was doing the checks on the rear they would compress to within 4mm remaining and be able to lift the car off the stand but are initially very compliant. They are 17.5mm free height and dont look trimmable.

I had forgotten about those, I look at them as being aimed at the "low rider" road car more than competition cars, move as a "save the piston from damage" philosophy. Whereas we use the bump stops as a secondary spring, particularly on the rear of a FWD.

For example if we have say a 400 lb spring in the front and then use full length 75 mm bump stop that is ~200 lbs at 15 mm compression then we have combined spring rate that progresses from 400 to 600 over 15 mm. That's good for jumping curbs etc.

If we have say a 400 lb spring in the rear and then use the same bump stop trimmed to around 50 mm that is ~400 lbs at 15 mm compression then we have a combined spring rate that progresses from 400 to 800 over 15 mm. That's good for limiting the rear squat, limiting the weight transfer off the front, but it's also still OK for curb jumping.

Not right or wrong, just different philosophy.

RE the toe V links I've gotten in contact with Peter Jones who ran that Kamei inspired Golf Mk 1 to see what he says about them.

My thinking would be that they are more useful for rigidity rather than toe adjustment, interested in the response.

Cheers
Gary