Sam's build thread

[Sydneykid]

remind me if I haven't done anything in a couple of weeks. We'll need someone (Gary!) to specify the best material to use...

I'll confirm it with the machinist but from memory our caliper brackets are 6082 T6.

Cheers
Gary

[Sydneykid]

actually if you made the shims more than just that and turned them into a 15mm spacer too, then you would have enough material available in the shim to run new angled threads into them. Still not sure about the alu vs steel arguement on that one though. I'm happy to de-lug my beam as I've got two, so I'm more than happy to be a guinea pig. Really to confirm calcs in the real world you'd need a reliable rear alignment to get a base line. Then say shim it with eibachs and measure the results to confirm you get the settings you want relative to the baseline, and then cut the alu/steel shims at a copy cat angle to what the eibachs were set at. make sense. Problem is your beam is probably completely different to other peoples so a one size fits all approach would be difficult. Dunno if I ws making them for my beam that's how I'd do it though.

I haven't done a beam/torsion axle for toe and camber but I have done a few trailing arms, a beam would be much easier. I just bolted it all up out of the car and measured the toe and camber, then used handful of washers in between the stub axle and the hub/upright until I ended up with the toe and camber that I wanted. Then counted/measured the washers and made up the spacer plates to those measurements. On a 4 bolt stub to get 2.5 degrees neg and 6 mm toe out it was something like;
3 x 1.0 mm washers top rear
4 x 1.0 mm washers top front
3 x 1.5 mm washers bottom rear
4 x 1.5 mm washers bottom front

I just told the machinist those thicknesses at the bolt holes and he adjusted the mill accordingly. When I stuck them on the car it was a mm or so out in the toe and pretty close on the camber. Not perfect, but with big bushes in the trailing arms there was more movement than the difference. Big win on the handling through, even if not perfect by the numbers.

Hope that makes sense
Cheers
Gary

[sambb]

Had a mildly bright light bulb moment today re the gearbox. I'd been running Motul 300 75W 90. I remember when I got the box built that the builder had said that was a little thick when hot for his liking for the synchros, but I went with it anyway as its what Wavetrac USA revommended for the diff and lots of others had run 75W 90's too. Thinking about it previous to that I'd only ever run the factory oil 75 monograde and Redline MTL 75W80 and had never had anything as thick as whats in there now. I just cant see how with more or less the same linkage throws and also new synchros I can be running into shift problems, particularly when its hot, so I'm thinking i'll go back to an oil that's thinner when its hot. After a tonne of searching around, lots of guys that track their cars are saying that they just cant fault the factory oil.

VW OEM recommended oil is part# G 070 726 A2 which replaces G 055 726 A2. Its $30 a litre. Its Ravenol MTF-3 which is SAE 75W monograde, so I'm going to give that a run.

This all hinges on the theory that what I've been experiencing is a synchro problem and not finding the gear that I'm going for. What happened at wakefield was that the linkage was so weak that when I went for the gear that I couldn't get, the linkage was the weak spot and was jumping out of its track. Once I'd strengthened everything up at SMSP the linkage wasn't coming out anymore, but I was still stuck between gears. This points to the linkage not being the drama, but synchros. However there's no crunch no nothing, just a silent no find of the gear I want?? we'll see.

PS I have a bottle of Redline MTL 75W80 on the shelf that I wont use now that I have the wavetrac as it has friction modifiers in it. If anyone wants it cheap, cash, Sydney let me know. Or if you have a bottle of the factory stuff for a swap we can do that too.

[sambb]

Gary did you ever have a crack at this RARB? If you can give me a best guess of what tube di/wall thickness might approximate a 20mm whiteline bar, I can probably get something happening.

[Sydneykid]

Gary did you ever have a crack at this RARB? If you can give me a best guess of what tube di/wall thickness might approximate a 20mm whiteline bar, I can probably get something happening.

Chrome molly 25.4 mm (1") OD with 6 mm (1/4") wall thickness should do it.

Cheers
Gary

[sambb]

Gary wondering if you might be able to tell me if I'm doing something fundamentally wrong when calculating front strut compression travel until spring coil bind. I've put my 200mm 7kg/mm springs in and pulled the 180mm 7kg/mm ones in the hope of picking up more bump travel, and am setting up the new damper stroke to accommodate that.
With the new spring off the car, its top and bottom tails where it has been ground flat sit more or less in line with each other. They are obviously coil bound against the first coil that winds off them. That distance wont change and is 16.10mm thick. There are then 5 free coils @ 11.68mm thick.
So I calculated the coil bound length at 16.10+16.10+58.40=90.6mm
Spring captive length at ride height = 155mm (seat to seat)
available damper shaft travel until coil bind = 155-90.6=64.4mm

Does that method look correct to you? Alternatives are to measure the freespace between the free coils with the car at ride height and add them up OR I could just go down to Eibach and ask them to put the spring in their press and drive it down to coil bind and check its length. What do you reckon?

[Sydneykid]

Gary wondering if you might be able to tell me if I'm doing something fundamentally wrong when calculating front strut compression travel until spring coil bind. I've put my 200mm 7kg/mm springs in and pulled the 180mm 7kg/mm ones in the hope of picking up more bump travel, and am setting up the new damper stroke to accommodate that.
With the new spring off the car, its top and bottom tails where it has been ground flat sit more or less in line with each other. They are obviously coil bound against the first coil that winds off them. That distance wont change and is 16.10mm thick. There are then 5 free coils @ 11.68mm thick.
So I calculated the coil bound length at 16.10+16.10+58.40=90.6mm
Spring captive length at ride height = 155mm (seat to seat)
available damper shaft travel until coil bind = 155-90.6=64.4mm

Does that method look correct to you? Alternatives are to measure the freespace between the free coils with the car at ride height and add them up OR I could just go down to Eibach and ask them to put the spring in their press and drive it down to coil bind and check its length. What do you reckon?

I'm not at my engineering computer, otherwise I could just input the data (# of coils, coil ID, free height and wire OD) and it will confirm the rate and the coil bind height.

You method looks OK (trying to visualise it) and the result looks about right @ 64 mm, rule of thumb bump travel required = 70 mm. Rebound (droop) travel @ 45 mm, rule of thumb = 35 mm. I'd look at around 10 to 12 mm of bump stop contact prior to coil bind, then stick some tell tails (cable ties) on the shock shafts and test it. Personally I'd like another 10 mm of bump travel with 10 mm less droop travel. To get that you really need less coils of thinner wire to give the same spring rate.

Cheers
Gary

[sambb]

legend. thanks for the numbers. Main thing is it looks like I have gained an extra 10mm of bump travel and it was crying out for it. Heading down to Eibach today so they can stick it in the press hopefully so that I can be certain. thx

[Sydneykid]

legend. thanks for the numbers. Main thing is it looks like I have gained an extra 10mm of bump travel and it was crying out for it. Heading down to Eibach today so they can stick it in the press hopefully so that I can be certain. thx

That (+10mm) would be due to the higher spring rate requiring less preload to hold the car up? While you are at Eibach you should get them to check if they have a spring spec (same rate, less coils, smaller wire) that will give you a bit more bump travel.

Cheers
Gary

[sambb]

just got back from Eibach and they were kind enough (for about the fifth time) to stick both springs in the press and measure their coil bound height. The 7kg/mm 200mm spring was at 9360N at a coil bound height of 91mm. The 7kg/mm 180mm spring at 9000N sat at 76mm when coil bound.
So for the 200mm spring I was off by 0.4mm and i'd calculated the 180mm spring at 75.8 so I was off by 0.2mm. I think from now on i'll leave Eibach alone re coil bound spring heights because I've sussed how to measure it, which is good for the future.
So after you subtract the coil bound height from the springs captive height when the car is at its desired ride height (this varies between the two springs and from left to right too due to a heavier rhs of the car) , you get the amount of bump travel available until coil bind. On right front (which is the shortest travelling corner as the spring is more pre loaded to hold ride height) he 200mm spring gives me 64mm travel and the old ones 58mm travel. That means I've only picked up 6mm extra of travel which on the face of it seems turd. However the 200mm spring needed 936kg to reach full coil bind vs the 180mm spring which needed 900kg which like for like makes the 200mm spring a bit more resistant to reach coil bind than the shorter spring in a like for like bump, which should help.
So I'll set it for 50mm on the shaft assuming that once its 14mm (2/3rds) into its 20mm bump stop everything will be coming to a halt anyway without a massive thump from the locked spring, totalling 64mm of available travel. That's for the RHS which is the worst case scenario corner - the LHS has more travel.