Rear arb drop link ‘bosses’.

[Nigel B]

Having owned my 420R for over two years, I finally got round to having it flat floored & properly set up a few weeks ago. 

I took it to DPR at Redhill who did a fantastic job & have transformed the feel of the car.

My rear arb is currently on the second softest setting. DPR recommended using the stiffest setting with the current set up. 

Although I’m delighted with the way the car feels, I am interested in trying DPR’s recommend rear arb setting. However, I don’t have sufficient clearance to be able to use the final, stiffest hole as the drop links make contact with the wheels. 

Apparently this is a recognised issue & Caterham have produced a boss which enables the drop links to be moved inboard of the arb to clear the wheels.

I’ve ordered the parts from Redline, but I’m not entirely sure how they fit! I presume they simply bolt to the arb bracket & the drop links are screwed into the other side?

Does anyone have a photo of the boss installed on your car? There is a threaded hole drilled through the boss, but the thread size is different on each side. I’m assuming the larger thread is the side that bolts to the arb bracket, but does anyone know what size the thread is & what type of bolt is used to secure it? Is a spring washer involved? 

I’m struggling to find the answers & I’d like to get it right.

Cheers in advance!

Nigel.

 

[Geoff Brown]

Do you really want to go that stiff?  The effect of that much adjustment may surprise you but not in a good way.

Firstly try going up one hole at a time to ascertain how the car feels on the road .

After experimenting with adjustment with my R400D RARB & frankly being scared to death of the back end handling when on the most forward hole I set it on the second hole up & is quiet pointy enough thank you!

[AG2728]

#2 Firstly try going up one hole at a time to ascertain how the car feels on the road .

I would wholeheartedly agree with Geoff.

I use my car (420R) for sprinting and it is purely for track use. I'm running the rear on one hole from full soft at the moment and would actually prefer to use the end (full soft) hole in the ARB blade Unfortunately this is not possible as the drop link and ARB blade then fouls the CV joint under compression.

Obviously just my opinion but I wouldn't even consider going any stiffer on my own car and am even seriously thinking about ditching the rear ARB altogether.

Andy

[Nigel B]

Well, I have to admit, I was very surprised when DPR suggested it! I was taken aback. Having briefly tried the second stiffest setting last year, I found the car felt very sharp & 'pointy' on the way into a corner, but would snap into oversteer very abruptly on the way out!

I questioned them very closely about the wisdom of using the stiffest setting, but they were adamant that it would suit the current set up. 
 

I'm assuming that it will feel different to my last experiment with a stiffer arb setting, because the rest of the set up has changed. But I am mindful of the previous experience (I changed back to the second softest hole after one blat!). But at the same time, DPR have way more experience than me with these things, so I feel prepared to defer to their better judgment, at least just to see how it feels.

[John Vine]

I'd agree with both Geoff and Andy.  I run my R400D on the second-softest setting, too.

Here's a build photo of mine, showing the extension piece:

And this is from my 2008 Assembly Guide:

According to my AG, the caphead attaching the extension piece is M10x12, with a plain washer under the bolt head.

JV

 

[Nigel B]

Thanks John, that's exactly the information I wanted!

Well, I'll give it a try, take the car out for a tentative blat & report back. But by the sound of things, I may well end up back on the current setting! 
 

Thanks for everyone's comments & experiences, it's much appreciated. 

[John Vine]

Re #5, this is what my AG actually says:

"In the case of cars fitted with a rear anti-roll bar, coat the threads of bolt (fastener pack 30R011A Item 17) with Loctite and pass through the lower hole in the ARB bracket, through a plain washer (fastener pack 30A001A Item 16) and into the hexagonal, threaded, extension piece.

Tighten all fixings to a torque of 47 Nm."

Item 17 is a fully-threaded caphead M10x12 (CC P/N BMCH10x12).
Item 16 is a 10mm plain washer.

Note that the washer goes between the bracket and the extension piece, rather than under the caphead as I suggested above.

JV

 

[Nigel B]

That's great John, thanks for the clarification. I'll have a rummage around in the garage & see if I have any of those bolts. I have some bits & pieces left over from the build of my first 7.

Edited to add I do have the relevant bolts & washers. I think I will go easy & just go one hole stiffer, given the general consensus! Thanks for the comments.

[aerobod - near CYYC]

I'm also running 2nd hole from soft on my R400D. Softest was a bit too soft on the track and next hardest was a bit too "snappy", as others have said.

[Roy Blyth]

#2

Call me childish if you like, but when I read "Do you really want to go that stiff?" followed by "Firstly try going up one hole at a time" I absolutely cracked up!    

[Nigel B]

Cheers James, you're reinforcing my concerns! 
 

I can't imagine WHAT you're referring to Roy! 

[aerobod - near CYYC]

Looks like my spacer is installed the same as John's, here is another photo from a different angle:

[Nigel B]

Thanks for the photo James.

I started fitting the offside boss this afternoon. What I was assuming was a fifteen minute job was complicated by the fact that the existing hole in the bracket is too small for the M10 bolt. I started enlarging the hole, but ran out of time.

There's always something isn't there? 

[Nigel B]

Well, having drilled out the holes in the brackets & fitted the new bosses, I initially tried the second stiffest hole.

I went for short-ish blats on Sunday & Monday evening & the car felt fine, so on Tuesday evening I moved the drop links to the stiffest hole & went for a long drive yesterday, south west from Edinburgh & down into the borders along some cracking moorland roads with very little traffic.

Again, the car felt really good. It’s strange, because when I briefly moved from the second softest hole to the second stiffest, last autumn you could immediately feel the effect of that, even when driving at a moderate pace, whereas the effect of the adjustments made this week feel more subtle. 

The car definitely feels more eager to turn in & it feels more agile, yet at the same time, composed. Particularly in a tight series of bends with sharp changes of direction, left & right. I was initially wary about squeezing the throttle too hard on the exit, but as I gained confidence with it, I pushed progressively harder on the way out of bends & there’s no sense of the ‘snappy’ oversteer I experienced before. Traction doesn’t seem to have suffered. 

Admittedly, the weather has been great this week, so I have no idea how the car will feel on cold/damp/wet roads, but the initial impressions are very good. I must confess, I was surprised by how the car felt, given the comments on this thread & with my own previous experiences with stiffer rear arb settings.