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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin 5exi builds

Marlin 5exi builds Calling all you sexi builders....sorry 5exi builders, show us your progress.

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  #1  
Old 27th June 2010, 15:59
Ric H Ric H is offline
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Default Suspension, ARB & Brakes

Hiya,
Been ages since I've posted on here but I've been continuing with various tweaks and changes, with quite a bit of success, so thought I'd give an update and get some opinions....

Rear Suspension
Not much new here. Last year I carried out the mod to the toe links pretty much as per Bigrich's scheme. Only recent change is that I've made some angle grinder adjustments to the bolt through the outer rose joint which has allowed me to lift it higher without fouling the wheel. End result, having measured bump steer carefully with a laser is that I've got rid of the vast majority, leaving just a very small amount of toe-in during bump, which should induce a little bit of roll understeer so I'm fairly happy with that.

Steering
Did some thorough re-checking of front bump steer and found that by elongating the adjustment holes in the steering arms I've been able to drop the steering joints a little lower and completely eliminate front bump steer. Just this weekend I've also finished stiffening up the arms along the lines John describes. This was after I also noticed the flex in the arms and managed to pick up about 5mm of toe-in on a drive a few weeks ago....potholes eh? Not driven on them yet - I'll report back.

Springs.... and anti-roll bar?
For the last year or so I'd been running on 325lb springs at the back and 300lb springs at the front. A decision that was based on....erm, nothing. Recently I've been doing some reading about spring rates and suspension natural frequencies (like here for example) and have measured the suspension geometry to suss out the wheel rates. After a bit of calculation I've now decided to keep the 325lb springs on the back but drop to 200lb on the front! This gives me frequencies of 1.95Hz on the front and 2.15Hz at the back. I've got a spreadsheet for the calcs that I can post up if anyone is interested.
Having dropped spring weight so much at the front I now don't have lot of roll stiffness so I'm planning to add a front arb to stiffen the front end in roll and hence induce a little friendly understeer. Not wanting to pay Marlin's prices, I've managed to pick up a used elise arb from ebay, for almost nothing, complete with aluminium mounting blocks and bushes but no drop links. The mountings are ideally spaced to sit above the front chassis member in front of the fuel tank but I'm pondering how to connect to the suspension arms. Does anyone have the marlin bolt-on kit or something similar? How have you picked up on the suspension arms? I'm wondering about either some modified lower shock bolts, or a welded on tab near the spring mounting plate but I'm open to ideas!

Brakes
As of a few months ago I'm now running 260mm ZR160 discs with alloy mk2 golf callipers at the back, to go with the 262 / willwood 4-pot combo at the front. Overall braking much improved from the 238's I previously had at the back but I'm suffering from too much pedal travel (makes heavy braking while blipping the throttle pretty tricky!) so I need more master cylinder area. Since it's still locking the fronts while it "feels" like the rears could do a lot more, I'm also wanting to change the balance. The decision to make is whether to fit a single bigger master cylinder and then a bias valve on the line to the front brakes, or to go the whole hog with twin master cylinders and a bias bar. Has anyone tried the assemblies that just bolt in place of the servo?

Sorry that was a bit of an essay. Results so far are very good (unlike this football match I have on in the background....) with the car finally feeling settled and fun (rather than frightening) to drive swiftly, but more can still be achieved. Right, still a sunny afternoon so time to go for a drive I think!

Richard
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Old 27th June 2010, 17:23
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alackofspeed alackofspeed is offline
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An interesting read, and pleasing to hear of someone tinkering away.

Front ARB - my car uses hex section aluminium, tapped with an m8 thread each end (one end is reverse thread), with rose joints into the aluminium bar (which is about 200mm long).

The lower rose joint connects to the lower wishbone via a clevis created on the lower arm.

I've got Civic Type-R rear calipers, along with 260mm rear discs, and with the rover master the front bias was still a problem, so I've now got two master cylinders of different bores, with a natural balance approx the same as a Mk3 MR2. Fine adjustment is done with a balance bar. Quite an easy mod, and the difference it has made, especially on track, is massive.
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Old 27th June 2010, 19:00
Ric H Ric H is offline
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Cheers John. I think I'll probably go the rose joint/turnbuckle route. I did wonder about shopping around and finding an off-the-shelf drop link for something that will do the trick but some adjustability would be nice. I guess I'll press on and mount the bar and then see how everything seems to line up.

Just been out for 40 miles or so round the Cheshire Lanes - very pleasant - no traffic as everybody is probably still in the pub mourning the football result. The steering arm stiffness is quite noticeable - particularly struck me when crossing catseyes at a junction when there was noticeable squirm before. Haven't tested yet but I bet it has less tendency to tramline HGV tracks as well.

Brakes - I think two cylinders will be the way to go. First step is to find out the piston areas on what I've got at the wheels. What's the braking effort like with no servo?

Richard
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Old 28th June 2010, 23:06
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Braking effort is acceptable. Yes it's higher than a typical servo assisted car, but it's not a concern. I'm running DS2500 pads on plain discs.

In addition to the benefit of balance adjustability, there's a significant increase in brake feel, so it's much easier to determine when the wheels are going to lock. I'm not sure quite how to describe the feedback, I can just sub-conciously recognise it easier than was previously the case, much like it's possible to do on a MTB.
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