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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 15th May 2013, 07:21
EXI Turbo EXI Turbo is offline
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Default Rear Suspension - Again

Now that i have a few miles under my belt and have fixed most of the initial issues that have come to light I need to turn my attention to the back end.

I have joined that group of people that have experienced that scary wayhay feeling when lifting of the power, must look strange from behind as I accelerate away only to swerve violently when I ease off.

I have been looking at the very comprehensive post from Big Rich (thanks Rich) and am planning to go down that route to see if it makes a difference.

Looking around it seems that the Aurora AM-8TS studded rod ends are no longer available .

Do I need to use a studded end on the outer side or has anyone gone for a rose joint and bolt and if so did it work ?

many thanks

Nick
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  #2  
Old 15th May 2013, 11:41
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Smile Rear End woes

Nick,

I know that Ric H has done a similar mod a few years ago after seeing mine and has used a bolt with nut.....very close to the wheel rim though and needed some trimming of the nut if I remember, but does work....and also has the benefit of more thread sticking through to get a full nut on.

Also, if I remember correctly either Steve (SDMC001) or Mike (MikeN) had some bespoke spacer turrets / bolts made that took a non studded rose joint.

....hope this helps.


Rich
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  #3  
Old 5th June 2013, 19:13
Ric H Ric H is offline
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Hi Nick,
As Rich says, I went with a rose-joint and bolt option. I used a high-tensile socket screw with, as he mentioned, the head ground down to lower its profile. The reason for this arrangement was that it allowed me to get more spacers under the joint and raise it as high as possible. I used a laser pointer projecting from the wheel onto a screen to plot the toe angle through the suspension travel and found that with this arrangement I could all-but eliminate the bump steer. And the end result is that there are no longer any lift-off change-of-pants moments. As you can see on the photos below there isn't a lot of clearance to the wheel though - put it this way, I had to move the wheel balance weights further into the rim to stop them fouling...
I realise it looks a bit in the second photo as if there is a corresponding groove worn in the rim but this is the shape of the rim (I just had to go out and check against the front wheels to be sure) and the fact that the joint stops brake dust building up on this bit!

Richard



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Old 6th June 2013, 08:27
EXI Turbo EXI Turbo is offline
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Thanks Rich I have gone for a similar option using Aurora rose joints and making up the bar as per the previous post from Big Rich and from the short distance I have driven it appears to have made a big difference.

But on the test drive I found

the steering column is fouling on the break pedal so working on that at the moment

Both rubbers on track rod ends on the steering arm have split (only done 200 miles) . when replacing these I found some sharpe edges so hoping that is the issue. Also having problems getting the toe in angle sorted as full adjustment does not allow for the correct alignment .

Also taking the opportunity to upgrade the springs to 10" 300lbs as mentioned in a few posts.


so hopefully will make a big difference on the next run
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  #5  
Old 6th June 2013, 11:24
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Nick,

I too had this issue on the front track rod ends....boots were getting cut by sharp 'welding spatter' on the arm. Having dressed the offending item and renewed the rod end joint I haven't had a reoccurrence in 5 years.

Rich
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Old 6th June 2013, 17:36
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Interesting to see the bump-steer solution in Richard's photos. Are people keeping a watch at the toe of the weld on the taper insert? The arrangement puts a substantially increased bending load into the insert, and if it were to fail you'd imagine it would first show at the toe of weld - combination of heat affected zone and relatively stiff insert meeting plate.
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Old 6th June 2013, 19:06
chrislandy chrislandy is offline
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err... looking at the photo I think thats a bad idea.

When you grind the top off the bolt you have re-heated the metal so it won't be gr8.8 or higher any more plus there's very little of the head left, one big pot hole on full chat round a corner and that could be game over.

The increased eccentricity with the spacer would as previously mentioned introduce a high bending moment into the bolt when it's probably designed (if designed) for pure shear.

You should also have a few turns of the thread sticking out below the nut. If you made a propper spacer up then while it wouldn't effect the actual bending moment in the arrangemet it would increase its section modulus when combined with a properly torqued bolt.

Is there no scope to move the steering rack somehow so you can decrease the spacer length and keep the rod angle down?

edit: just re-read it the rear do nix the steering rack comment! Still, you really need to reduced the spacer length
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Old 6th June 2013, 19:17
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John,
Good point about the weld. I do fairly regularly inspect the bits of the car I'm concerned about but that's not been on my list. I'd been working on the basis there isn't a great deal of load in it (and I hope there isn't given the stock arrangement it came with!) but I guess under combinations of hard acceleration/cornering it will load up as the contact patch moves outwards. I've wondered on and off about welding a new turret structure onto the upright (wouldn't need an insert or anything fancy with the rose joint) - I could move the joint forward a few mm while I was at it to increase wheel clearance at the expense of a little toe stiffness. I think I'm happy enough with my welding now to do that . I'll keep an eye on it anyway.

Nick,
I personally didn't find the 300lb springs on the front to be a good mod - not on the road anyway. It's too stiff for the weight on the front. I wrote something about it a few years ago here (I notice the link to spring/frequency info I posted then is now broken - try this instead). You'll see that 300lb on the front of this car gives very high frequency, not well matched to the rear. I've still got my calculator spreadsheet if you want to play around with the numbers.
Since then I've got the ARB installed and the combination of lighter springs and ARB is a winner I think. Also got split front/rear brakes and sorted the bias problem so the back no longer feels as if it's trying to overtake the front under braking. Much better all round. I'd almost say I'm happy with it these days!
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Old 6th June 2013, 19:42
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300 front, 350 rear on my car.
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Old 6th June 2013, 20:15
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Chris,
The screws are 12.8 and were ground carefully with cooling periods to avoid affecting the temper. There's actually rather more of the head left than it might appear in the photo, and the head is only resisting bolt tension rather than dynamic driving loads. Also, the nut you see is a nyloc (you can't tell from the photo angle) and does have a thread proud.
The bending moment is an interesting point though. As I mentioned in the post above (which crossed with yours I think), I'd not really been concerned about load in the toe link. Just done some back of envelope calcs based on conservative assumptions about how much load it might see in worst case scenarios with the conclusion that it's OK for a static load but does give me some concern over fatigue life - i.e. it's not necessarily the right side of the endurance limit where I'd like it. It's not going to see many cycles at that load but still, I shouldn't have to rely on space rocket safety factors. I might accelerate an improvement plan.
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Old 6th June 2013, 20:18
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John, are your spring ratios unchanged from stock? I guess given that you've got heavier springs at the back too then balance is restored...
High frequency though - I guess it makes for a more track focussed car (there's a surprise!).
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Old 6th June 2013, 21:21
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Can't remember what springs my car came with from Marlin, but they'd have been too soft for my MTB - the car was daft.

Don't forget my car has front and rear anti roll bars, different movement ratios and unsprung mass (might be greater than it was originally). Ride quality is still absolutely acceptable for what the car is - any softer and it'd lose its purpose.

I suspect the fact I've stayed true to "proper" 50% profile sidewalls has helped my case with primary compliance.
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Old 7th June 2013, 07:09
EXI Turbo EXI Turbo is offline
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With regard to the rear arm, I have more clearance to the wheel and have not needed to grind the head of the bolt off,

I have used these spacers with one pointing down so it fits snuggly in the hole and the other points upwards so the rose joint can move through the full range required. I did file the underside of the bolt head slightly so it did not catch on the rose joint, plenty of thread showing through also



http://www.ebay.co.uk/itm/1-2-UNF-Ro...item257b6f15ea


Got the springs now so will see how they go once I have fixed the steering column issue, doesn't take to long to swap out if I need to reduce and say go for 225 lbs as others have also done.
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Old 1st July 2013, 10:04
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I managed to get out at the weekend and finally check out the mods . The wahoo feeling when I lift off after accelerating to 70 has just about disappeared - thanks Rich.

Still a bit twitchy when driving constantly adjusting the wheel especially round here with the state of the roads.

Maybe 300lbs springs on front a bit too much , may change and will also re -check the alignment using the diy method mentioned on the forum

thanks everyone for your help in getting me this far
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