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Front Suspension Lower Arm Upgrade - Ride/Handling/Suspension/Brakes/Wheels/Tyres - The Lotus Forums #ForTheOwners Jump to content


Front Suspension Lower Arm Upgrade


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Ok, this may annoy the purists but to me it was a worthy upgrade especially after fitting the Wilwood brake conversion kit supplied by PNM Engineering.

I still enjoy pushing the car hard on track and while the Lotus brakes are adequate for the road, they fall short of what required for a good push around my local track, Mondello Park.

The problem with upgrades is that one leads to exposing the weakness in other areas. This was the case with the brake upgrade. Heavy braking and varying grip on the track surface led to an unsettled braking pattern where you could also feel the wheels folding up under the car accompanied by an unsettling steering wheel vibration.

The problem, as I saw it was the lack of triangulation on the lower suspension arm and a single lower arm bush taking all the braking load. The ARB was some help but even uprated bushes here were destroyed after a decent track session.

I stripped away all the suspension so I could see what was possible. Using a long threaded bar in the lower arm pivot point, I projected the bar forwards  to see where a new pivot could be positioned.

As it happened it fell just to the left and right of each of the forward chassis mounting point respectively. 

1895990747_StrengthingPlatefornewPivots.jpg.1920ed81b4eabe222bd612ec71b34863.jpg

 

aaa

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My next step was to somehow provide a locating bracket for the new additional pivot. This was achieved by making a plate that picked up on the ARB mounts and had welded tabs to fit the new pivot bush.

At this stage I had decided that the new lower arm addition would be a spare rear link arm chopped to provide the bush required for both from arms.

The tabs were welded to the strengthening plate and I also had to add spacers to the ARB mounts to ensure the ARB did not foul against the modified lower arms through out the full swing of the lower arm.109918234_NearSidepivotfornewarm.jpg.01bc6cfab82cee26dfcbab92656adafa.jpg

Once the pivot was sorted, it was straightforward to connect to the lower arm. This was done using the shock absorber mounting bolt and a carefully added M12 bolt.

 

644116261_OffSideconnectiontolowerarm.jpg.aa69c43947073dc504c7010b96dd3d6f.jpg

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OK, I know that ARB bush is a bit worn but hey, its not a garage queen if you know what I mean.  😁

Some more pictures as pictures can explain more than I can.

405156741_NearSidelowerarm.jpg.2bceb3979a544c29910c455ca8126fd3.jpg

 

1189535583_OffSidelowerarm.jpg.ab09ec55e9331247fffc7e698e0c9b67.jpg

This image shows how I positioned the additional link arm to pass through the the bend profile of the ARB. This meant the new lower link was more inboard than I would have liked but it was necessary to prevent ARM fouling the lower link arm.

Detail of the strengthening plate mount and spacer that was added to get the pivot position.

1246243374_OffSideARB.jpg.7a45322b26c1ee3dad7c5edf4f6ae1d0.jpg

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Almost exactly as I've done, except the front mountings were already a feature of the Spyder chassis, as were proper triangulated lower arms, but I ended up modifying my own similar to what you have done.

Negative011.jpg

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Nice work Michael!  I'm sort-of part-way through mine.  I've replaced the trunnions with spherical bearings to use with trunnionless uprights and have made up brackets to bolt in place at the front for a triangulated version of the lower arm, but I'm going to run with the arm as-is (once the car is on the road) for a while.  I've done the spherical bearing first as I want to be able to play with the caster settings - I've built an electric steering column and it may need a tad more caster for the right "feel".  I generally like more caster anyway - more self-centring action.

RIMG0554.thumb.JPG.d08245742e7acfa30d91fe150ec9698c.JPG

 

RIMG0555.thumb.JPG.6134371a861b8a17dd29c72fd82a7e4f.JPG

 

Pete

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I've grafted the end of the Excel front lower link on to my Eclat ones this allows me to use the Toyota uprights and I've also got 310mm dia brake disks. I carried this work out after snapping a trunnion at Brands Hatch. I have to say the car still handled quite well with only 3 wheels and the ARB dragging on the track.

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Does the spherical bearing modification eliminate the scrubbing when turning at crawl speeds. Ackerman steering angle I believe it called?

10 hours ago, eclat22 said:

I've grafted the end of the Excel front lower link on to my Eclat ones this allows me to use the Toyota uprights and I've also got 310mm dia brake disks. I carried this work out after snapping a trunnion at Brands Hatch. I have to say the car still handled quite well with only 3 wheels and the ARB dragging on the track.

That sounds like a very decent setup. Have you any pictures of that?

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The spherical bearing has no effect on Ackerman.  The "negative" Ackerman is associated with the steering rack being in front of the "axle".  Ackerman angle is only easily achieved with the steering rack behind the front wheel axle line.

Pete

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That's excellent Dan!  What have you done at the front inboard end?  Do the upper arms allow some caster adjustment as well?  I've copied the later Esprit arrangement for camber adjustment.

Pete

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Hi Pete, the top wishbone links are rose jointed and adjustable for camber. The anti roll bar has a drop link from the lower wishbone, this is what helped when I broke the trunnion as the roll bar rubbed on the track rather than the bodywork, it just scuffed the cill and the wheel rattled around on the wheel arch.

IMG_20210613_105035_6.jpg

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Hi Dan - yes, I can see that your arb sits below the suspension arm - good arrangement.  Did you make the drop links yourself?  They must be pretty short.  I've been looking for short, readily available drop links - but not with spherical bearings - mine's just going to be a road car this time!

Pete

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The drop links were supplied by Spyder who made the original lower front wishbone modification for me, I then carried out the Excel alteration after the trunnion snapping.the links are flat metal figure of 8 plate with cup washers welded both sides top and bottom.they bolt to the original mounting on the lower link and go through a hole in it to pick up the ARB the cups take the original ARB bushes from memory 

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