Front Upper Wishbones Upgrade

[fjmuurling]

As my car is a 1990 SE it has the non Camber adjustable front upper wishbones.

So as part of the refresh / renewal / upgrade etc of the complete suspension system I decided to upgrade the front upper wishbones for the later type of Camber adjustable ones. They also make the setting of the Castor far more easy (shim stack at ball joint).

Sounded easy but the truth is a little bit further off.

Having read the workshop manuals of my car and the later one more than once I thought ok there is a difference in the shim stack thickness (should be no problem) for adjusting the Castor. The Castor angles are different for my 1990 SE and the later cars (1 deg. vs 3.2 deg.) according to the manuals. The same manuals have a different "opinion" about the Castor angle change when transferring a 1.5 shim (aprox. 1 deg. vs aprox 0.4 deg angle change).

However upon trial fitting the new wishbones there was no way I could make them fit with the recommend LOTUS shim stack thickness at the chassis pivot point, I ended up with a big gap at between the wishbones and the ball joint (even taking into account of the needed shims at the ball joint).

 I needed to find out the difference between the old and new wishbones. Just putting them on top of each other or setting them on a flat surface with the flat ball joint face revealed there are differences but only in a course way. After a lot of head scratching I came up with a better plan (I think).

I made 2 stainless steel plates with 4 holes in each of them and bolted everything together.

New wishbones are the top ones.

Looking from the otherside revealed the differences......................

On the forward wishbone (left picture) there is a difference of 1.5 mm and for the rear (right picture) the difference is 9 mm. The measurement were taken with the straight edge against the metal inserts in the bushes.

 

So my plan is to compensate for the differences with extra shims (also at the ball joint, not using the lotus shim stack specification ), bearing in mind the 1.5 mm min clearance shim of the wishbone to chassis according to the SE manual.

 

So the big question is if there is a flaw in my plan or has someone a better idea..................

 

[Erikl]

ON My 94 there is spacers on the inboard side, at the chassis mount (bushings) as well.  They are different front to rear.  You might be able to make up difference there also.  I would not worry too much on the Castor because I believe that is because of the change to PS.  Might be better to stay at the original castor setting.

In the end if you can get the camber and toe correct it will be fine.

[fjmuurling]

thx Erik,

I need to make up the difference on the inboard side. I will keep the original Camber and Castor setings as I'm (still) running the original wheel / tire sizes.

My concern is that I will be using more shim washers (item 25 (SE) / 28 (S4) in partslist section 31.01A) than lotus specifies. Hopefully the 1/2" UNF stud will be long enough (first looks say yes).

[Chillidoggy]

In my view, the Lotus-specified shim totals were calculated so as not to put any strain on the rubber bushes. I do wonder whether the SE has a different length chassis tube than the later cars where the adjustable wishbone was fitted? I don't know.

Anyway, I think the important thing is to achieve the settings as per the book for your SE as has been said. When you take the car to have the geometry set up, they should tell you if there is any wheel set-back, i.e. the longitudinal front wheel positions in relation to each other (is one set further forward, or back, than the other).

[fjmuurling]

3 minutes ago, Chillidoggy said:

In my view, the Lotus-specified shim totals were calculated so as not to put any strain on the rubber bushes. I do wonder whether the SE has a different length chassis tube than the later cars where the adjustable wishbone was fitted? I don't know.

 

thx Ian

That is also also my view / understanding

 

[fjmuurling]

1 hour ago, fjmuurling said:

I need to make up the difference on the inboard side.

Scrap that.

Need to make up the difference at the ball joint end. So the 1/2"stud will be long enough.

[Erikl]

I am not exactly sure I am understanding.  Its weird - in the pics it looks like the ball joints are different widths?  The upper BJ looks like it is wider? Is that possible?  I thought the part number was the same over the generations - a Triumph Spitfire part.

[fjmuurling]

Ball joints are the same. It is an optical "illusion", picture not taken at a right angle with my telephone.

[fjmuurling]

Progress / Success

Stupid phone camera makes it look tapered at the ball joint end. This is not the case!!!!!!!!!!!!!!!!!

Step 1 - Bolted the upper wishbones to the chassis with 1.5 mm shim washers (lotus clearance WSM), hand tightened the nuts

Step 2 - Loosely fitted the baljoint with the camberplates, put a couple of castor shim plates in.

Step 3 - Tightened the nuts on the stud (inside) a bit more with some spannners so everything was seated properly at the chassis side.

Step 4 - I needed to put one more 1.5 mm castor shim plate in, Just by hand tightening the M8 bolts / nuts everything came nicely toghether.

The number (thickness) of castor shim plates (3 * 3 mm and 2 * 1.5 mm) are not completly on par with the above mentioned differences so most likely something wrong with the measurements. 

 

[drdoom]

Broadly on the subject of caster, with due respect to Lotus credentials on all things chassis, I am of the view one may fiddle the caster specs to good effect if called for. Case in point, I had a classic Elan with replacement chassis, fitted with alloy wheels of offset typical of a FWD car and found the steering feel wanting in terms of tyre loading feedback. Eventually made up some spacers and shifted upper wishbone bushes a touch in their sleeves, resulting in about 3 1/2 deg caster quite well matched side-side. Outcome was a triumph, the car well communicating limit of adhesion under hard cornering and tracking more serenely at speed. My at the wheel experience on track with a brand new SE was that I found the steering a bit short of the sort of feedback I enjoyed in the Elan. FWIW.

 Cheers

[cweeden]

I don't have much to add that will help with the geometry but I would recommend painting or powder coating the arms instead of relying on just the plating, they won't stay good looking for very long if you do. 😇

[fjmuurling]

I thought about it. (hindsight - I should have them hot dipped in zinc).

My main reason for not painting / powdercoating is that I don't want paint / coating on the mounting points where they meet the upper ball joint. It is possible to mask it (or scrap off) but that will also leave an area where corrosion can creep under the coating.

I did however paint the inside corners (problem area's for the galvanizing) with POR 15.

Hopefully they will last. If not then it will be some spanner time again.

[cweeden]

Hi Freek, 

I'm juggling a mixture of protective coatings, hot dipped galvanised and powder coated chassis, powder coated arms, zinc nickel (black passivate) on nuts and bolts and the larger components you see in the picture, Lanoguard for hard to reach out of sight places for extra protection and duralac where dissimilar metals might take offence with each other. 🙂

cheers

-Chris