Castor adjustment on an 850.

ramona300

True Classic
The castor is adjusted by shifting the shims on the control arms. At the moment I have 4 degrees and need 10. Does anyone know what effect shifting one shim makes? I have ordered a tool to measure the castor sweep but thought there might be some rough info out there!
 

kmead

Glutton for punishment
Sorry I have no idea but it would be great if you would post any findings. Thanks

Shim thickness relative to change would be good to know.
 

Dave Bassett

True Classic
Just curious. Ten degrees of positive caster seems like a lot, in Citroen 2CV territory. elaborations are of interest.
 

Dave Bassett

True Classic
The workshop manual states 9 degrees plus or minus one. All the racers recommend 10 degrees. With only 4 degrees you really have to steer the car out of corners.
Wow! I went back and checked the chart and am astonished that it calls for nine degrees. Every other model is in the 3-4 range.
 

Dave Bassett

True Classic
Yeah an interesting difference.

From what I have read the notable caster is due to how light the front end is.
That would be my guess. I've had a number of BMW' and they are known for having a good bit of caster for "speed feel." However, that's about 5 degrees.
 

ramona300

True Classic
I had a track day on Wednesday and I thought about castor everytime I was exiting a corner! With only 4 degrees there is a lot of effort to steer out of the corners compared to my previous track car, an MX5[Miata] which was particularly easy to drive. I have nothing on over the next few weeks so the front end is coming apart and I will widen the track by opening out the lower wishbones and altering the upper control arm mountings.
 

ramona300

True Classic
I'm going to raise the control arm position a bit which will help with the castor changes. Looking for a supplier of the trunnion adjuster kits. The ones in the first photo are out of stock at the moment. The second photo shows the item I want but they don't mention the 850 in the fitments. Or I will just make my own. Thoughts?
 

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kmead

Glutton for punishment
I tend to prefer the first solution.

You may want to investigate Fiatnutz nuts he used to be able to space the arm out and still ensure sufficient thread engagement.

The individual units version would allow you to adjust the angle front to back of the a arm easily which could assist with manipulating anti dive geometry (something the 850 needs a bit more of) as well as the caster.

I have seen similar units offered for 124s, in Spain in particular. I will see if I can find some pics of that solution I saved.

The plate solution could be replicated pretty easily and would be possible to create a variety of different variations. A dxf file for a company which has a laser cutter, water jet or possibly a plasma cutter (questionable tolerances) to be able to create variations on the solution to fine tune the application to your liking.
 

ramona300

True Classic
I have checked out the Fiatnutz ones. They put the control arm out a bit but don't alter the height. The first units are out of stock. I like the look of the alloy units Hegen Speed has on his car he manufactured from alloy. I think I'm going to fabricate my own out of steel. Raise the height about 30mm and have them out 10mm each side over standard. Then I'll adjust the lower wishbone rose joint out by the same amount so I will be starting with a similar alignment before I fiddle about.
Photo is Hegen's front end.
 

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kmead

Glutton for punishment
I have checked out the Fiatnutz ones. They put the control arm out a bit but don't alter the height. The first units are out of stock. I like the look of the alloy units Hegen Speed has on his car he manufactured from alloy. I think I'm going to fabricate my own out of steel. Raise the height about 30mm and have them out 10mm each side over standard. Then I'll adjust the lower wishbone rose joint out by the same amount so I will be starting with a similar alignment before I fiddle about.
Photo is Hegen's front end.

Sorry I was not clear. I was referencing the trunion nuts he made that ensured full thread engagement with the existing captive threads.

Hegen’s solution is very nice but I would have some concerns about that approach. I presume the bolts for retaining the upper arm would have a thread locking compound since the trunions have been replaced?

The advantage the individual parts offer is that due to them being individual points they will always bolt down square to the shims. A plate will not do the same as it will set on the edges of the shims if there is a disparity in the height of the shims, which on an 850 would be notable given the caster angle. An alloy unit could bend or deform to meet that but is less than ideal. A shim could be ground to have an appropriate angle going from the square to the body of the shims to the angle of the back of the plate.

Either way solvable.
 

ramona300

True Classic
John's method just moves the trunnions out. Does not address adjusting the height bit. The first photo is my set up and the trunnions look like they need to be higher.
The second photo is pretty much what I had in mind.
 

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kmead

Glutton for punishment
John's method just moves the trunnions out. Does not address adjusting the height bit. The first photo is my set up and the trunnions look like they need to be higher.
The second photo is pretty much what I had in mind.
Sorry, I meant to have an arrangement which used Johns nuts in combination with your first photo. I wasn’t clear.

Although simple the plate has its issues as well. However since it could be an assembly, making different versions wouldn’t be terribly difficult.

Whichever way you go please do offer up your experience. Thanks
 

kmead

Glutton for punishment
A nut plate or captive studs would be a better solution for the a arm attachment on the plate from Ricambio. Having those one time use nuts behind the plate wouldn’t be very convenient.
 

ramona300

True Classic
My current thinking is similar to the Ricambio unit but have the bolt the other way around with the head welded in place so I have a stud and use the same spacer system as the stock unit. I will make a start in the next few days after I get a few other jobs out of the way.
 

myredracer

True Classic
Berni Motori has these offset pins. They're listed under the 600-based section. 600 & 850 A-arms are interchangeable so no issues using them. But I read about someone who bought them and discovered you need to split the A-arms in half to get them in and then re-weld back together. I have the trunnion adapters on my 600-based Abarth replica. They work fine but I had to create dimples in the wheel well sheet metal because the A-arms clashed against the sheet metal. Not sure about on an 850.

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ramona300

True Classic
Thanks Gil. I did notice these and thought they would be expensive and would entail re-welding the A arms. I may have to grind a bit to get the new bits in but it will be minor.
 

ramona300

True Classic
My A arm brackets are in place. I went with 10mm thick mild steel. The new bolts are 30mm above the stock height. I will wind out the rose joints on the bottom A arms 10mm and go from there.
 

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ramona300

True Classic
The front end is back together. The bracket in the picture above is just visible under the top A-arm. The lower wishbone is adjusted out 12mm so the front track will be 22 to 24 mm wider depending on the camber.
 

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