More anti-roll bar antics

Refitting the original front anti-roll bar means working out exactly what washers and spacers are required. I have read that there are supposed to be both spacers, fender washers and/or spherical washers involved but I don’t have much to go on since all I have is a mixed up pile of old parts from the previous owner.

Ferrari 308 anti roll bar parts

My pile of used parts

First things first… the anti-roll bars themselves. After checking their measurements, I know the previous owner did in fact give me the correct OEM anti roll bars: 18mm diameter at the front and 15mm diameter at the rear. These are the correct specs for a 1978 308 GTB. The GTS came with a thicker 18mm rear bar to compensate for the less stiff roofless body.

A good write up on anti-roll bars, what the do and how they work, can be found here. The following diagram illustrates basically what they do. When a car turns, the weight transfers to the outside wheels compressing the suspension and rolling the car towards the outside of the bend. This is not what you want for quick, efficient cornering. The anti-roll bars counteract this effect by increasing the stiffness of the outside suspension relative to the inside suspension during the turn thereby reducing the roll angle:

Effect of anti roll bar on cornering

Effect of anti-roll bars on cornering (exaggerated)

While each individual bar defines the roll rate of the car in a bend from side to side, the balance of the car is affected by the relative stiffness difference between the front and back… this is called the roll coupling. The basic rule of thumb is the stiffer i.e. thicker, the front bar is relative to the rear, the more understeer the car will have and the stiffer the rear bar is relative to the front, the more oversteer the car will have. Many other things affect the car’s balance of course, and probably have a larger effect than anti roll bar set up.

Saner anti roll bar compared to Ferrari 308 bar

Saner bar (chrome) vs OEM bar (black)

While I’d like to eventually dial out any understeer on the car, that is not the immediate reason I’m reverting to an OEM setup. As I have mentioned before, my car had very stiff bars on it when I bought it: 25mm back and front. The front in particular was so stiff that it all but eliminated any independence in the front suspension. If the front left wheel hit a bump, the bar was stiff enough to unweight and even lift the right wheel. The effect is downright scary when it occurs – the entire front end would jitter around on rough roads.

With the correct bar in hand and restored drop links, the next challenge was working out how to correctly attach the bar to the drop link and the drop link to the suspension. The old Saner bar was attached with a non-standard Heim link, a SAE bolt and a ton of washers. It looked like s**t but I guess it worked. The original bar has a solid cast drop link attached to the bar with a some rubber bushes and to the lower wishbone with a bolt through a silent block type bushing; parts 12, 31, 11 below:

Ferrari 308 anti roll bar hardware

Anti-roll bar attachment hardware

This image is taken from the Ferrari parts manual for the 308. Unfortunately, it is wrong in two places. The bolt connecting the wishbone to the drop link (in red) is shown the wrong way round. It shows the nut against the drop link when it should be the bolt head. This particular bolt has a specially-shaped shoulder to transfer load to just the center sleeve of the silent block bushing and not the surrounding rubber. The wishbone has a corresponding shoulder that fits against the other side of the bushing to do the same thing.

Ferrari 308 suspension bolt

Drop link bolt with pronounced shoulder

If the bolt is inserted as the factory manual shows, the bushing will get squeezed when the bolt is tightened. Perhaps this is where the rumours of spherical or special washers being needed started. The correct solution is to insert the bolt the opposite way and no special washers are needed at the wishbone end of the link. And indeed, a little fishing on the internet shows a factory install of the bolt in the correct orientation, opposite to what is drawn in the manual.

With one end of the downlink figured out it’s time for the other end. The factory diagram above shows a couple of washers, a couple of rubber bushes and a nut (all in blue) – pretty straightforward. I had ordered replacement rubber bushes a while ago since it does not make sense to me to put in old rubber. There were some bushes in the pile that looked quite new but looks are deceiving: their age was known and they were actually pretty hard to the touch. The washers are oversized with the factory parts manual giving the dimensions as 32mm outer diameter, 12mm inner diameter and 3.5 mm thick. A metric fender washer could be used at a pinch since it will be large enough at 37 mm to hold the rubber bush but will appear a little too large. Looking closely at the pile of parts revealed some original washers albeit rather corroded and bent. I restored them with some oil and abrasives

Ferrari 308 drop link washers

Restored drop link washers

So here is the real world equivalent to the factory diagram with all correct pieces in place:

Ferrari 308 anti roll bar drop link

Correct drop link components – exploded

The rubber bushings were assembled with plenty of red rubber grease to eliminate any squeakes and protect the rubber.

Lubricating Ferrari 308 rubber bushes

Applying red rubber grease to drop link bushes

And here is it all assembled:

Assembled Ferrari 308 drop link

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2 Responses

  1. andrew says:

    Thanks for a simple and concise explanation. Great photos

  2. Roberto Simeone says:

    Thank you for the information on the parts diagram mistake. I read about such a thing on ferrarichat but the mistake was not explained there.

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