Brake compensator spring

Been overhauling my old coupe recently and along with CuNiFe pipes all round and the rear compensator that was almost a solid lump of rust.

Doh no spring with the comp and not available through fiat, had read as such on here in a post from way back.

Anyone found a supplier already ?

Fiat are still able to supply these springs new as I purchased a couple only last month.

Thanks Joe, which dealership did you get them from ?

My local for south west is Vospers and they said no longer available from Fiat or Alfa ?

Fiat dealer in Hereford.

Have you tried Steve at Alternative autos?

Yea tried Steve said he had them on back order for 6 months now so he wasn't even sure if they would ever come...

I have contacted an automotive spring company, given them dimensions, coil numbers and photos which has been passed to their tech department.

I will ring the dealer in Hereford in the morning maybe they just have a few left in stock ?

Yes give Hereford a try, part number 46438681.

If they have no joy ( ie I bought the last two ) let me know and I'll ask my suppliers in Europe.

So no joy with the Hereford dealer

The automotive spring manufacturer I approached will make me one, but the cost for a one off is prohibitive unless there are a few coups out there who fancy a group buy......

Joe- have sent you a pm, could you try your suppliers in Europe please...

I haven't but I will this weekend.

its only a spring to keep the arm pulled, could use a standard spring from a jumbo box of mixed ones i expect, no?

IF it's a spring with the same tension and length, yes - it's critical in the amount of pull it provides to balance the brakes front and rear.

But it's not the spring that provides the braking, it's the piston. The spring is to stop the arm from sticking in the open position.
A weaker spring might not be great, but could work of the arm is free moving and easily moved, a stronger spring won't stop the piston from opening imo and would therefore work.

But the spring maintains the position of the closing arm under the lifting moment of the axle. That's why it's set with a fixed weight and distance.

An engineer mate told me needs to be same K-value Hookes Law

The way I see the linkage functioning is that it translates the wide range of suspension movement into a much smaller range of movement at the piston with an amount of adjustment.

I would therefore guess that the spring is there to push the piston back into the compensator against the resistance of the fluid in the system as quickly as possible when the brakes are released, changing the piston position relative to the suspension.

Could it also actively control under braking ?

The clue is in the word compensator.

It is there to control the amount of pressure going to the rear callipers. If the full force of the brakes was always applied to the rear then lock ups and ultimately skids can occur. Forwards weight transfer under heavy braking reduces the effective grip of the back wheels.

When the rear end rises under heavy braking the spring link to the anti roll bar acts via the lever to push the pistons back in to the compensator and reduce the braking effort to the rear wheels.

Hence why the strength of the spring and its set-up is important.

Yea compensates for extra weight in the vehicle like rear passengers and load in the boot ?

Also I may be wrong but I think piston fully into compensator is full braking and piston fully extended out of compensator is minimum braking ?

Otherwise how could I bleed my brakes with no spring and a cable tie holding the compensator piston fully in ?

I think everything is in balance between pressure within the braking system, spring strength and suspension position which is relative to the weight in the vehicle combined with shifting loads due to deceleration under braking.

Just wondered if it was a truly active control on the braking in terms of adjusting front rear split as balance changes during braking or just setting a split dependant on the amount of weight in the car.

Either way I don't think it will work properly without a spring that has the same characteristics.

I am wondering if replacing it with a manually controlled compensator would be an option ?

No, it compensates actively; the amount of braking force applied to the rear wheels is reduced as the back of the car lifts under breaking moment from the front.

If there is more weight in the back, the tyres can supply more grip and because the back doesn't lift as much in that situation, more brake pressure is available.

If the rears lock, the back will lift up and remove all the pressure from the rears, so they unlock.

It's all a negative feedback situation, and that spring controls the gain factor.