Stick rear brake calipers - be patient or replace?

[tdskip]

Good morning gentlemen, hope everybody’s having a good weekend.

I replaced the soft brake lines and installed a new master cylinder on the 1968 this morning, I noticed that both of my rear calipers are a bit sticky, with the driver side being more so than the passenger side.

This car has sat, mostly unused, since 1982 so not a huge surprise that the calipers are a bit reluctant but I’m wondering if I should just suck it up and replace them both or if they’re likely to come up and function properly after I drive the car for a bit .

What do you think?

Thanks!

[SteinOnkel]

Get new ones. Pricey, but how much is your life worth to you?

I for one have never had much luck with the rebuild kits either

Oh also, check the clearance on the acorn nut at the mbc. That may also explain sticking, although on mine it was then sticking on all four corners. Hmm.

[tdskip]

Thanks for the reply, tend to agree.

What is the acorn nut and does it need to be adjusted?

System is dry at this point btw.

[18Fiatsandcounting]

Not to steal Steiny's thunder here, but the acorn nut he is referring to is between the brake booster and the master cylinder. The nut is on the shaft that comes out of the front of the booster, and the acorn nut rests in a cup-like plunger in the "input" (rearwards) end of the master cylinder. Basically, you want that acorn nut at the end of the brake booster to be just about to touch the plunger, when the brake pedal is all the way "up". There is a spec for this, and I recall it's basically how far the acorn nut should protrude from the front surface of the booster, with the master cylinder removed and the brake pedal up.

-Bryan

[tdskip]

Ah, got it. Usual stuff, just different name.

Thanks!

[RRoller123]

[tdskip]

Thanks!

[dinghyguy]

I rebuilt both rear calipers with new seals and bleeders for about 10$ total
Took time and multiple bits need to be disassembled and cleaned but not really hard to do
Search other threads for more details and pix

Dinghyguy

[tdskip]

Good point, thanks.

Assume the seals are available? Rear brake design remained the same across the years?

Thanks

[18Fiatsandcounting]

Good point, thanks.

Assume the seals are available? Rear brake design remained the same across the years?

Thanks

Yes, rear (and front) brake seals are readily available at just about any Fiat retailer, and the basic design remained the same across the years. No difference that I am aware of.

What often happens on cars (not just Fiats) that have sat for many years is that moisture in the brake system eventually corrodes the pistons in the calipers, leading to the sticking that you describe. The pistons are steel whereas the calipers are aluminum. If it's just some light surface rust, that can be cleaned up with emery cloth or the like. If the pistons (or the calipers) are pitted, then Steiny is right, you likely have to buy new calipers. Those are readily available as well.

If you do buy new calipers, make sure you get them from a reputable source, as there are many stories on this forum of new calipers right out of the box that never were "quite right."

-Bryan

[ORFORD2004]

Or install rear caliper from Fiat 500 2012. You remove backplate, Fiat 500 use larger rotor that you remove .1 inche in the center hole, use the adaptor that my friend make and use the Fiat 500 handbrake cable that you modify. The advantage is more braking for shure but the handbrake is like in new car.

[tdskip]

Clever

[tdskip]

Brian – meaning Vicks or Midwest rather than Rockauto

[18Fiatsandcounting]

Brian – meaning Vicks or Midwest rather than Rockauto

Exactly. Also AutoRicambi. I've used Vicks, M-B, and AR without issues, and all three work on Fiats on a daily basis. I do use Rockauto for routine stuff like spark plugs, but not much beyond that, and their bizarre shipping costs when ordering several items also frustrates me (shipping charges tend to pile up as the items are all coming from different locations).

-Bryan

[DieselSpider]

Regardless of whether you rebuild your own, purchase rebuilt or buy new calipers remember that the caliper and pad guides require silicone brake lube which needs to be cleaned off and renewed every 2 years when you flush and refill with fresh brake fluid. Its sad how many even "Professional" mechanics skip this very important/critical aspect of brake service. On calipers with the sliding wedge plates its even more critical to keep them well lubed than on more modern systems that used guide pins sealed up inside a bellows.