2400 rear brake calliper tutorial

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Dario
Posts: 84
Joined: Fri Nov 29, 2013 12:18 pm
Dino: Fiat Dino 2.4 Coupe

2400 rear brake calliper tutorial

Post by Dario » Sun Apr 07, 2019 9:04 pm

There have been many posts regarding how to refurbish the rear brake callipers on the 2400 Dino. The difficulty is that these callipers incorporate a floating two-piston setup that also serves for the handbrake. Often (like me, the first time), one takes it appart and only changes the front piston seal and boots. Unfortunately, this will not correct a sticky handbrake problem.

To fix the handbrake, you need to disassemble the rear piston and lever mechanism, which is a bit of a PITA. Since I had done mine, and a friend asked to help with his, I though I could document the process while it's fresh in my head. Here goes:

Remove the calliper from the car, disconnect the handbrake cable and use a soft mallet to drive out the piston assembly from the curved housing:
20190331_204703.jpg
Then, remove the rubber boot protecting the piston
20190331_204841.jpg
You will notice that the notch on the piston is pointing up (or maybe horizontal). You will need to turn it 45° so that it is diagonal. This allows the teeth from the piston insert to disengage. NB: I have heard of new pistons that were manufactured with an incorrect position of the insert, so beware!
20190331_205356.jpg
Then, you can use compressed air to push out the piston. You might be able to get it out with pliers, but be careful not to damage it. Here it is, badly scored near the rim. It did not leak, but it might be a good idea to replace it.
20190331_210053.jpg
Here is the piston from behind, you can see the notched shaft that is used by the handbrake mechanism to push the piston forward when engaged. It is a ratchet mechanism, meaning that the pad wear is progressively taken up as the pedal is pressed.
20190331_210059.jpg
Now for the rear piston. Start by removing the circlip and return spring.
20190331_210157.jpg
Then the nylon spacer and round plug to expose the circlip and washer that holds the lever mechanism in place. It is still held in place by a short pushrod inside the piston, so don't try to force it out. You should see what is left of the first (9mm o-ring).
20190331_210410.jpg
You have two possibilities: the first is that if it is not stuck, you can push it out with a wood drift which makes disassembly easier.
20190331_212604.jpg
The piston will come out the back:
20190331_212645.jpg

Dario
Posts: 84
Joined: Fri Nov 29, 2013 12:18 pm
Dino: Fiat Dino 2.4 Coupe

Re: 2400 rear brake calliper tutorial

Post by Dario » Sun Apr 07, 2019 9:15 pm

Now,,you need to remove a circlip that holds a metal cage and spring mechanism inside the rear piston. The circlip is held in by pressure and has one end beveled so that you can get a thin flat screwdriver in provided that you aligned it over one of the cutout holes. Then, remove the C-shaped clip that prevents the threaded insert from turning.
20190331_213102.jpg
Then, remove the cage, you can see the holes I mentioned above
20190331_213120.jpg
Now, you can use a pair of pliers to simply twist off the spring mechanism and expose the pushrod.
20190331_213302.jpg
20190331_213318.jpg
This can just get cleaned, no need for further disassembly. You can see all the grime that got in over the years, not to mention the O-rings that wear and let dirt in. No wonder these things fail!
20190331_213453.jpg

Dario
Posts: 84
Joined: Fri Nov 29, 2013 12:18 pm
Dino: Fiat Dino 2.4 Coupe

Re: 2400 rear brake calliper tutorial

Post by Dario » Sun Apr 07, 2019 9:39 pm

Reassembly is basically the reverse procedure. Here are the parts ready for reassembly.
20190404_213002.jpg
I use some lithium grease to hold things in place and lubricate the mechanism. Don't forget the larger (12mm) O-ring on the lever mechanism, next to the where the lever to the cable is attached.
20190404_215541.jpg
Don't forget the rubber boot!
20190405_204312.jpg
Place the smaller O-ring, then the washer, and then the circlip, followed by the nylon plug, the spacer, and the spring. Then, the rear pistons are ready for assembly. The circlip will not fit right away, you need to push down hard with a flat blade screwdriver to compress the o-rings and the clip will "click" in place.
20190405_204717.jpg
Once they are inserted all the way inside the floating body of the brake calliper, you can insert the front piston. Make sure it is aligned diagonal so that the teeth do not engage.
20190405_210211.jpg
Push it in ALL the way, before turning it by 45° and locking it into position.
20190405_210347.jpg
Locked:
20190405_210612.jpg
and secured in place. Ready to mount!
20190405_211538.jpg
I hope this helps anyone wishing to tackle this in the future. In addition to a rebuild kit, you will need two 12mm ID and two 9mm (both 2mm thick) O-rings.

From now on, your handbrake will work without any binding! :D

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Tobi
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Re: 2400 rear brake calliper tutorial

Post by Tobi » Sun Apr 07, 2019 10:11 pm

Great work! Thanks for sharing!

If someone has problems with a sticking handbrake, I'd sugest to lubricate the lever first before doing this refurbishment. It helped on my car.

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ThomasK
Posts: 103
Joined: Mon Dec 30, 2013 12:44 pm
Dino: Fiat Dino 2.4 Coupe

Re: 2400 rear brake calliper tutorial

Post by ThomasK » Fri Apr 12, 2019 10:34 pm

Wow, thats a Great Tutorial, Thanks a lot!

As an additional or Alternative hint: instead of disassamble the pistons One After the Other you can push them out together in the direction of the piston with the handbrake lever. Easy to do with a press and prevents the inner mechanism to be damaged when you put pressure on it for example with a piece of Wood.

Thanks again, Thomas

Dario
Posts: 84
Joined: Fri Nov 29, 2013 12:18 pm
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Re: 2400 rear brake calliper tutorial

Post by Dario » Sun Apr 14, 2019 9:38 pm

A great Idea from Thomas, I wish I had thought of that!

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ThomasK
Posts: 103
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Re: 2400 rear brake calliper tutorial

Post by ThomasK » Fri Apr 19, 2019 10:06 am

Thanks.
If you do that I would recommend still to turn the inner cylinder by 45 degrees so that the pressure does Not go via the handbrake mechanism but directly from inner to outer cylinder.

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