2400 rear brake calliper tutorial

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Dario
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2400 rear brake calliper tutorial

Post by Dario »

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
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Re: 2400 rear brake calliper tutorial

Post by Dario »

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: 117
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Dino: Fiat Dino 2.4 Coupe

Re: 2400 rear brake calliper tutorial

Post by Dario »

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 »

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
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Re: 2400 rear brake calliper tutorial

Post by ThomasK »

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
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Re: 2400 rear brake calliper tutorial

Post by Dario »

A great Idea from Thomas, I wish I had thought of that!
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ThomasK
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Re: 2400 rear brake calliper tutorial

Post by ThomasK »

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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doublegarage
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Re: 2400 rear brake calliper tutorial

Post by doublegarage »

Thanks Dario for this tutorial. Really nice work.

I discovered it while searching for whether there was an adjustment for the handbrake on 2400 cars. I have the usual manuals but the one that talks about handbrake adjustment is for 2000 cars and I think the caliper is different?

Basic problem - I replaced the handbrake cable and now the brake is binding - the cable is adjusted to the slackest possible, I can turn the wheels with the handbrake off, but it's definitely binding.

So question - is there an adjuster on the caliper to back off and slacken the adjustment, or do I have to dismount the caliper? I guess I could dismount it anyway to find out, but just trying to understand how large of a job that is.

Thanks again for the writing up the tutorial.

-Richard
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doublegarage
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Re: 2400 rear brake calliper tutorial

Post by doublegarage »

After 6 months of occasional work on my rear brake problem I believe I've finally resolved it. It all relates to rebuilding the rear caliper so I'll post some notes here in case it's useful to anybody.

The initial reason to start the job was the handbrake lever was engaging "high" - adjusted the cable but didn't seem to make a difference therefore bought a new cable and some other rear brake parts (caliper external lever return springs etc) that I could see were worn or missing. Also a caliper rebuild kit.

I rebuilt both calipers - as @barnfind states in this thread viewtopic.php?f=4&t=332, I also had two different types of caliper on my car - Right had a completely different retention part (left-side had this part: (t.ly/bi5B), right was different) - left side also had a ball bearing inside which just seemed..wrong, so I removed it.

Anyway, it took me a few disassembly/reassembly cycles before I understood how this caliper works - 2 pistons each side, lever mechanism, floating mount, ratcheting adjuster - it isn't simple. I believe what happened to mine was the ratchet adjustment mechanism teeth were worn, either on the inner piston: (t.ly/WsqA) or the "clamp": (t.ly/11Uw). I replaced both - and the handbrake is working now.

A few notes from rebuild(s):
- this Dinoparts part: (t.ly/gdec) needs to be modified to fit - the tab at 12 o'clock is too wide and won't fit between the sections of: (t.ly/PqKZ) - needs to be filed narrower.
- This part on my caliper: (t.ly/g6Fc) had a broken tab and needed replacing - the new part was a much looser fit and therefore didn't perform any anti-rotation function - maybe that will be a problem in future? don't know.
- after rebuilding, you have to pump the (hydraulic) brakes while the handbrake adjuster is loose so that the ratchet on the inner piston moves to the appropriate location for the new pads. Then you can adjust the handbrake cable tension (lever about 4 clicks to tight)
- the combination of 17mm thick disks (rotors) with the new pads supplied from Superformance (t.ly/NNLU) which are 29mm thick overall leaves very little extra room inside the caliper bracket. In fact on the right side it was impossible to compress the inner piston into the caliper-body enough to allow room for the new pads - so I had to retain the old pads (worn, thinner) - not sure why, another aspect of the difference L-R - maybe yet another disassembly of that side required for another look
- the retention rings supplied for the dust covers in the rebuild kits aren't tight enough - probably best to keep the old ones which will retain the rubber seals better. (t.ly/3Kqv)
- As noted by Dario here and elsewhere, the rebuild kits don't include the necessary o-rings located at the base of the outer piston and in the lever assembly. You'll need to get those from somewhere like: https://www.theoringstore.com/store/

This was a bit random, trying to gather 6 months' worth of thoughts, happy to answer any questions.

-Richard

PS ugh these shortened hyperlinks aren't working - i'll try to find a better way but if you cut/paste them they work.
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doublegarage
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Re: 2400 rear brake calliper tutorial

Post by doublegarage »

Some further work:
I couldn't leave it that I was forced to re-use the old pads on the right-rear caliper (because not enough clearance for the new/thicker set) - so decided to dismantle it one more time and see what was happening.

This caliper has a different internal construction to my left caliper, specifically in the way the handbrake mechanism ratchet-clamp is retained. Still i couldn't understand what made the clearance for the new pads different to the left side - this picture might help visualize the problem.
rear caliper.jpg
Shows the floating plate, both pistons and the pads, but with the caliper body 'removed'. The disk/rotor is 18mm thick and the remaining clearance available here between pads is about 16mm - so I had to find 2mm additional.

The obvious place for more clearance was the backstop for the outer pad (the inside of the floating plate on the right of this picture) - so I ground off the necessary 2mm of metal. Also, on the back of each pad (manufacturer Siffert, supplied by Superformance) there was a locating "pip" which was too large to fit in the groove of the inner piston, therefore wasting clearance, so I ground that off too - it doesn't serve any useful function that I could see (it might be there as a locating part for the outer pads)

That worked - there was enough clearance to reassemble with the new pads and the handbrake and hydraulic brake are working well. I never had both calipers off the car at the same time, so I couldn't measure to see where left is different from right - but my guess would be the dimensions of the floating plate.

-Richard
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