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Author Topic: Brake / Caliper disassembly  (Read 445 times)
Morne
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Posts: 27


« on: May 30, 2021, 09:23:06 pm »

I got my calipers refreshed at one of the well known Murena part suppliers. When I received them back, the rear calipers had a bolt fitted where previously the spring loaded pin was. Following Roy`s brake guide, I rather opted to change these for grub screws. I ordered the suitable size grub screws, and then a surprise when I tried to fit them.

The first one was fine, and the grub screws went in to a suitable depth. However when fitting the 2nd grub screw, it did not go very deep. On closer inspection it appears that the caliper assembly is misaligned. In other words, the tapped hole is not aligned with the old spring pin hold in the piston housing.

As a result I decided to attempt to split the caliper and assemble/move to ensure the holes align and the grub screw can be fitted properly. I opted to make the "wedge" as per Roy´s brake guide. Please see attached photos.  Now I am puzzle as how to use it correctly. The 2nd photo show the wedge placed in the caliper. No force applied yet, just loosely placed in position. As can be seen it is almost all the way through already, and not much left to be used to force the caliper open. Additionally the wedge is bumping into the piston and rubber boot. I checked the size of the wedge multiple times, and it is correct.

What am I missing? What am I doing wrong?
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roy4matra
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Posts: 1123



« Reply #1 on: May 31, 2021, 12:03:17 pm »

I got my calipers refreshed at one of the well known Murena part suppliers. When I received them back, the rear calipers had a bolt fitted where previously the spring loaded pin was. Following Roy`s brake guide, I rather opted to change these for grub screws. I ordered the suitable size grub screws, and then a surprise when I tried to fit them.

The first one was fine, and the grub screws went in to a suitable depth. However when fitting the 2nd grub screw, it did not go very deep. On closer inspection it appears that the caliper assembly is misaligned. In other words, the tapped hole is not aligned with the old spring pin hold in the piston housing.

As a result I decided to attempt to split the caliper and assemble/move to ensure the holes align and the grub screw can be fitted properly. I opted to make the "wedge" as per Roy´s brake guide. Please see attached photos.  Now I am puzzle as how to use it correctly. The 2nd photo show the wedge placed in the caliper. No force applied yet, just loosely placed in position. As can be seen it is almost all the way through already, and not much left to be used to force the caliper open. Additionally the wedge is bumping into the piston and rubber boot. I checked the size of the wedge multiple times, and it is correct.

What am I missing? What am I doing wrong?

From what I can see, and the wedge is slightly in the way unfortunately, it looks like the piston is not fully wound back in, as it should hardly protrude from the surface, and the wedge could then go further in if angled slightly to go past the piston face - but forget using the wedge Morne anyway, since that is designed to open up the yoke fractionally to break the corrosion seal or take away the pressure holding them together, when they haven't been apart for years.

In this case the caliper has been apart already and the caliper should not be that tight in the yoke, if the grooves were cleaned properly and the remains of the corrosion removed.  If it is really too tight to move it suggests the work may have not been done properly.  I can move a caliper in a yoke with just strong hand pressure immediately after cleaning and refitting with grease.  Yes it should be tight enough so the caliper is held firmly and not be loose in there, but even if you can't move it with strong hand pressure, it should move with some light taps from a soft faced mallet, since there is nothing locking them together at this time if there is no pin and spring and the holes are not aligned.

Therefore, depending on which way the caliper needs to slide along the yoke to get the holes aligned, you need to either press it in a suitable large vice (or under a press) or tap it with a large mallet, to move the caliper along the yoke to align those holes.  Compare the position of the other caliper in its yoke, and you should see that the opposite side of the caliper to where the handbrake bracket is bolted, is virtually flush with the yoke at the ends of the grooves.

On the one you have with misaligned holes, the caliper will probably protrude.  You need to get it back so those edges are level.  If you go too far, or if it is already too far out that side, you can hit it on the bracket face to move it the other way.  But from you photos I think it is the other side opposite the hand brake bracket that is sticking out.

There is one other possibility, and that is the holes are aligned but the pin and spring are still jammed in the caliper filling the hole as they never removed them!  If these were corroded in so badly they could not get them out, they should have been carefully drilled out.  If the hole in the caliper is clear then it just needs aligning with the hole in the yoke as per the instructions above.

Roy
« Last Edit: May 31, 2021, 12:10:43 pm by roy4matra » Logged

Morne
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Posts: 27


« Reply #2 on: June 03, 2021, 12:22:08 am »

Thank you Roy for the clarification and recommendation.

The unit is actually not finger tight and needs is bit of persuasion from a malet to move.

That said, the issue is not solved yet. I moved the yoke to a similar position as the other caliper assembly. Then looking down the hole in the yoke I still dont see a hole in the piston housing. This is when I also noted that the yokes are 100% the same. Normally I would expect that they are mirror images for left and right, however this does not seem to be the case. It this correct?
In other words, once the calipers are installed then one grub screw will be at the top and the other at the bottom when comparing the two mounted calipers. I am asking this as obviously I would have an issue to find the hole in the piston housing if the hole in the yoke is on the wrong side.

On the side but related, is the Bagheera rear brakes the same as the Murena? It seems close to impossible to buy a back-up pair of Murena rear calipers, as there are simply none available. That said, there seems to be more Bagheera ones around.
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roy4matra
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Posts: 1123



« Reply #3 on: June 08, 2021, 08:55:37 pm »

Thank you Roy for the clarification and recommendation.

The unit is actually not finger tight and needs is bit of persuasion from a malet to move.

That said, the issue is not solved yet. I moved the yoke to a similar position as the other caliper assembly. Then looking down the hole in the yoke I still dont see a hole in the piston housing. This is when I also noted that the yokes are 100% the same. Normally I would expect that they are mirror images for left and right, however this does not seem to be the case. It this correct?
In other words, once the calipers are installed then one grub screw will be at the top and the other at the bottom when comparing the two mounted calipers. I am asking this as obviously I would have an issue to find the hole in the piston housing if the hole in the yoke is on the wrong side.

On the side but related, is the Bagheera rear brakes the same as the Murena? It seems close to impossible to buy a back-up pair of Murena rear calipers, as there are simply none available. That said, there seems to be more Bagheera ones around.

If you have read my brake manual carefully, then you will see that the caliper, that is the alloy housing only, is the same for both sides and indeed the same as the Bagheera, (except the Bagheera uses different hand brake arms) and you can assemble the housing for either side by inserting the opposite hand brake arm the opposite way.  In fact the same housing is used in other applications such as one of the Alpine A110 and certain Fiats, but the yoke and hand brake arms are different in other applications.  Also the early Bagheera housing has an imperial thread whilst all later ones have metric threads.

Now the yoke on the Bagheera and Murena may be different although I haven't checked recently and I don't remember off hand, but on the Murena they are usually the same item and there is only one hole for the locking pin, so yes it is usually up the other way on one side compare to the other, but I have seen these yokes with a hole both sides so there is always a hole at the top and bottom.

The caliper housing only has the hole for the spring and pin on one side, and that is the side where the casting number 431174 is located. The other side with the DBA logo is blank.

So if both caliper castings are 431174, then the pin on one side will be at the top and on the other side at the bottom.  If the yoke has only one hole it must follow suit.  If it has a hole both sides it doesn't matter.  What it the casting number on your yokes?

Roy
« Last Edit: June 08, 2021, 09:29:33 pm by roy4matra » Logged

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