Jon Weywadt
YaBB God
Posts: 1002
|
 |
« on: May 23, 2010, 11:00:16 am » |
|
This winter I bought Grenn Stuff brake pads for front and rear braes. Yesterday replacing the old pads finally reached top of the to-do list. After cleaning off the caliper I made sure the frame holding the pads would slide back and forth with ease. Then when installing the pads I discovered that the outer pad hit the corner of the frame and rested at an angle instead of flat and parallel with the other pad.  When I compared the pad with the one I took out, I could see that the tabs holding hte pad in the frame were 4 mm closer to the wheel center than on the original. This caused the pad to sit further outward and even though it has the sam beveling on the outside corner, it could not be inserted all the way flat against the frame.  The previous owner had replaced the calipers all the way around and the disks are new as well. The old pads produce a perfect wear on the disk to within 1 mm of the rim. If I got the Green Stuff pad to lay flat in the frame it would actually extend over the rim of the disk. That could not be good??? Finding this on the first wheel I worked, I only did the same cleaning on the other front wheel and did not try the rear wheels. I was wondering if any of you have run into similar problems? I have the correct Green Stuff pads, according to Roys alternative parts list. So I wonder if there are differences in the front calipers and disks on the different year, or model Murenas?? Are there other cars, whose calipers fit the Murena front wheels and disks? I am speculating that the new calipers, that the previous owner had installed, perhaps are not a 100% identical to the originals. One major reason to try the Green Stuff pads was to reduce the black dust that quickly coats the front wheels. Fortunately the current pads have plenty of wear left in them, so I have time to figure out what to do. One thing seems clear.  I will have a set of Green Stuff pads for a Murena for sale. At least for the front. |
|
|
|
|
Logged
|
Matranaut par excellence  |
|
|
|
|
roy4matra
YaBB God
Posts: 1199
|
 |
« Reply #2 on: May 25, 2010, 09:54:10 am » |
|
This winter I bought Grenn Stuff brake pads for front and rear braes. Yesterday replacing the old pads finally reached top of the to-do list. After cleaning off the caliper I made sure the frame holding the pads would slide back and forth with ease. Then when installing the pads I discovered that the outer pad hit the corner of the frame and rested at an angle instead of flat and parallel with the other pad. When I compared the pad with the one I took out, I could see that the tabs holding hte pad in the frame were 4 mm closer to the wheel center than on the original. This caused the pad to sit further outward and even though it has the sam beveling on the outside corner, it could not be inserted all the way flat against the frame. If you have the correct pads Jon, were the originals correct? A 4 mm difference in the locating tab is the difference between front and rear pads - see my brake booklet or website for a side by side diagram of the front and rear pads. Front pads are 4 mm closer to the hub. Consequently fronts will not fit in the rear. Rear however will fit in the front but are 4 mm further out and the edge of the pad will be off the disc. The previous owner had replaced the calipers all the way around and the disks are new as well.
If the calipers have been replaced, are they correct. You can fit a later Bendix Talbot caliper but it is not quite the same. Maybe these were fitted? I was wondering if any of you have run into similar problems? I have the correct Green Stuff pads, according to Roys alternative parts list. So I wonder if there are differences in the front calipers and disks on the different year, or model Murenas??
No Jon, all Murena came from the factory with the same calipers. Are there other cars, whose calipers fit the Murena front wheels and disks? I am speculating that the new calipers, that the previous owner had installed, perhaps are not a 100% identical to the originals.
As I stated above this is a possibility. Roy |
|
|
|
|
Logged
|
|
|
|
Jon Weywadt
YaBB God
Posts: 1002
|
|
« Reply #3 on: May 25, 2010, 10:49:35 am » |
|
If you have the correct pads Jon, were the originals correct? A 4 mm difference in the locating tab is the difference between front and rear pads - see my brake booklet or website for a side by side diagram of the front and rear pads.
Front pads are 4 mm closer to the hub. Consequently fronts will not fit in the rear. Rear however will fit in the front but are 4 mm further out and the edge of the pad will be off the disc.
-
If the calipers have been replaced, are they correct. You can fit a later Bendix Talbot caliper but it is not quite the same. Maybe these were fitted?
---
Roy
Hi Roy. I compared the Green Stuff front and rear pads and can see the 4mm difference you mention. However, the front pads have a round disk mounted on the outside of one tab, just like the ones that are mounted now. This is not on the other Green Stuff pads. That is why I am assuming the one with the disk is meant for the front. There is also an inward rounded cutout on the tabs I removed, just like the ones I tried to fit. I did not remove my rear disk pads after running into the problem, but this coming weekend I will do that and compare the pads. It would be nice (though annoying) if I have just managed to get the pads swapped in their boxes.  One set of Green Stuff pads has a contact for the brake wear sensor, the other set does not. None of my current pads have this and the wire in the right rear is just hanging loose. On the left front, where there should be both a sensor wire and ground wire, someone has just cut them off at the inner fender. The connector on the pad looks like a small clip-on button type, but no matching wire is included, nor is there a matching plug on the loose wire. I looked at the drawing on your site and will compare with my Green Stuff pads. I should have known better than to attempt the job, without first checking your website.  |
|
|
|
|
Logged
|
Matranaut par excellence |
|
|
roy4matra
YaBB God
Posts: 1199
|
|
« Reply #4 on: May 25, 2010, 11:24:56 am » |
|
Hi Roy.
I compared the Green Stuff front and rear pads and can see the 4mm difference you mention. However, the front pads have a round disk mounted on the outside of one tab, just like the ones that are mounted now. This is not on the other Green Stuff pads.
Oh I think I know what you are talking about now. It is riveted in the hole in the tab yes? Simply use a pin punch and knock them out. This can be removed and thrown away Jon! Or re-rivet them in the correct side... These round studs were meant to be a wear indicator, as they are soft material, and as it touches the brake disc it makes a noise, but doesn't damage the disc. So you get a warning before the pad is completely worn out. The problem is, the people fitting them don't seem to know what they are for and, if they are fitted at all, have often fitted them the wrong side so the stud is on the back, instead of the same side as the pad material! There is also an inward rounded cutout on the tabs I removed, just like the ones I tried to fit.
The small cut out on the corner of the tab is for the anti-rattle spring. Sometimes these cut-outs are missing. If that is the case, simply file the corner off for the spring to fit. It would be nice (though annoying) if I have just managed to get the pads swapped in their boxes. Look at my side by side comparison again Jon. The front pads should be more rounded at their lower corners which distinguishes them from the rears which have a sharper corner. The rears should also have a pip on the back whilst the fronts do not. However, these are not really necessary and don't worry if they are missing, *as long as you make sure the slot in the rear piston is horizontal*. The pip on the back forces the slot to be horizontal because of its position. These pips are not to stop the piston rotating as is often mistakenly quoted! They are there simply to make you align the piston slot correctly. One set of Green Stuff pads has a contact for the brake wear sensor, the other set does not. None of my current pads have this and the wire in the right rear is just hanging loose. On the left front, where there should be both a sensor wire and ground wire, someone has just cut them off at the inner fender. The connector on the pad looks like a small clip-on button type, but no matching wire is included, nor is there a matching plug on the loose wire. The brake wear sensor wires in the boxes I find inconsistent! Sometimes they are there and sometimes they are not! Since the Murena only has one on the LH front and one on the RH rear, as long as you have one box with two in it, you have enough. The end of these wires have a black plastic end with a ridge. You push these through the hole in the tab from the back until the ridge locks them in. it should be in the top of the inner pad nearest the wire on the car. When the material wears down to the last bit, the disc touches the plastic and wears it off and touches the wire inside, earthing it, and bringing on the warning light. If those studs were fitted on the pad side of the tabs, they can be used too, and are more reliable since the wire sometimes breaks and therefore you get no warning. There can also be one on each pad giving you a warning no matter which pad wears first (as they don't always wear at the same rate). With the wiring system you only have a warning on the LH front and RH rear inner pads. Thanks. I have tried to cover most common things. Roy |
|
|
|
|
Logged
|
|
|
|
|
|
|
|
|
|
Oetker
YaBB God
Posts: 1097
|
|
« Reply #8 on: June 04, 2010, 09:01:02 am » |
|
Indeed some pressure is needed when turning, but I would check the pistons first. Most of them are pretty damaged and pitted after all these years.  I took them apart compltely and rivised them to Roy's tutuorial.  Also I didn't use the Green stuff but Ferodo's. Other compounds of the pads can give worse results. The Ferodo's work fine. |
|
|
|
« Last Edit: June 04, 2010, 09:04:28 am by Oetker »
|
Logged
|
I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
|
|
|
roy4matra
YaBB God
Posts: 1199
|
|
« Reply #9 on: June 05, 2010, 06:18:07 pm » |
|
Now that I have successfully replaced the front pads with Green Stuff, I am stumped by the rear calipers.
I have skimmed through Roy's Brake tutorial and read the Repair manual.
From what I can gather I have to loosen the bleed screw and then turn the piston clockwise with a ratchet wrench. When I do that and check the position of the piston, it has not retracted at all. 10 turns of the piston and no more clearance between the pads. What am I doing wrong. Do I have to hold on to the pin sticking out under the hand brake mechanism? and how would I do that?
No you don't need to hold the pin Jon. In fact the pin cannot rotate unless the wedge link has been knocked out. First let me explain why you need to rotate it. The piston has a one way 'ratchet' mechanism inside it so that as the pads wear down, and the piston has to move further out to apply them, this mechanism rotates around the centre pin which has a coarse spiral like thread. As it rotates it will pass a 'tooth' and cannot go back past that point any longer, so the piston stays out and it therefore 'self adjusts' to keep the pads close to the disc and the hand brake in correct adjustment. When you wish to push the pistons back in to fit new pads, you cannot, since it is held in position by this one way mechanism. However, you can rotate the piston to wind it back down the spiral, but you must apply pressure as you rotate the piston, and since the frame stops you using a conventional wind-back tool it is a little more difficult, particularly when on the car. If, as Oetker says, the pistons are corroded on the area outside the housing, this makes them especially tight. If there is corrosion in the frame grooves, the piston housing will be slightly oval also making it difficult to both rotate the piston as well as push it in. You should never need to open a bleed nipple to get the piston to go back in, since the reservoir should have room to take all the fluid it pushes back (unless the system has been topped up with the brakes worn and pistons out!) You should never top up a brake system with worn brakes. If the reservoir was correct when all pads were new, it has sufficient fluid to allow for maximum wear. The low level of fluid is actually another easy visual indication of worn pads, and will return to correct level when new pads are fitted. The only other time a system should need fluid is if you had a brake fluid leak or you are changing it for new. A point about the brake piston one-way mechanism. If the spring end was to break off inside, the mechanism could possibly rotate - the 'self adjustment' might not work, and it might be impossible to rotate the piston back in, but I have not come across this so far and I have seen some very corroded and seized units! However, if you do ever have the mechanism out, please make sure you put it back in correctly. I have done at least two caliper overhauls where the mechanism was incorrectly assembled and it would be almost impossible to bleed all the air out. The piston has a small cut out at the top in the back which is the same point as when you have the piston groove horizontal with the smaller groove uppermost. This is where the air finds the highest exit point. I have seen the internal bar which should be horizontal, blocking this exit point! If you have never stripped the brakes totally, you probably won't understand this so don't worry, but if you have had the pistons out and cleaned everything, please bear this in mind. Final observation - your overhauled calipers look good Oetker, but the pistons are incorrectly positioned at present. Since they are not on the car this is no problem, but when you do fit them to the car the pistons will need to be rotated to bring the groove horizontal 'in fitted position'. So if these are being left on the shelf for a while I would rotate them now whilst the seal is not stuck on the piston. Roy |
|
|
|
« Last Edit: June 05, 2010, 06:45:52 pm by roy4matra »
|
Logged
|
|
|
|
|
|
|
|
Oetker
YaBB God
Posts: 1097
|
|
« Reply #12 on: June 05, 2010, 07:26:36 pm » |
|
I had them out, and it went fairly easy. However last week I worked on the car from a fellow member and replaced pads. Needed some force to push and turn them in. We used a special tool to do it (sorry no pic at hand from that tool). Best to do with 2 men. Put 2 screwdrivers crosswise to apply force to the tool. The tool looked like the original tool.  Before I get critics, I never hang calipers like that, but was done to catch clean piston and pads in one shot. |
|
|
|
« Last Edit: June 05, 2010, 07:37:33 pm by Oetker »
|
Logged
|
I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
|
|
|
|
|
|
|
Author
