Brake Caliper Issue?

[NCGermerican]

87 Turbo but this could apply to the S2 folks as well. I've been hunting an issue where I get a grinding noise and feel in the front drivers side wheel when making a low speed right turn (foot off brake). It also used to happen when going slowly in reverse as well. Here is what I have done so far:

1) Checked the dust shield is not contacting the rotor. No change
2) Did a nut/bolt torque check on the strut, control arm, sway bar, etc. No change
3) Checked the wheel for play. No play at all, but replaced the front wheel bearings anyway. No change
4) Pulled the caliper and rotor and thoroughly cleaned both with brake clarn. No change
5) Installed new rotors (Zimmerman cross-drilled), pads (Hawk Ceramic) and replaced caliper piston seals. No more sound in reverse, but same exact sound/feel under slow right turns.
6) Brake fluid flush (Liqui Moli Dot IV) and bled brakes and clutch. No change

Safe to say I've reached frustration level 2. One thing I noticed (and the same was on my 87 S that I swapped to turbo brakes), is that getting the pads into/out of the calipers is rather difficult to say the least. In fact, it usually takes a few soft blows with a rubber mallet to get them in - especially at first, then when they get further in it gets a little easier. I have a few choices for my next things to try.

1) Bad control arm ball joint? PO had them replaced about 10 years ago with the 944online rebuilt control arms. What's the best way to check them? Steering feel is nice and smooth.

2) Could the stainless "sliders" in the calipers have some crud UNDER them, putting too much pressure on the pads and not allowing them to release fully when off the brake? I thoroughly cleaned the top side of all the sliders (that contacts the pads) and I do use the proper lubricant. I can't seem to find where to buy new ones and I've read some horror stories about stripping the allen head screw to get them out.

3) I could grind a little off the pads to get them in/out of the calipers easier, but if I grind off too much, they might "slap" and create even more noises.

Any thoughts?

[barnwerks]

Does the car have ABS?

[dr bob]

I think we share the same calipers. There have been several serious discussions over the years about corrosion under some little spring plates for the pads. You description about having to hammer pads in is a big clue. Those spring plates are held in with screws that tend to be a bit tough to remove. I rely on an impact driver, the kind you hit with the hammer, to get the screws loose. Then the corrosion in the aluminum, combined with brake dust packed underneath, gets cleaned out. New screws and a tiny drop of loctite high on the threads when you reassemble. Having pads that can slide in those plates is critical to correct braking function.

There's more to look at, like the bottom of the spindle where the bearings ride. Wear there allows the bearing to rock just a little, and the tendency is to try and tighten the spindle nut a little to remove all the play. The surface finish on the spindle gets polished on the bottom with this wear, so a visual inspection is an easy first step. Just clean the grease off, and look underneath for the wear. And regardless of what you feel when replacing or adjusting bearings, follow the factory guidance with being able to move the washer with a small screwdriver. Not by prying with the screwdriver, but just by pushing it around with the flat on the edge of the washer. If you can then feel excessive play, especially in the 6-12 axis, look even harder for that spindle wear as a possible cause. You can start by placing just a bearing on the spindle dry, and feeling for available 'rocking' where they normally ride on the spindle. At the fat end of the spindle, the face of the inner rides against a shoulder, so do your rocking test all along that section. Finding good used spindles, ones without that wear, is getting a little tougher. I have no idea the availability of new or aftermarket for the 944 cars.

----

These two issues play together. Brake pads that don't retract correctly will drag and heat the rotors, and that heat finds its way to the hub. The heat expands the hub, and that shrinks the clearance in the bearings. Maintaining a grease film between rollers and races is critical, else it's metal on metal and the bearing risks damage from heat. When you see discoloration, like blue in rollers and the outer races, and eventually galling on those, a sure sign that the bearings have been run without sufficient lubrication. This also means there was more heat added, so it's a self-reinforcing problem.

So... Look at the spindles, and replace them if they are worn. Finding good used spindles, ones without that wear, is getting a little tougher. I have no idea the availability of new or aftermarket for the 944 cars.

HTH

[NCGermerican]

Does the car have ABS?

No this car does not have the ABS option.

[NCGermerican]

I think we share the same calipers. There have been several serious discussions over the years about corrosion under some little spring plates for the pads. You description about having to hammer pads in is a big clue. Those spring plates are held in with screws that tend to be a bit tough to remove. I rely on an impact driver, the kind you hit with the hammer, to get the screws loose. Then the corrosion in the aluminum, combined with brake dust packed underneath, gets cleaned out. New screws and a tiny drop of loctite high on the threads when you reassemble. Having pads that can slide in those plates is critical to correct braking function.

There's more to look at, like the bottom of the spindle where the bearings ride. Wear there allows the bearing to rock just a little, and the tendency is to try and tighten the spindle nut a little to remove all the play. The surface finish on the spindle gets polished on the bottom with this wear, so a visual inspection is an easy first step. Just clean the grease off, and look underneath for the wear. And regardless of what you feel when replacing or adjusting bearings, follow the factory guidance with being able to move the washer with a small screwdriver. Not by prying with the screwdriver, but just by pushing it around with the flat on the edge of the washer. If you can then feel excessive play, especially in the 6-12 axis, look even harder for that spindle wear as a possible cause. You can start by placing just a bearing on the spindle dry, and feeling for available 'rocking' where they normally ride on the spindle. At the fat end of the spindle, the face of the inner rides against a shoulder, so do your rocking test all along that section. Finding good used spindles, ones without that wear, is getting a little tougher. I have no idea the availability of new or aftermarket for the 944 cars.

----

These two issues play together. Brake pads that don't retract correctly will drag and heat the rotors, and that heat finds its way to the hub. The heat expands the hub, and that shrinks the clearance in the bearings. Maintaining a grease film between rollers and races is critical, else it's metal on metal and the bearing risks damage from heat. When you see discoloration, like blue in rollers and the outer races, and eventually galling on those, a sure sign that the bearings have been run without sufficient lubrication. This also means there was more heat added, so it's a self-reinforcing problem.

So... Look at the spindles, and replace them if they are worn. Finding good used spindles, ones without that wear, is getting a little tougher. I have no idea the availability of new or aftermarket for the 944 cars.

HTH

The hubs looked really good when I replaced the bearings. I think the PO had them replaced as well, but I figured doing them myself would not only eliminate that from being the issue but I also know they are done.

I'm really nervous about getting those spring plate screws out. I've read that some recommend using a dremel to cut a slot instead of using an allen, which will probably strip. I have one of the impacts you talked about, so I could give that a shot. I would need to find some new screws though and the spring plate replacement kits for sale are....pricey (over $150/caliper).

[dr bob]

The hubs looked really good when I replaced the bearings. I think the PO had them replaced as well, but I figured doing them myself would not only eliminate that from being the issue but I also know they are done.

I'm really nervous about getting those spring plate screws out. I've read that some recommend using a dremel to cut a slot instead of using an allen, which will probably strip. I have one of the impacts you talked about, so I could give that a shot. I would need to find some new screws though and the spring plate replacement kits for sale are....pricey (over $150/caliper).

The concern on the wear is at the spindle itself, less for the hubs. Inspect the bottom of the spindles where the bearings sit, looking for little 'polished' areas that no longer support the cones evenly.


On the little screws and the spring plates in the calipers, I've managed to get the screws out with a little heat cycling on them and the impact driver. Unless you damage the spring plates, they should be reusable. Perhaps the critical point here is that the caliper won't correctly support the pads or allow proper movement when the plates are crammed up with brake dust and corrosion. You can sorta solve on of those by grinding the edges of the pad so they can move more freely in the caliper frame without removing and cleaning the plates. But without the spring tension loading the pad a little, brakes will squeal and rumble.

More:
I follow the screw holes in the frame with a bottoming tap after some brake-clean flushing. Those holes need to be clear and have nothing in them for the new screws to fit correctly. Again, a small bit of Loctite (think toothpick end...) on the screw thread near the top will keep the screw in place. The screws are stainless so not very tough. Loctite means they don't need to be tightened more than just barely snug. The loctite will hold it, plus it blocks any entry via that thread for contaminants that might make it a challenge next time. I've learned the hard way that disassembling those screws and plates with every pad change is a Good Idea. New screws then is also a Good Idea. I keep a bag of them somewhere in my spares collection just to reduce the temptation to cheat and leave the old ones in. I still have the original plates in there on the current car.

[NCGermerican]

The hubs looked really good when I replaced the bearings. I think the PO had them replaced as well, but I figured doing them myself would not only eliminate that from being the issue but I also know they are done.

I'm really nervous about getting those spring plate screws out. I've read that some recommend using a dremel to cut a slot instead of using an allen, which will probably strip. I have one of the impacts you talked about, so I could give that a shot. I would need to find some new screws though and the spring plate replacement kits for sale are....pricey (over $150/caliper).

The concern on the wear is at the spindle itself, less for the hubs. Inspect the bottom of the spindles where the bearings sit, looking for little 'polished' areas that no longer support the cones evenly.


On the little screws and the spring plates in the calipers, I've managed to get the screws out with a little heat cycling on them and the impact driver. Unless you damage the spring plates, they should be reusable. Perhaps the critical point here is that the caliper won't correctly support the pads or allow proper movement when the plates are crammed up with brake dust and corrosion. You can sorta solve on of those by grinding the edges of the pad so they can move more freely in the caliper frame without removing and cleaning the plates. But without the spring tension loading the pad a little, brakes will squeal and rumble.

More:
I follow the screw holes in the frame with a bottoming tap after some brake-clean flushing. Those holes need to be clear and have nothing in them for the new screws to fit correctly. Again, a small bit of Loctite (think toothpick end...) on the screw thread near the top will keep the screw in place. The screws are stainless so not very tough. Loctite means they don't need to be tightened more than just barely snug. The loctite will hold it, plus it blocks any entry via that thread for contaminants that might make it a challenge next time. I've learned the hard way that disassembling those screws and plates with every pad change is a Good Idea. New screws then is also a Good Idea. I keep a bag of them somewhere in my spares collection just to reduce the temptation to cheat and leave the old ones in. I still have the original plates in there on the current car.

To tackle the "easiest/fastest" test first, I very slightly ground down the edges of the pads and thoroughly scrubbed the tops of the spring plates. I was very careful with the grinding - only taking off enough that I can now slide the pads in/out of the calipers without the use of any plyers or any other tools, but not too lose that they just flop around. I took it for a test drive and while there was slight improvement, the issue persists.

Here's where it gets strange. I totally flushed out all the brake fluid from the entire system last week, including the clutch. However, the fluid in the reservoir is already VERY dark. Plus, when I hold down the brake when cold, it's firm at first and then very slightly starts to fade - not when the brakes are hot, but bone cold.

I'm grasping at straws, but at 177K miles and 38 years old, I have a feeling the brake master is starting to fail. Since the car has that many miles, I just went ahead and ordered a new ATE master and a new reservoir, just so it's pretty like my new coolant reservoir. The car had stainless lines installed sometime around 2008, but there weren't many miles put on the car since then. I would switch them out, but whoever did the job must have put some sort of sealant at the junction with the hard lines and they are NOT moving without destroying the fitting on the hard line.

Once I get the new master cylinder in, I'll report back.

[dr bob]

The dark fluid is perhaps a clue. What fluid did you use?

Until the last few years, I was a loyal Castrol LMA DOT4 customer for the Porsche (and all the other cars). The last few flush/bleed exercises have been with a Bosch DOT 5.1 full synthetic fluid. I haven't noticed any discoloration in the Porsche, but on another car (Honda Pilot DD) the fluid was quickly dark. I tested for moisture, and all OK, but I replaced it again out of caution. No problems with that next flush and bleed or others since, still using the Bosch fluid. Some Honda owners have reported seeing dark fluid very soon after using Valvoline synthetic fluid too. It's more readily available now than the Bosch, so more folks have been reporting on it.

[NCGermerican]

The dark fluid is perhaps a clue. What fluid did you use?

Until the last few years, I was a loyal Castrol LMA DOT4 customer for the Porsche (and all the other cars). The last few flush/bleed exercises have been with a Bosch DOT 5.1 full synthetic fluid. I haven't noticed any discoloration in the Porsche, but on another car (Honda Pilot DD) the fluid was quickly dark. I tested for moisture, and all OK, but I replaced it again out of caution. No problems with that next flush and bleed or others since, still using the Bosch fluid. Some Honda owners have reported seeing dark fluid very soon after using Valvoline synthetic fluid too. It's more readily available now than the Bosch, so more folks have been reporting on it.

I used Liqui Moly Dot 4. I siphoned out a bunch of fluid and there is definitely black particles at the bottom of the reservoir. I'm thinking some rubber is degrading somewhere and the master cylinder is the oldest link in the chain....

[notny41]

I used to get a rattle on my rear brakes when going over bumps. Turned out my rear pads were missing the shims. I put those in and the sound is gone. I don't know if yours requires the shims or not though.... Just a shot in the dark.