Sticking front wheel

[r65lsk75c]

In my effort to find the cause of a sticking front wheel on my '76 R90S I got as far as inserting the 8 mm x 1.25 x 50 mm bolt into the bearing pin. I assume the bearing pin must be removed. Showing my loss of mental capability, I am unsure how to proceed. Does the bearing pin need to be removed from the caliper to release it from the disc? The master cylinder and the surrounding are clean and dry. The calipers show no sign of brake fluid leakage. The front wheel can be turned by hand but there is much more resistance than I would expect.

Recommendations will be appreciated.
rickt

[20774]

rickt -

I usually don't remember what the specs on the bolt is but remember that the pinch bolts on the lower fork slider is a perfect size. Once that large cap is removed, the bolts is hand threaded into the end of the eccentric pin. Then take a pair of pliers or maybe a crescent wrench and loosely grab the shank of the bolt and lightly tap the side of the wrench with a hammer. The eccentric should drop out. If not you may have some corrosion inside which may require squirting some penetrant into it. And yes, once the pin is removed, then the caliper is freed up to be removed...once the brake lines are removed.

If you're just trying to free up the wheel so it turns easier, there could be a variety of reasons...so I wouldn't remove the eccentric pin just yet. If the brakes haven't been bled, that should be done. Possibly the original rubber brake line should be replaced. If those things don't free up the brake pads from dragging on the disk, then an overhaul might be in order. What is supposed to pull the pads back from the disk is the square o-ring that is inside the caliper bore. When the brakes are activated, the piston distorts the o-ring and when the brake lever is released, the o-ring tries to "undistort" back and it pulls the piston with it. Could be the o-ring has lost it mo-jo and/or there's internal corrosion. That's when an overhaul is needed.

[r65lsk75c]

rickt -

I usually don't remember what the specs on the bolt is but remember that the pinch bolts on the lower fork slider is a perfect size. Once that large cap is removed, the bolts is hand threaded into the end of the eccentric pin. Then take a pair of pliers or maybe a crescent wrench and loosely grab the shank of the bolt and lightly tap the side of the wrench with a hammer. The eccentric should drop out. If not you may have some corrosion inside which may require squirting some penetrant into it. And yes, once the pin is removed, then the caliper is freed up to be removed...once the brake lines are removed.

If you're just trying to free up the wheel so it turns easier, there could be a variety of reasons...so I wouldn't remove the eccentric pin just yet. If the brakes haven't been bled, that should be done. Possibly the original rubber brake line should be replaced. If those things don't free up the brake pads from dragging on the disk, then an overhaul might be in order. What is supposed to pull the pads back from the disk is the square o-ring that is inside the caliper bore. When the brakes are activated, the piston distorts the o-ring and when the brake lever is released, the o-ring tries to "undistort" back and it pulls the piston with it. Could be the o-ring has lost it mo-jo and/or there's internal corrosion. That's when an overhaul is needed.

Following your instructions the pin on the left came out quite easily. Taking the same approach on the right afforded much frustration. Pounding on the bolt using a crescent wrench then a chisel on the lip of the bolt produced no movement. Several lubricant sprays also yielded failure. I suspect this caliper is the problem as the wheel can barely be turned by hand with the left caliber off the bike.

Any other suggestions for freeing the problematic pin?

rickt

[6322]

Try heat. Careful use of a propane torch.

[Na Cl K9]

I think its time to get the brake disc out of the way. It sounds like the eccentric pin is being held in place by the tension between the frozen brake caliper piston with pads tight against the brake disc and the position of the eccentric pin in the bore of the caliper. Put the bike on its center stand using a 1 x 12 x12 or 2 x 12 x 12 under it to get a little more height at the front wheel and pull the front axle. Lower the wheel to the ground and roll it forward enough to extract the brake disc from between the pads. The wheel cant be completely removed until both calipers are loose and able to be rotated out of the way, You will or should be able to rotate the caliper in its mount and that should free up the eccentric so it can be pulled. The eccentric pins ride in brass bushings inside the mounting flanges on the sliders so it's not frozen in the mounts except in this case by trapped tension. Once the caliper is off the slider you can pull the wheel completely or put it back so you'll be able to roll the bike around your shop. No heating required. Just wiggle the caliper back and forth as you pull the eccentric down and out of its bore.

[r65lsk75c]

I think its time to get the brake disc out of the way. It sounds like the eccentric pin is being held in place by the tension between the frozen brake caliper piston with pads tight against the brake disc and the position of the eccentric pin in the bore of the caliper. Put the bike on its center stand using a 1 x 12 x12 or 2 x 12 x 12 under it to get a little more height at the front wheel and pull the front axle. Lower the wheel to the ground and roll it forward enough to extract the brake disc from between the pads. The wheel cant be completely removed until both calipers are loose and able to be rotated out of the way, You will or should be able to rotate the caliper in its mount and that should free up the eccentric so it can be pulled. The eccentric pins ride in brass bushings inside the mounting flanges on the sliders so it's not frozen in the mounts except in this case by trapped tension. Once the caliper is off the slider you can pull the wheel completely or put it back so you'll be able to roll the bike around your shop. No heating required. Just wiggle the caliper back and forth as you pull the eccentric down and out of its bore.

Following Johns advice and freeing the front wheel allowed me remove the right side caliper. Even with the wheel forward it required some pounding to remove the caliper pin. Now I have the two calipers with brake lines removed. I believe the next step is to use the compressor to free the pistons from the calipers. Unfortunately due my stroke from 6 years ago I have no short term memory. Please give me advice on which openings I should use for the air input. There is a significant amount of rust on the surface of the right piston so I’m what I will find on the inside.

I appreciate the advice.
Rick

[20774]

Rick -

You should inject air into the same place that the brake fluid goes into, so the spot where you removed the bleed nipple. Be advised that the piston may shoot out of the caliper. I believe the best thing is to stick a thin piece of plywood or stuff in some rags to soften the pistons when they come out. Might want to wrap a towel over the whole affair just for good measure.

[r65lsk75c]

Rick -

You should inject air into the same place that the brake fluid goes into, so the spot where you removed the bleed nipple. Be advised that the piston may shoot out of the caliper. I believe the best thing is to stick a thin piece of plywood or stuff in some rags to soften the pistons when they come out. Might want to wrap a towel over the whole affair just for good measure.

First issue: I believe the bleed outlet and the fluid inlet provide two entry/exit points for brake fluid. Do I need to block one of these and provide the air to the other?

Second issue: Although the fluid inlet tube on the right caliber came out fairly easily, the inlet tube on the left caliper would not come loose with the caliper in my vise. It would appear that it has not been removed in quite a time.

Third issue: I assume that I should plan on replacing the pads. Particulary since I now cannot remember which pads are inner or outer and which came out of which caliper.

Fourth issue: Looking for pads on a couple of vendors websites, it appears that there may be a difference between English and German bikes. The bike that I purchased has a speedometer in kilometers. Does this indicate that the R90S is German? Does it make a difference for the brake pads?

By now everyone should have a true appreciation for my damaged mental state.

Rick

[20774]

First issue: I believe the bleed outlet and the fluid inlet provide two entry/exit points for brake fluid. Do I need to block one of these and provide the air to the other?

Yes...plug one, air into the other. Usually the bleed port is left closed and air goes in the inlet port as one must disconnect the brake line from the caliper to get it off the bike.

Second issue: Although the fluid inlet tube on the right caliber came out fairly easily, the inlet tube on the left caliper would not come loose with the caliper in my vise. It would appear that it has not been removed in quite a time.

You'll need to use penetrants and time to loosen up the input port/nut. Be careful and proceed with a light touch as you might end up damaging the threads in the caliper and then you'll have another issue.

Third issue: I assume that I should plan on replacing the pads. Particulary since I now cannot remember which pads are inner or outer and which came out of which caliper.

Probably a good idea. Brakes are crucial on a motorcycle. Get the best so you have confidence when the bike is back on the road.

Fourth issue: Looking for pads on a couple of vendors websites, it appears that there may be a difference between English and German bikes. The bike that I purchased has a speedometer in kilometers. Does this indicate that the R90S is German? Does it make a difference for the brake pads?

Yes, the R90S is German...it's a BMW. Personally, I get my pads from a dealer. Other's will come along to give their recommendations for aftermarket pads. EBC?? Ferodo???

[Anyname]

Following Johns advice and freeing the front wheel allowed me remove the right side caliper. Even with the wheel forward it required some pounding to remove the caliper pin. Now I have the two calipers with brake lines removed. I believe the next step is to use the compressor to free the pistons from the calipers. Unfortunately due my stroke from 6 years ago I have no short term memory. Please give me advice on which openings I should use for the air input. There is a significant amount of rust on the surface of the right piston so I’m what I will find on the inside.

I appreciate the advice.
Rick

Some people consider compressed air to be potentially risky. These folks suggest using a grease gun. While I have never tried it myself, it does make sense since grease guns actually generate a lot more pressure and grease is non-compressible so that a exciting sudden release can't happen. Or so they say...

[PGlaves]

Some people consider compressed air to be potentially risky. These folks suggest using a grease gun. While I have never tried it myself, it does make sense since grease guns actually generate a lot more pressure and grease is non-compressible so that a exciting sudden release can't happen. Or so they say...

I would NOT do this. The seals designed to contain DOT 4 brake fluid are certainly damaged by petroleum products. This is a good way to require all new seals and a new total rebuild.

[ccolwell]

Compressed air works well to get the pistons out. But. Place a piece of wood to prevent the piston from completely exiting the caliper. At the very least you will be startled when it pops out with considerable force. Worse, major mechanical surgery will be required to remove the piston from what it ends up embedded in. Worst, real surgery if it becomes embedded in flesh. DAMHIK

[ccolwell]

Also, get some red grease to reinstall the pistons. This stuff http://www.redrubbergrease.com/
Somebody used to sell small amounts on ebay. I got one of those tins, did four or five caliper rebuilds and still have most of it left.

[Na Cl K9]

I haven’t tried a grease gun before simply because air pressure works so well. Seat one bleed valve and introduce high pressure air through the remaining open hole. Either hole works. Wood is referenced but not completely explained- I use a wood house paint stirring stick cut in half to double the thickness and then placed against the stationary pad supports opposite the caliper piston to act as a backstop. When the piston exits its bore it does so with a loud pop and hits the stirring sticks hard enough to crack them. The piston will be tight against the wood so work one of the two stirring stick halves loose. The other stick falls away and the piston can then be fully extracted using pliers to grasp the piston pad backing flange. Wiggle, turn and pull till it comes free. If there are any rust pits present on the piston it has become a souvenir. I perform this operation with the caliper held in a vice - don’t damage the nylon buttons by clamping across them. Soft jaw covers, gloves and eye protection advised. More later...

The "red grease" or 'caliper assembly paste' as Brembo refers to it works fine but only use a very small amount of the stuff. The first time I loaded a piston into a caliper using the product I used too much of the stuff and created a "soft lever" where the brake lever feels soft and spongy. Mostly I use brake fluid coating the caliper bore and the piston with new seal. Holding the caliper in a vice again, I use a 'c' clamp to slowly press the new piston into the bore of the caliper. There is a pin on the back of each pad. One pin, on the pad that moves with the piston has an O' ring and that pin seats tightly in a receptacle in the piston pad backing flange. Don't load the piston so far in that you can't get the pin to seat in the receptacle - once the pad is attached, you can use hand pressure to push the piston the rest of the way seating it against the caliper body. A spring clip holds the stationary pad to the supports opposite the piston.

Notes: Your master cylinder is most likely 'bad'. that is the bore has become pitted and the seals are leaking and the fluid return hole is probably plugged up. You can spot this by simply looking at the paint on the frame below the brake fluid reservoir. I will have evidence of damage from brake fluid or, if not, there will be fluid at the rear of the master cylinder around the piston plunger pin. If the master cylinder is working properly there will be a jet of fluid present inside the reservoir as the brake lever is released plus of course, no leaks. Be careful and cover the reservoir when bleeding the freshly overhauled brakes as the jet of brake fluid will shoot out and damage painted surfaces. Cover the fluid reservoir with a shop cloth while bleeding.

Mark Frappier (and others) restores ATE master cylinders, He sleeves the piston bore using stainless steel. He makes them to fit the exact size of your new piston which you must send along to him with the body of the master cylinder. The fluid reservoir has an O'ring between the tank body and the master cylinder. Replace that too. Clean the threads and seating surfaces of the metallic brake pipes to get the best seal. Replace them if they are kinked. Replace rubber bushings between the rubber brake hose and pipe at the hose support bracket bolted to the slider. Use new BMW rubber hoses. Use only Dot 3 or 4 fluid.

I haven't looked to see if complete master cylinders with reservoirs are still available in a while preferring to rebuild them since re-sleeving works so well. I believe the caps are all gone though so treat yours carefully. Buying a used master cylinder can be an exercise in replacing junk with more junk. Your goal is to make your bike stop at least as well as it did when it left the factory.

[r65lsk75c]

I haven’t tried a grease gun before simply because air pressure works so well. Seat one bleed valve and introduce high pressure air through the remaining open hole. Either hole works. Wood is referenced but not completely explained- I use a wood house paint stirring stick cut in half to double the thickness and then placed against the stationary pad supports opposite the caliper piston to act as a backstop. When the piston exits its bore it does so with a loud pop and hits the stirring sticks hard enough to crack them. The piston will be tight against the wood so work one of the two stirring stick halves loose. The other stick falls away and the piston can then be fully extracted using pliers to grasp the piston pad backing flange. Wiggle, turn and pull till it comes free. If there are any rust pits present on the piston it has become a souvenir. I perform this operation with the caliper held in a vice - don’t damage the nylon buttons by clamping across them. Soft jaw covers, gloves and eye protection advised. More later...

The "red grease" or 'caliper assembly paste' as Brembo refers to it works fine but only use a very small amount of the stuff. The first time I loaded a piston into a caliper using the product I used too much of the stuff and created a "soft lever" where the brake lever feels soft and spongy. Mostly I use brake fluid coating the caliper bore and the piston with new seal. Holding the caliper in a vice again, I use a 'c' clamp to slowly press the new piston into the bore of the caliper. There is a pin on the back of each pad. One pin, on the pad that moves with the piston has an O' ring and that pin seats tightly in a receptacle in the piston pad backing flange. Don't load the piston so far in that you can't get the pin to seat in the receptacle - once the pad is attached, you can use hand pressure to push the piston the rest of the way seating it against the caliper body. A spring clip holds the stationary pad to the supports opposite the piston.

Notes: Your master cylinder is most likely 'bad'. that is the bore has become pitted and the seals are leaking and the fluid return hole is probably plugged up. You can spot this by simply looking at the paint on the frame below the brake fluid reservoir. I will have evidence of damage from brake fluid or, if not, there will be fluid at the rear of the master cylinder around the piston plunger pin. If the master cylinder is working properly there will be a jet of fluid present inside the reservoir as the brake lever is released plus of course, no leaks. Be careful and cover the reservoir when bleeding the freshly overhauled brakes as the jet of brake fluid will shoot out and damage painted surfaces. Cover the fluid reservoir with a shop cloth while bleeding.

Mark Frappier (and others) restores ATE master cylinders, He sleeves the piston bore using stainless steel. He makes them to fit the exact size of your new piston which you must send along to him with the body of the master cylinder. The fluid reservoir has an O'ring between the tank body and the master cylinder. Replace that too. Clean the threads and seating surfaces of the metallic brake pipes to get the best seal. Replace them if they are kinked. Replace rubber bushings between the rubber brake hose and pipe at the hose support bracket bolted to the slider. Use new BMW rubber hoses. Use only Dot 3 or 4 fluid.

I haven't looked to see if complete master cylinders with reservoirs are still available in a while preferring to rebuild them since re-sleeving works so well. I believe the caps are all gone though so treat yours carefully. Buying a used master cylinder can be an exercise in replacing junk with more junk. Your goal is to make your bike stop at least as well as it did when it left the factory.

I will give the MC a more careful inspection. Upon the first look there was no visible leakage and the paint below did not show damage. In terms of how things have gone so far, I would not be surprised to find yet another issue. Speaking of another issue, my initial attempt to free the piston from the caliper with air pressure was a rousing failure. I removed the safety tip from the end of the compressor line and attempted to inject air through the fluid inlet. Of course it resulted in the expected spray of residual brake fluid. Turning my regulator to 80 psi did not yield success. So, do I need a better connection between the caliper and the end of the compressor hose? I had the caliper loosely mounted in my vise with a lot of padding hoping for the piston ejection. I ordered new pads - hoping for a chance to install them.

rickt