Torque for bolts holding caliper halves together - BMW Luxury Touring Community
 
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post #1 of 16 Old Sep 1st, 2013, 7:11 pm Thread Starter
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Torque for bolts holding caliper halves together

2002 LT - 65K miles

The pistons on my rear caliper were sticking, so I am in the process of a rebuild. Does anyone happen to know the torque spec for the M8 x 1.25 bolts that are used to hold the caliper halves together? About 3/4 inch of bolt threads goes into the threaded caliper half. I also plan on using blue Loctite for insurance.

Thanks,
Ken
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post #2 of 16 Old Sep 1st, 2013, 9:49 pm
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Angry Re: Torque for bolts holding caliper halves together

Quote:
Originally Posted by kend52
2002 LT - 65K miles

The pistons on my rear caliper were sticking, so I am in the process of a rebuild. Does anyone happen to know the torque spec for the M8 x 1.25 bolts that are used to hold the caliper halves together? About 3/4 inch of bolt threads goes into the threaded caliper half. I also plan on using blue Loctite for insurance.

Thanks,
Ken
I looked thru the torque values chart in the HoW forum and either missed it, or its not listed. I did see a warning in the OEM manual to not separate the halves of the calipers! Hopefully, one of the wrench experts will chime in shortly. Good luck.
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post #3 of 16 Old Sep 1st, 2013, 11:06 pm
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Re: Torque for bolts holding caliper halves together

Yes the manual states "Do not separate the caliper halves". Now I don't know why BMW has that warning but the MGB had the same warning and the only way you could recover was to use a special kit that Moss Motors created with new - one time use bolts and seals.

So there is no published torque specification. Hope it holds fluid.

John
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post #4 of 16 Old Sep 2nd, 2013, 10:06 am Thread Starter
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Re: Torque for bolts holding caliper halves together

Quote:
Originally Posted by jzeiler
Yes the manual states "Do not separate the caliper halves". Now I don't know why BMW has that warning but the MGB had the same warning and the only way you could recover was to use a special kit that Moss Motors created with new - one time use bolts and seals.

So there is no published torque specification. Hope it holds fluid.
Yes, I hope it holds fluid, too. The calipers do not have an O-ring between the halves sealing a fluid passage. Fluid goes from the hose side to the other side via the pipe at the bottom outside of the caliper. I think that makes the chance of leaking fluid because of a rebuild pretty low, but we'll see.

I need to order a new banjo bolt because I had to destroy the one connecting the brake hose to the brake line to get the old hose off so I could put a new hose on. I was hopeful that bolt is used on a BMW auto, so I could go the local BMW auto dealer and pick one up, but it is not and I'll have to order it.

I was able to find one torque spec for an M8 bolt going into aluminum, which was 17 N-M. I think I'll go with that and blue loctite. The bolts I removed were not stretched and would thread into the caliper quite easily, so I think they can be re-used.

Ken
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post #5 of 16 Old Sep 2nd, 2013, 10:49 pm Thread Starter
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Re: Torque for bolts holding caliper halves together

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Originally Posted by kend52
Yes, I hope it holds fluid, too. The calipers do not have an O-ring between the halves sealing a fluid passage. Fluid goes from the hose side to the other side via the pipe at the bottom outside of the caliper. I think that makes the chance of leaking fluid because of a rebuild pretty low, but we'll see.

I need to order a new banjo bolt because I had to destroy the one connecting the brake hose to the brake line to get the old hose off so I could put a new hose on. I was hopeful that bolt is used on a BMW auto, so I could go the local BMW auto dealer and pick one up, but it is not and I'll have to order it.

I was able to find one torque spec for an M8 bolt going into aluminum, which was 17 N-M. I think I'll go with that and blue loctite. The bolts I removed were not stretched and would thread into the caliper quite easily, so I think they can be re-used.

Ken
One more question. Rather than wait to get the banjo bolt mailed from a BMW dealer, what would be wrong with getting one of the appropriate size from a local auto parts dealer? The BMW bolt is used for both non-integral and integral brakes, so it doesn't seem to be integral-specific.

Thanks,
Ken
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post #6 of 16 Old Sep 2nd, 2013, 10:52 pm
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Re: Torque for bolts holding caliper halves together

You should be fine if you can find one the right size. The jumper tube does make sense that there are no cross body fluid paths. You should be OK there as well.

John
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post #7 of 16 Old Oct 23rd, 2013, 5:19 am
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Re: Torque for bolts holding caliper halves together

How did your caliper rebuild work out, good...bad...? I found I have pistons which are sticking on the right front caliper while replacing brake pads. Anything you can share would be greatly appreciated!

Boots
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post #8 of 16 Old Oct 23rd, 2013, 7:43 pm Thread Starter
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Re: Torque for bolts holding caliper halves together

Quote:
Originally Posted by kedwards005
How did your caliper rebuild work out, good...bad...? I found I have pistons which are sticking on the right front caliper while replacing brake pads. Anything you can share would be greatly appreciated!

Boots
2002 K12LTE
2006 R12GS
1972 R60/5 Toaster
Boots,

I'd say the rebuild was a success.

One thing to note, first. The rear caliper halves have a crossover tube to let brake fluid travel from one side to the other. The tube has standard brake line fittings. The front calipers do not appear to use a tube. Instead, like airhead BMW M/C calipers I've rebuilt, the front halves appear to have an internal fluid passage that uses an O-ring at the joint between the caliper halves to prevent fluid from seeping out. That's just from an outside look at the front calipers on my bike (a 2002 like yours), though.

The rebuild was actually very simple, and like any other caliper rebuild I've done (except with the crossover tube). I took the halves apart and cleaned them up with spray brake cleaner. Sprayed brake cleaner through all the passages to make sure they were clear. Bought the rebuild kit from a BMW dealer. Kind of pricey, but what else was I going to do? The kit came with new seals, new pistons, and some lube to use on the seals and pistons when putting them in the caliper halves. I also replaced the rear brake hose while I was at it. BTW, the banjo bolt that connected the upper end of the brake hose to the brake line was absolutely stuck and I destroyed it getting it loose, so buy an extra banjo bolt or two, and some extra crush washers, too. I recall the diameter of the bolts holding the halves together was M8. I used some blue loctite and torqued them to about 15 Newton-meters (NOT FT-LBS!!!!), I think. You can get some torque info here - http://yetmans.mb.ca/kohler/page3/page3.html Put the brake hose and the caliper on, filled the wheel circuit, and bled the rear control and wheel circuits (took some time, but not a difficult bleed job).

Went for a test ride and came home. No leaks, but the brake pads were still rubbing the rotor more than I felt they should. Took some more test rides of increasing distance and decided to see how hot the rotor was getting. Couldn't hold my fingers on it, so it was VERY HOT. I'm embarrassed to say that at first it didn't dawn on me that what made the rotor VERY HOT was that I used the brakes to slow the bike right before checking the rotor temp. Duh!!! So, after I got my head out of the clouds, I took another couple of rides up the interstate and let the bike coast to a stop at a rest area. Success - the rotor was warm at best and I could keep my fingers on it easily. The rotor was not discolored and did not have any other indication that it overheated. So, I would say my rebuild was success.

Good luck with yours.

Ken
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post #9 of 16 Old Oct 23rd, 2013, 8:22 pm
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Re: Torque for bolts holding caliper halves together

they are not metal pistons, or were not on my other K's so with no scratches or marks of any kind I just replaced the piston O rings and dirt seals, never had a problem

Gary
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post #10 of 16 Old Oct 24th, 2013, 5:49 pm
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Re: Torque for bolts holding caliper halves together

Serviced the right front caliper today, definitely had stuck pistons.

Removed the new pads which I had installed, cleaned the pistons with brake clean, lubricated the pistons, re-assembled with the old pads, switching right for left and left for right, tried residual pressure and got no movement.

Energized the bike, lightly touched the brake lever and got movement of the stuck pistons. Dis-assembled the caliper, re-cleaned pistons, re-lubricated and re-assembled using the new pads, all is good.

Went for a short 6 mile test ride, all was good, went for a 15 mile test ride all is well. Went back out for 30 mile ride , stopped about half way, rotors look fine, no unusual heat.

So far I have avoided the re-build, we'll see how this service goes.

Thank you for sharing your experience with re-build, at least we know it can be done!

Ride Safe, Ride Often!

Boots
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post #11 of 16 Old Oct 24th, 2013, 9:10 pm
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Re: Torque for bolts holding caliper halves together

Quote:
Originally Posted by kedwards005
Serviced the right front caliper today, definitely had stuck pistons.

Removed the new pads which I had installed, cleaned the pistons with brake clean, lubricated the pistons, re-assembled with the old pads, switching right for left and left for right, tried residual pressure and got no movement.

Energized the bike, lightly touched the brake lever and got movement of the stuck pistons. Dis-assembled the caliper, re-cleaned pistons, re-lubricated and re-assembled using the new pads, all is good.

Went for a short 6 mile test ride, all was good, went for a 15 mile test ride all is well. Went back out for 30 mile ride , stopped about half way, rotors look fine, no unusual heat.

So far I have avoided the re-build, we'll see how this service goes.

Thank you for sharing your experience with re-build, at least we know it can be done!

Ride Safe, Ride Often!

Boots
Did you clean the exposed pistons well before you pushed them in to install the new pads? Pushing in pistons that have been extended for a long time and accumulated dirt and such can cause sticking or worse. Always wash thoroughly with soapy water (a toothbrush works well for this) and then rinse and dry before pushing the pistons in. This goes a long way towards lessening sticking or causing seal damage. I avoid brake cleaner as it can be rough on the seals and rubber parts.

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post #12 of 16 Old Oct 25th, 2013, 5:21 am
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Re: Torque for bolts holding caliper halves together

Did use a toothbrush and brake cleaner, did not use soap and water. Will remember to wash up with soap and water in the future!

Lubricated with silicone spray. Plan today is to pull the pads after another test run to check wear pattern.

Brakes now operate smoothly with no vibration, tested at speeds up to 75 mph, smooth actuation all around.
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post #13 of 16 Old Oct 25th, 2013, 10:39 am
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Re: Torque for bolts holding caliper halves together

Under normal circumstances there really should be no need for splitting the calibers. Block of wood in between the pads and some compressed air in from the brake hose hole has so far always released stuck pistons for me.

Born to be wild so why not

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post #14 of 16 Old Oct 25th, 2013, 1:56 pm
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Re: Torque for bolts holding caliper halves together

Quote:
Originally Posted by kedwards005

Lubricated with silicone spray.
Not entirely sure that is a good idea as every time I have rebuilt a caliper the manuals always stated "use only brake fluid to lubricate the seals". And I know if you put DOT 5 (silicone based fluid) in a DOT 4 system you destroy the seals. Just sayin'.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #15 of 16 Old Oct 25th, 2013, 5:06 pm
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Re: Torque for bolts holding caliper halves together

Let me elaborate on the "service" I completed on the caliper with stuck pistons.

First: caliper was never disconnected from the hydraulic line
Second: caliper was never split.

Entire service was external in nature.

I am keeping a close eye on the caliper which as of this writing has over 220 miles since service completed. Have made over a dozen "emergency" stops from speeds of 35 mph to 85 mph, caliper is functioning normal.

Braking is smooth from every speed, with the pistons stuck I was experiencing severe front shimmy under heavy braking, no more.

Let me also add, the issue which helped me discover the stuck pistons was the 95% used left brake pad versus a 45% used right brake pad, pads on the left caliper were equal in wear.

All in all, everything appears to be operating normally, keeping a close eye on situation and doing a lot of brake checks prior to intersections!

Thanks to all for the advice and interest in solving this issue, I will keep you posted as I add more miles!

Every time I ride the LT I remember why I bought it, and nothing else compares!

Ride Safe, Ride Often!
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post #16 of 16 Old Nov 5th, 2013, 5:18 pm
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Re: Torque for bolts holding caliper halves together

560 miles later the stuck caliper issue appears solved.

Brakes are operating normal, pads have seated and wearing evenly.

Thanks again to all for the input, I hope to be of assistance to all of you in the future!

Ride Safe, Ride Often!
Boots

Regards,
Boots
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