Topic: Front Brake Caliper - Stuck Piston/Brake Pad

[ZTatZAU]

My K1 resurrection is coming along and now dealing with the front brake master cylinder and caliper.  I assume I'll need new seals/cup/piston (?) etc in the handlebar MC but I'm going after the caliper first.  I disassembled the two halves of the caliper and can't pull the active brake pad and piston out of the caliper bore.  I tried some compressed air in the feed line port but only made a mess.

Then I searched past threads here for advice/suggestions and liked the idea using a grease gun to force the piston out.  I couldn't find any more details on the grease gun procedure but figured a grease (zerk) fitting installed in the brake fluid port was the way to go with the bleeder valve closed.

I'm not too familiar with the metric hardware  yet, but pretty sure the brake line fitting into the caliper is 10mm but the thread pitch has me stumped.

Can anyone tell me what thread size I'm looking for for a zerk fitting that will fit in the brake line fitting port?  i.e. 10mm x 1, 10mm x1.25, 10mm x 1.5? And who might carry such a grease fitting?

TIA, for any info/advice,  ZT

[CycleRanger]

I bought a box of assorted metric zerks from Harbor Freight.
I can't remember exactly what size/thread pitch I used but there was one that worked among that assortment.
https://www.harborfreight.com/32-piece-metric-grease-fittings-67569.html

The grease gun method works great, I've used it a couple of times but it is somewhat messy.

[ZTatZAU]

I bought a box of assorted metric zerks from Harbor Freight.
I can't remember exactly what size/thread pitch I used but there was one that worked among that assortment.
https://www.harborfreight.com/32-piece-metric-grease-fittings-67569.html

The grease gun method works great, I've used it a couple of times but it is somewhat messy.

Hmmm!  I actually just returned from harbor freight and looked at that assortment before posting my questing here..  But the threads on 10 mm fittings in that assortment looked a lot finer than threads on the bleeder valve I brought with me for comparison.  If I'm not mistaken the threads on the bleeder looked to be the same size as the threads on the brake line fitting.  So I passed, on that assortment.

It's too bad the CB750 Parts Manual don't list the size of either caliper fitting.  I sure don't want to mess up the threads in the caliper.

ZT

[willbird]

NAPA had a fitting that fit into the brake line hole. Behind the counter on a shelf they had a small box of metric fittings. Was not expensive, 4-5 bucks maybe. I am thinking it was 1/8NPT to the metric flare thread/seal. So it was easy to find a grease zerk to thread in.

Here is the same part generally  on Amazon, it was worth a trip to NAPA to have a shot though :-).

https://www.amazon.com/Adapter-Female-M10x1-0-Reducer-Pressure/dp/B085VCXTCS/ref=sr_1_17?crid=39E94WAKSHUIY&keywords=10mm+x+1.0+Inverted+Flare+Male+to+1%2F8+npt&qid=1686859945&sprefix=10mm+x+1.0+inverted+flare+male+to+1%2F8+npt%2Caps%2C104&sr=8-17

[RAFster122s]

You aren't doing anything but finger tight, you aren't trying to get it to screw all the way in, just get it screwed in until it stops. Once it stops it is good enough. You might get a tiny bit of grease out that area but the bult is going to fill the caliper and force out the piston. Then you just scoop out the grease and put it on a piece of cardboard. Lots of that grease won't be contaminated. You can separate it in good from bad and put the good in a small container to use on things that are just providing a barrier to rust...or just toss it and mark it up as cost of separating piston from caliper.

The grease method is effective and pretty quick. Wipe out the caliper with some paper towels and then spray with brake cleaner inside and out the bleeder screw and hose connections to clean it completely.

Replace your bleeder screw is a good idea and clean the slot for the caliper seal so it is spotless.

[willbird]

Replace your bleeder screw is a good idea and clean the slot for the caliper seal so it is spotless.

Both good suggestions. "Stuff" building up in the groove where the piston seal lives causes the piston to not retract.

Bill

[CycleRanger]

I bought a box of assorted metric zerks from Harbor Freight.
I can't remember exactly what size/thread pitch I used but there was one that worked among that assortment.
https://www.harborfreight.com/32-piece-metric-grease-fittings-67569.html

The grease gun method works great, I've used it a couple of times but it is somewhat messy.

Hmmm!  I actually just returned from harbor freight and looked at that assortment before posting my questing here..  But the threads on 10 mm fittings in that assortment looked a lot finer than threads on the bleeder valve I brought with me for comparison.  If I'm not mistaken the threads on the bleeder looked to be the same size as the threads on the brake line fitting.  So I passed, on that assortment.

It's too bad the CB750 Parts Manual don't list the size of either caliper fitting.  I sure don't want to mess up the threads in the caliper.

ZT

You are probably correct but like RAFster122s said, I too just screwed in the zerk finger tight until it stopped, not enough to mess up the threads if they were a different pitch. It was secure enough to get the job done with no harm the caliper.
However I do agree that a fitting of the proper size/pitch would be best. As was suggested NAPA might be worth checking.

[ZTatZAU]

... You are probably correct but like RAFster122s said, I too just screwed in the zerk finger tight until it stopped, not enough to mess up the threads if they were a different pitch. It was secure enough to get the job done with no harm the caliper.
However I do agree that a fitting of the proper size/pitch would be best. As was suggested NAPA might be worth checking.

I appreciate everyone's replies!  I went back to HF and tried the 10MM x 1.00 grease fitting from the assortment CycleRanger suggested, and could only turn it 3/4 of one turn.  But then stopped.  I was more concerned about tearing out the first starting thread in the caliper than I was about leaking some grease.

I think I'm going to try to find a correct sized metric thread grease fitting or go to a 10MM male adapter to a common SAE grease fitting as Willbird suggested.  Unfortunately, I'm still not sure if the brake line fitting thread is 10MM x 1.25 or 10MM x 1.50.  Does anyone know?

I'll be back on this tomorrow and will let you know how I do.  ZT

[CycleRanger]

I measure the thread pitch as 1.25.
Sorry the HF stuff didn't work for you.

[ZTatZAU]

I measure the thread pitch as 1.25.
Sorry the HF stuff didn't work for you.

Thanks CycleRanger!  1.25 is what I was tending towards!

Stay tuned for updates!  ZT

[bryanj]

Ubscrew the fitting from your greas gun and the thread on the pipe will screw in 1 to 2 turns before going tight then pump away, never failed me yet

[BenelliSEI]

I used an old fitting from the metal pipe. Remove the pipe and drill and tap the fitting to take a grease fitting. Takes a few minutes, but then you have the “tool” forever.

[willbird]

That is the fitting that NAPA had, and I have a 1/8 NPT grease zerk threaded into it. I just left it in the caliper when I sand blasted and painted the caliper.

[Doobie]

Do yourself a favor and rebuild the MC first and then use it to pump the pad and piston out. I gave up trying to find a fitting that would work with either of the two grease guns I have.

[ZTatZAU]

Do yourself a favor and rebuild the MC first and then use it to pump the pad and piston out. I gave up trying to find a fitting that would work with either of the two grease guns I have.

Thanks Doobie!  That certainly would have been another option but I kinda' got my head around using the grease gun method and once I got going down that road, I saw it somewhat as a challenge to see it through.

The brake puck and piston are now out of my caliper!  It took a bit of fiddling but the grease gun method worked great.  No big mess and very controllable, once I had the right fitting components to install a "leak-free" zerk fitting in the brake line fitting port on the caliper.

I went with BenelliSEI and Willbird's suggestions and started with this Dorman brake line brake line Metric to SAE adapter...

Dorman Products  327852.1 Brake Line Adapter-Bubble Flare Female -3/8-24 In. x 3/16 In. x Male M10-1.25
https://www.dormanproducts.com/p-23863-3278521.aspx

I first tried installing the M10 x 1.00 zerk as far as it would go into the 3/8-24 female end of the adapter but the grease leaked through the mis-matched threads and didn't move anything.  So I spent some time modifying the Dorman fitting to accept the zerk.

I started by grinding off the flare end below the male M10 x 1.25 metric threads to get farther down into the brake line port and counter-bored the hole so as not to damage the flare in the bottom of the caliper threaded port.  Then I drilled out the 3/8-24 female end with a 23/64 drill and tapped the slightly larger hole to accept the M10 x 1.00 zerk I tried first.  Everything tightened up quite nicely.

Here's my setup...



And here's my new custom "caliper piston removal grease fitting" tool, and what came out....



The brake puck was stuck the worst with much more corrosion than the piston but the grease pushed both out quite smoothly.  I haven't checked the specs but it looks like there's some meat left in the pads, so I may be able to clean everything up and reuse the components.

I assume the red lines on the puck are wear indicators but don't know how much meat should be left on the bone.  Do those of you more familiar with this K1 brake, see these pads as being worth saving?

I still need to clean out the grease and remove the seal in the piston bore, but the piston is relatively clean (compared to the brake puck), so I do think the piston will clean up too.

Thanks again for all the helpful suggestions and advice.
ZT 

[willbird]

The new brake pads from 4:1 were only $13, the lining on my piston side pad had detached from the metal backing.

Bill

[seanbarney41]

Ubscrew the fitting from your greas gun and the thread on the pipe will screw in 1 to 2 turns before going tight then pump away, never failed me yet

+1...I have also done this several times

[bryanj]

Get the seal groove super clean, especialy the corners, with a dental pick or similar and always a new seal when they are that siezed/crudded

[CycleRanger]

I wouldn't reuse that pad. It looks like it may have been soaked with brake fluid and might separate or disintegrate under pressure. At the very least it may no longer provide optimal stopping ability.

[dave500]

#$%* man?put new pads for #$%*s sake!!

[BenelliSEI]

Get the seal groove super clean, especialy the corners, with a dental pick or similar and always a new seal when they are that siezed/crudded

Best advice, above! I scrape and scrape and then use a small, brass wire wheel on my Dremel. If that groove is not absolutely spotless and square in cross section, the seal will grab the piston and it will stick…… when you think it’s clean, do it all again.

And definitely new pads.

[bryanj]

Yup but dental pick BEFORE the wire brush or all you do is polish the crud

[BenelliSEI]

Yup but dental pick BEFORE the wire brush or all you do is polish the crud

Yup….. made that mistake too.

[MauiK3]

Brakes are such a key safety item I never try to save a buck, just make it shiny and new so you can be confident you've done all you can do.

[ekpent]

I've always found that the old worn front brake pads on the 750's never wear nice and flat but make a beveled slant surface to them as they wear down.