Hi all. I'm trying to free a dragging rear brake on my 89 1st gen.vmax. I bled some brake fluid out of both sides but it didn't help. I pulled the caliper off and found the inside piston out about 1/2 inch. The outside piston was all or most of the way in. I pumped the brake pedal both piston moved out. Long story short. I put clamp on the inside piston to pull it in and it didn't budge.. I'm reading online theres a return hole somewhere that clogs up. Can anyone tell me where that is? Thanks for reading . any help appreciated.---chuck
Brake fluid return hole
- Thread starter intruder2
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Hmmm interesting, where did you read about the return hole?
I've not heard of this. From my experience the volume behind both pistons is connected to the hose. Fluid is pushed by the master through the hose and then pushes both pistons. The pistons seals together with the spring in the master that pushes the piston in the master back pulls the fluid thus pulling the pistons back. That's all there is to a simple hydraulic system.
I have found that trying to push a piston back, using a clamp, can be very difficult as you have to be sure you are pushing it back squarely whereas pushing it out by pulling on the lever is much easier.
Basically what I'm saying is that I'm not convinced that your problem is a blocked return hole.
I would suggest removing the calliper, popping each piston out, one piston held in place with a clamp or cable tie, and compressed air applied to the inlet.
Clean the area behind the seal, check seal is in good condition and not gardened, replace as necessary and clean the piston. They are chromed steel so the part beyond the seal will rust.
Edited as I was incorrectly referring to front master.
I've not heard of this. From my experience the volume behind both pistons is connected to the hose. Fluid is pushed by the master through the hose and then pushes both pistons. The pistons seals together with the spring in the master that pushes the piston in the master back pulls the fluid thus pulling the pistons back. That's all there is to a simple hydraulic system.
I have found that trying to push a piston back, using a clamp, can be very difficult as you have to be sure you are pushing it back squarely whereas pushing it out by pulling on the lever is much easier.
Basically what I'm saying is that I'm not convinced that your problem is a blocked return hole.
I would suggest removing the calliper, popping each piston out, one piston held in place with a clamp or cable tie, and compressed air applied to the inlet.
Clean the area behind the seal, check seal is in good condition and not gardened, replace as necessary and clean the piston. They are chromed steel so the part beyond the seal will rust.
Edited as I was incorrectly referring to front master.
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I would say no. The banjo bolt for the hose is easy to undo (remember to anneal the copper washer if not replacing it.
Potentially you could work on it in situ but far easier if calliper is on a bench plus as one piston is pushed out, the fluid will leak out all over the place., then you'll have the same when doing the other side.
BTW if there is a blocked hole, then that would mean neither piston would be able to be pushed back.
I can't remember if the calliper is 1 or 2 piece. I think it's 2, but you don't need to split it to overhaul.
Potentially you could work on it in situ but far easier if calliper is on a bench plus as one piston is pushed out, the fluid will leak out all over the place., then you'll have the same when doing the other side.
BTW if there is a blocked hole, then that would mean neither piston would be able to be pushed back.
I can't remember if the calliper is 1 or 2 piece. I think it's 2, but you don't need to split it to overhaul.
If air won't move a piston and you can't get a tool on it to move it, use a grease gun. A decent grease gun develops close to 2000 psi where a good air compressor is probably ~150 psi at its highest. You have to clean it thoroughly to return it to service, but I've never had a caliper not yield to the grease gun.
Pics of breaking into a SOHC Honda 750 caliper, and the gooey muck that was all that remained, after 30+ years.
Pics of breaking into a SOHC Honda 750 caliper, and the gooey muck that was all that remained, after 30+ years.
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If it is that bad, change the caliper. They are relatively cheap used and why bother.
I work on heavy equipment and if a machine dies and won't run, we sometimes use a grease gun with hydraulic oil in it to release the brakes so we can tow the machine back to the shop. You can get 5,000 psi if needed and surprisingly it will hold that pressure for quite a while. If it was me, I would just get another caliper or use the opportunity/excuse to upgrade to another more modern caliper.
Gbianchi
Well-Known Member
Hey, just did this same job, my seals were old and needed replacement, order new seals, remove caliper, remove old seals, clean up the caliper interior, put in new seals, install caliper, reconnect brake line, bleed brakes, done! Air compressor should work for removing piston, I reused copper washers twice, so far all working with no leaks 
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Yamaha OEM seal and dust seal kit for the rear, '89 VMax:
Caliper Seal Kit
31A-W0047-00-00
Retail Price: $43.99
Your Price: $34.03
https://www.ronayers.com/oemparts/a/yam/50042e2ff8700209bc78a2d4/rear-brake-caliper
Some 180 or 220 wet-or-dry sandpaper, use it on both the piston and the caliper interior, a can of brake cleaner spray (wear eye protection!) and thoroughly-flush-out the brake line/master cyl until the brake fluid is completely clear. The 'reverse-bleed' method, using a syringe to push brake fluid from the caliper bleeder upwards to the master cyl, is for me the quickest way to purge all the air from the line. You have to pay attention the master cyl doesn't overflow. You may need to remove excess brake fluid.
Directions on making an inexpensive brake bleeder syringe, how to use it to do the 'reverse-bleed,' and replacing your clutch slave cyl:
https://www.vmaxforum.net/threads/clutch-slave-cylinder-replacement.45011/
Caliper Seal Kit
31A-W0047-00-00
Retail Price: $43.99
Your Price: $34.03
https://www.ronayers.com/oemparts/a/yam/50042e2ff8700209bc78a2d4/rear-brake-caliper
Some 180 or 220 wet-or-dry sandpaper, use it on both the piston and the caliper interior, a can of brake cleaner spray (wear eye protection!) and thoroughly-flush-out the brake line/master cyl until the brake fluid is completely clear. The 'reverse-bleed' method, using a syringe to push brake fluid from the caliper bleeder upwards to the master cyl, is for me the quickest way to purge all the air from the line. You have to pay attention the master cyl doesn't overflow. You may need to remove excess brake fluid.
Directions on making an inexpensive brake bleeder syringe, how to use it to do the 'reverse-bleed,' and replacing your clutch slave cyl:
https://www.vmaxforum.net/threads/clutch-slave-cylinder-replacement.45011/
