Question about front brakes / Need help

[pearljam724]

I finished restoring my 750 last November. Leaving very little time to enjoy it. Anyhow, at the time of completion. My front brakes were locking up. They had a death lock grip and the only thing I could do to release that grip was loosen the 2 allan pins that secure both halves of the calipers. So, in order to enjoy riding the bike for a couple days and not having time to investigate the front brakes. I rode with only back brakes. I need to address the brakes before taking it anywhere this year and having it inspected. I opened the reservoir to find I had no fluid. I found a leak at the lower left caliper coupler hose. I understand the bike had a brake fluid leak. But, prior to finding that nearly several months later. I had great pressure and the brakes would clamp down, but not release. What reasons would they not release ? Would, the fact that I had a leak in pressure, not allow them to release ? Should the allan pins be manually adjusted tighter as the pads wear ? Even, if I loosen the 2 pins to release the brakes, they lock back up if I apply them again, having left the pins at the loose setting. I'm going to sand down the recess that holds the pads ever so slightly and perhaps line that recess with grease being careful not to get any on the face of the pads. Thinking the pads are not relaxing due to paint behind them. Anyone, please shine some light on the fact that my brakes will not release after they are implied, thanks.

[GT750Battleship]

Hi,I think it's about time for you to overhaul the brake calipers
You can start by giving them a good clean internally,think you'll find the brake fluid is now mud,piston is seized totally or partially the pad that is supposed to move in its holder is suffering the same problem,Depending on how bad the calipers are....? you may have badly scored pistons that will need replacing ! Pull them apart,one side at a time.....at the very least you will require new piston seals & piston dust boots,but probably better to buy two caliper overhaul kits,around $59 US each & get everything you need
Then of cause you can look at the master cylinder which also must be in need of an overhaul Dirty brake fluid is the enemy + air in the system,change fluid regularly,to avoid this problem in the future By releasing the pins..all your doing is allowing the two halves of the caliper to move further away from each other,thus moving the pads away from staying in contact with the Disc.the piston seals actually perform two functions,one to stop fluid from leaking,& flexing to aid the piston to retract when pressure is released at the lever,this is helped by the Disc slightly knocking the pad. Getting everything clean in the system is a must for good braking & safety

Cheers,
Roger.
Suzuki GT750A

[Coyote]

If everything is clean and in good shape, the most likely cause of this situation is lack of lubrication on the 2 axle pins (the bolts you are loosening). The caliper needs to float on those pins to self align. To see if this is what is happening, tighten those 2 allen bolts. The should be extremely tight. That's why they are so large. Apply the brake and let it lock up. Then using a very thin (.002) feeler gauge, see if it will slide in easily between the disk and the pad on either side. If you can slide the gauge in one side, then the caliper is only locking on one side of the disk. Again, this is due to lack of lube on the pins. The caliper can't float, so one side locks up.
Also, look down ate the caliper when you apply the brake. If it seems to cock one way or the other, it's lack of lube on the pins. The pads never really retract, they only relax.

[Barry S.]

There are 2 types of brake pads, the early one is flat on the back side next to the piston and the later one is cupped. The cupped one goes on the piston, if it's flat it will bind up.

[pearljam724]

If everything is clean and in good shape, the most likely cause of this situation is lack of lubrication on the 2 axle pins (the bolts you are loosening). The caliper needs to float on those pins to self align. To see if this is what is happening, tighten those 2 allen bolts. The should be extremely tight. That's why they are so large. Apply the brake and let it lock up. Then using a very thin (.002) feeler gauge, see if it will slide in easily between the disk and the pad on either side. If you can slide the gauge in one side, then the caliper is only locking on one side of the disk. Again, this is due to lack of lube on the pins. The caliper can't float, so one side locks up.
Also, look down ate the caliper when you apply the brake. If it seems to cock one way or the other, it's lack of lube on the pins. The pads never really retract, they only relax.

I think you are exactly correct, Coyote. I replaced the o rings that wrap around those pins and rest in a groove. Because the originals, well they were old. The new o rings I substituted for the originals were not oem and seemed to be ever so slightly, thicker. I knew this, when sliding the pins into the caliper halves. Because I had to grease and hit them fairly hard with a hammer to actually get them to slide through. The new o rings even tore slightly, because I had to force them through. The calipers don't need rebuilt. They worked fantastic, before I reinstalled them. The pistons are not rusted, I reused the previous pads, etc. All I did was paint them, replace those rubber o rings on the pins and new brake lines. Thoroughly cleaned the pistons, etc. I didn't lube the pins. I don't have Suzuki oem o rings for those pins at the moment. To be honest, I can't see that it would create a huge problem, if I removed the o rings that wrap around the pins all together ? I assume a little dirt or brake pad dust may get in unwanted areas. But, that should only mean that I would have to clean them sooner ?

[GT750Battleship]

Hi,the advice on the pins is 100% correct,they must be WELL lubricated & tight,if tou use anything apart from the Suzuki "0" rings you will have trouble as described ! Non floating calipers =binding brakes! you can leave these "0" rings out all together if you like...a lot of guys do,personally I don't. As long as the pins are well lubricated with silicone or rubber grease they will function as designed,as you can see only one pad moves,the other is fixed,retained by a screw...so rather hard to make a mistake fitting them to the correct side
Cheers,
Roger

[pearljam724]

On second thought. I can't see how lubricating these pins does anything. They are not like modern calipers. With modern calipers the brake pads rest on ( guide pins go through holes attached to the steel backing on modern pads ) guide pins. With those pins I speak of, absolutely you have to lubricate those because the pads glide side to side on those pins. The GT pads and pins are nothing like that. It seems to me, that the pins only purpose is to house the 2 calipers tight together. I could be wrong, but if you were to look at the calipers, neither pad has any relationship to the pins that we speak of. The calipers, nor pads do not readjust themselves where a lubricant would be needed on the pins. I tried looking at a manual, but the only manual I have refers to the early model drum brakes.

[pearljam724]

Disregard post above. I forgot about the middle piece that holds the piston side pads. That pad does move on the pins. Anyone know the torque spec for the pins ?

[GT750Battleship]

Funny you should mention torque settings for the pins/bolts !
I over hauled my calipers recently,as the braking was only happening on the left rotor !!!
I went looking on the Internet for a "number" couldn't find a spec anywhere,so I just did them up evenly to what I consider tight !! Brakes are now excellent,no dramas at all
Cheers,
Roger
Suzuki GT750A

[pearljam724]

Funny you should mention torque settings for the pins/bolts !
I over hauled my calipers recently,as the braking was only happening on the left rotor !!!
I went looking on the Internet for a "number" couldn't find a spec anywhere,so I just did them up evenly to what I consider tight !! Brakes are now excellent,no dramas at all
Cheers,
Roger
Suzuki GT750A

Thanks, for mentioning that. If someone doesn't respond with that correct torque setting. I'll use my torque wrench to set them evenly. Guessing, 30 pounds should be close to what Suzuki probably suggests. If one pin is tighter than the other, I can see how that would put things on a bind. Not allowing that middle guide plate to move properly on the pins. Thanks

[tz375]

When the brakes don't retract, 90% of the time, the problem is in the master cylinder. Try the trick that Vintageman suggested. Apply brakes hard. release the lever, crack open the banjo at the M/C and if brake fluid almost squirts out, it's because the pressure is not being released and the problem is in the M/C.

It is also possible to have sticky seals or corrosion in the caliper body that is preventing the piston from retracting.

[pearljam724]

When the brakes don't retract, 90% of the time, the problem is in the master cylinder. Try the trick that Vintageman suggested. Apply brakes hard. release the lever, crack open the banjo at the M/C and if brake fluid almost squirts out, it's because the pressure is not being released and the problem is in the M/C.

It is also possible to have sticky seals or corrosion in the caliper body that is preventing the piston from retracting.

Ok, thanks Richard. Is there a link, etc. on how to disassemble the master cylinder if need be ?

[GT750Battleship]

+1 on the master cylinder !!
Cheers,
Roger
Suzuki GT750A