Brakes not building pressure

[GabrielGoes]

Good day mates, just wondering what yall think the culprit is the master cylinder or the calipers for my issue here on 80's G model not building pressure on the lever.

I completely disassembled my calipers, took out the o rings, cleaned the bore, and re-used the piston seal- they looked good.

I also cleaned the hoses and positively confirmed they are not blocked. i also checked the T fitting/junction where the 3 brake lines meet.

The problem is the lever never builds pressure. If I pump them up really fast I can feel a slight resistance. If I use a pair of vice grips to either side of the left or right hoses there is no difference... I already took my calipers apart and was about to order a caliper rebuild kit but I am thinking I should probably try switching my master cylinder.


For an issue with no pressure building up is it typically the master cylinder that is issue? I can't imagine it being the calipers because if the piston was seized still somehow, I would imagine at least the lever would get stiff.

Thanks for insight I just need to clear my head this is day 2 with these brakes am getting frustrated..

[bonanzadave]

Tell us how you bled the brakes after the rebuild.....

[GabrielGoes]

Tell us how you bled the brakes after the rebuild.....

With a vacuum pump. And also traditionally by hand. There's no air in the lines.

I'm going to end up in the garage again probably covered In brake fluid soon anyways just wanted to take a break and see what you guys thought. Master is an original I guess is probably the culprit. I really just hate brake jobs

[alke46]

Did you make sure that tiny hole in the m/c was clear and did you poke a very small wire through it to be sure? It has something to do with the returning fluid to the m/c (I think). But anyway, there are two holes in the master. One is a very tiny hole as opposed to the slightly larger one.

Hope this helps.

[GabrielGoes]

Did you make sure that tiny hole in the m/c was clear and did you poke a very small wire through it to be sure? It has something to do with the returning fluid to the m/c (I think). But anyway, there are two holes in the master. One is a very tiny hole as opposed to the slightly larger one.

Hope this helps.

I have not done this and you bring up an excellent point, I will check both holes. I haven't rebuilt too many m/c and I don't understand them fully. I might just throw the whole thing in the sonic tank for starters.

[alke46]

Clean the holes for starters, I think you will like the results.

[KiwiAlfa156]

Were the seals assembled dry? The piston has to be able to slip through the seal to self-adjust for pad wear. I had the same problem with new seals after a caliper rebuild and lubing the seal with a smear of rubber grease on the face of the seal solved the problem. The seal was distorting under hydraulic pressure -which its supposed to do as this is the 'spring that pulls the piston back off the pads- but because the piston couldn't slip past the seal it could never take up the excessive clearance between the pads and the disc. Pulled my hair out for weeks before finding the solution.

[Gorminrider]

Judging by your description, the problem IS air.

My most common problem when this occurs is a bubble in the MC...indeed the tiny hole in the Master is involved in my solution.

Firstly, protect the MC area and your painted surfaces -the gas tank! with clean rags...remove the MC cover and then the little shield from the top of the tiny hole-(there usually is one a vigorous pull of the lever may squirt fluid out of the MC )... if the little hole is clear, you will see some "activity" when you pump the lever slowly-(no more than 3/4 of the way)...Now, .get a small syringe from the drugstore-you don't need the needle- and apply some suction as you squeeze the lever slowly-a bit of technique involved one hand to pull on the syringe as you hold it against the tiny hole. OR an elastic to hold the lever in the pulled position.. I expect you will get bubbles as you patiently repeat this a few times....

Helps:
Tap your brakelines to shake bubbles....

There might be a better way to apply suction than the small syringe but they are useful so I keep several around...you MUST wash them out immediately for re-use later. The needle itself? cut the sharp end off and it's a "micro-oiler"etc

[chuck hahn]

did you put the cup that goes against the spring in correctly? The cupped side goes toward the spring.

[Nessism]

Clean the hole as mentioned, and force some fluid into the pumping chamber of the master. Before doing that though, replace the brake lines. It's silly to continue to use 40 year old rubber parts like those.

[chuck hahn]

If the return ports plugged what generally happens is the master pumps up till the pads are locked to the rotor and wont pump up anymore. I dont think its a return port issue.

[GabrielGoes]

Gosh it took Me a long time between waiting for parts etc. I found my solution to this issue to be that my piston seals were installed in the incorrect orientation. The larger "mouth" end needed to be installed towards the caliper, like the tapered skinnier end of the seal to be installed towards the piston. I had no idea that this was even a thing. I also used a smear of grease on the seals themselves.

Thank you all! I have double checked every suggestion here, so it is possible it was a collaboration of everything and not just the seals, however my return port was clear

[Nessism]

Grease on the seals? Was it special brake system grease? It's BAD to use general purpose grease inside a brake system since it will contaminate the fluid.

[Suzukian]

You should lube the brake seals with brake fluid.

[Nessism]

There is a special grease for lubing brake calipers and seals, but a special order product...

https://www.amazon.com/Brembo-Caliper-Seal-Grease-Packet/dp/B01M3Y10WV