1979 GS1000 rear brake bleeding issues

[sealpup]

A while ago I replaced the rear pads and the original rear brake hose with a stainless braided one. I flushed the fluid, and the first lot to come out was brown mud, but I continued until it was completely clear. The pedal was firm and I was happy. Noob mistake....

Since then, the brake won't hold a prime - I've bled it 3 or 4 times and each time it's only effective for a short while. The brake line crush washers are new, and the banjo bolts are tight.

Where is air most likely to be leaking in - the master cylinder, or the caliper?

Before stripping down the master cylinder and caliper for overhaul, are there any quick checks I could do to save me a pile of time and money?

Thanks in advance.

[hillsy]

Normally air doesn't tend to leak into a system like this - it's usually the case that fluid leaks out.

I'd say it's your MC piston seal leaking / worn out. Can you get pressure back with a couple of pumps of the lever? If you can, then it's the MC seal rather than air in the system.

[sealpup]

There are no fluid leaks anywhere, and I can't get pressure by pumping the lever. I can only regain pressure by bleeding the system all over again, and it's only a temporary situation.

My gut tells me it is most likely the M/C, but I don't understand how bleeding provides a firm lever (albeit briefly).

[hillsy]

Is air coming out when you bleed the system?

[850GT_Rider]

If that first flush produced brown mud, merely getting clear fluid now doesn't mean its a clean system. Dirt lurks everywhere.

There are no half measures here, no shortcuts. Tear it down. Clean EVERYTHING. Inspect EVERYTHING. If pistons and bores are not pitted, you can get away with rebuilding and just replacing seals. Recommend you use Suzuki OE parts, not K&L. Brakes are no place to go cheap.

[sealpup]

Is air coming out when you bleed the system?

Yes, air is coming out when I bleed the system. That's what has me confused.

[sealpup]

If that first flush produced brown mud, merely getting clear fluid now doesn't mean its a clean system. Dirt lurks everywhere.

There are no half measures here, no shortcuts. Tear it down. Clean EVERYTHING. Inspect EVERYTHING. If pistons and bores are not pitted, you can get away with rebuilding and just replacing seals. Recommend you use Suzuki OE parts, not K&L. Brakes are no place to go cheap.

I was fully expecting to have to rebuild the whole system (with OEM components, as I did on the front brakes), but the weird behaviour had me putting it to the Forum members in case someone had experienced something similar.

[geol]

I installed speed bleeders on the rear caliper of the 80 GS1000GL i owned to help bleed the system in the future. Russel makes two lengths M7 speedbleeders and one of each length is needed because if you use both the same length, one actually doesn't seat well enough to keep from allowing air into the system. It didn't leak much, if any brake fluid. If you changed bleed valves, this might be an area to look at. Sorry, I don't recall which was needed and where; only one needed to short and the other long and not sure if this applies to other brands of bleed valves but it did to the Russell brand.

[Big T]

Pull the caliper apart and see what's in there.
Then, replace the seals

[sealpup]

I installed speed bleeders on the rear caliper of the 80 GS1000GL i owned to help bleed the system in the future. Russel makes two lengths M7 speedbleeders and one of each length is needed because if you use both the same length, one actually doesn't seat well enough to keep from allowing air into the system. It didn't leak much, if any brake fluid. If you changed bleed valves, this might be an area to look at. Sorry, I don't recall which was needed and where; only one needed to short and the other long and not sure if this applies to other brands of bleed valves but it did to the Russell brand.

So one more question before I starting pulling stuff apart. geol got me wondering about the different length bleed valves. I did replace the crappy old ones with new OEM items, and they were different lengths.
Now I can't recall whether I replaced like for like, or used the Suzuki fiche diagram to guide me (they are described as Breather No.1 and Breather No.2, with different item numbers, but same part numbers) as to which one goes where.
Can anyone confirm that they are different lengths, and if they are, which one goes where?

Thanks everyone.

[chuck hahn]

the one closest to the rear hub is longer than the front bleeder.

[sealpup]

Thanks Chuck.

[chuck hahn]

Wrap the threads with some thread sealer tape or teflon tape. This makes bleeding easier as it stops air bypassing down the threads when you crack the bleeders open.