Brake bleeding

[Scott in Canmore]

Hello, I have a 1986 Defender 110 that I'm trying to get road worthy. 

I replaced the rear brake shoes and managed to dislodge the seals on the cylinder causing some fluid to leak and likely let some air in the system.  After the brake shoes were in place the brake peddle goes fairly easily to the floor - worse than before.

So, I have been trying to bleed the brakes.  I'm using a small hand vacuum pump.  I wasn't able to get it to fit the front brakes (as the online tutorials say to do) but I was hopeful that perhaps I could just do the back as I didn't touch/break the front brakes.

When I bleed the rear brakes I have drawn off about  1 L of fluid and still have lots of big air bubbles with no sign of an end in sight.  I can also hear air being drawn in from somewhere - gurgling noises - possibly the connections in the hand pump itself.  The peddle is still very spongy.

Any suggestions? 

[Red90]

Just bleed the brakes the normal way. One person pushes the pedal and the other opens the bleeder.  Do all four wheels as it is good to get fresh fluid in there.

Make sure the shoe adjusters are set correctly as well.

[ugly_90]

The brake bleeding I've done is a real pain to do alone, it's a two-man job usually. Be sure to use a completely non-synthetic brake fluid, relatively hard to find nowadays, as most is semisynthetic or full synthetic, which will ruin your new seals. I used DOT3 Kleen Flo non-synthetic from Greggs

Your master cylinder should be replaced with new at this point as well, it is an inexpensive part with a finite lifespan.

Be sure to note your PDWA valve, which may hinder some of your bleeding if not bled correctly.

[Matt H]

I used all the fancy methods and tools in the past. Pressure bleeding, vac bleeding etc. But I tend to gravity bleed as a first step as I am nearly alway working alone. Then it just needs a final quick operation as described above but if you are by yourself you can finish with your vac pump.
It also allows me to work on other stuff at the same time. A hangover from my 'flat rate' days.
My 2c

[Red90]

The easiest method I've found when alone is the pressure bleeder.  Hook it up and bleed the lines.  Very simple.  Works for the brakes and the clutch.  I find vacuum methods can get air into the system if the bleed nipples are not quite right.

I've never used any special brake fluids.  I've never had a seal leak.  I've heard people say you need something special.  I think it is a hang over from the old Series trucks where they used strange seal materials.  The brakes in the Defenders are made the same as any other brakes in the world.

[ugly_90]

I've never had any seals leak due to my use of conventional DOT3 either. I miss the upside of adding a synthetic brake fluid to an older defender.

The matching era service manual states only that the fluid is to be FMVSS 116, DOT3. I suspect a DOT4 would work as well, but I see no requirement for that in the disc rear axles.

[Red90]

DOT 4 has a higher boiling point so adds a safety factor with brake fade.

[Scott in Canmore]

Thanks for the direction everyone.

I bleed the brakes normally and I've improved the brakes quite a bit.  They seem to work well and the peddle feels fairly good but I still get the the brake warning light after the first time I push the peddle down when I start it.  It seems to clear up after that.  Not sure if it's just a few bubbles left or something else.  I've got 3L more brake fluid so I might just bleed them again and try to catch any straggler bubbles.

[Red90]

With an 86, the brake warning light is connected to the PDWA.  It is a switch that actuates when it detects a large pressure difference between the front and rear brakes.  Are the drum adjusters working properly and as tight as possible without the shoes rubbing?

[Scott in Canmore]

Thanks Red 90, that was the issue.  The rear snail adjusters were too loose.  I tightened them and backed off just a wee bit and it's all sorted out.  There is no desirable speed loss while coasting and no brake smell so I don't think they are dragging either.

Thanks again for your help!