Reverse Brake Bleeding for cars

[rcx132]

Quick question: Has anyone tried reverse bleeding car brake systems? How well does it work, and any tips?

I’ve got a home-built buggy with a Jimny master cylinder, calipers, and cylinders, no ABS. The brake lines are braided, wrapping around the extra long suspension links to the axles, then a splitter and copper lines along the axle to the calipers/cylinders.

Since day one, I can’t get all the air out. There’s a lot of brake pedal travel before the brakes engage, but they’re firm once they do. The rear drum cylinders aren’t horizontal, so air moves to one end while the bleed nipple is in the center. I squeezed the pistons together to reduce the air trap and bled the system, which helped a lot.

Recently, I had to rebuild a front caliper and the pedal travel has increased again despite lots of bleeding.

I have a 50ml glass syringe, but I’m not sure if it’s big enough for reverse bleeding since each corner needs to be done in one shot. Waiting on some fittings before I give it a try.

 

[JOEPRO]

I would not try that. The caliper fluid is usually the most contaminated and pushing it back through the system would be a bad idea. There may also be non return valves or similar which may get damaged.

What method are you currently using to bleed the brakes? Or list all methods you have tried.

In my experience only pressure bleeding from the reservoir or pumping pedal methods work. Pulling a vacuum in the bleeder at caliper end is not so reliable since the bleed nipples won't have 100% air seal when cracked loose.

Pressure bleeder- start at furtherest caliper in.

 

[steveo3002]

i wouldnt be keen as you are sending filth towards the master , have you tried a pressure bleeder and possibly remove caliper so that the nipple is as high as it can be ?

 

[Rrobson]

Vacuum bleeder will probably be your best option if you can’t force the air out

 

[jsf55]

Pressurise the brake system overnight with a stick etc jamming the brake pedal down it will possibly fix it without resorting too other ways

 

[sg66]

Surely this is what kids are for, I spent half my childhood bleeding brakes with my dad, rarely getting praise but often getting a spanner thrown at me

 

[rcx132]

I've only used a vacuum bleeder. The system is effectively new, as the parts were all rebuilt when I assembled the buggy.

 

[JOEPRO]

I've only used a vacuum bleeder. The system is effectively new, as the parts were all rebuilt when I assembled the buggy.

I have never had success with vacuum bleeding. Some people do, but that's your problem I think.

Get a decent pressure bleeder and go again.

 

[steveo3002]

my vac bleeder seems close to useless ...pressure bleeder set as high as you dare

 

[Morrisman]

I’ve reverse bled the brake on my old Sportster. It defied logic that such a simple, single piston system could refuse to bleed by conventional methods, but forcing fluid back up using a big syringe was the only way I got it to work.

 

[Robotstar5]

I’ve reverse bled the brake on my old Sportster. It defied logic that such a simple, single piston system could refuse to bleed by conventional methods, but forcing fluid back up using a big syringe was the only way I got it to work.

I've done the same on a couple of bikes using a 200cc syringe, I did struggle with a Fazer back brake and ended up removing the caliper to hang it up high to get the air out.

 

[Nomad]

If you've only disturbed the front calipers I'd not expect to have to bleed the rears.
Is it an option to remove the caliper mounting bolts so you can hang the calipers with the bleed nipple at the top?
Would putting one end of the car up on ramps help bleed the rears ( if the car tilts does it make the cylinders more level)?

I've been using a cheap one-man bleeder for many years, sometimes it takes a few attempts ... similar to https://www.amazon.com/FIRSTINFO-Service-Bleeder-Receiver-Non-Return/dp/B010PXUN58/

Try stamping on the brake pedal a few times until it goes firm, hold the pedal down and have your helper / assistant / passing stranger crack open the bleed valve then close it again.
Or crack the bleed valve open and pump the pedal quickly several times (make sure to keep the fluid reservoir topped up)
One car had odd problems for several years, new master cylinder seals eventually fixed it.

Mates tell me they have had good results leaving the pedal chocked down overnight ( use a bit of timber against the front of the seat)

 

[Keithmac]

When I built all my Golf AN-3 lines I put the rear Bias Valves high on the rear turrets with a blead nipple banjo bolt, makes bleeding the system a breeze!.

If you have a line that will be really awkward to bleed it maybe worth fitting a union at the highest point with a bleed nipple.

Some motorcycle have 10+ bleed nipples and a specific order to bleed the system.

Ideally your Master Cylinder should be the highest point.

You could attempt a gravity bleed (leave nipples open and keep topping up the fluid).

I have a Sealey Pressue Bleeder that works well, fill it with brake fluid and it puts the master cylinder reservoir under pressure.

 

[bricol]

If the pedal is firm, then I would think the air is gone - the long travel is due to pad knockoff perhaps?

 

[rhubarb7]

If you have a firm pedal then adjustment is needed.

 

[colnerov]

Pressurise the brake system overnight with a stick etc jamming the brake pedal down it will possibly fix it without resorting too other ways

I was taught that is only a short term fix, because it forces the air into the fluid and appears to give a firm pedal, but it comes back out again, and you're back to square one. If you do that, then the next day do a fluid change/purge to get the contaminated fluid with air out.

Edit: Is the master cylinder used or new? If used then it sounds like the seal on the piston has rolled over on the wear ridge at the end of the usual existing stroke, and is no longer effective

 

[qwakers]

Other way round. it forces the bubbles out of suspension and make them gravitate to the top. then you wobble the pedal a bit and all the bubbles pop out of the master.

 

[Melvyn Best]

Never really got on with any vacuum bleeder either. Pressure bleeding normally works except with systems that need diagnostic equipment to bleed the braking system like some Jaguar models. I have often seen kit cars where the bleed nipples are not at the top and have to be rotated so they are to enable bleeding , I have also seen a standard car a workshop with new calipers fitted on the wrong side, the guy that fitted them couldn’t work out why he couldn’t get a pedal. As for holding the pedal down overnight , it compresses any air bubbles which eventually expand . With rubber hoses it’s possible to clamp them to work out which part of the system has air in . The Sealey type pressure bleeder can be used with an adaptor to fit Japanese master cylinders and by removing the quick release adaptor from the hose can be used to reverse bleed by fitting directly to the bleed nipples, obviously you have to keep an eye on the reservoir level . The only car I can remember reverse bleeding was a Toyota Sera on which any other method failed

 

[rcx132]

Outcome:

(1) I removed the master cylinder and bench bled it by circulating fluid through each port.
(2) Reinstalled the master cylinder, used a vacuum bleeder to remove the newly introduced air. I appreciate vacuum bleeders aren't the best but they're cheap (£15) and clean one-person tools.
(3) Next, I reverse bled, pushing 100ml of fluid back up from each corner using a glass syringe.

The brakes now feel firm with minimal travel.

The 100ml syringe is quite small, but since my pads are new, there’s minimal fluid in the calipers and it worked. With worn pads, 100ml may not have been enough. I found that connecting the syringe with the piston pulled out, then opening the bleed nipple and letting gravity flow through removes any air from the new connection. After that, I filled the syringe and pushed the piston in to do the bleed.

 

[Smallfry]

I reverse bled my Renault clutch with a Gunsons ezeebleed on very low pressure and it worked a treat.

However, do remember to nearly empty the reservoir AND keep an eye on it. I knew this was what I was supposed to do, but in all the excitement, didn't.

Had to give everything a good wash with very soapy water.