This relates to a previous thread on brake fluid changes. What is the reasoning behind bleeding calipers/wheel cylinders starting with the ones furthest away from the master cylinder and working your way back to the m/c. I never could figure this one out.
Brake Bleeding
- Thread starter George7941
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Starting with the farthest brake and going in leaves the least amount of older contaminated fluid in the system. Less chance of older fluid leeching back into the just flushed lines. Almost need a diagram to explain it for people who do not understand hydraulic plumbing. (Note: not meant as a insult)
Hootbro
Hootbro
Never made much sense to me either. Where a line tees off, the fluid has no idea which branch is longest. Many newer manuals give a different order. Whatever you are working on, I would find a manual for it and follow it exactly. Try Ebay or www.factorymanuals.com You may find a real shop manual for what you would pay for a Haynes or Chiltons at the parts store.
To add to the confusion, some automakers say to start with the closest wheel. Some say to that on a diaginal system to do them in the diaginal pairs.
Personally, I don't think it really matters. I do what is convenient.
Personally, I don't think it really matters. I do what is convenient.
When cars had four wheel drum brakes, there was always a little back flow when the brakes were released.
If a system was open, and had air in it, it helped to go farthest to nearest [on a normal split diagonal system].
If a modern car has no air in the lines, with 4 wheel discs, there probably is no difference to the order of bleeding.
If a system was open, and had air in it, it helped to go farthest to nearest [on a normal split diagonal system].
If a modern car has no air in the lines, with 4 wheel discs, there probably is no difference to the order of bleeding.
I don't buy Hootbro's reasoning. While it is true that the longest branch would have the largest volume of contaminated fluid, the longest branch also has the largest interior volume to hold this fluid till it is flushed out. I can see a valid argument when there is air in the lines since longer lines with more air would mean greater volume of compressed air due to the slight positive pressure generated by the bleeding process. This compressed air could cause contamination by driving contaminated fluid back. This would only apply for manual bleeding, when pressure bleeding the pressure stays constant and there would be no back flow of contaminated fluid.
Do what you want then. On cars it really depends on the application. Some cars you anti-lock manifolds to contend with and even check valves. Like others have said, buy a manual for your application and follow it. I have bleed brakes on mumerous vehicles and have done it on almost a daily basis in the aviation sector. Rule of thumb has always been to go out the farthest brake from a master cylinder or accumulator. Unless you are doing a pressure fill from the master cylinder and are bleeding all brake points at once, then you will still have a residual amout of old fluid remain.
It does make a difference, and it does vary by car model. For example, rear wheel drive Volvos have the bleeding pattern from farthest to closest to the master cylinder...RR, LR, RF, LF. Front wheel drive Volvos must be bled the opposite way...LF, RF, LR, RR.
My Toyota Tunda needs to have the brakes bled RR, LR, rear proportioning valve, RF, LF.
Ken
My Toyota Tunda needs to have the brakes bled RR, LR, rear proportioning valve, RF, LF.
Ken
Historically, most cars have had a crossover dual braking system. The RR and LF are on one circuit; the LR and RF are on the other. Each circuit has its own master cyclinder piston. Together, this provides greater safety and makes catastrophic, total failure less likely.
In most situations, you start bleeding the wheel cyclinder/caliper that is the farthest from the master cyclinder. This is usually the RR. All other things being equal, it will have the most air and moisture in it, since it is the longest section. That circuit is completed by bleeding the LF. Using the same logic, you progress to the LR and then the RF.
The bleeding sequence varies from car-to-car. It's an attention to detail item that I think is worth checking out.
[ July 24, 2005, 04:50 PM: Message edited by: TxGreaseMonkey ]
In most situations, you start bleeding the wheel cyclinder/caliper that is the farthest from the master cyclinder. This is usually the RR. All other things being equal, it will have the most air and moisture in it, since it is the longest section. That circuit is completed by bleeding the LF. Using the same logic, you progress to the LR and then the RF.
The bleeding sequence varies from car-to-car. It's an attention to detail item that I think is worth checking out.
[ July 24, 2005, 04:50 PM: Message edited by: TxGreaseMonkey ]
okay folk, let me pick your brains on this...1993 Dodge p/u Dakota 2.5, 5 speed 83k miles...now from what I can see it does not have the ABS brake system...
but the Brake light comes on...the Anti-lock is on, and I've seen ABS light up...sometimes this stuff is on, sometimes its off....
I do have a notice I printed out from the web,about "some" Dodge P/U ABS vehicles were bilt with undersized brake return check valve and may cause brake failure in hard stops....So Itook it out and slammed on the brakes...hard several times,,,it stops true and square, but the lights stay on...But if this check valve should be replaced..is not that the dealers responsibility???? master cyclinder if full of fluid....and I had brake fluid replaced on it..2-3 months ago...this light coming on just started like 3 weeks ago...I don't know what to think...
but the Brake light comes on...the Anti-lock is on, and I've seen ABS light up...sometimes this stuff is on, sometimes its off....
I do have a notice I printed out from the web,about "some" Dodge P/U ABS vehicles were bilt with undersized brake return check valve and may cause brake failure in hard stops....So Itook it out and slammed on the brakes...hard several times,,,it stops true and square, but the lights stay on...But if this check valve should be replaced..is not that the dealers responsibility???? master cyclinder if full of fluid....and I had brake fluid replaced on it..2-3 months ago...this light coming on just started like 3 weeks ago...I don't know what to think...
terra,
It's probably better to start a new thread about your problem in the maintenance section.
It's probably better to start a new thread about your problem in the maintenance section.
Here is something interesting. On the Mityvac website (mityvac.com) there are instructions on how to vacuum bleed brakes and the bleeding order is reversed, you start with the caliper/wheel cylinder closest to the m/c and finish off with the farthest one.
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