Brake Bleeding Sequence??

[TDI Guy]

Is there a sequence to bleeding the brakes on a NAS 90 ? I have bled many brakes in the past and I am having a problem with the SW's brakes. I started from a completely empty system. I bled them and now the brakes work but you basically 2 feet to push the pedal down... Would there still be air in them? Any Ideas? :angry

By the way, the truck has all new SS flex lines and new pads and rotors.

[jimmy salmon]

rear passenger, rear driver, front passenger front driver

[sherpamike]

i agree w/ Jimmy. The FSM says to start furthest away from the master cylinder in the bleeding sequence... i've heard that makes a world of difference.

[ini88]

I thought it was rear driver, then rear passenger. I thought rear driver side was farthest away.

[landrovered]

me too, rear driver is further because the brake line goes across the axle.

[sherpamike]

That's right. I guess that would make sense.

[cgalpin]

Randy, 2 feet to push the pedal down doesn't sound like a problem with air in the lines to me. If you had air in the lines you'd feel a spongy pedal wouldn't you?

[TDI Guy]

thats what I thought with the air.. What else would it be?

[cgalpin]

Blocked line? I'd say stuck caliper piston but you didn't indicate you touched them although they could have gotten stuck if you pressed them in too far putting in the pads. But you can test for this. Pry the piston back, then press on the brakes and verify it moved (or look for a piston not pushed out maybe).

[jimmy salmon]

HARD BRAKE PEDAL Lack of power assist may be due to low engine vacuum, a leaky vacuum hose or a defective booster. Sometimes a faulty check valve will allow vacuum to bleed out of the booster causing a hard pedal when the brakes are applied. This condition can be diagnosed by starting the engine (to build vacuum), shutting it off, waiting four or five minutes, then trying the brakes to see if there is power assist. No assist means a new check valve is needed.

A quick way to check the vacuum booster is to pump the brake pedal several times with the engine off to bleed off any vacuum that may still be in the unit. Then hold your foot on the pedal and start the engine. If the booster is working, the amount of effort required to hold the pedal should drop and the pedal itself may depress slightly. If nothing happens and the vacuum connections to the booster unit are okay, a new booster is needed (the vacuum hose should be replaced, too).

On vehicles equipped with "Hydroboost" power brakes, a hard pedal can be caused by a loose power steering pump belt, a low fluid level, leaks in the power hoses, or leaks or faulty valves in the hydroboost unit itself (the latter call for rebuilding or replacing the booster).

[TDI Guy]

this is on a TDI truck Jimmy with a vacuum pump. I took the vacuum line off of the booster and there was vacuum.

[FlaD90]

This is right out of the manual:

Complete circuit bleed
1. Disconnect battery.
2. Bleed front calipers, driver’s side first. Fit bleed
hose to bleed screw.
3. Dip free end of bleed hose into brake fluid in
bleed bottle.
4. Open bleed screw of caliper.
5. Depress brake pedal fully several times until fluid
is clear of air bubbles.
6. Keeping pedal fully depressed, tighten bleed
screw, then release pedal.
7. Repeat procedure on other front caliper followed
by rear calipers.
8. Fit all bleed screw protection caps.
9. Check/top-up fluid level when bleeding is
complete

[cgalpin]

10. reconnect battery
11. Fix your radio codes/presets/whatever
12. shake head and ask yourself wtf you had to disconnect the battery in the first place

[flippedrover]

Its something in the vacuum side of the system. Few years ago I had this happen on the ambulance I was driving.

[TDI Guy]

Its something in the vacuum side of the system. Few years ago I had this happen on the ambulance I was driving.


maybe the vacuum pump on the tdi ?????

[cgalpin]

But you said you had vacuum. I don't know how much it should be, but seems thats an easy one to test right?

[flippedrover]

I'd think a leak somewhere in the line.

[sflash868]

Been a while since I've bled my brakes but how many valves are on each caliper? Made the mistake one of only bleeding the outer valves on the race car forgetting there were to valves on each caliper. Caused the same symptoms.

[cgalpin]

Should just be one.

[crown14]

I assume you bench bled the master?

Isnt there a proportioning valve on the RH side of the bulkhead?

[TDI Guy]

I assume you bench bled the master?

Isnt there a proportioning valve on the RH side of the bulkhead?

Yes, the valve is on the right side foot well...

[TDI Guy]

Bled the brakes again today... No air in them. My guess is that it is the vacuum pump on the tdi. I took the pipe off and there is barely any suction at all.. DOes anyone know what the vacuum should be at idle?

[TDI Guy]

replaced the vacuum pump today on the engine... Fixed...