Brake Booster Problem!

[eric jacobsen]

Hello all!
I just finished replacing my brake booster on my 94 Land Cruiser.
After finished I turned on the car and pressed on the brake pedal.
Nothing....
The pedal traveled all the way to the floor. No pressure.

Did I forget something?
Do I need to bleed the system?
Help! Super frustrated!

Eric

 

[IRLGW]

umm when you say booster do you mean master cylinder or just the booster or both? Why did you feel the need to change it in the first place? I am assuming you are petrol and that you have a vacuum generator somewhere? I guees the first thing you do it pull the vac hose to the booster off and then start the engine, put either a vac guage or your finger over the hose and see if you are getting a noticeable vacuum. If you can get a cheap vac guage/brake bleeder off ebay then attach it to the booster and pull a vac and see it holds it. You willnow knowif the problem is the booster, vacuum source or brake circuit. Its purely an eliminator round.

 

[eric jacobsen]

I know that the booster itself is not the problem. It's brand new. I'm wondering if the brakes need to be bled(or the master cylinder) as part of the process of replacing booster. I do have a vacuum hose attached to booster. It just doesn't seem that I'm getting any fluid pressure. Brake pedal easily goes all the way to the ground. Never did that before installing new booster. Master cylinder was removed during the process. Do I have air in the system? Ughhh, I hate working on brakes!!!! Is bleeding the brakes always the last part of replacing the booster? Most you tube videos I've seen mention that it is a good idea.

 

[IRLGW]

Ah so you removed the master cylinder in the process (why did you change the booster?) so Id say its air. Ideally you would bench bleed the Master cylinder before refitting and again assuming that you haven't inverted the rubbers I would go with a full bleed. Get about 1.5m of 5mm rubber hose and feed it to a catch pot. Attach it to the caliper nipple before cracking it off and duct tape the pot up higher than the brake system and then pump with very short strokes on the pedal until you have pushed enough fluid through for it to run clean and go to the next one. The only other cause would be a weeping caliper/leak but you would be loosing fluid

 

[eric jacobsen]

Can I bleed the master while it's still attached? Really don't want to take it off again...

 

[IRLGW]

Yes you can but any air will be pushed through the whole system but if you get clean fluid out of each line then should be ok. Some people use different coloured fluids ( I think race grade fluids are green or something) to see when the new fluid is through in a case where your fluid is already very clean. the Master cylinder has two in-line pistons inside. Just another thought- does the pedal feel like its moving the piston ok in case the linkage has dropped off when you fitted the new booster

 

[IRLGW]

 

[eric jacobsen]

That was the other problem I was suspecting. I can't tell if the pedal is moving the piston or not. Not sure how that can be adjusted now without taking the entire booster off. Thanks for the video!

 

[IRLGW]

once you start bleeding you will soon know! do the drivers caliper first and you will see the fluid rise as you press the brake. if it doesn't rise then maybe the linkage is the problem. Worth getting the FSM out for setting the pedal in tolerance if you do need to in there and re- adjust it

 

[eric jacobsen]

Yes, I think I am going to do that first. I was suspecting that all along. When I got the new booster, I simply just installed it the way it came. I diodn't adjust anything. That may be my problem. Thanks for all your help!

 

[IRLGW]

why did you fit a new booster?

 

[eric jacobsen]

The brake pedal gradually became impossible to press down. No power assist at all. You could stop but you had to press down extremely hard. Booster had obviously failed...

 

[IRLGW]

Or Vacuum generator....

 

[SeaJay]

80's can be a real pain to bleed because of the LSPV

 

[Dave2000]

Petrol engines do not need a vacuum pump like a diesel, the manifold vacuum is sufficient.

If you fitted the booster or vacuum servo, did you set the pushrod length correctly? Too short means long pedal travel, too long and pedal travel great however, brakes will not release after driving a few miles.

If you removed fluid lines the system will need to be bled.

Regards

Dave

 

[Dave2000]

Booster had obviously failed...

Not necessarily so, as per @IRLGW, if your car is diesel the vacuum pump may have failed or, the vacuum resovoir may have a leak, or a split vac line leading to the servo this line is on petrol and diesel.

Regards

Dave

 

[frank rabbets]

If you've undone a pipe you'll defo have to bleed the brakes whether or not you think you've got full pedal resistance.

There are plenty of new faulty parts out there. Many people on here have been assuming new parts are not a cause and have been chasing shadows.

Was it a Toyota part?

 

[flint]

If you haven't replaced the MC it should be ok, but might be worth slackening the unions a little and giving the pedal a couple of pushes to clear any air, then sequence should be furthest rear from the master cylinder (MC), other rear, LSPV, furthest from MC front, other front. It might take a few sequences to get all the air out.

 

[SeaJay]

also you should only use DOT3 fluid with an 80, shame you didn't put a kit thru the master cylinder while it was off, as bleeding it and pressing the pedal to the floor can damage the seals if there is a slight wear spot on the cylinder. once you get fluid moving thru the master cylinder unbolt the LSPV rod from the diff and tie or get someone to hold it up, then bleed the rears, then hold it down and bleed the fronts

 

[Dave2000]

also you should only use DOT3 fluid with an 80,

DOT 3 virtually unobtainable here, DOT 4 and 5.1 fully backward compatible, all glycol based, DOT 5 is silicone based.

Block of wood will stop full pedal travel and prevent too much piston travel up the master cylinder bore, TBH if there are enough miles on the clock I would change that as well.

Regards

Dave