Brake Booster diagnosis

[fj80T]

Brakes became hard all of a sudden. I have 225,000 miles. I followed the test in the service manual and it seems to pass the pumping with the engine off test but the pedal does rise up after turning the engine off with the pedal depressed.

The booster will hold a vacuum so I am thinking my problem may be elsewhere .

Has anyone else had these symptoms and fixed it with a new booster. I hate to drop the money if i don't have to. I replaced the hose and that did not help.

Thanks.

 

[SupraTuRD]

Did you ever get this problem resolved?

 

[CJF]

Very hard pedal when driving/braking is pretty much exclusively a bad booster.

 

[DARKNESS]

Mine would randomly do this when cold. It was the check valve on the booster. Cheap and easy fix.

 

[SteelHunterFJ80]

Mine would randomly do this when cold. It was the check valve on the booster. Cheap and easy fix.

Got this exact same problem today. Can someone explain further by the check valve?

 

[flintknapper]

Got this exact same problem today. Can someone explain further by the check valve?

There is a hose leading to the Vacuum Booster. It attaches at the booster to a fitting that is a 'check valve' (one way valve) that is designed to not let the vacuum escape. The Check Valve is inserted into a 'Grommet' which also can become brittle and not make a good seal. So....the things to check BEFORE declaring the booster faulty are:

1. Vacuum hose from intake to booster is not cracked and has good connections on each end.
2. Grommet in Booster is not cracked or otherwise compromised.
3. Check Valve is working correctly.

IF all of the above are OK...then that pretty much leaves the booster as the culprit. Typically the diaphragm inside of them fails.

 

[SteelHunterFJ80]

There is a hose leading to the Vacuum Booster. It attaches at the booster to a fitting that is a 'check valve' (one way valve) that is designed to not let the vacuum escape. The Check Valve is inserted into a 'Grommet' which also can become brittle and not make a good seal. So....the things to check BEFORE declaring the booster faulty are:

1. Vacuum hose from intake to booster is not cracked and has good connections on each end.
2. Grommet in Booster is not cracked or otherwise compromised.
3. Check Valve is working correctly.

IF all of the above are OK...then pretty much leaves the booster as the culprit. Typically the diaphragm inside of them fails.

Ok thank you @flintknapper I'll check that first thing in the morning. Funny thing is that the booster is brand new and was replaced because the diaphragm went out. I'll report back what I find.

 

[SteelHunterFJ80]

Ok the grommet looks like it's original. I'm going to replace it with a new one along with the valve.

Does anyone know if I need to bleed the system afterwards. The FSM doesn't say

 

[flintknapper]

Ok the grommet looks like it's original. I'm going to replace it with a new one along with the valve.

Does anyone know if I need to bleed the system afterwards. The FSM doesn't say

Negative.

You'll be dealing with the vacuum in the booster system only. Separate from the hydraulic side of the braking system. Should be good to go IF the brakes were properly bled prior.

 

[Michael Hanson]

Hi, Brand new booster ? What brand? Mike

 

[SteelHunterFJ80]

Hi, Brand new booster ? What brand? Mike

Booster is OEM. Its new as the diaphragm went out a couple months ago

 

[leonard_nemoy]

Rule #3 of diagnostics. New does not always = good.

Maybe the new booster sat on a warehouse shelf for 15 years....

Still follow the advice listed above and start with the hose, grommet, and check valve.

 

[SNLC]

Booster is OEM. Its new as the diaphragm went out a couple months ago

Did the depth of the pushrod get set when the new booster went in?

Cheers

 

[SteelHunterFJ80]

Rule #3 of diagnostics. New does not always = good.

Maybe the new booster sat on a warehouse shelf for 15 years....

Still follow the advice listed above and start with the hose, grommet, and check valve.

Did the depth of the pushrod get set when the new booster went in?

Great advice/questions. I should have written with a little more detail. The brake booster was replaced a couple months ago by torfab but now that I look back on my receipts, it could have been the master cylinder we replaced. I'll find out Monday. Since the replacement, the truck has been braking just fine. Only this week with much colder weather did it start acting up. My guess is that torfab checked the depth of the pushrod but I'll ask about that too.

The hose looks good with no cracking and still pliable, clamps are fully secured. I replaced the grommet and put in a new check valve. Old grommet looked fine, but the old check valve didn't operate smoothly. Definitely less smooth than the new one.

Took for a test drive and it still did the same thing, pedal freezing up on light braking. Seemed to happen most when I would feather the brakes. But it did seem to do it less and less the more I drove it but that could be wishful thinking.

 

[deltapine1]

Brake Booster R&R

I've got a 1970 FJ40, and I need to replace my booster. The one replaced by my brother is just not quite right. I can't adjust the rod enough to get 100% of the help from booster. Where did you get your booster?

forum.ih8mud.com

I replaced my hose, grommet and check valve in hopes that would fix my problem. Mine was no power assist on cold morning starts.

I swapped my booster yesterday. I posted some pictures at the end of the thread in the link above.