BJ72 BRAKE Problem

[cicak]

Hi

Have a reasonable modified BJ72 - 22R and Gearbox removed and 13B-T and AUTO transplant (all from a japanese BJ74). Electric H4 engagement and 8/39 Electric locking differential all with 12-24V conversion. Brakes are gicing me the s***s.

Brake pedal goes to the floor and then with one pump will be stilff. It also goes from normal to nothing in a split second. Sitting at traffic lites the pedal slowly depresses same offroad on a steep slope.

There are no leaks at all. Have changed via mechanic all flexible hoses, Rear slave cylinders, Servo and booster and master cylinder same result. New vaccume hose also. Noticed during my own debugging that now the 4x4 vaccum engage is disconnected the vaccum only hooks to the brakes. THe vaccumm hose is not a tight fit and is not clamped. Can thjis be the problem. The mechanic has given up and has no ideas lefft he is guessing can anyone give me some clues.

Thanks in advance.

 

[Jan-78FJ40]

Hi

Have a reasonable modified BJ72 - 22R and Gearbox removed and 13B-T and AUTO transplant (all from a japanese BJ74). Electric H4 engagement and 8/39 Electric locking differential all with 12-24V conversion. Brakes are gicing me the s***s.

Brake pedal goes to the floor and then with one pump will be stilff. It also goes from normal to nothing in a split second. Sitting at traffic lites the pedal slowly depresses same offroad on a steep slope.

There are no leaks at all. Have changed via mechanic all flexible hoses, Rear slave cylinders, Servo and booster and master cylinder same result. New vaccume hose also. Noticed during my own debugging that now the 4x4 vaccum engage is disconnected the vaccum only hooks to the brakes. THe vaccumm hose is not a tight fit and is not clamped. Can thjis be the problem. The mechanic has given up and has no ideas lefft he is guessing can anyone give me some clues.

Thanks in advance.

I assume you are sure that there are no leaks, and you are not only taking your mechanics word for it.

Is the fluid level in the master going down ever?

It seems like you have two issues. One is the pedal going to the floor, and the other is it becoming rockhard.

The pedal going to the floor (assuming that there are relly no leaks) can only mean that the master cylinder leaks on the inside, and fluid is going by the plungers. Is the replaced master a toyota, or some refurbished or some aftermarket? go toyota, and go new.
When you take the master off, is there any leak in the booster?

the pedal becoming hard probably means that there is no vacuum, or that the booster is losing vacuum.
when you run the engine, then shut it down and after minute or so take the hose off the booster, is air rushing in? if not, there is a leak somewhere.

Are you sure your vac pump is operating well? sometimes the holes out of the pump to the tank can get plugged. Does the vac tank hold vacuum-it should be goverened by one way valves.

Finally, it could be the booster itself. when your engine is shut off, step on the brakes. then start the engine. is the pedal going down a few centimeters or staying in the same position?

oh, and of course, are you SURE the system is bled perfectly?

I'd start with the bleeding, then the master, then the non invasive booster/vacuum tests.

 

[lowenbrau]

In additon to what Jan said, check your wheel bearings as well. A loose wheel bearing can cause odd brake symptoms. The rotor tilts and pushes the pads away resulting in needing a pump or two to straighten things up and produce decent pedal feel.

 

[Jan-78FJ40]

In additon to what Jan said, check your wheel bearings as well. A loose wheel bearing can cause odd brake symptoms. The rotor tilts and pushes the pads away resulting in needing a pump or two to straighten things up and produce decent pedal feel.

yes, correct. I had that and it took me forever to figure it out. However, there should not be a fading pedal-it should be fine after a pump or 2.

j

 

[roscoFJ73]

Hi

Have a reasonable modified BJ72 - 22R and Gearbox removed and 13B-T and AUTO transplant (all from a japanese BJ74)..

Hi Cicak. Is this originally a RJ72 made from 94-96? If so there wouldnt be too many around.
Does it have a rounded front like a Surf?

 

[cicak]

rosocBJ73

It is a common model here in Asia (due to huge duties on large engined 80s and 100s) and South America and europe and africa. Made from 91 (and earlier) to 96/97 (96/97 model was called "Prado" and became the Prado as Australians are familair with). You will have seen the FRP BJ74 in OZ and the Bunderra all of which are from the same family. Over here it is LIGHT for the Malaysia Jungles weighing in at 500+ KG lighter than a fully equipped 80 Series (or Ninja) hence it will not sink into the mud as quick and will not break the temp log bridges we build in the jungles to get over rivers and is narrower (same dash and front windo as a 75 series a 75 Series sems to take the two door Bunderras doors.). A 80 is laughed at here in the Jungle as they are to HEAVY no one wants to recover them and them and the RANGE ROVERS are generally left at the back of any Jungle convoy for hence obvious reasons. I have a 80 Series in OZ and I luv this little Cruiser. I am now equipping it with air operated engage and disengage for both the winches and a few other goodies to make an awesome road and jungle vehicle.

As for the brakes we believe it is now the pedal as the brakes are hard after turning the engine off but then as soon as the engine is started the pressure is lost and the pedal goes to the floor. WE have fitted clamps to the vaccume hose as it slid off to easy. I am talking RED way over to the original mechanic tomorrow as the "local" is deemed to be an idiot (not good mechanic lah!) by the local parts suppliers near him. He has disconnected the vaccum 4x4 engage on the transfer case (tossed away the t-junction and I cannot engage 4x4) H4 dash button - I found out the hard way on sand last weekend. We are going to replace the SERVO again tomorow and check out the pedal operation. There is no fluid loss but it is DOT3 and not DOT4 as it should be. THere is no air leaks either we have checked..

cheers

 

[Jan-78FJ40]

rosocBJ73


As for the brakes we believe it is now the pedal as the brakes are hard after turning the engine off but then as soon as the engine is started the pressure is lost and the pedal goes to the floor. WE have fitted clamps to the vaccume hose as it slid off to easy. I am talking RED way over to the original mechanic tomorrow as the "local" is deemed to be an idiot (not good mechanic lah!) by the local parts suppliers near him. He has disconnected the vaccum 4x4 engage on the transfer case (tossed away the t-junction and I cannot engage 4x4) H4 dash button - I found out the hard way on sand last weekend. We are going to replace the SERVO again tomorow and check out the pedal operation. There is no fluid loss but it is DOT3 and not DOT4 as it should be. THere is no air leaks either we have checked..

cheers

Hi, the pedal really does nothing that can break. It is just a lever that actuates the pushrod in the booster/master cylinder. your cylinder could still be leaking inside.
cheers,
J

 

[Entaran]

Re you sure the vac system is actually working properly or only intermittently? do 22b's have a dedicated vac pump?

 

[cicak]

Entaran

Yes you are correct we diagnosed this last Friday after spending the whole day firstly changing the Master Cylinder to a Supra one to get extra power for the times when it is wearing 35" sneakers. Then we discovered diesel (yikes it should not have) in the vaccum pump and realised the problem was the vaccum hose being out of time it is going back in this week to get the vaccum pump looked at and replaced.

Internet been down the whole weekend at home so cannot get on.

The brakes when they work properly operate heaps better with the new master cylinder.

Will let you know when I wander all the way to the mechanics again - being over 30k away causes me some problems.

Anyway being at the mechanics the whole day gave me the oportunity to lift the rear of the bonnet and install a 12mm lift to assist in the cooling of the engine compartment and it seems to be working.

Saturday was spent ripping out and rebuilding the stainless steel rack in the rear of RED and sunday putting a marine ply undercoated with rubber on the floor and the first shelf to quieten down the rear.

Mechanics thursday.