Brakes auto engaging when car heats up.

[Liam jones]

Hello,
I have a 1990 hzj75 series land cruiser. I recently got the brake proportioning valve, rear drum brake cylinders and master cylinder replaced.
The brake system seems to be working but after roughly 10 minutes of driving the car has massive brake lag and can barely pass 50kmh.
I assume it could be worn out drum brake components and maybe warped calipers.
any advice would be awesome.
Cheers,
Liam

 

[outdoordan]

Hi Liam.

Touch each of the wheels in turn at the centre where they bolt to the disc/drum. If the wheel is hot that will tell you it is binding.

It is not unusual for the drums on rear to bind somewhat when they have been disassembled if they have not been adjusted correctly when reassembled.

Assume you had brake shoes replaced at the same time as the cylinders?

also, the self adjust mechanism on the rear drums can malfunction and cause it self adjust when it is not supposed to causing the brakes to take up slack every time you use the handbrake.

so, first take temp of wheels to identify which is binding.

i'd put money on it being the rear ones.

if it is get two small flat head screw drivers and a mirror. Pop out the rubber bung on the back plate and back off the adjustment cog. you are looking for the wheel to spin freely with no rubbing noise with the handbrake off. Handbrake on the wheels should lock as normal.

to check if the self adjust mechanism is malfunctioning sit in the drivers seat and activate the handbrake as you would normally about twenty times.

if everything is working as it should be the rear wheels will spin freely with no noise again as they did before. If the self adjust mech is malfunctioning there will be increased noise and resistance.

good luck

 

[outdoordan]

warped callipers would cause massive juddering under braking, obviously coming from the front

 

[Liam jones]

Hi Liam.

Touch each of the wheels in turn at the centre where they bolt to the disc/drum. If the wheel is hot that will tell you it is binding.

It is not unusual for the drums on rear to bind somewhat when they have been disassembled if they have not been adjusted correctly when reassembled.

Assume you had brake shoes replaced at the same time as the cylinders?

also, the self adjust mechanism on the rear drums can malfunction and cause it self adjust when it is not supposed to causing the brakes to take up slack every time you use the handbrake.

so, first take temp of wheels to identify which is binding.

i'd put money on it being the rear ones.

if it is get two small flat head screw drivers and a mirror. Pop out the rubber bung on the back plate and back off the adjustment cog. you are looking for the wheel to spin freely with no rubbing noise with the handbrake off. Handbrake on the wheels should lock as normal.

to check if the self adjust mechanism is malfunctioning sit in the drivers seat and activate the handbrake as you would normally about twenty times.

if everything is working as it should be the rear wheels will spin freely with no noise again as they did before. If the self adjust mech is malfunctioning there will be increased noise and resistance.

good luck

Hi Liam.

Touch each of the wheels in turn at the centre where they bolt to the disc/drum. If the wheel is hot that will tell you it is binding.

It is not unusual for the drums on rear to bind somewhat when they have been disassembled if they have not been adjusted correctly when reassembled.

Assume you had brake shoes replaced at the same time as the cylinders?

also, the self adjust mechanism on the rear drums can malfunction and cause it self adjust when it is not supposed to causing the brakes to take up slack every time you use the handbrake.

so, first take temp of wheels to identify which is binding.

i'd put money on it being the rear ones.

if it is get two small flat head screw drivers and a mirror. Pop out the rubber bung on the back plate and back off the adjustment cog. you are looking for the wheel to spin freely with no rubbing noise with the handbrake off. Handbrake on the wheels should lock as normal.

to check if the self adjust mechanism is malfunctioning sit in the drivers seat and activate the handbrake as you would normally about twenty times.

if everything is working as it should be the rear wheels will spin freely with no noise again as they did before. If the self adjust mech is malfunctioning there will be increased noise and resistance.

good luck

Thank you so much for the advice, This helps me a lot. all the wheels were fairly hot, the drivers side front wheel had a noticeable burning smell.

take care.

 

[AlKilgore]

Comon for brakes to heat and lock due to air in the lines. I would go there first. Secondly the calipers tend to stick and drag when Pistons are rusty.

 

[graysworld]

Also if the flexy hoses are old they can collapse on the inside, this has the effect of part blocking them, not letting the fluid return, so it can also make the brakes bind. When doing the overhaul that you have it is in my opinion always worth replacing all the rubber hoses. You may also have sticking pistons in the callipers as mentioned.

Graeme

 

[AlKilgore]

Yes that is true also, the hoses do collapse
easy way to check is to pump the brakes up and release then loosen the bleed screw. If fluid sprays out while not depressing the pedal you have a collapsed line.
Al