Help Diagnosing Brake Fluid Leak 1999 LX 470 250k miles (1 Viewer)

[Eltestro]

The emergency brake light on my vehicle came on last week. I went to investigate and found a puddle of brake fluid under the driver's side. I refilled the brake fluid reservoir with DOT-3 brake fluid and drove sparingly over the next few days.

Despite the refill, the leak persisted and the fluid level dropped drastically after a 20-minute drive. I refilled the reservoir again above the maximum level. Since then, the leak seems to have slowed down or stopped completely. I examined the reservoir and assembly and found some play in the assembly, but I did not make any other changes so I'm confused as to why it has stopped leaking from what I can tell.

After cleaning the area with brake parts cleaner, I observed occasional drips which I think is residual brake fluid. The fluid level in the reservoir has only slightly changed with system pressurization, but not to the extent it did before.

The source of the leak appears to be the seam between the ABS module and the master cylinder aluminum on the driver's side.

Has anyone actually pulled apart this part of the assembly before and can tell me what's inside? Are there gaskets or O-rings? Additionally, I'm trying to understand the cause of the leak and why it was constantly leaking before but has now almost stopped. If anyone has any ideas on where the leak might be coming from or what could have caused the change, I would greatly appreciate it.

Thanks!

 

[Tres Toys]

I had a similar issue a couple years back on my 2000LX. I ended up replacing the ABS module with a used one and have had no problems since. There are a couple different versions of the ABS module over the years, so if you go that route make sure you get the correct one for your particular VIN. See thread
Sudden external leak from brake Master Cylinder/ABS Help - https://forum.ih8mud.com/threads/sudden-external-leak-from-brake-master-cylinder-abs-help.1235236/#post-13537623
Best of luck

 

[2001LC]

Let me first say, I'd recommend a new booster w/master assembly (the entry master). You'll be good to go for next 20 to 30 years, if properly maintained.

Where I have repaired these with used parts, it's not advisable. I've a shelve full of these parts. But I no longer will use on a customer rig, with few exceptions. Toyota drop the price of Masters last year and all models became available. Which prior to then, we not only couldn't get some yr's, the cost was much higher.


That said:

I guessing, neither picture above is from of your master? Which there are clues to overall health of master, that need consideration. i.e color of fluid, staining in reservoir, brake control wire condition, leak from pump/motor or debris in it's breather, etc..

If leaking between ABS black plastic & aluminium block and or cover on face of ABS, it's internal leak. The seal between those plastic components are not a high pressure brake fluid seal.

Between the Aluminium block of ABS and the aluminium of master, is a high pressure seal plate.

Also 3 grommets (blue shop towel, stuffed in them) between res & master, can leak but unusual and mat indicate other issues.

 

[Eltestro]

I had a similar issue a couple years back on my 2000LX. I ended up replacing the ABS module with a used one and have had no problems since. There are a couple different versions of the ABS module over the years, so if you go that route make sure you get the correct one for your particular VIN. See thread
Sudden external leak from brake Master Cylinder/ABS Help - https://forum.ih8mud.com/threads/sudden-external-leak-from-brake-master-cylinder-abs-help.1235236/#post-13537623
Best of luck

Good to know, thank you!

 

[Eltestro]

Let me first say, I'd recommend a new booster w/master assembly (the entry master). You'll be good to go for next 20 to 30 years, if properly maintained.

Where I have repaired these with used parts, it's not advisable. I've a shelve full of these parts. But I no longer will use on a customer rig, with few exceptions. Toyota drop the price of Masters last year and all models became available. Which prior to then, we not only couldn't get some yr's, the cost was much higher.


That said:

I guessing, neither picture above is from of your master? Which there are clues to overall health of master, that need consideration. i.e color of fluid, staining in reservoir, brake control wire condition, leak from pump/motor or debris in it's breather, etc..

If leaking between ABS black plastic & aluminium block and or cover on face of ABS, it's internal leak. The seal between those plastic components are not a high pressure brake fluid seal.

View attachment 3239677

View attachment 3239679

Between the Aluminium block of ABS and the aluminium of master, is a high pressure seal plate.

View attachment 3239683

View attachment 3239703
Also 3 grommets (blue shop towel, stuffed in them) between res & master, can leak but unusual and mat indicate other issues.

View attachment 3239718

Very helpful, this is exactly what I was looking for. Thank you!

 

[2001LC]

BTW. If you do repair. Clean the 3 little round screens.