1999 Accord Brake Leak
 

Hey folks, a friend of mine has 1999 Accord LX, 2.3L automatic. Brake fluid gets low after a few days of driving and she has to add fluid. Got it in my shop today, and it is a bit of a head scratcher. No sign of leaks at the calipers, or along the parts of the brake lines I could see. No sign of fluid leaks on either the inside or the outside of the firewall. If I had to venture a guess I would say the master cylinder leaking directly into the power booster. But I hate to throw a part at it without some level of certainty that it is in fact the right part.

Is there a common leak point in the brake system on these cars that I should look closer at? She’s still currently driving the car which has me quite concerned, so before I throw a master cylinder at it does anybody have any suggestions? Thanks!

Also wanted to add that this being my first time on this forum if I have posted in the wrong section I apologize and feel free to move the thread to where it will get the most exposure to help for this issue. I am not new to online forums or to turning wrenches working on stuff. Thanks again!

Welcome, you posted to the right place.

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I think you could check your idea pretty easily. Leave all the hydraulic lines connected. Unbolt the MC from the vacuum booster & pull it away. The booster has a push-rod that pushes on the piston shaft of the MC. Watch the position of the gasket #20. There shouldn't be any fluid back there, so if you find a lot of brake fluid, then you need a new MC. edit: IF the fluid gets into the vacuum booster, then you probably want a new booster as well because the brake fluid will probably eat through something.

Another place might be the ABS modulator. That is, IF the car has ABS... (LX could be had with or without ABS)

This is the proper spot to post.

With that much fluid loss, the leak should be noticeable.

Since the car is 21 years old, you may want to look closely at the lines running under the car to the rear.

If this was leaking into the brake booster, you should see evidence of it also running down the firewall inside the car where the brake pedal attaches.

The ABS system uses the same fluid reservoir, so you may want to look there.

Maybe add some green fluorescent dye to track down the leak?

There didn’t appear to be a leak inside the car on the firewall area, so my thought was perhaps it hasn’t leaked and been refilled quite enough yet to where the booster is full enough of fluid that it is leaking inside yet. Didn’t see any leak signs around the ABS module either but I did find it interesting to note that my scan tool said ABS module failure. The ABS light is not illuminated in the car while running, so perhaps this is a glitch of some sort in communication with the scan tool.

I do do like the idea of pulling the MC off the booster to look for signs of leakage between the two units, and will certainly give that a try next time I can get my hands on the car. This is a high mileage car that appears to have had very limited maintenance over the years, so the basic idea is just to do the necessary repairs rather than replace anything as preventative sort of maintenance as it is only needed to be kept on the road for long enough for her to get into a position to be able to purchase a newer vehicle.

But it of course safety is of paramount consideration in my mind regardless of how long it actually ends up being nursed along. Brake lines did not appear to be corroded with age and the soft lines also appeared to be in decent condition. This is in the Southern Oregon area, so we are not in a heavy rust area like the Northeast states are subject to.

Another thing to add, it is the EX model, not the LX. I was thinking of my mother’s 2002 Accord when I originally posted. Either way shouldn’t make a difference in actual diagnosis, however clarity is important. I mostly do work on pickups and SUVs, but primarily agriculture tractors and equipment, so while principles are the same I am not entirely intimately familiar with the exact systems on smaller foreign cars.

EX & LX are very much the same. The biggest difference is 4-cyl vs. V-6 (both EX & LX could have either engine). EX has a sunroof & trim stuff, and rear disk vs. drum in the LX. Drum brakes can hide leakage for awhile, but disk brake calipers don't have anyplace for the leaking fluid to hide.

There might be a balancing valve somewhere under the car, to reduce the pressure to rear brake under heavy braking. If that leaks, it might drip off & not look wet. Then in the garage it doesn't leak because it's not very pressurized. You might look for something leaking underneath that only leaks while someone stands on the brake pedal??

I think there's a fair amount of fluid that can hide in the vacuum booster before it starts leaking out somewhere. If you start to mess with the pushrod under the pedal, be aware that the adjustment (#2 & #16 in the picture above) has to be maintained. There's a strange gauge tool that you'll need to set it up, so don't lose the exact position of that. If you need a new MC, post back about that adjustment...