1990 Isuzu Amigo 4 wheel drive, We are losing brake fluid but there is no evidence of leaking on the concrete. We replaced the master cylinder and that didn't help. It has to be going somewhere, but where

Mary, check the firewall where the plunger from the pedal goes into the master cylinder.
Nick

ok, be right back

there is no sign of fluid------anywhere------it does have a brake booster but even so fluid has to go somewhere, we have filled the reservoir on the master cylinder 3 times

Mary, master cylinder may be leaking back into the booster?
Nick

Maybe, but you would think after filling the cylinder 3 times that it would be leaking out of the booster by now. Guess we will have to tackle that tomorrow after work.

If fluid gets into a certain part of the booster, it could be sucked into the engine. Is it an Aisin booster?

hold on, I'll go look

don't see brand name, will do picture in a minute

Mary, do you tow the Amigo? I have one and am told you can't put the transfer case in "n" it will burn up the transfer case. There is a spot where the power will not transfer to the road on the transfer case shifter but no detent. Just curious.

I look at mine on the brake system to see if any similarity.

Thanks

Ed, I have never towed it, but I have a trailer if I need to take it somewhere (never have though)

quote:

Originally posted by Mary Ray:
We are losing brake fluid

Do you lose it while the vehicle sits or when it is driven?

How fast do you lose it?

filled the reservoir last nite, left it alone until this afternoon. Checked reservoir and it was almost empty. Did not drive, start or otherwise touch it. It has not been driven because brakes or so bad. We replaced rear pads and master cylinder but never could get brake pedal to come up. It will stop, but not quick enough for me to drive.

quote:

Originally posted by Mary Ray:
filled the reservoir last nite, left it alone until this afternoon. Checked reservoir and it was almost empty. Did not drive, start or otherwise touch it.

OK, good. This fast, non-driving, non-engine running leak makes it easier to find.

The leak is either in the front lines or the rear lines or at the push rod entry to the MC. Let's see if we can eliminate either front or back or both........ Buy a length of brake line with fittings that will screw into your master cylinder. Cut one end off to about 2 inches, leaving the nut on the flared end. Use a vise grips or a hammer and anvil to crimp the cut end tightly closed. Remove one brake line from the master cylinder and install the crimped tube and top it off. Wait until the next day.

What happens?

If no leaking took place, it is possible that the leak is in the line you disconnected or the seal where the push rod enters the master cylinder. I am inclined to doubt that the leak is at the push rod seal, though, unless you got a bad one from the store. I would follow the line you disconnected and see where it goes and be sure there is no leak.

If the level still went down, replace the line you disconnected, and install the crimped line in the other outlet, top off, and see what happens, again, the next day. If the level still goes down, either both front and rear have leaks or it is where the pushrod enters the master cylinder.

If you are fairly fast, you can do all of this with little concern for bleeding. Air rises.

Have you been underneath with a bright light and a lot of patience? Follow every line from the master cylinder to the wheels.

Does it have disks in front and drums at the rear? If so, it should have a proportioning valve or a even a load sensing proportioning valve. A load-sensing PV is connected to the rear axle by a rod, and has three brake lines going to it.