My brakes are fading on me really bad when under maintained pressure (stop light, etc). Have enough brakes (for now) to slow, maneuver, come to stop if I take it slow. But only if I go slow and only if it ain't downhill. Otherwise it "catches", then drops to the floor after a few seconds.

Checked master cylinder for fluid level - it was fine - but seals on underside of lids were so bloated that I had a nasty time getting them back on.

I know that mineral oil in transmission fluid can degrade seals, etc, but no such mishap has occured (definately different bottles). Aside from a rather paranoid conclusion that someone slipped tranny fluid into my brake fluid bottle for shits and giggles, what gives? What else could cause this?

I am probably in for an expensive fix (oh joy), as the lines will need to be drained, refilled, and the seals etc replaced. Where exactly are all the seals, gaskets, etc on an 88 Dodge Dakota 6 cyl? Is this a huge take-it-to-a-pro-job, or could I muddle through it laying on my back on gravel in the rain (sigh)? I checked the Hanes, but it wasn't really clear.

-- Soni (thomkilroy@hotmail.com), January 23, 2002

Answers

Response to Bloated seals on master cylinder caps - cause?

As an ASE certified mechanic I will give you a little insight on a couple of things here by starting with a disclaimer.

You have the potential to damage not only your life but someone else's life with your brake's current condition. DO NOT DRIVE IT any further until you get them repaired!!!

Now with that said ... it appears that the Master Cylinder is faulty. The "catch" that you are feeling is coming from the brake proportioning valve and it is operating normally concidering the current condition of the master. Here would be my current plan of attack.

Start by replacing the Master Cyl. If you are semi-mechanically inclined this is a task that you can perform yourself in your gravel driveway. You will need to someone to help you bleed the brakes and maybe as moral support. Follow your Manual for the process on bleeding the system.

The next order of biz is to purge all the old brake fluid from the system. A good way to do this is to fill the new m. cylinder with fresh fluid and starting at the closest bleeder valve and begin the brake bleeding process. Note this is just the opposite procedure from the way you bleed air from the system -- when bleeding air always start at the furtherest brake bleeder. This will make sure you have all the contaminated fluid and dirt removed from the system.

Next, I would remove all 4 wheels and check the condition of the brakes. A simple eye exam here is adequate. You need to pay particular attention to to the brake slave cylinders which are the cylinders that push the brake shoes & pads outward. If they have brake fluid on any one of them, it will be safe to assume that you have tainted fluid in the system and you will need to replace the wheel cylinders and the front brake calipers too. I would offer to say that it will be to your advantage to REPLACE them instead of rebuilding them unless you feel the liability is worth the risk. Unless you are sure that someone tainted your fluids, I would tend to guess that what you are experiencing is a common case of where your brake fluid has absorbed some water (condensation & etc.) and has began to rust the system interally. Even possible that some dirt has entered the system due to the faulty cap seal and it was introduced into the system. This dirt or a flake of rust has "cut" the piston plunger rubber cup inside the master and that is why the pedal has no back pressure ... the brake fluid is by-bassing the plunger and you have no pressure to accuate the slave cylinders.

I feel there are many here that can coach you through the replacement process if you feel comfortable doing it yourself.

Good Luck

-- BRENT in 10-uh-C (bt@nospam.com), January 23, 2002.

It definitely appear that you have a bad master cylinder and it needs to be replaced, first. Pumping brakes to stop is no fun and you never know when this procedure will quit working.

-- BC (desertdweller44@yahoo.com), January 23, 2002.

Ive seen these bloated seals before and believe the cause is contamination of brake fluid. One thing I will add to what has already been said: you must bleed the master cylinder itself during installation. There are two ways to do this. One: dip the entire master clyinder in a bucket of brake fluid and depress the end (where the rod presses) until no more air bubbles ccome out of the holes where the brake lines connect. Two: get the master cylinder bleeder kit (cheap) and it has two small lines... just put the plastic lines where the normal lines connect and hold them into the fluid chambers in the m.c. and have some one pump the brakes until the air bubbles quit flowing. As far as the rest of the system, check the rubber lines from the body to the calipers on the front, as these do sometimes split. Also, there is one above the rear end on your truck. The drum brakes on the rear should be checked for leakage- there is a small double ended piston that sits at the top of the drums, look for damp spots on either end of the plungers. These whole deals are about 10 bucks each, so if yousee dampness, replace (if you need walk through on this on, I can help, as Dodges are my forte). On the front, I have over 400,000 miles on combined Dodge products, never had too much problem out of disk brake calipers, unless the pads get excessively worn and the piston gets stuck out too far. Once in a while, one caliper will get stuck and not return to its proper position- this will be indicated by one set of pads being VERY worn, and the other set being ok. Your problem is almost certainly master cylinder- should run between 10 and 20 bucks for a rebuilt unit, maybe 30.

-- Kevin in NC (Vantravlrs@aol.com), January 23, 2002.

last time I bought a master cylinder it came with the bleeder kit.

-- Dave (something@somewhere.com), January 23, 2002.

Soni, all the above advice is good. It is definitely a candidate for do-it-yourself but I would suggest getting a price for obtaining replacements for all cylinders (either new or rebuilt). Working on old brakes is the dirtiest, filthiest job you can do on a vehicle and if you can replace everything in one go it is so much easier. You can be sure if the master cylinder has been damaged by contamination all other cylinders are at risk too.

Go to your local brake specialist to check on prices and ask if they can do an 'exchange' where you trade in your damaged cylinders for rebuilt ones.

-- john hill (john@cnd.co.nz), January 23, 2002.

I had the same problem of all rubber parts swelling up. After 2 master cylinder rebuilds I found out the "Heavy Duty Brake Fluid" I was using was not "DOT 3" brake fluid which was specified. I had to go through and rebuild everything.

-- Dave (drcomer@rr1.net), January 23, 2002.

Mystery solved - took it to the shop (it's going to rain all week, I have no garage, and we need the truck NOW) and it turns out some PUT about 1/2 cup of motor oil in the master cylinder. We both know better, so the only option is that it was done intentionally, with intent to get back at us for something, or just plain old hatefulness. The opened, barely used oil bottle was still in the bed (one of ours, but hubby and I only open them to empty them - we never just use a little). Thom thinks he may know who might have done it (oportunity and motive) but has no proof or even anything but a best guess gut feeling. The idjit probably never even considered that someone could get hurt, just did it to cost us money and get even for us having a better life (if it is him, he has expressed himself often on the subject of how horrible his life sucks and how "good" everybody else on the planet has it - mainly to justify not paying hubby for work done.)

That being said, we had the lines flushed, and the MC replaced. Rubbers at wheels were okay. No harm done, aside from the money spent replacing it and one crappy night driving it home from work - in the rain, no less. WHEEEEE!

I feel sad that someone's life is so pathetic that doing something like this makes them feel better. I will use this as an opportunity for spiritual growth by praying for them and doing my best not to let the immediate gratification of anger spawned by my fears take root in my heart. Anger only hurts the angry. (This is harder than the gurus make it seem :{ )

On the other hand, I write mysteries, and now I have a new way of killing off (or almost killing off, depending on what works) a victim. My character will be smarter, though, and use less obvious oil, something clear. With luck, any sales from the story will generate brake repair costs in return. In the words of great writers everywhere - it's all material!

-- Soni (thomkilroy@hotmail.com), January 24, 2002.

Gadzooks you sound like a christian! Not to worry, the Lord will kick his butt for you later.

Something to consider about car maintenance. Your car can refuse to start. It can run lousy. It can die at inopertune moments. You can live with that.

BUT anytime you step on that brake pedal it MUST stop. Normally you don't see much trouble with the brake system. When you do, it is really cheap insurance to rip the entire system out and replace with rebuilt components (hydraulic and mechanical).

You can do it in a day. There are a few inexpensive tools to assist in the task (drum brake spring compressors, brake spring tool, set of tubing wrenches).

In preparation for that day, crawl under the car and apply grease to all those EXTERIOR fittings that tend to rust up and make the job miserable. If you've not done this, squirt WD-40 followed by a top coat of motor oil on them for a day or so. Even an overnight soak will help in breaking the tubing nuts loose. The WD-40 will wick in and draw the heavier motor oil with it.

I routinely apply grease to all exterior adjustment points, attaching hardware, tubing nuts, etc... as soon as I purchase the replacement car.

-- Don Denhardt (desulfator@yahoo.com), January 24, 2002.