The Stovebolt Site Forums The Shop Area Engine Shop My brakes hate me

Hi all,
The brakes on my '42 3/4-ton are continuing to laugh at my efforts. They were working just fine when I started in on them, except for a leak at one rear wheel cylinder. I replaced both rear wheel cylinders and switched to DOT5 fluid. I pushed through 2 quarts of DOT5 to flush the system.
Now, not only does the brake pedal hit the floor, but it also feels like the MC piston doesn't return as quickly as the pedal. If I bottom out the pedal and then let it back up quickly and immediately press it again, it will go most of the way down with no resistance at all before it starts to push fluid. If I wait a second before pressing the pedal again, then it'll go about halfway down w/o resistance. If I wait 2-3 seconds, then it'll push fluid from the start (but still go to the floor).
The MC worked perfectly before I started, and I can see that it's not leaking, so I been assuming that I have air in there. I've been trying to bleed it, but without success. Am I just not doing it correctly, or is something else at play here?
-Jon

Also, Would a Mityvac help with this?
-Jon

When you convert to DOT5 you need to replace all of the rubber that comes in contact with the fluid. Master cylinder, wheel cylinders and flex hoses. Sounds like the master cylinder rubber is binding. That's how bad the incompatability is between the fluids.

Given those symtoms, I think you still have air in the system. Not sure what method you are using but I would suggest 2 people. One working the pedal, one on the bleeder. Push, open bleeder, close bleeder, release pedal. repeat... Go in sequence from furthest wheels from the master cylinder.

I would fathom a guess that your master went bad. When it works in a certain amount of travel for a long time then get pushed beyond that point, it ruins the cup seal. Either way with the air and fluid not moving and the introduction of DOT 5, the master needs to come off. I would blow the fluid back out of the lines back towards the master cylinder and start over with a rebuild and DOT 3 fluid,
Scott

jon,
speedbleeders rule! try them you'll like them. they're available at most auto parts stores & alot cheaper than those pumps & brake bleeding becomes a one man job.
it does sound like you still have air in the system. follow what dennism suggested & repeat it 2 or 3 times. sometimes it takes that to get all the air out.
i wouldn't reccomend dot5 for a vehicle that is driven very much. it has different expansion & contraction rates from heating & cooling than dot3 or dot4. when i'd take my '50 1/2 ton for long drives ( especially in the summertime or in the mountains ) the rear brakes would start to lock up. more & more the hotter they got. then i found this info. about the dot5 fluid & found out what the problem was. most of the aftermarket brake suppliers reccomend dot4 for vehicles that are driven much & dot5 for showcars that aren't.
robert.

The master cylinder is probably trashed. Changing the type of fluid without all-new parts was a mistake, as I doubt the older natural-rubber MC cups will work with the silicone-based fluid. Rebuild or replace the cylinders, or at least the master cylinder, if the others were redone rcently. Flush the system with alcohol, or pump a couple of quarts of DOT 3 fluid through the system to get rid of the DOT 5 stuff.
Jerry

You need to rebleed the brakes. I do it by myself because I ain't got nobody to help me. I just figure out how to do things myself.

Start from the closest wheel and work to the farthest. Take the top off the master cyl reservoir and fill to the top. Loosen the left front wheel bleed screw and attach a hose to the bleed screw nipple. Put the other end of that hose into a small jar of brake fluid, sitting on the ground. Get back into the truck and push down on the brake peddle slowly a few times then leave the peddle to the floor. Wedge a precut piece of 2x4 between the seat and the brake peddle, holding it down to the floor. Tighten the bleed screw at that wheel. Repeat this process for all four wheels then, repeat the process again. This works! I have done it several times. My brakes are working perfectly.

I would rebuild the master cyl. & than try bleeding it again. I have never used them but those speed bleeders seem like a great idea. Like 48big says when you change possition on a cylinder you stir up all the crud & work in an area that is pitted & corroded.

OK, well it looks like I've got more time and $ ahead of me than I thought. I guess I'm replacing all the rubber in the system. Will the WC and MC repair kits from Jim Carter have everything I need? I already have new hoses ready to use. After rebuilding, should I stay with DOT5 or go back to 3? I had read that DOT5 was better in every way (except ABS), but it seems like a lot of you are recommending going back to 3. Why is that?
Thanks for all the advice, even when you're just telling me how badly I messed up.

DOT 5 vs 3 debates can get heated. Most either swear by 5 or swear at it. It has a big advantage of not absorbing water like 3 will. However, it does not have quite as good hydraulic properties as 3, making it harder to bleed. It also doesn't give you quite as good of pedal response, but most people will never know the difference on that part.

If you plan on driving the vehicle at least once a week and don't mind flushing the system every two years, go with 3. Otherwise, take a serious look at 5.

As far as Carters kits, you will have to call them. Their customer service has not been praised by anyone here for some time, which has sent a lot of business to Chevy Duty or Bowtie Bits. Both (and others) are in the links section.

Can you use either DOT 3 or 5 with new parts?

Flushing the brake lines is a PAIN IN THE AZZ so go with dot5. Just make sure that the rubber is compatible before you purchase.