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82 Ramcharger- odd brake problem
https://slantsix.org/forum/viewtopic.php?t=61851		 Page 1 of 3
Author:  Reed [ Sun Jan 21, 2018 9:56 am ]
Post subject:  82 Ramcharger- odd brake problem
The truck is an 82 Ramcharger, power brakes, but it sat for about 11 years before I bought it. Right before I bought it, the previous owner had a bunch of brake work done to get the brakes working again. Rotors and drums were turned, new pads and shoes, rear drums were rebuilt, new rear hard brake line, new rear wheel cylinders, and it looks like the calipers were at least inspected because there are new anti-rattle clips on them.

With the motor off the brake pedal is firm and the pedal returns fully to the top of its stroke and the brake lights turn off. However, when the engine is runing the brakes are extremely soft, the brake pedal will not return to the top of the stroke making the brake lights stay on, and with the engine running the brakes do not start to apply until the pedal has gone throug about 1/2 of its stroke. Also, with the engine running I can push the pedal almost completely to the floor and the brakes are very weak, almost like just the rear brakes are working.

In addition to the above identified work done by the previous owner, I have replaced the master cylinder and the brake booster. Neither fixed the problem.

I am going to try bleeding the brakes today (I did bench bleed the MC when I installed the new one), but after that I am almost at a loss.

The factory service manual says low engine vacuum can cause "premature booster runout" (what does that mean?) which has at least some of the symptoms I am experiencing.

Anybody have any suggestions?
Author:  afastcuda1970 [ Sun Jan 21, 2018 11:42 am ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Usually low vacuum makes the pedal hard like it has no power brakes.

New calipers are cheap and worth the money. I replaced both of mine, $$$ well spent. Check the condition of all 3 front brake hoses. I had to replace mine. A weak spot in the brake hose can cause them to feel spongy as well as cause a failure.
Author:  Reed [ Sun Jan 21, 2018 12:02 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Thanks for the input. Bleeding seemed to help a little. The pedal felt better and at first the brake pedal returned to its correct osition and the brake lights went out, but after driving for about a mile with normal stops for stoplights the brake pedal was no longer fully returning an the brake lights were staying on. I am going to try another round of bleeding and inspect all the soft lines.
Author:  afastcuda1970 [ Sun Jan 21, 2018 12:17 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
2wd or 4wd?
Author:  Reed [ Sun Jan 21, 2018 12:36 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Four wheel drive, but I haven't run it yet in 4wd. I am going to try using a vacuum pump to bleed the brake lines. The front calipers were either replaced or rebuilt because the bleeder valves are new and still have the little rubber caps. The rear wheel cylinders have definitely been replaced because the bolts are new and the bleeder valves have dinky little 7 mm bleeder screws.
Author:  DadTruck [ Sun Jan 21, 2018 3:05 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
I have good luck with gravity bleeding,
Start out with Right Rear, furthest from MC,
Put a piece of hose from the bleeder to a small
container, I use a disposable water bottle for the container and clear vinyl for the tube.
Open the bleeder and let it set for an hour or so,
Top off the MC as needed.
Then go to the Left Rear, then Right Front then Left Front.
Author:  Reed [ Sun Jan 21, 2018 6:00 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Thanks. I have pressure bled it twice (open bleeder, have assistant press brakes, close bleeder, assistant releases brakes, repeat) in that order (rr, lr, rf, lf) and will take it for a test drive tomorrow. If the brakes are still having problems, I will try the gravity bleeding method. I know I have good flow with no bubbles from any corner.

If gravity bleeding does not fix the problem, I am thinking I will try replacing the rear wheel cylinders. I suppose there is a possibility that whoever rebuilt the drum brakes used wheel cylinders with a larger-than-stock bore. This would make the pedal travel more and make the pedal easier to push. However, I am grasping at straws here. I can't figure out what would cause these symptoms if the booster and master cylinder are new and there is no air in the lines. The system just isn't that complicated. Maybe there is something weird going on with the metering block because the truck sat for so long? :?:
Author:  DadTruck [ Sun Jan 21, 2018 6:16 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
There are pressure gauge sets available that plug/screw into the bleeder valve that allows one to measure the hydraulic brake pressure applied to to wheel
cylinder/caliper.
I don’t have definate knowledge but that may be a tool available through the Autozone tool program.
would be worth checking out prior to randomly swapping in new parts.
Good luck
Author:  emsvitil [ Sun Jan 21, 2018 7:23 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
1. Wrap Teflon tape around bleeder valve threads so air can't slip by when you crack them loose.
2. Get an aquarium airline check valve (flapper kind) and put on bleeder line.

Image

3. Now you don't have to open,close,open..... the bleeder valve, but can leave it open.
4. pump away.

Once you're sure you have only new fluid, you can reuse the fluid.

I've routed the fluid back to the master with a long section of airline tubing (also allows you to see bubbles while you're pumping away)
Author:  Reed [ Sun Jan 21, 2018 7:52 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Hey, those are some great ideas! I will use them. Thanks!
Author:  tophat [ Mon Jan 22, 2018 3:20 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
The first thing to do is figure out where the problem is. I would clamp off all 3 of the rubber brake lines with something like these.
https://www.summitracing.com/parts/lil- ... gK_YPD_BwE
Run the truck but of course do not drive. Running the pedal should be rock hard. With all lines clamped if the pedal is not rock hard, your problem is not at the wheels. Release the rear clamp and try the pedal. Reclamp the rear and release one of the front clamps and recheck the pedal, and so on.
Author:  Reed [ Mon Jan 22, 2018 4:46 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Thanks, Tophat. I will give that a try. I have been working all day and haven't had a chance to test out the brakes after bleeding them yesterday. I will keep your suggestion in mind when I get back to troubleshooting.
Author:  Reed [ Wed Jan 24, 2018 7:47 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Well, bleeding seemed to help for a short while, but now the spoginess is back and the taillights are staying on. Time to take it all apart and look for odd problems. Seems like somehow air is getting into the system but no fluid is leaking out.
Author:  emsvitil [ Wed Jan 24, 2018 7:59 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
MC leak into the carpet...........

or brake booster
Author:  Reed [ Wed Jan 24, 2018 9:33 pm ]
Post subject:  Re: 82 Ramcharger- odd brake problem
Both MC and booster are new, and the problem existed with both the new and the old units.
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