SOS 1977 Bronco braking & idling issues

Hello, I have a 1977 Bronco and the brakes are acting up. Just recently I've notice the brakes are getting horribly worst. Use to be very sensitive brakes, now there is so much pressure to even apply the brakes. I've checked brake fluid and bled all 4 brakes. Pumped the brakes to build up pressure, crack the drain to relief any air while holding the brakes down then tighten up the nut. Thinking this would help but not go. Like I stated I almost cant depress the brake and the pressure is back? No I haven't looked at the front brake pads yet. This brake issue also started when the bronco started running real crappy. What I mean by that is it idle's real low and dies sometimes at a stop unless I put my foot on the gas pedal. I just thought maybe I needed to adjust my carb. Notice also when I start the Bronco in the morning that it has a hard time running, choke doesn't kick in. So with that can you guys help me pinpoint the vacuum leak. Thought I'd ask before diving in deeper and a fellow member can help me. Any suggestions or advice would greatly be appreciated. Thanks!

Do you have power brakes? If so maybe the booster has failed or you have a vacuum leak? If you had air in the lines that would make the pedal spongy, not harder to push. Failing that I would start suspecting a problem with proportion valve or master cylinder

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The bronco is basically stock except for the paint. Yeah I believe I have power brakes. Disc brakes up front and drums in the rear. Anyway to diagnose it it is indeed the master cylinder or proportion valve? What is and where is the proportion valve? Thanks!

Find out if your vacuum boost is leaking. Vac boosters should hold vacuum and not leak. Use a vacuum pump for the job. Mine went out and now it feels like manual brakes, which I'm used to driving. At some point, I'll grab a reman unit.

Best way to test if I have a vacuum leak? Thanks

meanwire said:

Best way to test if I have a vacuum leak? Thanks

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You can buy a miti vac from AutoZone or somewhere and use it with the appropriate fitting to pull a vacuum on the hose to your booster and see if it will hold vacuum

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Sorry for all the questions. Can you point out this appropriate fitting to where put the hose to my booster to if it will hold a vacuum? Thanks

Hey meanwire. Sorry to hear of your problem. Does sound like a failing vacuum booster though, as air in the lines would end up with the pedal going farther and feeling "mushy" instead of firm and hard and high up like you're feeling.

Can you post up a picture of your engine compartment? That way we can point out what you need to look at and for. Maybe someone with photoshop or paint skills can even draw circles and arrows to point out individual points of interest.

That would be the best way, but basically in the driver's side rear corner of the engine compartment would be a large can-like item on an angled bracket with the brake master cylinder bolted to it so that it hangs over the inner fender/wheel well.
The booster could be black, or gold cadmium plated, but if I remember the stock originals were all black.
There is a large vacuum line (3/8" diameter) using rubber hose and formed steel tubing to get vacuum from the back of the intake manifold to the booster. It attaches at a plastic elbow fitting in a rubber grommet that is also a one-way valve.

If that description doesn't get you there, here's a page with some of our products on it: http://www.wildhorses4x4.com/category/Bronco_Power_Brakes
The first four images are variations on what you should see under your hood.
The last two images are just the booster by itself, and also on the bottom row is the angle bracket that they attach to the firewall with.

Paul

If you get a spray bottle of water and use it all around the upper side of the engine while it's running, including the base area of the carburetor, you can detect vacuum leaks by any changes in the idle quality. You can use this same trick to spray around the vacuum line to the brake booster to also see if the idle quality changes.

But vacuum leaks are not the only way a booster can fail. They're not even the most common frankly.
The little valve on the back that opens when you push the brake pedal to allow the vacuum to help can fail in the open position or just leak.
The main diaphragms inside can rupture and leak, causing the vacuum to equalize inside the can and not offer any boost.
Guessing other things can happen too, but that's the main issue usually. An old tired diaphragm.

Have you owned the Bronco for a long time?
Did the problem appear slowly (as it sounds), or happen all at once?

Good luck.

Paul

Grab a booster Bud. It really sounds like that's your issue. Probably orderable at your local parts store but all of the....or nearly all of the vendors on this page have them in stock.

Power brake booster...but that doesn't mean you don't have other issues as well. Deal with the biggies first and work from there.

Thank you for all the suggestions and advice! I've owned the bronco for about 6 years now, haven't had any real problems. You guys brought up a real interesting thing, this brake issue also started when the bronco started running real crappy. What I mean by that is it idle's real low and dies sometimes at a stop unless I put my foot on the gas pedal. I just thought maybe I needed to adjust my carb. Notice also when I start the Bronco in the morning that it has a hard time running, choke doesn't kick in. So with that can you guys help me pinpoint the vacuum leak. Thanks so much you guys!

Had the same problem on my 70 camaro.
Check time see if the vacuum line has popped off the booster. The brakes will be useless and then there is a major vacuum leak which effects the motor. Good luck

Only you can pinpoint a leak. Way too many small and large possibilities. But as said, look for the obvious first. Hose that's popped of fit's fitting. Hose that's deteriorated. Vacuum cap (rubber or plastic plug for an unused tube) deteriorated. Leaky gasket at the base of the carburetor. Leaky fitting anywhere. And of course, leaky brake booster or fitting or hose.
But short of verifying that you have sufficient vacuum reaching the booster (which you may not) you can't know if the lack of braking is due to lack of vacuum, or the booster actually failing to utilize the vacuum.

Yes, you can throw parts at it shotgun-style and that may work. Eventually it does of course, but it might not have been necessary to throw some parts at the problem.
But at least you'll have new parts!

Word of advice though. Don't throw away the old booster just yet. If it turns out to be an original EB booster from the factory, then having it rebuilt at a specialty shop could end up being better than the modern replacement.
If you get a new one and it works as good as the old, then you're in business. But otherwise don't be too quick to toss.

Paul

Here are a few pictures of the engine bay, anything look out of the ordinary?http://s436.photobucket.com/user/brkncly/library/Engine%20Bay%20Pics

Put your foot on your brake peddle fairly hard. While holding pressure on the peddle start the truck. When the truck starts the peddle should feel like it moved. If it doesn't the booster isnt working properly.

Your key issue is the engine isnt running properly. Check all of the vacuum hoses for cracks and splits especially where they the attach to fittings and parts. There is usually a vacuum tree on te back of the intake manifold. This vacuum fitting is a central location where a few vacuum hoses connent. Sometimes there are caps that plug the unused vacuum ports. This caps fall off or split you can have bad vacuum leaks.

Behind your carburator you see a vacuum can standing up on edge. Looks like a small flying saucer. There is a vacuum hose attached to it. That is vour egr valve. This valve opens under right conditions and lets exhaust into the intake manifold. At idle this valve is supposed to be closed. Sometimes this valve gets stuck open and causes the ideling problems you are having. Make sure this valve is working properly before you start spending money on parts.

Looks like the typical '77 after 40 years. Much of the smog stuff is removed, but not all of it. Lucky yours still runs well actually. Sometimes yanking this, that or the other leads to funky stuff going on.

The evaporative canister needs a hose stuck back on it too. That little washer with a screw through it facing the passenger side of your air cleaner should have a plastic fitting sticking out of it where a hose connects over to the open port on the charcoal canister there on the firewall.
It's a fiber type emmissions hose you should still be able to get at your local parts store hopefully. If you have the occasional gas smell, especially after filling up, doing this should get rid of it.

Now, back to your booster issue. Either test it or replace it. Up to you.
If you really want to really test for vacuum leaks, buy a can of brake cleaner and go to town on the engine. Looks like, from the oil and dirt, that the paint is old and fully cured by now. You don't want to use brake cleaner on fresh paint, but on old stuff it evaporates before any harm can be done. If you're careful that is. Just don't over do it.

You make sure to use the little red tube so you can pinpoint where the cleaner is being sprayed, and just spray little spurts around here or there near the carb, egr, vacuum tubes, and the booster.
If you detect ANY change in the idle quality, whether up, down or just rougher, you've found a leak. Keep checking until you've found them all.

But this is just secondary really. At this point unless you can test the vacuum to the booster and determine that it's insufficient, you might as well just replace the booster, or have it rebuilt locally, and then move on to the next issue if there is one.

There are still things that it can be other than a bad booster, but it's really number one on the list.

Paul