1977 Bonanza BRAKE Warning Light ON
 

I did a search here for BRAKE LIGHT ON and didn't really find what I was looking for. My 77 Chevy 5/8 Ton Bonanza just had the BRAKE light come ON after I had noticed the brake pedal was going farther to the floor than normal the last time I drove it last week. After the light come on today, I opened the master cylinder and the REAR reservoir was almost empty. Front reservoir was full. I put more fluid in and started the engine and pumped the pedal. The light would go off then on then off, but stayed on after all that. The master cylinder was BRAND NEW 2 years ago, so, kinda think I have a leak somewhere in the rear wheel cylinders or the vacuum brake booster is going bad. I replaced the booster a good 12 years ago and it was a rebuilt one at that, so might be a bad vacuum booster. I looked at the rear brakes for leaks and didn't see anything like a fresh leak, but a previous possible indication at the TOP of the drum backing hubs. I assume the master cylinder rear reservoir goes to the rear brakes, correct? Two years ago I replaced almost all of the brake components such as Master Cylinder, front (rubber) brake lines, calipers, and pads. I don't recall doing anything to the rear brakes. Any ideas on the most likely cause of the problem?

Re: 1977 Bonanza BRAKE Warning Light ON
 

Unplug the wire going to the proportioning valve & see if the light goes out.
It appears your PV piston has traveled far enough to let the plunger drop into the slot making a ground path for the light to illuminate.
I think the rear reservoir is for the front brakes.
After you make your repair you will have to unscrew the plunger on the PV & move it to the neutral position & re-install it & the wire.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Hi Andy, thanks for the reply. One more thing, why the low reservoir? Wouldn't that indicate a leak somewhere? Unless the brake pads have worn and allowed the reservoir to drop. But, since all new parts, I haven't put more than 1000 miles on the truck in 2 years. Seems kinda strange it's from brake pad wear.

I also found another possible answer from a mechanic I know. He said if the rear reservoir is way low, I have a leak in the master cylinder. Even though the master cyl is "new" it's likely still the source of the problem. I asked him if there's any really brand new master cylinders for old cars and he said they are all just remanufactured from cores. They come in a new box, maybe, but that's all. He added that I can loosen the bolts holding the master cyl to the brake booster, it will likely show a leak out of the back end. If the leak is real serious, it will collect in the brake booster and leak into the cab where I should be able to smell it. So, still nothing definite till I do some more checking.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Could be simply new pads wearing a bit while matching to the rotors/drums. New ones tend to settle a bit then will pretty much stay the same except for the normal slow wear.

Top off the MC then watch. If it keeps going down, probably a leak. If it stops, probably new parts getting broke in. Could also be the rears self adjusting.

Re: 1977 Bonanza BRAKE Warning Light ON
 

The ironic thing is that such problems don't show themselves when the temps are in the 80 to 100 Deg F range, but waits till it drops to the 40's and the wind is blowing 30 MPH! haha. Temps here in N Central TX are unusually cold for Mid November. Usually still warm this time of year. Gotta be a few more "normal" Texas days ahead before Winter really hits. My safety-only State inspection is due in January for relicensing, so would like to get this problem fixed before then.

Re: 1977 Bonanza BRAKE Warning Light ON
 

I always have to add brake fluid in my old vehicles. I have been doing it for 15 years with my convertible. If it sits for a couple weeks I always check the fluid before driving it. Wheel cylinders can weep but still work for a long time. I don't think it's the master.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Hi Al, but the real kicker is that the BRAKE warning light stays ON. I can pump the brakes up and the light goes off, but then let it sit for a bit and SLOWLY press the brake pedal and the light comes ON again and stays on. Kinda weird. But thanks for your input. I will check it out when the temps come up in a week or maybe less. Too dang chilly out there. Supposed to be in the 20's tonight. groan.

Re: 1977 Bonanza BRAKE Warning Light ON
 

It's full of fluid and you pump it up and the light goes off, then it sits and you pump it and the pedal travels almost to the floor and the light comes on, and it's full of fluid, I think it may be the master after all.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Al, yes, that's pretty much the story. Not the worst of repairs except for having to bleed the brakes after the new master cyl installed. Once it warms up, will get on it. Thanks.

I ordered a new master cylinder from Rock Auto to have it here when I am ready. Raybestos, New, delivered = $32.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Bench bleed your master cylinder before you install. Saves a lot of pumping

Re: 1977 Bonanza BRAKE Warning Light ON
 

Hi xrcr, I did that on the last one. Worked out nice. Came with a bleed kit. Strange to have to replace the master after only 2 years and 1000 miles, or maybe not even that many miles. Pain in the @#$%! I wonder if this is one of those things that happen to a vehicle that isn't driven much? Could be.

Re: 1977 Bonanza BRAKE Warning Light ON
 

First one could have been bad out of the box. Missed step during rebuild, nicked seal during assembly, etc. Sometimes you do everything correctly and it still fails.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Got a decent day to look at the brakes. Pulled the master off the booster to look for any leakage behind the master - zero, clean as new. So, I am going to pull the rear wheels off and look at the wheel cylinders back there. They show some oil at the top of the backing plates. That's the next likely place for a leak. Especially if the aft reservoir is dedicated to the rear brakes - adds up. But, now I have a brand new Raybestos PG Professional Grade master cylinder on the table. Guess it will be a spare part. Ha. Or who knows, may end up installing it after all.

Haha. Now that I pull off the left rear tire, I see it's a wheel cylinder leak. Oh well, the Master Cyl was only $32 delivered. Not a big cost. Now will likely have to replace the rear shoes and cylinders as they are likely soaked. But, first, have to figure out how to pull off the drums, not budging. Been many many years since I've messed with the rear brakes.

Re: 1977 Bonanza BRAKE Warning Light ON
 

Ok, done with the brakes. Got the drums off with some gentle tapping with a 5 lb hammer! ha. They just needed some motivation to move off. Drums were not even worn enough to have a ridge around the edge. Shoes were so good I just sprayed them down with brake cleaner and wiped them off. Just the left cylinder was leaking but replaced them both. Got the neighbor to come pump the brakes while I bled and I was done. The new Master Cyl will go in the 77 Chevy parts container for another time. Thanks for all the input here, fellow Chevy owners. LBJ