Long Downhill Brake Fade!

[swissarmychainsaw]

1973 Suburban 1500
350/350

Had the truck for about a year, took the family on some deserted back road and encountered a very steep and long down hill. This, on the brakes for 15 mins, going really slow, steep, winding one lane road.

At some point my brakes overheated, and I got massive pedal fade.
I stopped and the rotors/calipers were smoking a bit.

I think to myself, "I'm going to fix this! Having your brakes disappear sucks!"

(several months later)

Replaced:
* New pads
* Front Brake hoses (rubber)
* Master Cylinder
* Brake Booster (did not seem to be keeping pressure)
* Front Rotors
* New fluid
(also did wheel bearings in front, and tie rods, etc.)

I did not touch rear brakes, which show about 1/3 left on the pads.

THEN, I took the Burb out camping again, and came down a steep slow downhill, and YEP. It happened again. Brakes get hot, fade, and I lose pedal.
(It felt like I lost power assist. It would stop but I had to really put some force on it.)

What am I doing wrong here? I really want this thing to have brakes that I can trust you know?

Thanks!

[homemade87]

My guess would be if your riding the brakes that long and hard you are most likely loosing the rear brakes first . Drum brakes do not like heat . Once they get hot and loose there braking power the fronts are really having to work hard .

You would benefit from a drilled and slotted front rotor . They get rid of the gasses from the heat build up under the pad and help to get rid of some of the heat . Most wont see benefits from a drilled and slotted rotor because they never put them to use for what they are designed to do . It sounds like you could definitely use them . You could also convert the rear to disk and do the same on the rear to get rid of most of the drum brake fade . Just do your research on that conversion to get matching components . My biggest deal on my conversion was getting a master cylinder that worked with my setup to have good peddle travel and feel .

[J Knight]

How slow were you going down the hill? If you would have down shifted to second gear the engine could have taken some of the load off the brakes.

[swissarmychainsaw]

Originally Posted by J Knight

How slow were you going down the hill? If you would have down shifted to second gear the engine could have taken some of the load off the brakes.

VERY Slow, like 15 MPH, and yes I downshifted into 1st gear.

It was more like "Creeping down the hill".

[old Rusty C10]

are the rears properly adjusted?

[GRX]

My advice would be to drive differently to avoid heat soak. Slow in pulses with short periods of little to no brake pressure in between. This skill is essential when using 4-wheel drums on long hills and works for disks too.

[68Timber]

Check this link and see if it describes what's happening. I'm wondering if you are getting so much heat soak the fluid is boiling.

[Keith Seymore]

Originally Posted by GRX

My advice would be to drive differently to avoid heat soak. Slow in pulses with short periods of little to no brake pressure in between. This skill is essential when using 4-wheel drums on long hills and works for disks too.

This is correct.

K

[Dead Parrot]

Heavy suburban + several hundred pounds of family + several hundred pounds of camping stuff is hard to stop. One thing that can help if you have AC is to run the AC even if you have to set the temp control on hot to keep the compressor from kicking off. The extra drag from that large compressor will help the engine slow the vehicle. Be sure you disconnect the AC idle solenoid if equipped. Make sure your engine idle is proper. A too fast idle will decrease engine braking.

Since the brakes last about 15 minutes before fading, the best, safest and cheapest answer is to take scenic rest stops every 8 to 10 minutes.

[1976gmc20]

Wow - I've never had any trouble with Chevy disk brakes fading. We had a 1977 C-10 Suburban in Colorado but it had a four speed manual.

Are you pulling a trailer too ???

[swissarmychainsaw]

Thanks for the replies everyone.

( Heat Soak )
Yes I believe that the brakes are getting hot and boiling the fluid, which is why the pedal “fades”.

( Rear brakes adjusted properly? )
This I need to check. So far this is the most compelling test to make. It would explain why the fronts get overly hot. For what it’s worth the parking brake does work, which I assume is a sign that the rears should be doing something (or are capable of it!).

( Drive differently )
I was going very slowly and in no way did I feel like I was over taxing the brakes.
I feel like they should have been able to handle the relatively mild load I put on them.
I believe there is something wrong here, and it’s not safe!

( trailer )
Nope and I’m pretty much not going to tow anything with the brakes like this.

[Super_Dave]

ALL brake fluid has a limited life span, hence the small cans.

Brake fluid is measured in terms of dry and wet, dry being right out of the can and wet being at a 3.7% water content at the boiling point. I have always used Silicone Brake Fluid. It operates well at higher temps (takes more heat to cause it to boil). However, the higher the temp rating the more hygroscopic sensitive it becomes (sensitive to water contamination). All brake fluid has water in it by design, again, 3.7% is one of the the measuring specs. Helps absorb heat.

So finding a good silicone brake fluid with a reasonable hygroscopic sensitivity, would give you a lot of improvement over what you are doing now. However, that being said, silicone fluid has a tendency to trap air, so bleeding the brakes regularly is not a bad idea. On the whole, replacing any brake fluid annually is highly recommended.

There was a relatively recent development of a non-silicone brake fluid that had all the positive characteristics of silicone (same minimum boiling points wet and dry, but didn't have the air trapping issues.)

Here is a good article that really explains it in detail and is an easy read. Should give you a great place to plan any changes you need to make. Granted, it's from Down Under, but brakes are brakes... for the most part...

http://www.rdabrakes.com.au/page/TB04.aspx

[Tom]

edited

[68Timber]

Some interesting reading on the subject.

[swissarmychainsaw]

So I pulled the rear drums off, and it seems that the rears were really not engaging.
I adjusted them and the brakes feel WAY Better, I think that solves this mystery!

Not sure why the auto adjusters were not working.
Brakes only have about 1/3 life left, and the adjuster screw was pretty dirty.
Cleaned it up and all, but I will be replacing the shoes before too long.

So far so good!

Thanks all for the replies!

[GRX]

Glad you figured it out. Dirt is the enemy where the auto adjusters are concerned. The rear brakes on my '69 were still original, right down to the shoes which were badly cracked. A total rebuild made all the difference.

[1976gmc20]

Originally Posted by swissarmychainsaw

So I pulled the rear drums off, and it seems that the rears were really not engaging.
I adjusted them and the brakes feel WAY Better, I think that solves this mystery!

Not sure why the auto adjusters were not working.
Brakes only have about 1/3 life left, and the adjuster screw was pretty dirty.
Cleaned it up and all, but I will be replacing the shoes before too long.

So far so good!

Thanks all for the replies!

I knew there had to be something going on - those old Chevy pickups had pretty good brakes. They were far superior to anything else on the road in 1973

[swissarmychainsaw]

Originally Posted by GRX

Glad you figured it out. Dirt is the enemy where the auto adjusters are concerned. The rear brakes on my '69 were still original, right down to the shoes which were badly cracked. A total rebuild made all the difference.

Yes my "I fixed it post" did not go into enough detail about how much dirt/brake shoe dust was caked on the adjuster.
The Shoes are about 25% left, so I'm thinking it's due for a full re-do.
Much better now.
Thanks again all!

[swissarmychainsaw]

So I'm reviving this thread because I'm still not happy with the brakes on this thing.

Here is what I have done:
1. New Brake Booster
2. New Master
3. New Rubber Lines Front
4. New Rubber Lines Rear
5. New Rear Cylinders, spring kit and shoes
6. New Front Calipers (yes) and pad

And yet, they feel is largely the same.

Emergency Braking (simulated):
Press real hard, and at some point you get a hard pedal. Feels like it takes WAY to long to stop.
Rears don't lock up even going down a steep hill. (all my other trucks this was easy to do)

Couple of weeks ago I was out in the sierras doing some 4x4-ing.
At one point it felt like I lost my power brake boost, I was trying to turn around on a hill and had to push really hard to get the monster to stop.

At this point, I was convinced that my engine was not producing enough vacuum to operate the Power Brake Booster, so I bought a gauge and plugged in the vacuum gauge right where the booster connects and got something like 18".

Is it possible that under some conditions I'm not making enough vacuum?
( planning on putting new heads on it )

I'm at a loss and want better brakes. What do I do next?

Thanks,
--Nick

[nonstop]

What really made the biggest difference for me was converting to hydroboost. With 4 wheel discs you could stab the pedal and it would instantly lock up the 36 inch tires. Is the truck 4 wheel drive? If so, I'm not aware of much for front brake upgrades.

Did you replace the check valve when you replaced the booster? Could there be an internal problem in the proportioning valve? Is there a load sensing valve on the rear brakes? Just a few thoughts of things to check.