• Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!
    If you have problems registering or can't log into your account, please contact Admin.

Are the disks supposed to lock up before the drums???

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
I was reading Chuzie's post on brakes, I have a '76 with stock disk up front and 33" tires, so for fun, I drove down a dirt road at about 5 - 7 mph and stomped on the brakes.
The two rear drums locked and left skid marks, the two disks did not.
I thought the disks were supposed to lock too.
(maybe this is why on a "panic" stop on pavement, the truck wants to turn whils stopping)?
 

Heus33

Bronco Guru
Joined
Jun 1, 2005
Messages
7,407
Do you have a prop. valve? If not, your drums will probably lock up first, mine do and I do not have a prop valve.
 

Bronco73

Bronco Guru
Joined
May 29, 2003
Messages
2,989
Loc.
Cape Coral, FL
That is normal. I would much rather have the bake brakes lock up before the front. Once the front lock up you no longer have control over the truck. You have to remember that hitting brakes while moving forward at different speeds will unload the rear axle differently causing the back brakes to lock up at different times. The road conditons will also affect this situation. The only way you will get complete and even control is with anti lock brakes.
 

Heus33

Bronco Guru
Joined
Jun 1, 2005
Messages
7,407
Bronco73 is right, slamming on the brakes transfers more weight to the front and makes the rear lighter so the rear wheels are more likely to lock up since less pressure is needed to get them to stop.
 

76 bronco J

Bronco Guru
Joined
Oct 20, 2005
Messages
1,480
Do you have a prop. valve? If not, your drums will probably lock up first, mine do and I do not have a prop valve.

>>>> I think you should have mention these "minor" details right off the bat in the thread where you ask about how good are your 76/77 brakes.... so you don't have the stock '76 combination valve(pressure differential,metering & porportioning valve) & rear brakes lock up first.... that's a problem ....... I'm not sure where y'all are getting your theories from ,but rear drums locking up before your discs that should be doing the majority of the work isn't right & shoudn't be considered "normal"...................
 

Action

Sr. Member
Joined
Oct 15, 2004
Messages
579
Back up.

Try backing up. When I installed power disc to the front I tried forward and could only get the rears to lock so Back I went and kept adjusting (adjustable PV) untill I got it where I wanted. Going forward on gravel road the rears always locked first. In reverse you can get the fronts to lock first. Just kinda tells ya how everthing is working.
Jack
 
OP
OP
reamer

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
Yep, my rig's brake system is competly stock. they have to handle the 33" tires and 3.5" lift, so I think I will look into the front end to see if there is a frozen caliper or two
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Actually you dont want either end to lock up but The rears are not supposed to lock up before the fronts. I wouldnt want that to happen although I have had it happen and when going down hill its not fun to have the backend pass you by because the rear brakes locked up.
You also have to keep in mind that drum brakes actually work better than discs due to the self energizing feature when the brakes are applied. Many times front discs need to heat up a little befroe they work the best.
Might have a little air in the fronts or like you said maybe a caliper is sticky. Sometimes dirt/rust gets between the calipers and brackets and can make it a little sticky.
 
OP
OP
reamer

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
Well I just took apart the fronts, pushed in the calipers, anit-siezed the housing mating surfaces, and still the rears lock up and the fronts don't.
Very scary, as you said, the rear wants to pass the front.
On the dirt road the rears lock, fronts don't ( when going forward) in reverse, the fronts locked and the rears did not.
I'll bleed the fronts again though.
 

76 bronco J

Bronco Guru
Joined
Oct 20, 2005
Messages
1,480
I'll bleed the fronts again though.

>>>> just double checking if you were aware that when bleeding the front brakes on a 76/77 with the stock combination valve the rod(on front) connected to the internal metering valve needs to be pulled outward & held outward with a special clip or homemade one like mine.......
 
OP
OP
reamer

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
76bronco, What do you mean? I don't know what you are mentioning.
Details???
reamer
 

DonsBolt

Bronco Guru
Joined
May 5, 2005
Messages
5,249
Loc.
Chestnut Hill, Mass
Well I just took apart the fronts, pushed in the calipers, anit-siezed the housing mating surfaces, and still the rears lock up and the fronts don't.
Very scary, as you said, the rear wants to pass the front.
On the dirt road the rears lock, fronts don't ( when going forward) in reverse, the fronts locked and the rears did not.
I'll bleed the fronts again though.

Don't use Anti sieze on any of the moving(sliding) parts of the brakes, it is ok on the bolt threads. It is actually a little abrasive. Use brake lube for any of the moving parts.
 

76 bronco J

Bronco Guru
Joined
Oct 20, 2005
Messages
1,480
76bronco, What do you mean? I don't know what you are mentioning.
Details???
reamer

>>>>> the stock proportioning valve on a 76/77 is really a combination valve even though most call it a just a proportioning valve..... it contains a pressure differential valve , a metering valve & a proportioning valve ...... on the front of this assembly is a pin sticking out ..... the pin is connected to the metering valve inside & will not allow fluid to reach the front caliper assemblies while bleeding unless you pull that pin outward & hold it there while you bleed the front brakes...... the make a special clip for this ,but anything rigged up to hold the pin out will work......... once thumbnail is clicked ,click it again to enlarge more so text can be read
 

Attachments

  • 100_0689.JPG
    100_0689.JPG
    65.6 KB · Views: 53
Last edited:
OP
OP
reamer

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
WHere is te vale and pin located?
Is it the brass blok on the frame?
 

76 bronco J

Bronco Guru
Joined
Oct 20, 2005
Messages
1,480
WHere is te vale and pin located?
Is it the brass blok on the frame?

>>>> yes it's on the frame with lines from the master cylinder .... see pic added to previous post from me ..... once thumbnail is opened , click it again bigger to read text
 
Last edited:

mudstud

Contributor
Bronco Bonehead
Joined
May 19, 2005
Messages
1,504
Which is best the front locking up or the rear locking up?

A simple little science test.

Take a small toy car (like a Hotwheels car) and tape the front wheels as though the brakes were only applied to the front. Place it on an incline where it will slide relatively easily let it go and note what happens.

Then take a small toy car (like a Hotwheels car) and tape the rear wheels as though the brakes were only applied to the rear. Place it on an incline where it will slide relatively easily let it go and note what happens.

You will see that if you have the brakes to lockup you would prefer the front to lockup and not the back. I agree with broncnas antilock is preferred but I have not seen anyone upgrade an Early Bronco to antilock brakes yet.
 

L&D's Broncos

Full Member
Joined
Nov 11, 2006
Messages
290
Rear Anti-lock

On all the 76 & 77's I've owned ( 8 ) when rebuilding the brakes to get trucks to pass inspection for NC, "factory" disc & drum setups always have slid the rears first. I have changed alot of master cylinders and prop valves and rebuilt, then bought reman calipers. One thing to consider is the 4 years I worked at Ford the 87' trucks and broncos were introduced and if anyone is familiar that year they introduced anti-lock brakes <on the rear axle only>
Most will be familiar with the wire harness going to the rear axle on 8.8's and 10.25's. Before 4 wheel antilock was available that is what they did, control the rear wheels for locking up so you could retain control of skidding vehicle. Weight transfer will always unload opposite end of travel whether it be forward or reverse. My 91' Bronco has the infamous "rear antilock brakes" and it lights up when you crank it to verify bulb still burns. From all my experiences, a 76-77 that slides rears in a panic stop is normal.
 
OP
OP
reamer

reamer

Contributor
Bronco Guru
Joined
Mar 20, 2008
Messages
1,249
The fronts do 60%+ of the stopping. (ever notice the fron end pitches down on corrent cars/trucks when panic stopping)?
I have not found this pin on the valve you speak of. (not in the drawing)
???
 
Top