Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part MAY's Ride of the Month Challenge!

1 - 20 of 39 Posts

·
Registered
Joined
·
1,164 Posts
Discussion Starter · #1 ·
Since I'm fairly new to the classic car scene, I have nothing to compare it to, but should you be able to lock up your brakes when you want/need. I'm not expecting the same feel as modern brakes, I get that.



I currently have disks front and drums rear on my 66. I have a dual bowl MC. My old brakes were scary so I added a vacuum booster ( i know what some people feel bout this) and I do like that I don't need as much pedal pressure now. The car stops but there is no way I could lock them up. I recently changed the pads. Got Hawk high performance pads form NPD per their recommendations. Just put them on a few days ago and bedded them per recommendations. Haven't had time to take the car out yet as I need another alignment and will wait until that's done.


Curious what people think.
 

·
Registered
Joined
·
978 Posts
It depends on several factors.

If you had drums on all four and normal street tires then yes, you should absolutely be able to lock them all up.
If you have front disc and rear drum with normal street tires then you should be able to definitely lock up the rears. Fronts might lock up depending one how hard and fast you stomp the brake pedal. If the pavement has some loose sand/gravel on it then the front discs can definitely lock up.

Once you get into special pad/shoe materials then that will change things a bit.
With soft compound “high performance” tires the improved grip with the pavement will reduce locking up.
 

·
Registered
Joined
·
10,260 Posts
You don’t WANT them locked up in use..... you should be able to lock them up though. Something is not right.

ex-Global West GM
1991-1995
 

·
Registered
Joined
·
1,164 Posts
Discussion Starter · #5 ·
Yes. If you stand on 'em they should lock.
It depends on several factors.

If you had drums on all four and normal street tires then yes, you should absolutely be able to lock them all up.
If you have front disc and rear drum with normal street tires then you should be able to definitely lock up the rears. Fronts might lock up depending one how hard and fast you stomp the brake pedal. If the pavement has some loose sand/gravel on it then the front discs can definitely lock up.

Once you get into special pad/shoe materials then that will change things a bit.
With soft compound “high performance” tires the improved grip with the pavement will reduce locking up.

Thanks for the quick responses. I think the car stops very well. Just curious. Now don't flame me on this but every time I watch some car show in TV and they are testing their brakes, I always see them slamming on the brakes and locking up all 4 wheels and I thought, Hmm I should be able to do this.


I'm hoping I never have that "Holy Crap" moment when I need to brake that hard!
 

·
Registered
1970 Sportroof Mustang Grabber Value Package
Joined
·
245 Posts
Since I'm fairly new to the classic car scene, I have nothing to compare it to, but should you be able to lock up your brakes when you want/need. I'm not expecting the same feel as modern brakes, I get that.



I currently have disks front and drums rear on my 66. I have a dual bowl MC. My old brakes were scary so I added a vacuum booster ( i know what some people feel bout this) and I do like that I don't need as much pedal pressure now. The car stops but there is no way I could lock them up. I recently changed the pads. Got Hawk high performance pads form NPD per their recommendations. Just put them on a few days ago and bedded them per recommendations. Haven't had time to take the car out yet as I need another alignment and will wait until that's done.


Curious what people think.
I been wondering the same thing for my 70', what would be a decent stopping distance from say 55 mph? Mine do not lock up either, I have 245 40 ZR 18 in front and 275 35 ZR 20 in the rear.
 

·
Premium Member
Joined
·
13,955 Posts
You don’t WANT them locked up in use..... you should be able to lock them up though. Something is not right.

ex-Global West GM
1991-1995
^^^^^^^^ +1

Just as a test, with a stock K-H disc / drum setup, it needs to be somewhat easy to stomp on the brakes and get all 4 wheels to lock up. Having decent brake pads helps tremendously. I don't know the Hawk's that well, but ebc redstuff or Porterfield R-4s are choices that people here have liked. But even with old stock pads , a well adjusted and maintained stock system needs to exert enough pressure to lock up the wheels at highway speeds.

In actual practice, if you know your brakes well enough you can apply the maximum pressure to the brake system just short of locking up the wheel(s). With some familiarity of your car's brakes, you can stop very quickly, without locking up any wheel, an thus maintain maximum control.

Z
 

·
Registered
Joined
·
801 Posts
Tires always achieve best stopping power in the moment before they lock up. That's why antilock brakes became a 'thing'. Once they start to skid, there's not as much rubber in contact with the ground. However, on vehicles without antilock brakes, you should absolutely be able to lock the tires from any speed. For obvious reasons, that's not something you would want to do, just something you should have the ability to do, proving that you can reach 'maximum braking force'.

It's your job as a driver to modulate the braking power to something appropriate for the situation. If your car can't deliver enough stopping power to skid (and this includes having front disc brakes!) then there's something wrong.
 

·
Registered
Joined
·
217 Posts
On my car with 4 wheel discs brakes, the proportioning valve should be adjusted so that the front and rears lock at the same time. If one locks up before the other, you could have severely adverse handling/steering characteristics that are unwanted during panic situations. That may be the intent behind the TV snippets you referenced cause there is only one way (that i know of) to determine when they lock up respective to each other.

But i'm just a knucklehead and this makes sense to me. I'm sure others will chime in if i'm off base here.
 

·
Registered
Joined
·
10,260 Posts
I been wondering the same thing for my 70', what would be a decent stopping distance from say 55 mph? Mine do not lock up either, I have 245 40 ZR 18 in front and 275 35 ZR 20 in the rear.
148' from 60 mph for a 428 car on polyglas tires.
You should be able to beat that number by several feet on today's radial tires.

ex-Global West GM
1991-1995
 
  • Like
Reactions: JSHarvey

·
Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
Joined
·
21,484 Posts
I try to take any recently acquired or modified vehicle out to an accommodating empty road or large parking lot and do some "panic braking". That way I have a feel for the capability of the brakes, at least ideal conditions.

My old '68 had four wheel drums. One day I was doing about 40-45 in the right lane of a five lane and a lady in a newish Benz came sailing up the intersecting road on my right and technically stopped for her stop sign but literally halfway into my lane. Talking on the phone. With no traffic around me and not going very fast I could have easily dodged around her, but what fun would that be? I jogged left a little and locked up all four brakes. Smoking and squealing tires all over plus under such conditions the car would drift to the right, even better. I may have flat spotted a tire or too but it was totally worth it to see her face and see her juggle the phone right out of her hands while she frantically tried to get the car into reverse and backed out of the road. She did, but long after I had stopped a few feet from her door and was just sitting there looking at her. Practice those panic stops, you never know how or where it might pay off!
 

·
Registered
Joined
·
553 Posts
Just be aware, as GypsyR mentioned, it doesn't take much skidding to create a flat spot on tires. You'll notice it right away after they start rolling again.
 

·
Registered
Joined
·
1,778 Posts
On my car with 4 wheel discs brakes, the proportioning valve should be adjusted so that the front and rears lock at the same time. If one locks up before the other, you could have severely adverse handling/steering characteristics that are unwanted during panic situations.



My understanding was the rear should lock only AFTER the fronts so the rear of the car would never start with the fishtailing- (as the braking will allow the weight to shift forward and unload the rear (which then lets the rears lock up- )

So maybe I am confused-
 

·
Registered
1970 Sportroof Mustang Grabber Value Package
Joined
·
245 Posts
148' from 60 mph for a 428 car on polyglas tires.
You should be able to beat that number by several feet on today's radial tires.

ex-Global West GM
1991-1995
Thanks that gives me something to gauge mine by
 

·
Registered
Joined
·
217 Posts
My understanding was the rear should lock only AFTER the fronts so the rear of the car would never start with the fishtailing- (as the braking will allow the weight to shift forward and unload the rear (which then lets the rears lock up- ) So maybe I am confused-
I go with the philosophy that in an ideal situation, they should lock at the same time. Next best would be the rears locking just after the fronts. Def don't want the rears locking before the fronts. I feel like i learned this from my dad many moons ago, so i just assumed it's correct. I'd be interested to hear any thoughts on this matter though... always like to learn new things!
 

·
Registered
Joined
·
978 Posts
If you want to maintain any control of the car, you don’t the fronts to lock up at all. When the fronts lockup you have no steering control and will continue to plow straight ahead.
 

·
Registered
Joined
·
1,861 Posts
If you want to maintain any control of the car, you don’t the fronts to lock up at all. When the fronts lockup you have no steering control and will continue to plow straight ahead.
True, but if the rears locked up first you lose ALL directional stability and the likeliness of the rear end moving to the front via a pirouette is almost guaranteed. For safety's sake, fronts should lock before rears (kinda like how car manufacturers build in understeer).
 

·
Registered
Joined
·
37,786 Posts
On most dual-circuit braking systems the metering valve, part of the combination valve that includes the proportioning valve and the differential pressure valve, will delay the application of the front brakes so that the rears will apply first, helping to maintain a straight braking path. The delay is well under a second....IIRC something like 1 or 2 tenths.

Should you be able to lock up your brakes? You betcha, unless you're going a gazillion miles per hour... I know I can lock up all four at 60 mph... and probably faster although I haven't tried THAT...

Most common causes of not being able to lock up the brakes when they are properly sized to the application and correct diameter master cylinder bore/wheel cylinder bores are used?

1. Poor quality friction materials, aka "cheap Chinese pads and shoes". Recommend EBC or Porterfield.
2. Glazed friction materials, aka "damaged" from improper "bedding" or abuse, such as riding the brake pedal or trying to keep from running off the Mt. Washington Toll Road.
3. Glazed rotors and/or drums, aka "same as above" but also dragging brakes causing overheating... improperly adjusted or actuated parking brake, use of a residual valve in the front circuit when not needed (disc brake application).
4. Contamination of lining material, aka leaky wheel cylinder, axle seals, etc.
5. Improperly adjusted pedal pushrod or booster pushrod causing insufficient application or dragging.
6. Flexing of master cylinder on mounting surface causing additional pedal travel, aka the mounting surface ain't stiff enough for your foot (or feet).
7. What else am I missing? Rug bunched up under pedal?
 

·
Registered
Joined
·
1,164 Posts
Discussion Starter · #20 ·
Thanks Woodchuck. Good info.

I installed new brake pads from NPD, Hawk street pads. Guy at NPD said they were good. I bedded them in per the instructions. I was curious about whether or not to scuff up the rotors. Car stops pretty good but still can't lock them up.

All the lines look good. No leaks.

Very early after I bought the car, the MC was shot and I had to replace it. Honestly, I don't know when size I got (didn't know there were different size). Got one form CJ's recommended for my year and model. It's going in for an alignment so I'll have my mechanic look at it.

As an aside, yesterday I noticed that the car still does not want to stop when backing out of my driveway. I have to really satnd on the pedel to get it to slow down. I'm not going fast but I am going down a slight incline. Any thoughts why stopping in reverse would be soooo bad?
 
1 - 20 of 39 Posts
Top