chevy c10 rear brake blocks too early ('78 C10 Short)

[ChrisD]

Hi,
my truck has new brake lines, rear break cylinders and a 11 brake booster from performanceonline.
The brakes has good values and also the mesured values front-rear are in a normal difference.
But if i brake in real, the rear wheels stops quick. So it‘s not good if i have to brake in a curve.
The back of the truck seems to be to light.

Is there normally a weigth at rear axle?
My mechanic told me, that i can buy fixed break pressure regulators. Can you tell me, which one has the right regulation value?

Regards
Chris

[VileZambonie]

  This is why grammar matters. Brake blocks too early? What does that mean? What values are you referring to? What do you mean if you brake in real?

[ChrisD]

Hi,
thank for your inquire and I‘m sorry, that i don‘t use the right words. English isn‘t my normal language.
I‘ll try it with other words
My mechanic has a brake test bench where he can check if the brakes per axle works similar and there you can also see, that the front brakes has more power (350Newton) than the rear brakes (220Newton)
If i drive the truck on the road and press the brake pedal with growing pressure, than the rear wheels bocks earlier than the front wheels. This must be vice versa, because the rear wheels holds the car on track, so in an emergency brake the front wheels has to block first.

The proportional valve came with the power brake and is ordered for disc brakes on the rear.

Hope now I have explained it right

Regards
Chris

Edit: I wrote „ The proportional valve came with the power brake and is ordered for disc brakes on the rear.“ thats wrong. Its been ordered for rear DRUM brakes.
Sorry for that mistake...

[Mr Diesel]

I gather your rear brakes are locking up faster than the fronts, and that the mechanic's measurement shows there is more pressure being applied to the front brakes via the hydraulic lines.

I believe this situation in general is fairly normal, especially for a 1978 C10 truck that is very light in the rear and has rear drum brakes. While I don't know what the pressure difference should be, I've always been told these trucks were designed to apply more brake pressure to the front disc brakes and that most of your braking power should be from the front disc brakes. All my trucks are 3/4 and 1 ton these days and it's been a long time since I owned and drove a 1/2 ton truck, but it is pretty normal for the rear brakes to lock up fairly easy in an empty bed situation. The one thing we have no way of knowing is just how much brake pedal pressure you are applying to cause the rear brakes to lock up. It is possible you have something wrong, but pretty hard to us to diagnose over the internet. A lot depends on the condition of your front and rear brake pads, and the adjustment of the rear pads inside the drum. Remember this is a 42 year old truck and not a modern truck with anti-lock brakes.

You mentioned something to the effect of having rear disc brakes. If in fact you have modified your old truck to have disc brakes on the rear instead of drum brakes then everything I said above may not apply to you. I believe your stock proportioning valve should be applying more brake line pressure to the front, but if you have installed rear disc brakes then you might need a different proportioning valve setup.

If you still have drum brakes on the rear you can adjust them some to reduce or increase the braking effectiveness. They have a "self adjustment" mechanism that in theory activates when you reverse and slam on the brakes, but I have found this mechanism design to not work very well and often does not properly adjust your rear brakes. I usually adjust mine by removing the rubber/plastic adjustment hole cover and poking a flat screwdriver through to adjust the brake while spinning the wheel with my hand.

[TexasRed]

How do the front brake pads look?

[ChrisD]

Hi Mr Diesel,
sorry, i wrote it wrong, i have disc brakes on the rear and all i bought was for drum brakes.
Driving cars without modern brake systems, anti lock or whatever is no problem for me.
My other car is a 1990 BMW 320i with no extras, i think it‘s one of the most spartan equipped bmw in germany. Most time of my live i drove german cars from the end of '70th - begin '80th.

Your tip, that it could be the adjustment of the rear brakes, i‘ll tell my mechanic.
But i think your right with it, that the truck is too light at rear.

Hi TexasRed,
my front brake pads and discs aren‘t new, but in a good condition.
The brake test bench didn‘t show any problem with the front brake.

Thanks you for your answers!

Regards
Chris

[TexasRed]

If you have rear disc brakes and a proportioning valve for rear drums, that may be your issue.

I believe that the proportioning valve for rear drums may send pressure to the rears first because you have to overcome the springs in the drum unit.