Need more braking force

[Edahall]

The braking is kind of weak on my 1990 3/4 ton 4x4 Suburban I believe. It's got vacuum assisted brakes. I can stand on the brakes with both feet and it still doesn't have enough clamping force to skid. When hauling a load, it becomes much worse.

1. Is this normal?
2. Is there a way to increase clamping force such as installing a different master cylinder. If the master cylinder had a smaller bore, it would give more clamping force.
3. Could it be that I've got the wrong master cylinder on the vehicle?

Thanks.......

[Mattman2010]

I see that you have a cummins in the truck. Diesels don't put out enough vacumm and I'm sure the vacumm pump does not put out enough vacumm either. You would upgrade to a hydroboost system. Mine would make my crew cab slide on pavement.
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[Jonboy]

Do you have a vacuum pump? Swtiching to a hydroboost setup may help if not. I thought most GM trucks originally equipped with a diesel was so equipped.

[gchemist]

Wow, that's a lot of power and weight to stop. Do you have a 14 bolt rear end? It's time to upgrade it to disc brakes.

Hydroboost is probably the best upgrade.

[Edahall]

Originally Posted by Jonboy

Do you have a vacuum pump? Swtiching to a hydroboost setup may help if not. I thought most GM trucks originally equipped with a diesel was so equipped.

Yes, the Cummins has a vacuum pump and there is plenty of vacuum there. The engine in fact came out of a truck that had vacuum assisted brakes.

[Mattman2010]

I would really suggest hydroboost. Most 1 ton trucks came with it. It can be expensive to first put on the truck, but after you do it I am sure it will make a big difference.
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[Edahall]

Originally Posted by gchemist

Wow, that's a lot of power and weight to stop. Do you have a 14 bolt rear end? It's time to upgrade it to disc brakes.

Hydroboost is probably the best upgrade.

Yes it has a 14 bolt rear end.

My 1982 1/2 ton Suburban has the hydroboost setup and it has a lot more clamping force even with the much smaller brakes. I would have thought a 3/4 braking system would be even more effective than that.

[Edahall]

Originally Posted by Mattman2010

I would really suggest hydroboost. Most 1 ton trucks came with it. It can be expensive to first put on the truck, but after you do it I am sure it will make a big difference.
Posted via Mobile Device

Shouldn't vacuum assist brakes be able to put as much clamping force as a hydroboost setup? Both setups are just force multipliers. I'm really wondering if maybe I might have an incorrect master cylinder on the truck.

[Mattman2010]

Originally Posted by Edahall

Yes it has a 14 bolt rear end.

My 1982 1/2 ton Suburban has the hydroboost setup and it has a lot more clamping force even with the much smaller brakes. I would have thought a 3/4 braking system would be even more effective than that.

What are you running for a front axle? From what I have seen half ton and 3/4 ton 4x4 trucks all have the same front brakes. The rears are different but most of your stopping power is from the front because of the weight shift when you apply the brakes.

Originally Posted by Edahall

Shouldn't vacuum assist brakes be able to put as much clamping force as a hydroboost setup? Both setups are just force multipliers. I'm really wondering if maybe I might have an incorrect master cylinder on the truck.

Yes they are both force multipliers, but I think buy using your power steering pump makes it more effective because liquid can not be compressed where as air can be. And I think the pressure of the power steering is more consistent than the vacumm pump. There is a big difference between my k10 that has vacumm and my crews cab (my rear brakes don't work on the crew cab right now) and the crew cab stops way better and they have the same size front brakes.
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[Edahall]

I thought 3/4 ton trucks have 12.5" rotors and 1/2 ton trucks have 11.86" rotors.

[Mattman2010]

Ok you are right they do use a bigger rotor and I guess the calipers are different as well. I just know basically all the outer parts except for the brakes is the same expect for the hubs being 6 or 8 lug. My 12 bolt 6 lug and d44 8 lug all used the same ujoints, shafts, spindels, and knuckles, so I assumed the brakes where the same my bad. I still think hydroboost would really help tho. All diesel equipped Chevys came with thr hydroboost because the vacuum pump wouldn't handle the brake system that well. Are you sure you are getting good vacumm? Maybe your brake booster is going bad?
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[Edahall]

Originally Posted by Mattman2010

Are you sure you are trying good vacumm? Maybe your brake booster is going bad?
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Yes, I'm getting very good vacuum.

Bad brake booster? Well that's a possibility. Is there a way to test it and if so, how do I test it?

[INSIDIOUS '86]

Try ss braided lines. I got some for my 1/2 ton abd i have hardly any vacuume and they just about turned my brakes to normal
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[Mattman2010]

I really don't know the answer to that question. I've never had a bad one so I'm not sure how to test if it is bad or not
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[Keith Seymore]

Here are the brake system release charts for an '87 V20 Suburban:



This would show you what your truck would have come with originally, in terms of master cylinder and wheel cylinder sizes, proportioning valves, etc, by part number.

Here are some other charts, in case you want to do some "shopping" and see if there is another system you might like better:

http://67-72chevytrucks.com/vboard/s...d.php?t=510519

[Edahall]

Originally Posted by Mattman2010

I really don't know the answer to that question. I've never had a bad one so I'm not sure how to test if it is bad or not
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Based on the following test procedure for testing the brake booster, the booster on my Suburban passed with flying colors. Anyways, I think we can eliminate that as being deficient.

http://www.ehow.com/how-does_4829365...-boosters.html

[Edahall]

Originally Posted by Keith Seymore

Here are the brake system release charts for an '87 V20 Suburban:


This would show you what your truck would have come with originally, in terms of master cylinder and wheel cylinder sizes, proportioning valves, etc, by part number.

Here are some other charts, in case you want to do some "shopping" and see if there is another system you might like better:

http://67-72chevytrucks.com/vboard/s...d.php?t=510519

Keith,
Thanks a lot. This is exactly what I needed. As I suspected, there are master cylinders with different bores for my truck. My truck happens to be the heavy duty 8600 GVWR. It looks like if I install a master cylinder off a lighter duty 6600 GVWR (which has a smaller bore), it'll increase the pedal ratio and increase clamping force.