Need More Braking Force

[Edahall]

1990 Suburban 3/4 ton, 4x4, 8600 GVWR:  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.  In fact, I don't even think I could even get it to skid with wet pavement.  The issue is even worse if I have a load.  There is plenty of vacuum going to the brake booster.  I also tested the brake booster using the following test procedure http://www.ehow.com/how-does_4829365_testing-procedure-brake-boosters.html and it passed with flying colors.  So I believe my brakes are working as designed.  However, the vehicle is carrying more weight than from factory due to the weight of the Cummins engine, 6 speed manual, Gear Vendors and Iron case NP205 trans case.  My guess is that those items added 800-1000 lbs of weight.

What can I do to increase the braking force on this vehicle?

Here's one idea I have.  Install a master cylinder off a 1/2 ton Chevy.  The master cylinder on Suburban has a bore of 31.8mm vs 28.6mm for a 1/2 ton Chevy.  This would give the brakes more force multiplication at the expense of a little more pedal travel.  What do you all think?  Has anyone tried this before I go and try it myself?

How about softer brake pads?  It's got semi-metallics right now.  Would soft organic brake pads help?

[Edahall]

Here's a brake system release charts for a '87 V20 Suburban.  It looks like they did use a master cylinder with a smaller bore on the 6600 GVWR Suburbans (28.6mm vs 31.8mm).  However, the 6600 GVWR also had a smaller bore caliper piston diameter (74.68mm vs. 80mm) to compensate.  With my plan in the previous post, I would be running a smaller bore master cylinder with a bigger bore caliper piston to increase force multiplication.

[slammed79]

Why not switch to hydroboost? My 91 dually had it and that thing stopped pretty well, even with a gooseneck on the back of it.

[slammed79]

Also, ceramic pads tend to stop better than semi metalics, but be prepared to change rotors more often.

[Edahall]

Why not switch to hydroboost? My 91 dually had it and that thing stopped pretty well, even with a gooseneck on the back of it.

That's an option that I hope to stay away from if I can.  I had a truck with that system and it burned to the ground due to the hydroboost spraying fluid on the exhaust manifolds.

Also, ceramic pads tend to stop better than semi metalics, but be prepared to change rotors more often.

How about organic pads?  I would think the softer the material, the better it would grab.  I don't mind changing the brake pads often since they're so easy to do on these vehicles.

[zieg85]

My $.02 so here goes...  I have the 8600GVW brakes on my 1985 C20.   I am impressed how good they stop with a load in the bed or not.  I can lock up mine.  I know there is a weight difference between the Suburban and a pickup but 1 ton brakes should be enough to properly stop your rig.  I would look to your power booster as a possible issue. 

[Edahall]

My $.02 so here goes...  I have the 8600GVW brakes on my 1985 C20.   I am impressed how good they stop with a load in the bed or not.  I can lock up mine.  I know there is a weight difference between the Suburban and a pickup but 1 ton brakes should be enough to properly stop your rig.  I would look to your power booster as a possible issue. 

Hmmm,  Mine definitely does not have that kind of stopping power.

I tested my power booster using the following test procedure and it still had vacuum after shutting off the engine for a minute so I think it's OK.
http://www.ehow.com/how-does_4829365_testing-procedure-brake-boosters.html

I'm also wondering if the vacuum pump on my Cummins engine is putting out enough vacuum to operate the power booster.  This engine originally came out of a Dodge truck that used vacuum operated brakes.  The vacuum pump does put out strong vacuum but it's not particularly high flow.  Also, its flow rate is much lower at idle than if the engine is revved up.  This is opposite of a gas engine.  I'll have to try operating the brakes with the engine revved up and see if it works better.

[zieg85]

The power booster may pass the test for not leaking but may not be giving you the stopping response you are looking for.  I had a similar issue with a FURD Bronco I had.  I did everything to get it to stop better.  I took the power booster out of the picture and fabricated up a rod to take up the space after I gutted the booster.  Yes it was like stepping on a brick and did take some leg pressure, more than a manual brakes feel, but it stopped way better.  I eventually replaced the booster when I saved the money to do it.  This was a long time ago when I had to get creative because the finances wasn't there and I didn't have the internet to look up stuff...  Keep us posted...

[Edahall]

Pedal pressure seems normal when stopping gently.  However, there is a point where applying more pressure to the pedal doesn't seem to make the brakes grab any harder.  Basically, it seems normal unless you have to do a panic stop.  Was your Bronco like this?

[zieg85]

Pedal pressure seems normal when stopping gently.  However, there is a point where applying more pressure to the pedal doesn't seem to make the brakes grab any harder.  Basically, it seems normal unless you have to do a panic stop.  Was your Bronco like this?

Yes it was exactly like that.  Almost like the power booster had a "catch" in it.. Hard to explain but after I took the booster out of the equation I could lock up all 4 tires on demand... it took 2 feet but I determined the booster was the culprit in my situation.  IMO a brake system in proper working condition should be able to lock the tires up "stock or slightly bigger in size" or something isn't right... unless you have ABS or rear ABS or are way past the GVWR for the braking system on your truck. 

How old is the rear rubber brake hose.  Those can do some funny things when they go bad as the springs will release the brakes but not allow the full pressure especially in a panic stop. 

[Edahall]

Yes it was exactly like that.  Almost like the power booster had a "catch" in it.. Hard to explain but after I took the booster out of the equation I could lock up all 4 tires on demand... it took 2 feet but I determined the booster was the culprit in my situation.  IMO a brake system in proper working condition should be able to lock the tires up "stock or slightly bigger in size" or something isn't right... unless you have ABS or rear ABS or are way past the GVWR for the braking system on your truck. 

How old is the rear rubber brake hose.  Those can do some funny things when they go bad as the springs will release the brakes but not allow the full pressure especially in a panic stop. 

I'm pretty sure all the brake hoses are original.  I've experienced bad brake hoses before and they act similar to a leaky check valve.  This is a little different than that though.  Also, bad brake hoses tend to go out one at a time which will cause pulling during hard braking but this stops very straight.  It's definitely like the "catch" you described.  Anyways, I think we're on to something now. 

[zieg85]

[

I'm pretty sure all the brake hoses are original.  I've experienced bad brake hoses before and they act similar to a leaky check valve.  This is a little different than that though.  Also, bad brake hoses tend to go out one at a time which will cause pulling during hard braking but this stops very straight.  It's definitely like the "catch" you described.  Anyways, I think we're on to something now.

I don't think you are close to me however I have a 8600 GVW power booster you are welcome to try.  It came out of a 1985 C20 Suburban I parted out a couple of years ago. 

[jaredts]

Have you ever put a vacuum gage on the vacuum pump to see what kind of vacuum it produces?  If you run out of volume during a quick stop it would explain the problem.  Do you have a vacuum reservoir hooked inline?  That would be an easy thing to try if its just a volume issue.  Get some kind of rigid container thats maybe 1/2 gallon in size--add two nipples and run your vacuum line in one side and then out the other to your booster.

[ehjorten]

Something is seriously wrong with your setup!  Your brakes shouldn't be that bad period!  It isn't something that changing to different pads or the like is going to fix.  The factory brakes should be more than adequate to lock them up.