New rear brake setup

[OneQuikSix]

I just wanted to post my experience with the larger s10 wheel cylinders. I finally got everything back together this evening and went for a drive. With the current adjustment of the rear shoes, I can only hold 2-3psi boost before the driver's side starts to break loose (slightly before the passenger side). I think I have some adjustment to do since I repeated the test with the emergency brake engaged with the same results. I will say that with my setup and the current drum/shoe adjustment, the car still noses over a bit when braking at highway speeds. The pedal has the same feel as before the swap and seems to stop equally well. There is absolutely no danger of the back brakes locking up before the front in rain, sleet, or snow! Maybe that will change as I adjust them. I'll update this thread accordingly. Here's my setup:

Vacuum master cylinder - I don't know what model
LS1 front brakes w/dual piston calipers
Factory brass proportioning valve
Factory rear drums
Larger wheel cylinders off s10 w/manual brakes 7/8" bore
4 long brake shoes of the softest compound I could find

 

[malibudave1978]

Chis,

What rear shoes did you end up going with? Organics, semi metallics? Who makes them?

 

[OneQuikSix]

They are the Wearever silvers from Advance Auto. I forget what the composition is. I bought the cheapest ones thinking they would be the softest. I'm probably going to adjust the rears (expand) to see if i can get another couple of pounds. I think if I can get 5psi, I'll be in decent shape.

 

[malibudave1978]

Chris,

I looked up the Wearever silvers and the specs say they are "Ceramic". I would go with an organic compound, which should be softer. The Wagner ThermoQuiet are "Organic" EE rated. I run these on my elco with manual brakes and 7/8" wheel cylinders and rear drum lock up before the fronts do. I am running the stock long/short shoe setup. Bad thing is that these shoes cost twice as much as the Wearevers.

You might want to look for some cheaper organics than the thermoquiet shoes. The Autozone Duralast brand say "Low-Metallic Organic" around $19
Oreilly's has the "Semi-metallic" shoes for $22, which are most likely like the Duralasts. Napa has the Performer series which look to be "Organics" for around $20. Rockauto.com has shoes from $6 to $30 per pair, but not a lot of info is given on the specs of any of these shoes.

Are you running vacuum, manual, or PM brakes?
What bore size are you running on the master cylinder? A smaller bore master will create more line pressure, but if boosted will make the brakes "touchy". Stock manual brake master cylinder bore is 7/8", stock vacuum boosted master cylinder for a g-body is 24mm, stock PM boosted is 1.0" (I think).

I always double check my master cylinder bore sizes, if I can, before I buy just to make sure I am getting the correct bore sizes. I have found auto parts stores selling the power version for the manual versions.

I would also double check you wheel cylinder bore size just to make sure that they are 7/8" diameter. Autoparts stores have been known to sell you vacuum boosted wheel cylinders instead of the s10 manual brake wheel cylinders.

 

[OneQuikSix]

Thanks for the info David. I may have to shop around for some different shoes if I can't get a few more pounds of boost by adjusting the ones I have.

The car was already converted to vacuum by the previous owner. I went ahead and upgraded the front disc brakes to the larger LS1/f-body dual piston caliper brakes.

I was wondering about the master cylinder bore myself. I'm still a bit unclear on how the larger surface area of the dual piston calipers would affect the pedal feel and braking ability over the stock single piston calipers. Right now, the car stops very well, though it does "nose" over a bit. I'm really happy with the stopping ability of the system...just wish I could increase my launch boost a bit. Do you think if I went with a larger master cylinder this could be accomplished? I'm worried about the back brakes locking up during heavy braking (like the end of a quarter mile pass). Then again, maybe a different size master cylinder is needed to offset the increased volume of the dual piston calipers??? Any thoughts are welcome. Thanks.

 

[malibudave1978]

The piston sizes for the LS1 calipers are 1.77" each which is a 4.92 sqin piston area. The stock size g-body metric caliper has a 2.38" piston which is a 4.45" sqin piston area. The LS1 calipers have roughly a 10% larger piston area.

What you are gaining with a LS1 brake swap is rotor diameter (extra braking leverage), thicker rotor (better heat dissipation), twin piston caliper (force spread out over the pad), and, I think a larger pad (more friction material).

With all else being equal, you will loose caliper/rear drum clamping force by going to a larger master cylinder. More caliper/rear drum clamping force will come from a smaller bore master cylinder. But the smaller the bore, the more sensitive your brakes will be. I will require little effort to stop the car and the brakes will be touchy and will have no brake feel. I am guessing that you have a 1.0” bore master cylinder on the car now.

If you are not getting the holding power you want.

Adjust the shoes out.

Check your actual bore size of your master cylinder.

Go with an organic rear shoe instead of ceramic (ceramic is based on what shows up on the advance auto website for these shoes).

Check your actual bore size of your rear wheel cylinders.

Go with a stickier rear tire.

 

[OneQuikSix]

The piston sizes for the LS1 calipers are 1.77" each which is a 4.92 sqin piston area. The stock size g-body metric caliper has a 2.38" piston which is a 4.45" sqin piston area. The LS1 calipers have roughly a 10% larger piston area.

What you are gaining with a LS1 brake swap is rotor diameter (extra braking leverage), thicker rotor (better heat dissipation), twin piston caliper (force spread out over the pad), and, I think a larger pad (more friction material).

With all else being equal, you will loose caliper/rear drum clamping force by going to a larger master cylinder. More caliper/rear drum clamping force will come from a smaller bore master cylinder. But the smaller the bore, the more sensitive your brakes will be. I will require little effort to stop the car and the brakes will be touchy and will have no brake feel. I am guessing that you have a 1.0” bore master cylinder on the car now.

If you are not getting the holding power you want.

Adjust the shoes out.

Check your actual bore size of your master cylinder.

Go with an organic rear shoe instead of ceramic (ceramic is based on what shows up on the advance auto website for these shoes).

Check your actual bore size of your rear wheel cylinders.

Go with a stickier rear tire.

That is some really useful information! What exactly do you mean when you say "will have no brake feel" when using a smaller master cylinder? I think I understand the rest.

I forgot to mention I haven't tried to build boost using my drag radials since doing the rear overhaul. I installed a line-loc while I had everything apart. In summary, I'm able to hold 2-3 pounds of boost after switching to larger wheel cylinders and four long shoes (though some adjustment may help here) on my street tires when cold. I'm hoping to ultimately be able to launch with 5-8 pounds at the track with my drag radials after a burnout.

 

[malibudave1978]

"you will have no brake feel" = touchy = hard to modulate, easy to lockup. Thats the downside to a smaller bore master cylinder.

With a larger bore, you get better brake feel and easier to modulate the brakes and can feel when the brakes are going to lockup, but you get less clamping force. A larger master cylinder is not usually an issue with power assisted brakes, you can apply more leg strength to get the appropriate pressure needed.

If you are sure you have soft shoes, then the best way to hold the rear is with stickier tires. Sticky tires do more to reduce tire spin than the softest brake shoes ever will.

 

[tbone87]

With vacuum breaks with stock rear breaks with factory aluminum drums I could foot break 14-15 lbs of boost on radials with a 49. Ya blow the tires off but fun!!

 

[OneQuikSix]

That all makes sense now. I think I'll try the adjustment first. If that doesn't seem to help, I might be shopping for a new master. Any ideas on what models to look up at the parts store?

Condition of the drums being equal, I wonder if the aluminums hold more boost/clamping force than the steel units? I know the aluminum drums should dissipate heat faster, but I have a line loc and heat should not be an issue for me. 14psi launches sound fun though!

 

[OneQuikSix]

With vacuum breaks with stock rear breaks with factory aluminum drums I could foot break 14-15 lbs of boost on radials with a 49. Ya blow the tires off but fun!!

Any idea what size master cylinder you had with your setup?

 

[malibudave1978]

Adjust the brakes.
Check the size of the rear wheel cylinders
Change out the pads if you think the "ceramics" are not working.
Add stickier rear tires

I would not change out the master unless its over 1.0" bore.

 

[OneQuikSix]

Well, the sticky tires made a world of difference. I went from getting 60' times of 1.95 with the old setup to consistent 1.75's with the larger wheel cylinders. I think the biggest difference was installing the line loc and not heating up the back drums before staging. I'm sure I can knock off another tenth just by tweaking the mostly stock suspension. Unfortunately, I discovered a major gremlin that needs some major attention. I'm going to keep the vacuum setup for now and see how far I can take it.