View Full Version : LS1 fronts with drum rear, questions???

08-27-2004, 09:29 AM
I remember on the old forum that someone had asked what MC you would use if you wanted to use the LS1 front discs with stock drums in the rear. IIRC no one had answered it so... I'm bring it up again.

I have a set of LS1 discs/calipers. My Camaro currently has the stock disc/drum with PB and a 1 1/8" MC. Will this work or does the MC need to be changed? :dunno:

Thanks guys.

08-27-2004, 04:05 PM
i would think that it wouldnt matter cause the proportioning valve is what makes the difference

08-30-2004, 06:14 AM
My concern is if there is enough fluid volume with the dual pistons (larger then the C4 style calipers) that I would run out of MC piston stroke before getting enough fluid to the calipers.

I'm sure someone has had to try this before. Thanks.

Rick Dorion
08-30-2004, 06:24 AM
The LS1 and C5 caliper are the same except for minor stiffening rib differences. For both the C4 and C5 applications(power), I was recommended to use a 1 1/8" MC.

Q ship
08-30-2004, 10:07 AM
Rick, I am curious about the recommendation you got, as I have been led to believe that a smaller master than 1 1/8" would be optimal. I am putting C5 fronts on mine, and have switched to a 15/16" MC. (I am keeping my old 1 1/8 MC, though!) I have not been able to get the car off jackstands though, so I cannot say which is correct. I do know the caliper piston area on the C5 is much less than the old 2 15/16" bore iron caliper(3.88 sq in. vs. 6.77, off the top of my head). The 1LE Camaros that used the C4 style calipers used a 1" MC. Does anyone know what a C5 vette MC bore is, I can't find that to save my life.

Mike, for a while I'm going to be using drums on the back of mine(11x2"), and I am, like you, wondering about the MC I've chosen. There will be less volume, and I don't know how the drums will react. The permanent solution (for me) will be LS1 rear discs. I plan to do a lot of low speed testing once I'm up and running!

Rick Dorion
08-30-2004, 10:53 AM
My recommendation was in conjunction with a Hydroboost system so perhaps any higher pedal effort isn't a key factor. But, I would think any volume considerations are not a problem area? My current setup is C4/13" front and drum rear with a 15/16" in manual mode. No problems once I settled on pads that would give good bite. If we're all talking power applications, I myself wouldn't think a 15/16" is the MC to use.

Q ship
08-30-2004, 11:01 AM
Placeholder here, I have to go get my calculator!
Something I found in the old forum....
__________________________________________________ _________
Here is a copy of a post on Team Camaro by dunult:

"I was reading an old Camaro Performers Magazine the other day (Winter 2002) and discovered an article about braking. I found it interesting and wanted to share what it said. I'm currently fiddling with brakes on my 68 Camaro. This article at least put the problem into better prespective. As with all rules of thumb, these are to get you close. The optimal spec for your car may fall outside these specs. Here's what the article said...

1) The angle between the push-rod and pedal should never be less than 90* or a soft pedal under hard braking will result. This will be more of a problem on small bore master cylinders that stroke a fair amount.

2) The Caliper to Master Cylinder piston surface area ratio should be between 12% and 19%. (Not sure if this is true for both Manual and Boosted brakes). Take the surface area of the MS piston divided by the suface are of one front caliper (d^2 / 4 * 3.14159). If using four piston calipers, take the sum of one side for caliper area. In other words sum the surface area of two pistons. The opposing pistons will apply similar force once the pads contact the rotor and cancel out. My 1" bore MS and 2.84" single piston caliper result in a ratio of 12.4% It was interesting to note that a 1.125" MS resulted in a caliper ratio of 15.7% which is right in the ball-park, but I believe experienced users will say this is a firm pedal.

3) The pedal ratio should be between 4:1 and 6:1. To calculate, take the distance between pedal fulcrum and pushrod attachment point. Divide that lenght by the distance from fulcrum to peddle centerline. The article further sited a recommendation of 4:1 for power brakes and 5:1 for manual. My 68 is 2"/12.5" for a 6:1 pedal ratio in the manual brake setting. The boosted position is another 1 and 1/2" lower resulting in a 3.5:1 ratio (low by comprison to 4:1).

(I measured a 69 pedal assy out of the car, found a 6.25 to 1 ratio for manual, 3.8 to 1 for power brakes. David)

4) The suface areas of the front caliper piston (for 4 w disc) should be at least 25% larger than the rear piston surface area. They go so far as to recommend 40% larger and site a 93-97 camaro as being 55% larger. What they don't say is if there is a relationship between this ratio and the rotor size. In other words, if the rotor size is not 1:1, how does this rule of thumb change?

While I was on a kick with brake math, I calculated the pressure provided by a vacuum booster. Using a 9" booster at 17"Hg, I came up with 531 lbs of force applied by the booster. Now I am looking for details on how the booster works. Surely this pressure is reserved until the brakes are applied. 531 lbs is enough pressure to create 417 lbs of line pressure with a 1" MS. That's more than enough to overcome the pressure of the spring in the MS. Still trying to noodle that one.

Hopefully this is useful information. I now feel a bit better about my 1" bore MS in a manual application. The resevoir size is my only concern at this point. But the quest continues.

I haven't verified any of the above info or tried to use those numbers on a system.
It does seem he made an error in calculating his boosted brake line pressure since his pushrod pressure is higher than his line pressure and that should't be.
A 1" bore master cyl sq inch area is .7854" I get 676 psi.
67 RS Camaro, 69 Camaro vint racer, 65 Lola T-70 Can-Am vint racer.
__________________________________________________ _________

Does the booster, or lack thereof, affect the hydraulic aspects of the MC/caliper relationship? In other words does the booster "compensate" for a theoretically "wrong" MC/caliper ratio?

I think I may be glad I have both.

Q ship
08-30-2004, 01:05 PM
AAARRRGGGHHHH. I just typed a long winded post and it dumped me. So, multiple smaller posts, sorry.
In searching for the correct MC for my Caprice/C5 brake swap, I was told that a 15/16" MC would be optimal, but I wasn't sure about boosted/unboosted applications.

For all the following calculations, I used area=3.14 x radius/sq. Rounded pi for conveniance.

Q ship
08-30-2004, 01:11 PM
Ok. 1.125 master area is .9935sq". .9375(15/16") master area is .6899sq". And a 1.25 master area is 1.227sq".
For calipers, a 2 15/16" caliper area is 6.77sq", and the C5 is 3.895sq ".

for the percentage noted above(MC area to caliper area ratio), the calc is MCarea/caliper area= ratio.

A stock Caprice--.9935/6.77=14.7%. Soft (grandpa) pedal.

Q ship
08-30-2004, 01:17 PM
The 1.25" bore master comes from the 9c1 Caprices, which are widely reported to have a firmer pedal(better feel).
9c1--1.227/6.77=18.1%. Hmmm, ok.

1.125 MC with the C5's--.9935/3.895=25.5%. Which seems pretty high. I don't know if anyone has any more info, the referance above noted 12-19%. I ran some other stock apps through this, and I can't remember any above 20%.

Q ship
08-30-2004, 01:24 PM
And finally, the 15/16 MC/C5 combo. .6899/3.895=17.7%

So this is what led me to believe that the 15/16 MC is optimal(or close, at least)for the C5's. Note that all these figures are for a vacuum boosted system. As far as Hydroboost systems, I believe late model Cobras are using these, with 1" bore MC's and 38mm calipers.

Sorry about the post whoring, but I hate getting dumped.

So this is my thought process on this subject-any thoughts/corrections?

08-31-2004, 01:02 PM
Well, thanks for all the replies. Lots of good into but it does leave me with this answer.

The way I have read these replies, I am being told I could use a 1 1/8", 1" or 15/16" MC. Not quite the clear cut answer I was looking for. Sounds like a crap shoot. :hammer:

I guess I can really complicate things and say that I am going to use the LS1 (C5) fronts with stock drums and stock booster for now, then change to disc rears (C4 style) with a Hydroboost setup down the road. Sounds like a lot of different MC's will be used.

I guess this will be one of those answers that make you go "Hummmm".

Thanks guys.