I tried posting this on LS1 in the LT1 area, but it was suggested that nobody there would know, so now I'm trying here.

Does anyone know what's different about them and if the LS1 maaster cylinder and brake booster would fit an LT1 car and if it has a larger capacity? I'm guessing it might be different/better since the LS1 calipers (which I have on my LT1) have 2 pistons instead of the 1 piston LT1 calipers.

I roadrace my 95 W2W at up to 150 mph (I hope), so spending a little more on brakes isn't a problem.

thanks for any info

BobC

 

The LT1 MC is 1" I don't know what the LS1 MC is. Although the LS1 calipers have more pistons, the LT1 caliper's piston is BIG (71mm or something IIRC). It's possible the combined area of the LS1 pistons is very close to the same as the LT1 piston.

The above info for LT1's is in my Hayne's manual. I would assume anybody with the LS1 edition could look it up for you.

 

I'm no fluid dynamics major, but once the brake system is solid, there is very little, if any, movement of fluid, right?

The only real fluid movement is when the pads wear and the pistons extrude from the caliper. Then fluid moves in to take up the volume. But it doesn't flow, does it?

 

Yeah that's my understanding as well. Obviously there wuold be some fluid motion from convection (heating), especially if it was boiling (but you have bigger problems by then.

I once looked at the surface area of the LS1 pistons (2x44mm), C5/ZO6 pistons (2x40mm), and the LT1 piston (70+mm?) and believe the LT1 had the largest. If anything I'd keep the LT1 MC since it's most likely the largest of them looking at that logic. For that matter, the Brembo 4-piston calipers would also take less fluid during pad wear... they run 38mm and 40 mm I believe (the opposed piston design makes fluid displacement 1/2 as nessesary for each piston, so they are directly comparable to our floating-caliper 2-piston designs using only 1 side of the caliper in piston area).

You shouldn't have to change your MC and may actually find it benificial as the LS1 guys seem to complain about brake hop under hard decelerations. I've never been clear on weither this is due to the LS1's different F/R bias or whether the LS1 rear brakes are that much more effective... couldn't tell you for sure, but their's no point in pushing your luck. I'd stay (and will) with my LT1 MC now that I'm going to C5 calipers, and even if get addicted and run Porsche/Brembo calipers in the future.

 

Bob,

The only thing I can see you gain from a different master cylinder is possibly a change in the amount of pedal pressure or travel you have to exert to depress the caliper piston a given distance. I have no problems with my existing LT1 master cylinder while using stock rear brakes and C5 fronts.

Steve,

I always understood the LS1 rear brake locking up issue was because of their ABS tuning combined with bad brake biasing. ?

 

I read once that all other things being equal, a larger master cylinder piston means lower pressure at the caliper. Also that lower pressure will give better "feel". Maybe someone can confirm or correct me on this.

 

I swapped out my LT1 master cylinder when I converted to LS1 brakes a few years ago. Since then I've changed to the C5 calipers and rotors. The LS1 master is larger than the LT1. I cant complain about the braking...I beat on the car pretty hard and put over a hundred miles on it at the roadcourse at Moroso a couple of weeks ago.

 

Mitch, I'm no physicist, either, but the fluid moves every time you press or release the pedal.

Maybe its just the pads or air in the system. I'm outbraking many cars (I'm very hard on brakes), so its not that they aren't working well, just that the pedal doesn't feel solid till the 2nd pump.

I think I'll re-bleed it (I change fluid completely each time) again each day and give it another weekend or 2 to see if it sorts itself out. And if it doesn't get any better, then I'll try the LS1 master cyl.

thanks

BobC

 

It's not the master cylinder that's at fault it's the calipers. This is a common complaint about the LS1 calipers with or without an LS1 MC. I had the same problems with my LS1 car. I think most of it was from extreme taper wear of the pads that this caliper seems to have a problem with. But some of it is from the two piston design of which this caliper seems to be a particularly poor example of.

When I switched to brembo four pots which have only slightly less effective caliper piston area than the LS1s, my pedal became so much more firm and consistant. The reduced travel wasn't a result of changing the MC since the stock LS1 MC is used with the Brembo kit. Nor was it the result of changing caliper piston area since the Brembos are almost the same as the LS1s. It's the caliper design.

If you could find a MC larger than either the LT1 or LS1 you could reduce the pedal travel with the LS1 calipers, but at the price of increased pedal effort. It doesn't take much of a change in MC diameter to make a big change in effort.

Do the class rules you race under dictate using a stock f-body caliper?

 

other calipers allowed as follows:

6.5.6.1.3 Braking system may be replaced with a system listed in the SCCA American Sedan or the
MCSCC American Grand Sport Specifications for the same Make and Model.
6.5.6.1.4 Braking system may be replaced with any system that uses the same brake pad as the Wildwood
Dynalite caliper, or Superlite, without any modifications to the caliper or pad.

Wildwood pad surface area is smaller, so I think I'm better off as is...

 

Bob,

I don't think your problem is pad taper. A 2nd pump of the brakes wouldn't do anything to help the feel if that was your problem. Are you sure when you bleed it that you also bleed the ABS module? If you get air in there and bleed your brakes you won't get that air. The way you brake I bet you activate your ABS pretty much every corner. You either have to use a Tech tool or use the method stated by someone on here before. I'm sure someone else knows the details better than me. I've never had that problem, but maybe I'm just lucky. I bet Mitch knows the procedure by heart after chasing his brake problems a lot last year.

 

On LT1's the abs can be bled w/o a scan tool according to my helm manual. The procedure is as follows...
1) start car and let idle for 10 seconds or more (Do not touch brake)
2) shut down
3) bleed 4 oz from rear bleed screw on abs modulator
4) bleed 4 oz from front bleed screw on abs modulator
5) bleed brakes at wheels as normal

I think you're ok if you touch the brake pedal while bleeding just do not while starting or during run as this cycles the abs. I bled mine like that w/o touching the pedal and pressure bleeding (motive brake bleeder kit) at 12 psi. Afterwards the pedal was much better.

 

hmmmm .... I'm trying to picture it in my head .... let me illustrate how I've always thought it worked.

As I understand a closed hydraulic system, if you pressurize it, the fluid seeks the point of least resistance.

In a brake system, which is closed, mashing the pedal just pressurizes the system. The fluid seeks the point of least resistance, which is at the caliper pistons.

The pistons move out, but only a slight amount till they come in contact with the brake pad which is sandwiched between the piston and rotor. So it stops.

The fluid movement equals the amount of piston movement, which is just thousandths or even 10 thousandths of an inch. The fluid doesn't circulate rather stays stagnant.

Thoughts .... anyone?

As far as bleeding goes, I STILL have an intermittent long pedal, even after installing the Prospeed kit. But, I have it narrowed down to a particular section of track.

A hard brake from 110 to 40, a series of low speed low RPM "S's" exiting into a long sweeper to the left onto a short straight. Short shift to 4th and through a kink to the left exiting onto a straight. All of this without using the brakes. Coming to the next right hander, needing to brake from 100 to 60, the pedal will stroke long. However, if I bring my left foot over and give the pedal a quick, slight stroke, my pedal is back at 100% .... every time!

That HAS to be air or knock-back.

And I have changed or rebuilt everything in the brake system except for the rubber pad on the brake pedal itself.

I've used every method and suggestion of bleeding, except for a Tech II. I'm gonna try that this weekend if I can get my hands on one. I've got a couple of friends who own shops in town. Hopefully, I can get some cooperation ...

 

Sure would. The first pump puts the pads fully in contact with the rotor, so the second one is nice, firm and high.

I went through the whole bleeding process serveral times with the stock brakes in an effort to to get a firm pedal with no luck. The only thing that worked was replacing the old tapered pads with a fresh untapered set of the same compound....without further bleeding BTW. The pedal was firm for a while until the pads wore a bit then the long pedal was back. I repeated this several times and the results were the same each time. Tapered pad equaled long, soft pedal; fresh untapered pad equaled firm, high pedal with no other changes

When I installed my Brembos, I bled the calipers of course but not the ABS. It was the end of my soft pedal problems. So the only thing I changed was the caliper...and rotor of course...and it solved my problem. Now the pedal is firm no matter how worn the pads are.


Bob,
They didn't give you much leeway did they. Pad area is not the only measure of a brake systems performance but all else equal a smaller pad will wear quicker. I don't have any experience with Wilwood so I can't comment from personal experience.

I'm not trying to push or bash any particular brake system other than to relate my experience with what I have personaly owned, driven and pulled my hair out trying to make work. I came to the conclusion from hours of bleeding, rebuilding calipers, and changing pads that it was the LS1 caliper that was at fault. YMMV.

 

Not quite how it works.

The fluid volume changes are equal not piston travel. It will take a certain volume of fluid movement to move the caliper pistons a certain linear distance. Piston area X linear travel of the piston = volume change. Remember since the MC is much smaller in area than the caliper pistons, it has to travel much further than the caliper pistons to take up a given volume change at the caliper. The LS1 caliper has a total of four front caliper pistons of about 1.75" diameter. If all four caliper pistons move, for arguments sake, 0.1". Thats a change of volume of 0.962 in^3. If the MC is 1" diameter it will have to move 1.22" to take up the slack. That's more than 12X further. In addition the pedal ratio is greater than 1, meaning that the pedal has to travel even further than the MC. I don't know what it is but let's say it's 3:1. That means that the pedal will travel 36X as far as the caliper pots. If there is any knockback or slop in the caliper or lines, you can see that it translates into a large increase in pedal travel.

If it's air why doesn't do it everywhere instead of just in one particular series of corners? It's got to be knockback or something else.