Rear Brake Caliper Placment

I would like to get some peoples input on the placement of the rear calipers on the 40. Most modern cars have the caliper mounted in the leading edge (in front of the upright) where as the 40 has it in the opposite. What is the advantage of each and would you recommend changing it?

Not that critical. Having it in the front gets weight more toward the center of the car which helps the inertial moment, or something like that. It's probably a .01 percent improvement, not necessary except in formula one etc.

I put mine in front on the rears, and in the rear on the fronts, makes the brake lines shorter too.

Probaly more critical is what caliper you're using and what direction the E-brake cable comes off of it. Another related question is bleeder screw placement, on stock units it's fixed but AM units it can go either way.

Richard,

I have heard that there is some slight advantage to placing the caliper in front of the upright, although it wasn't explained exactly why.

With the postiion of the trailing arms of the Sabre design in combination with the DRB uprights I am using, the rear position worked best for me. The disadvantage is that I have to remove my calipers to bleed them since I have not had them machined to switch the locations of the bleeder and the surface that accepts the banjo fitting. This is something I plan to do in the future.

Had I not been using 88-92 Corvette calipers, which give me the very elegant built in parking brake mechanism (vs the PITA brake drum of the older parts), I may have been able to locate the brakes in front. Indeed the Sabre cars had them there as do DRBs both of which use the '85-'87 Vette brake parts, I believe. (You can use '84 but they are inferior to the '85 and up parts.)

Lynn

I think that siting the caliper in front of the upright gives a downward force acting on the caliper and therefore the hub and wheel under braking, that slightly offsets the forward weight transfer effect. It is only slight but it is significant, if so it will have an effect at the limit of braking allowing a slightly greater rearward brake balance. I 90% convinced myself that this was true by drawing free body diagrams /ubbthreads/images/graemlins/confused.gif. The actual forces can be worked out from the deceleration, weight, c of g, and brake dimensions etc. Any engineers here care to try that and see whether they agree or not.

Hi Lynn, I too have the 88 Vette rear calipers (mounted at the back of the rotors), but had a devil of a time getting a handbrake lever which could pull enough cable length to make them really lock up. In the end, I used a Porsche 944 lever with a pulley mounted on the bottom - the cable core comes around the pulley & then onto a bracket fixed to the seat belt mount point. This doubled the length of pull, but also doubled the effort required on the lever - measured at about 35lbs to get the car to stay put on a 17deg slope (RTA test requirement).

My cable setup at the back is standard DRB, which is very much like the 88 Vette - the cable sheath "floats" on a slider & the core goes to another slider. Both sliders are pulled together & each slider pulls on a short cable to the caliper levers. 1" pull on the main cable then results in 1/2" pull on each of the caliper levers.

I'm not that happy with the setup, so would appreciate any ideas you have.

Kind Regards,

Peter D.

Peter,

I used a fairly standard Lokar parking brake handle with a matching Lokar stainless covered cable system. I must say I have not fine tuned the parking brake system, but I did adjust it enough to hold in the garage and it seemed to hold quite well. I certainly didn't see any issues with to little throw on the cables. I'll see if I can find some photos of the system. I don't recall taking any of the parking brake bits specifically, so they may not be the best. BTW, there are also adjusters on the calipers themselves for the parking brake part of the system. I have not touched these, but there are allen screws that adjust the engagement point: its a kind of pre-load adjustment for the levers that activate the system so the tighter this is the sooner lever movement starts causing the pucks to grab. Are your's like this?

Regards,
Lynn

I would be very interested in knowing if anyone has gone to a line lock type setup. This would be a valve in the rear brake lines that would be closed after the brakes were applied resulting in holding pressure on the main calipers.

I am having a hard time fitting a ebrake on the rears with 1 1/4" thick rotors and also it is becoming a buget thing.

Howard,

The line lock is fairly straight forward to implement. The issue arrises from the fact that most safety regulations state that the parking/emergency brake has to have a separate actuating system. Holding pressure on existing brake lines does not meet this requirement. The idea being that if your primary braking system was to fail, the emergency system should continue to function.

Regards,
Lynn

Lynn, thanks for the info - I am assembling a file on the whole h'brake issue & I'll add the Lokar stuff. Big re-design coming up next year !

Yep, I am all too familiar with that little pre-load screw adjuster in the calipers - at my age, its a bugger to get down to even see it ! Then I needed an Allen key about 9" long to get to it - in the end, we replaced them with 1/2" longer versions to make access a bit easier.

I think that my problem came from inheriting '88 brakes, rather that the original DRB spec for '87 (drum brake type). The whole lever/cable setup was for the earlier ones & guys who have that are quite happy. With the '88's, if your lever/cable setup gets 1/2" pull on each side with a 1/2" pull on the main cable, you should be fine.

Kind Regards,

Peter D.

The location of the caliper creates an internal force within the caliper via the uppright to wheel-axle. You might think of it as a ko-bar with the lever arm placed in the centreline of the wheel, and the "foot" acting between the caliper and axle.
This is more of importance at the front of the car as more weight is transfered to the front wheels during hard braking. If the caliper is mounted aft of the disc, this will help to cansle some of the spindle load out during braking. However, in some cases depending on spindle geometry, this "canceling" forces may get so great that the load reverses in the bearings, which is not very good. In such case we should move the caliper to say 2:a clock. This is no real problem, I just mentioned it to clerify what I am saying. Notice that this effect does ONLY concerne forces within the uppright, spindle-tap and caliper. It has nothing to do with A-arms and coilover loads.

Regards
Goran Malmberg

Goran,

Forever the consumate engineer. Thank you!

Regards,
Lynn

So what do you think Goram? Would you move the caliper on a GTD rear from the bottom to the front or back. This would require a sort of 90 degree L shape adapter. Or just leave it on the bottom with a less complex adapter when fitting larger brakes and a different caliper.

I am a little worried about the loading on the 90 degree piece. Either I would need to make it VERY strong or leave the caliper mounted on the bottom with a more conventional adapter.

Howard,
You may send me an image of the uppright with caliper mounting.
[email protected]
I dont think this is very much of a problem at the rear so you may leave it as is.
Kind regards
Goran Malmberg

Thanks Goram, My car is in the shop right now, I'll send you some pictures when I get it home, Maybe in a couple of weeks.