Brake booster to rear wheels

[Onno le Roy]

I am about to do some work on my brakes and was wondering whether anyone ever tried to connect the rear brakes to the servo? Personally I think the problem with the original setup was that the front brakes were not too powerful but the rear brakes not powerful enough to compensate....

Because most of the weight is sitting on the rear axle, it would make more sense to connect the booster to the rear brakes? Any comments:?:

[Wallace]

Oh no it wouldn't ! At least with the front wheels locking first, the car will skid in a straight line. Lock the rears up first and it will spin ! Hence the servo on the front OR the limiter on the rear. IMHO !!

[Onno le Roy]

Have you tried it? I wonder whether the rear would lock up - it has a lot more weight than the front. The only reason why the front locks up is because of the lack of weight....

[Will]

The rear would DEFINITELY lock up under hard braking!
Because of weight transfer under hard braking, the front weighs a lot more than the rear does. This is why it was boosted originally.
The problem lies in that under slick conditions, the rate of deceleration is lower, and therefore, the front is underweighted for its boost level, and thus locks up.
You can solve the front lockup problem just by fitting stickier tires and keeping them on dry pavement.
Other options are a manually adjustsble proportioning valve that you can tailor to suit the available traction. This would allow you to use 4-wheel boosted brakes. Or fit ABS. The Bosch 5 is one of the better candidates for this, according to my research a while back..
-Will

[A1.6HPE]

Just about every car I have ever driven locks up the front wheels under harsh braking and the rears lock first. Perhaps with rear passengers or a load in the boot the rears would not lock up. My Thema has ABS and does that horrible jittery stuff when braking harshly, but then of course the braking effort is diminished by the jitters.
IMHO the vast majority of the braking effort is on the front wheels, except at moderate speed where the rear brakes provide some useful effort. So boosting the rear circuit would not help. It comes down to the fact that a booster simply reduces the pedal effort required, it does not improve the braking effect as such. The best way to improve braking effort is to increase the diameter/radius at which the pads clamp on the rotor (ie bigger discs and move the calipers outwards). Removing the booster from the front circuit only helps to prevent lockup by the fact that you need to push harder on the pedal to get the lock up force.

As Will says - avoid wet weather. A long term Montecarlisto said to me that he has "Lost his bottle" on wet roads and drives very sedately in the rain - makes up the difference when it is dry!

Leo

[Warren Horby]

You have ABS on your car?
Is it easy to do?

[Onno le Roy]

Hm....sounds interesting. Just was wondering whether anyone had ever tried it. But guess I should leave it alone as my brakes do work well at the moment - have Fiat uno Turbo discs at the front and OE at the back. No booster. Maybe not bad after all....

[Wallace]

Have a look in "Wallaces" photo albums - ABS is do-able but not easy.
This is going to turn into a rant but here's my two-penneth worth on brakes.

I think it is very important to keep the "ballance" of the brakes as is. If you start swapping calipers around, then fit pressure reducing valves and adjust accordingly. Lancia wouldn't have bothered fittng slightly different rear calipers than the x1/9 if they didn't have to. I think sonmeone scared themselves silly during whatever devlopment they did on the car and was determined to make sure the rears didn't lock first.

Been trying to figure out WHY the monte is bad in this respect (or at least why it has a bad reputation . .. .) I think (Will - feel free to argue !!) that the problem is that cars brake heavy on the front end because of the weight transfer to the front under braking. Basically, the car trys to trip over the contact area between the tyre and the road - and as it's centre of gravity is higher than this, there is a increase in force on the front wheels. you can guestimate this to a certain extent - 500 pounds rings a bell. (given say, 1g braking, the mass of the car and a "guessed" effective mass height).
Right, all fine and good as more weight or mass on the front means you can actually brake harder. Think of trying to drag a spare tyre across the ground - and then try with an elephant sitting on it - which one's more difficult ??!!
The problem is when you start to exceed the grip or between the road and the tyre. The coefficient of friction drops dramtically as the tyre now effectively "hops" (on a very small scale) and no longer has total contact with the road - producing the tyre "squeel". Less braking, less weight on the front, it will get worse very quickly. What I'm trying to say, is that once you've started a skid, the only way to stop it is to reduce the brake pressure to substantially less than just before the point before the skid starts - which is why cadence braking or ABS is considered to be a good idea. Obviously, if your a really good driver and know your car AND the road surface you can judge your braking just up to this point, i.e. just before the tyres start to let go. But I'm not - and I suspect when that dog, car, old lady comes out in front, very few of us are !!!

The siuation is a lot worse in the wet as you really need the tryes to be going round to shed the water off them.

Now this is as true for a front wheel front engined car as it is for the Monte. so why's the problem so specific to us ? I THINK it's becasue the percentage difference in weight transfer when braking is MORE on the Monte due to it's rear engine configeration. So when you start to get into the siuation described above, on the edge of skidding, the effect of the looss of the weight rtransfer is a lot more noticable dueto the lack of mass on the front in the first place !!

Does that make sense ??? !!!

Anyhow - ABS - I think is a good idea - I wasn't prepaired to drive my thing again until it was fitted. problem is, you cant just lift parts opf another car so you'll stuck having to make the pick-up rings. The rest is pretty easy - a bit of wiring and plumbing.

I've also fitted Wilwood 4 pot calipers - and a twin MC set-up as the standard one won't supply enough fluid. Again, picture is the photo section. The ratio of piston area front to back is the same as standard - 1.5 to 1 or there abouts. I see no reason to change it - although a bias bar is fitted to the pedal box, I'm not expecting to adjust it. And the ABS will take car of braking in the wet.

In the UK, you cant use a hydraulic parking/hand brake. Which is another problem (more or less finnished - photo's to follow !).

[Onno le Roy]

Clear as mud!! Thanks for your huge effort to explain this!!