Outer Limits 4x4 Board

just wondering if a Vitara brake booster will fit in to a sierra

Not as far as I am aware- the vitara booster is larger in diameter and I don't think it will clear the steering shaft. From memory there is another clearance problem somewhere too.

What was the reasoning behind the vit booster? A bigger booster only lightens pedal feel, it doesn't improve the performance of the brakes, and Sierra brakes are pretty light anyway.

I'm not a huge fan of boosted brakes at all really in a 4wd- unboosted gives a pedal with much better feel, and the pedal doesn't go weird once you have stalled the motor.

Steve

unboosted brakes in a 4x4 is a horrible thing. can't believe someone said they would prefer it. i used a vit v6 booster and master.....and damn my brakes are good. the vit 1.6 ones are a better fit than the larger v6 version.

Why do you say that Joe? Are you basing your experience on factory 1.0/LJ brakes?

99% of race cars (even offroad race cars) run unboosted brakes, stopping far more weight from much higher speed than we are ever doing. If pedal ratio, master cylinder size etc is all correct, there's no problem with unboosted brakes at all, but they feel sooo much better than boosted brakes. This is not the same as driving a car with the booster disconnected.

It is possible to get excellent pedal feel with boosted brakes, my DD has really nice pedal feel, but it's not a "normal" braking setup. (Brembo brakes) funny though, they have very high pedal effort compared to a normal passenger car - they almost feel unboosted. Might be something in that.

It's important to not confuse brake performance with boosting. "Boosting" the brakes does not improve their performance, it only lowers pedal effort at the expense of feel.

Steve.

Gwagensteve wrote:Why do you say that Joe? Are you basing your experience on factory 1.0/LJ brakes?

nope!

Gwagensteve wrote:99% of race cars

like comparing the brakes of a jet fighter to those of a jumbo....

Gwagensteve wrote: but they feel sooo much better than boosted brakes.

that might be because you are alot closer to the pedal and can get a better angle to lay into them than most of us.

itufgq wrote:just wondering if a Vitara brake booster will fit in to a sierra

Yes it will fit.. sort of...
The studs line up and the pedal fits in the shaft but the center diameter of the hole on the body is around 1mm under-size for the booster so some die grinding was needed to get it to seat nicely on the firewall. It will clear the steering however from memory some trimming was needed on the battery tray and some other thing may have been moved a little.

I will stay out of the boosted vs unboosted bit

Disagreeing with Joeblow always brings out the best tech!

My bad. Race cars don't have calipers, master cylinders or brake pedals.

Steve.

Sorry to go a little off topic here, why don't race cars have brake boosters? Is it mainly because of cam timing that reduces manifold vacuum available, which would cause a problem especially when pumping the brakes repeatedly like they often seem to have to do? Just wondering.

Brake boosters add weight
They add complexity (when it's not required -it's something else to go wrong, a hose to pop off etc.)
Many race cars use twin master cylinders, one each for front and back and a balance bar to adjust brake bias (much harder with a booster maybe impossible?)
Boosters dilute brake feel. Race drivers threshold brake, so they are trying to hold the car on the edge of lockup - boosters make this point harder to pick and much harder to modulate.

and there may well be a vacuum (or boost) related issue too - lots of race drivers left foot brake, and variations in vacuum/boost between one hit of the brakes of another would be a nightmare.

I think to understand why race cars don't have boosted brakes it's also important to understand why road cars generally do. Race car's aren't being built to be driven by the 85th percentile. (i.e a 45kg 4'6" girl, or an 80 year old with arthritic knees. Brakes in road cars are boosted to the point where they can be threshold braked with the pressure of two fingers on the brake pedal. This is neither a good or bad thing, in a road car, but it's important to recognise that this has nothing to do with brake performance.

If you're not building a car for the 85th percentile, there's no need to set the braking system to allow for them either, so there's no need for a booster.

Steve.

Do the engine conversion and everything else will fit

i am doing it to make the better for my girlfriend who's car it is bc she is only 5foot tall and 50kg dripping wet.

thanks for the info joe its for hayley's cattapans sierra. got to drop up and see u soon bout power steering as the engine is all out now so would be a good time to put it all in before it gets painted. cheers

john

itufgq wrote:5foot tall and 50kg dripping wet.



j

Pics?

GTI boosters fit VERY well.

itufgq wrote:i am doing it to make the better for my girlfriend who's car it is bc she is only 5foot tall and 50kg dripping wet.

thanks for the info joe its for hayley's cattapans sierra. got to drop up and see u soon bout power steering as the engine is all out now so would be a good time to put it all in before it gets painted. cheers

john

your gonna get a shlapp across the head for this......