Brakes and Steering

[aji]

Well now

It is time to start thinking about steering and brakes for my effort.

Being the donor car is audi, the brake setup is quite nice with 4 piston calipers and power disk brakes this maybe the setup.

On the steering rack or box, I have to decide power or manual.. I'm thinking Mustang II Rack & Pinion or something like this. Power steering is highly likely.

any thoughts or experiences would be helpful..

best

 

[Ian Anderson]

Non power steering is (IMHO) better and if done properly will give better feel on the road. Again if designed correctly it does not even need to be heavy at parking speeds. (Also less to break down)

Brakes the biggest and best you can afford that will fit your application and inside your wheels. Look at Willwood they are more reasonable than most and have a bit of pedigree

My 2c

Ian

 

[aji]

Hey thanks Ian

I'm thinking power brakes and steering off the same fluid boost pump system with Hyd fluid. Unclear what else with be Hydro-boost most likely variable suspension damping.

Pneumatic brakes and suspension damping is not out of the question... with manual steering..

Carbon fiber rotors would be good!...

All of my parts will be from used salvaged cars. This is the rule of the car build effort. Only purchase new when nothing else will work. Then a buy / make decision will have to be made.

best!

 

[Ian Anderson]

Don't even bother with boosted brakes / not even vacuum assisted (OK if you are designing a 3 ton tow vehicle this may be different)

Get the correct pedal ratio and cylinder sizes and no "assistance " needed

So simple works for me (in you case less to scavange)

In a GT40 style car you are only stopping about 1100kg - compare that to an Audi A6 which comes in at about 1800kg so then the boosing is required to get more stopping power for the same foot effort.

Cheers
ian

 

[aji]

Hey Ian

It appears our driving style is a bit different. Pedal force being the same and the design be different, well,,, feather touch with antilock servo maybe different then press harder to stop faster. Best wishes...

The reason I want "assisted" it so I may vary the input from the driver to make the systems operate as the driver decides it should. Change the bias and this sort of thing.

Variable camber on the steering geometry maybe also assisted... LOL
this GT 40 style car is for Research and Development to make it go faster around a circuit...

I agree on the power/weight ratio for force calculations F=MA and that stuff...
so simple works for me also...
scavange is an interesting notion,, yes...

 

[Russ Noble]

Hey Ian

to make it go faster around a circuit...

KISS and KILL

Those are the two overiding principles when choosing components and designing a car to go fast around a circuit. After that, provided handling and brakes are optimum, more horsepower is the way to go. QED!

Cheers

 

[aji]

Hey thanks Russ

optimum is highly subjective.. This is what make racing fun!

Power assist and high tech... remember traction control in F1,,, nada... anymore!

dynamic adaptive assist is hard to make optimum... this is why people go simple and adapt to the system. I want the system to adapt to me...
The GT40 was pure R&D... still is...

 

[ChrisL]

AJI,
I might be jumping the gun here, but are you using the Mustang steering rack because it’s correct or because it’s available? The critical issue with a steering rack is its contribution to the overall geometry. Geometry is everything for a well handling car, and especially if it’s a track car. If the steering rack and its placement is wrong, you will end up with bump steer and incorrect ackerman etc etc. Can be pretty scary on the road let alone a race track.

 

[Ian Anderson]

Find yourself and old Citroen DS20 / DS 21

Power everything, brakes, steeering, lights that turned with wheels, and the suspension that pumps itself up and down.

But I would not fancy pushing one hard into a corner!

Ian

 

[aji]

Thanks Chris

The rack has yet to be chosen and which everyone it is will most likely have to be modified.

This is what I have found to be the typical rack & pinion 2.5 turns lock to lock.

from a GT 40 builder
The steering rack that I used was from the Ford Cortina and all that is necessary to get it to fit is to cut about ½ inch off each threaded end to reduce the overall length by 1" , you can use the steering rack from the Ford Escort but that needs extension pieces made and fitted as it is too short as standard. Many other racks could be used and the only criteria is that they are the correct length, can be made to fit the track rod ends which have to be suitable to fit the Ford Granada uprights. You have to position the steering rack so that the steering column can be easily coupled and to avoid bump steer. Some might not know what "bump steer" is, well its when the wheels are steered by the suspension as it moves up and down, this is obviously an undesirable feature. The reason for bump steer is basic geometry and I won't go into that as I'm sure you won't want to start remembering all that from your school days. As neither the Cortina or Escort racks are exactly correct for the geometry (and I don't know of any rack that is exactly right) you have to position the rack so that you don't get any significant movement of the steering over the range of suspension movement that it will be working over. This should only be around 3" of vertical movement and not the total movement that the pivots will allow. Offer the steering rack up and fit the track rod end to the uprights and then move the suspension through the movement range that is required and check for bump steer movement, when you have this correct note the steering rack position and plan the mountings to suit. The mounting that I added for my steering rack were supported off the lower chassis members but again in hindsight I should have mounted them from the upper chassis members as that would have given me more space for the pedal assembly to be fitted later.

balance is good Ian, not way to the right and way to the left,,, all or none is not the way am going ...LOL your cracking me up with the citroen... I could also get with the low riders out here! They have some trick stuff also..

In theory the Brakes will be antilock servo with bias control front to rear. Power assist and adjustable pedal force would be good.

It will be fun asking you folks about the electrical system design...

 

[Ian Anderson]

On Brakes

Have a look at Saab Front brake systems

they run a handbake on the front axle.

Take their front brakes and move them to the rear and you will get some pretty good rear brakes

If you don't do something along these lines you will not get a parking brake with normal wreckers calipers and probably have to buy aftermarket

Ian

 

[aji]

Good Idea Ian

The saab brakes maybe a bit small for this, however any car with 4 wheel disc brakes that has a parking brake will be just fine. I have also looked at light truck brakes and rotors. The servo antilock sysytem is also being reviewed.

I'm now thinking of just making a racket assy for the brake pedal with on/off function so I do not need a cable parking brake system at all..

Thanks for your thoughts.

best

Best

 

[John W]

Since you mentioned Audi, why not look at the offerings made by MTM, etc.

I have an RS4 that has Sportec 380mm front rotors and calipers from a mkII Porsche GT3. This is a standard upgrade to the cars, using standard porsche rotors bolted to special alloy hubs. The newer kits use 6 pot calipers with 360mm rotors. The very latest kits use B7 RS4 rotors & calipers which use 365mm rotors and 8 pot calipers...

The rear upgrades use vented rear rotors (I forget the size) with a normal 4 pot caliper, and a seperate caliper used for the handbrake.

This kit is offered for S4 & RS4 cars, so if you want monster brakes, have a look.
two web sites (both in the uk) to try are
http://www.amdtechnik.com/productnews.read.cfm?articleid=5
and
http://www.qstuning.com/list_for_car.asp?car=rs4

Not cheap, but believe me they do the job !!
(I can outbrake an Elise/Exige into corners on track using road tyres )

 

[aji]

Thanks John

Yep looking at the Porsche yes, the only german sports car starts with a P. I may well take the rotors and hubs and other stuff for mod to make the rear end of my setup. I already have the transaxle out. The halfshafts look great also. 944 S turbo, The GT3 is a bit hard to find in the bone yardepper:

The front also looks good,, then I can run VW, Audi, Porsche wheels... LOL

I have yet to decide on the calipers, there are many to choose from could be MB or who know what I can find.

best

 

[CliffBeer]

The brembo brake calipers off porsche 911's from '89 to '94 would be great - four piston front and rear, and, they're cheap and plentiful. These calipers also come in a variety of piston diameters depending on the particular year/model (turbo/non-turbo, front/rear, etc.). Unless you plan on installing a variable proportioning valve you'll need to ensure you have the proper front-to-rear balance and this is done through careful selection and testing of brake piston diameters front-to-rear. I believe the caliper mounting spacing is 3.5 inches on all these brembos - you'll need an adapter bracket for most any caliper you choose. Good luck!

 

[aji]

Thanks Cliff

The brembo's look great

I plan to install a needle valve for front rear bias with adjustable bypass to the rear for braking. I have also looked at the antilook servos and boost pumps which are somewhat heavy with wires/sensor to each wheel,,, who knows could be. I need to check the controller out for modulation adjustment for applied force via the pedal. I want this adjustable. The servos appear to work on line pressure and wheel speed for modulation to start.

Making the caliper bracket will be somewhat easy and required no issue. plasma cutter, mill and tig welder good to go. Then the steel.. or aluminum could be...

I have yet to checkout the Porsche steering rack... could be good!

best

 

[CliffBeer]

Re: 911 steering rack, I can highly reco this rack. About the right dimension and very precise and light weight. All the 911 racks from 1966 through 1988 are the same so just go for one which is either rebuilt or low mileage.

Sounds like you've got the balance issue fore/aft well under control. Regarding ABS, the pump, accumulator, sensors, etc. can add a substantial amount of weight. Personally, I'd hate to have to try to adapt a whole ABS system - while they're somewhat simple in theory, the practical application can be very difficult. We're talking your brakes here so they've got to work right, and reliably! Hope the project goes well.

 

[Bill Musarra]

Cliff,
Would you have any dimensions of the Porsche units, like body lenght or turns rack to rack. Have thought about using one in my aplication. Running the corvett suspension should only require the proper lenght contol rods to hookup.

Bill

 

[aji]

Hey hey Cliff
The newer racks appear to be good!
Hydraulically assisted force sensitive rack-and-pinion.
Based on what I could find variable ratio as force is applied

on the older racks
Steering type: Rack and pinion, with 3.5 turns lock-to-lock I would guess for most 911's without the "force sensitive electronics"

On the Brakes and antilock. I will have to weigh the parts and see what is what. Running the lines and wire should not be much of an issue for the sensors. The servo/controller will be mounted inside the car most likely someplace in the engine bay. I would like to have some control over modulation start and applied pressure. This could be fun! The Front/Rear bias control will likely be a adjustable spring loaded proportation valve with needle valve fine adjustment

The Porsche Rack looks very compact and light weight. I will be looking at the 944 Turbo S most likely could be 924 also.

Thanks

Best

 

[Chris Duncan]

and power disk brakes this maybe the setup.

I'm thinking Mustang II Rack & Pinion or something like this. Power steering is highly likely.

any thoughts or experiences would be helpful..

best

you definitely don't want a mustang II, it's somewhere around 4 turns lock to lock. I'm using a 1st generation 240Z, it's 2.7 turns

a 2,000 lbs car has no need for power brakes or steering. It just adds weight, complexity and crowding, this is supposed to be a race car. Adjust pedal feel with hydraulic cylinder sizes and a bias bar. Adjust steering feel with KAI and caster.