Race Engine Forum UK

haha a trick question!

With the unusual wheel angle I thought something had broken!

Great post!

G

It looks that with the new suspension steering and planned no brake booster ( two pumps with brake balance bar ) I will have to start visiting gym a bit more often ...

You have been warned about that.
Several times in fact.

regards
Tom

Well,

Fitness is good for you !

Have whole winter to work out (LOL)

Miro

As mechanical work is advancing slowly ( collection and fabrication of parts takes time) I have turned to a nice item to complement the looks:
This is a replica but both material and workmanship is excellent ( so are the measurements)

M

I'd have had it made BERT_ONE as they sometimes got called...

G

Guy Croft wrote:I'd have had it made BERT_ONE as they sometimes got called...

G

I can bet my boots it was called "Bert One" by the Americans.

M

Now a bit of thinking on brakes ...

The resolution of the brakes issue is not an easy one. In fact it is probably the most difficult to resolve issue so far.

My planned brake setup for my car is this :

Front 3x48 ATE RS 911 calipers 295 vented disks
Rear 2x38 ATE calipers in the rear 252 vented disks

Hand brake :

I do have original gr 4 hydraulic hand brake caliper , however current FIA regulations exclude use of hydraulic emergency brake. So I am forced to have a mechanical hand brake. I have no idea how to do it except to deviate from original Abarth setup and use a rear caliper which can be activated both mechanically and hydraulically. Such caliper would allow to meet FIA regulations as well as to have what I want - a hydraulic hand brake.

Hand brake on rear hand brake caliper will have to fit a vented 252 disk. We are tracking such calipers which are quite rare. Mechanical circuit f this caliper will satisfy FIA regulations and serve as emergency brake ( probably hooked to a pull handle or a pedal under dash on the drivers side) and the hydraulic circuit of this caliper activated by a gr 4 handbrake pump operated by a gr 4 hand brake handle.

Balance bar .

I reviewed the 131abarth gr 4 homologation and in fact there is no balance bar homologation - only the rear calipers pressure regulator. This means the rear brakes must have been grossly overpowered , and proportioning (front/rear) was done by limiting pressure in the rear.

I am still trying to understand how did they achieve wide variety of balance gr 4 used :
This could not be achieved only by a proportioning valve decreasing the rear brake line pressure. They probably changed pumps and front rear calipers and disks.

Conclusion : As I d not have an Abarth ex-works service team to support me I need to limit mechanical changes I need to do to the car setup between different rallies. Therefore I need to have system which can be altered on a fly by turn a knob. Also I will not use the car on ice , mud and gravel will be incidental. So if my system can be adjusted between say : 63/37 and 55/45 this is all the adjustment I need.

So the use of a Tilton and a proper selection of the brake master cylinders ( for the front and rear)

Thus I seem to have two options : go for an original Abarth gr 4 setup ( no balance bar but with rear calipers pressure regulator) or
a more modified setup with a balance bar and a remote adjustment knob .

I am not sure which to chose, but the balance bar seems a bit more user friendly and is likely to offer wider range of adjustment. It will have the possibility to balance front/rear by effecting both rear and front at the same time and not just limiting the rear.

Any comments / corrections/ suggestions.

Miro

Hi Miro

I am also struggling finding a mechanical rear hand brake for my spider rally project.
I have 256 rear disc with Porsche calipers. There are a few bespoke mechanical hand brake calipers on the market, and there are even calipers marketed as go kart/parking brake calipers. Some companies give specs for holding force etc. One other possible option is to find a production car with rear hydraulic caliper with mechanical linkage. You could then use this just as a mechanical unit. This gives some more problems as you have the panhard rod linkage on one side of the axle restricting mounting of the additional caliper.

Regarding balance, and your comment regarding ease of changing, I totally agree. As you already know there are so many possible variables. One method of adjusting brake balance used by works Skodas was to use pads with grooves machined in them to alter the balance/performance. I dont know if this would work on a rear wheel drive car, but could be worth considering- another variable.

Good Luck.

Rallyroller

Hi Miro,

Had a quick look at some of the alternatives we discussed more than a year ago to check. There are possibilities of putting a reducing (Tilton) valve in the back or in the front circuit, and choosing the overall balance with the valve fully open or fully closed. That dictates the amount of balance shift you will have but also the total amount of braking capacity at the wheels.
The largest balance shift comes from reducing the front, as these have the largest capacity at the wheel. However it also means losing the most overall capacity. Since you would shift balance more to the rear on more slippery surfaces (ice, mud) it seems you would not need that much braking capacity anyway because the wheels will lose traction much earlier than on tarmac. It can even help you driving on those surfaces because you do not have to 'pussyfoot' the brakes so much to keep them from locking up all the time.
In that case you would set it up for maximum braking at the front (tarmac) with valve open and shift balance towards the rear by reducing pressure in the fronts. This is also how Tilton documentation describes a rally/gravel setup.
Still, with the components and numbers as provided I can not reproduce this enormous range of adjustment. They may very well have used a different valve.

There are many calipers that provide a mechanical hand brake, you could retain the original gp4 and add a second or just choose to fit one that offers both functions. This is the easy way out.
Also, there are models that use the inside of the disc bell as drum and have a small drum brake setup within. Look for BMW and Volvo, probably others. I do not know how well you can integrate a backplate from such a setup into your rear axle, or if your discs are compatible. From my memory I think there were some BMW discs that would fit your needs, so there may be a way to get a compatible set of parts for this to work. It is another complication in fabricating your rear brakes. You also divert from gp4 specification, so some originality is lost.

regards
Tom

Miro

I bet you any money you like Abarth did use a hydraulic handbrake on that car even if it was never recorded as officially homologated. I have heard a lot of strong annecdotal reports of things like that over the years.

Can you seriously imagine someone like Michelle Mouton rallying without a hydraulic handbrake on that car?

If I were you I would find someone like member Mick Wood who has many friends in the Gp4 FIA legal rally scene and ask them what they think.

G

I can imagine quite well the main caliper being operated hydraulically both by foot and hand, with a small additional caliper operated mechanically just for legal and/or homologational reasons.
Just as most racing bikes have a tiny caliper from a moped on an alloy brake disc at the rear. You never touch it on track but regulations state you must have one.

regards
Tom

It's a bit late to say but I would have used drum brakes at the rear...


G

Well,

It is always a to get your advice, gents.

Instead of responding to each of you separately , I will reply in bulk.

Suggestion to stay with the drums is "a bit off timewise" to use an American term. It also is departing too far from originality.
I share the skeptical view of human race, and do not believe Abarth was more sainter than the Pope ( as thye Polish saying goes).
I have also heard a lot of stories starting with the built numbers of 124 spider or transplanting chassis numbers from genuine Abarths to stock chassis by the Abarth team. Not very surprising ! Thus I do not want to be "sainter" the Abarth, so to speak.

Re:Gr 4 had hydraulic hand brake homologated in a variety of configurations. Incidentally , brakes were aside from suspension, the largest number of variations homologated. The one version we were looking to build is on of the three homologated hand brake setups.

I have went through original homologation papers ( Note Homologation is in Public domain) and this is what I have found :


1/ Original Homologation filing :
This is really a Stradale setup.

2/ First change/modification/variation

This now offers an option of two calipers setup - the hand brake being either a Bembo 2 x 38 mm hydraulic caliper (Abarth part # 7024099) or a mechanical handbrake (Abarth part # 7024136). Some data I have found indicates there was a second disk on which the mechanical handbrake was sitting on. Anybody can confirm deny this?

3/ Second change/modification/variation .
This is to supplement the above two calipers on rear disk with Brembo hydraulic handbrake caliper.

4/ Third change/modification/variation
I am not quite sure what it is. It looks like a hand brake handle which both pulls a cable of a mechanical hand brake as well as pushes a hydraulic hand brake pump (BMC). inappropriate knows why why one would want this ? it could be either for an in line hydraulic hand brake caliper and a mechanical caliper or to be activated simultaneously , or to operate the dual action hand brake caliper ( mechanical and hydraulic). Anybody knows why they came up with this ?

5/ Forth change/modification/variation
This looks like a rear brake fluid pressure limiter (like the current Tilton).

6/ Fifth change/modification/variation
This is an in-line hand brake pump effecting a single rear hydraulic caliper (serving both : "foot brake" and hand brake.


We have chosen version with two hydraulic calipers the Brembo 2 x 38 mm hydraulic caliper (Abarth part # 7024099) operated by a hand brake pump on a separate brake line with ist own brake fluid canister and own BMC.

These are the parts we collected :
What we still missing is the handle to go with the Ducati pump . The complete set looks like this.
This was going to be fully genuine setup. I was counting on possibility that FIA regulations would allow originally gr 4 homologated brake setup for historic racing. From What I hear now is that they do not. Will still verify with the 2013 regulations to be issued soon.

If not we are doomed to less than a genuine setup. As pointed out before the issue is finding a rear caliper that would accept a 22 mm vented 252 disk but also have a mechanical action. What is available is calipers tat can accept non vented disks and smaller than 252. The disk size can be work around but I do not want to give up the vented disk and original ATE 2 x 48 rear caliper.

Incidentally I would risk arguing with stewards at the technical control before a rally , but the system ( we have already mounted on the rear requires a twin BMC setup. And we did not have the parts and or time to install them before the last rally of the season.

So Here we are. Hopefully we will track down a rear caliper.

Update to follow.

Miro

As regards pussyfooting the brakes and valve placement ( rear /front). Mechanical issue question aside, I want to go for adjustable pedal box with balance bar setup with remote adjustment knob. This should give us the possibility of real balancing the front rear , not only by affecting the rear or the front ( depending where the proportioning valve is placed. This to me looks the most attractive solution.

I will nevertheless also look for a valve with greater than Tilton adjustment capability.

One other possibility is going for the last modification setup and a "symbolic" mechanical emergency brake based on parking brake solution. Few options are still open to us.

M

hi Miro,

Hom. 1
A drum for handbrake, picture shows a disc with caliper, so that would be a setup like BMW as I mentioned.

Hom. 2
Lost the drum, added a mechanical second caliper.

Hom. 3
Second caliper now hydraulic.

Hom. 4
No idea, picture is way too unclear. Maybe regulations demanded mechanical emergency brake and this is how they solved it?
Got any better picture of this somehow?

Hom. 5
A regulating valve, probably with more range than your Tilton. No idea where they put it, front or rear circuit.

Hom. 6
Hydraulic hand brake, now acting on the main caliper. Dual MBC setup. No valve visible, none necessary now anyway.
No mention of a secondary caliper anymore either.

The dual MBC with adjustable balance bar is of course the most versatile and prettiest too. Extra bragging rights for you there ;-)
There are some calipers that go with a 20+ mm disc; look for cars that have the hand brake on the front wheels (Citroen, Saab) but be aware that the pistons are no less than 48mm (BX etc). Some of the very powerful cars may have vented rear discs as well, but I have no idea (yet) what sort of hand brake they use. May be second caliper, may be drum-in-disc, maybe electrical nowadays.
Of course you will have to fabricate some sort of adapter for mounting it on your hub carrier.

regards
Tom

Thanks Tom ,

This only goes to prove this is a never ending story ...
By the way I just found our I need to upgrade to a gr 4 wipers.
..

I have the fast gr 4 wiper mechanism
and found out that what we used a gr 4 wiper setup was used in Poland on our Nysa 5322 van since 1968

( maybe Abarth copied this from Nysa) ...

Miro