Brake pedal adjustment

[OliveR]

Hello,

I own GT40P/2193 (MKII / Roush 427IR / ZFQ) and I have a question about brake masters cylinders adjustment.

I replaced last week both brake masters cylinders and set the rods/shafts to equal length for front and rear brakes.

Well it's not at all the correct settings !!!! Yesterday I had lot of chance !

I was driving the car at 65/70 miles when I met a very close right turn (no indication before the turn of course...). I pushed on the brake pedal first when I still was on the straight but I didn't remove my foot of the pedal when I started to turn in the corner as I was a bit to fast...

Before replacing my brake masters cylinders there won't be any problems but yesterday one or both rear wheels brake too much (the wheel(s) stopped) and the car started to oversteer. The car left the road and that's why I have many chance I met large place of grass where I've been able to take control of the car and put it back on the road.

What I'd like to know is if one of you can tell me what are the good seetings for the length of shafts/rods of the brake masters cylinders.

Thanks for your replies. I really need to set it correctly my car is currently too dangerous to drive.

Sorry for my English if I made mistakes.

OliveR

 

[roaldin]

Hi OliveR,

I have no knowledge of the brake setup in your car but from your description it sounds as though you braked hard just before the corner and then continued to brake just as hard as you turned in to the corner, is that correct?

If this is the case then while it is possible that there may be a brake balance issue, I suggest, without appearing rude I hope, some sort of driving course where things like weight transfer are discussed.

I have a method that I use for basic road brake bias setup before fine tuning at track, but I won't be putting it forward on a public forum as any sort of suggestion. I'll leave that to someone braver or more knowledgeable about the world of modern lawfare.

Tim.

 

[DaveM]

Sounds like you have too much rear brake bias Oliver. Hope this isn't a language misunderstanding, but is the cross shaft in the bias mechanism equal side to side? Length of each cylinder fore to aft should always be equal. Initial setting of the cross shaft involves jacking up all 4 wheels and having someone operate the brake pedal. Have them increase pedal pressure until one set of wheels locks. This should be front wheels. With just a little more pressure rears should lock too. Fine tuning is done after a road test. Rears should never lock first. Also the cross shaft on SPF can turn with use so tighten a lock nut on one side of the cross shaft to prevent this.

 

[Seymour Snerd]

Also the cross shaft on SPF can turn with use so tighten a lock nut on one side of the cross shaft to prevent this.

Oliver --

This old thread is about the lock nut Dave refers to.

http://www.gt40s.com/forum/gt40-tec...-wheels/23873-spf-gt-brake-bias-bar-lock.html

Also another thread on the same subject that should help illustrate how the mechanism works:

http://www.gt40s.com/forum/superformance-gt40s/24720-brake-bias-bar.html

Note in particular this post:

http://www.gt40s.com/forum/superformance-gt40s/24720-brake-bias-bar.html#post222778

which not only has very clear pictures of the mechanism and lists the source of the parts, but was posted by your car's manufacturer! (A practice that sadly ended at about that time).

The Howe website is here:

http://www.howeracing.com/p-7311-howe-floor-brakeclutch.aspx

and shows a similar part number 52613 (not 52612 as our cars use). I don't know the difference.

As Dave says, the individual master cylinder pushrods need to be equal in length, but only to the extent needed to allow the bias bar mechanism to work. They do not control brake bias. It's the left-to-right position of that ball in the center that determines the ratio of front to rear braking. To determine which direction to move it, you simply need to determine which master cylinder controls the front, and which the rear, by following the hydraulic lines. The side the ball is closer too will get more brake force.

(PS: if there is an interesting story behind your replacing your master cylinders I'd love to hear it. )

 

[OliveR]

Thank you very much for your quick replies Dave and Alan.

Well understand for the adjustment I'll check/adjust quickly the mechanism and test it next week-end.

Alan, concerning the replacement of my master cylinders I'm going to try to answer with my words - I was a bit terrified about doing that job because you know how the access to the pedal box is difficult.

In fact the only difficult is to find how to "send" your two hands at the bottom of the foot box.
First and of course you have to remove the steering wheel, the driver seat and the center vertical dash (6 little screws - 3 on each side).

First step is to remove the 6 bolts that hold the pedal box. For the 4 lower bolts it could be done stomach towards the ground but for the 2 upper bolts you will need to sit down on the fuel tank, move on your side and start lowering your head behind the dash. Once your two hands are behind the dash you just have to move on your back and you will have your head upward and your hands ready to unscrew the 2 upper bolts.

Next as you are in this position you can unscrew the bolts that hold the clutch hose and the brake hose (hoses that go to the remote reservoirs). Before that take a can to get the fluid once you'll remove the clutch and brake hose.

Once done you'll be able to move a bit the pedal box towards the driver seat. It will be easier in order to remove the brake and clutch lines. Take again your can to get the fluids...

Well now you just have to bring the pedal box on the driver seat the throttle cable could be kept in place it is long enough.

Next you can remove the bias bar and after the 2x3 Allen bolts that hold the 3 master cylinders.

To reinstall all, same steps from the end and a good bleed of the clutch and the 4 brake calipers.

Hope it is clear enough to understand..

OliveR

 

[OliveR]

Dave, Alan, I have lock nut + pin lock on both side of the cross shaft.

I'll make pictures to show you how the initial assembly have been upgraded (I've read Alan's links web pages) on my car.

The only mistake I've done when reassembling this system is that I've installed the ball in the middle of the two master cylinders.

Now I'm just going to remove the pin lock on each side of the cross and unlock the lock nut and turn the cross shaft in order to move the ball close to the front master cylinder.

Still same problem to do that: accessibility !!! but I have the habit now...

OliveR

 

[Michel]

Hello to all
Apologise for giving some indications in french but it's better from frenchie to frenchie LOL

Bonjour
Pour ce qui concerne le réglage de la pression de pédale de frein voici quelques infos "basiques"
1/ On suppose que les maitre- cylindres remplacés l'ont été en mettant les mêmes diamètres de piston aux mémes endroits !
2/ il aurait fallu avant de démonter les tiges de commandes relever pour chaque la longueur filetée vissée dans chaque chape du répartiteur afin de les revisser de façon identique et non pas "symétriques"; ceci étant cela conditionne surtout l'inclinaison de la pédale puis ensuite seulement la vitesse de réaction du répartiteur lorsque l'on freine fort
3/ en revanche ce qui était très très important de conserver c'est la position de la rotule du répartiteur à l'intérieur du tube pédale de frein car c'est cette position qui crée la prédominance de frein avant et arrière
4/ pour régler de nouveau cette prédominance il y a 2 façons ( on peur même les combiner )
Façon cool ( bricoleur) mais sécuritive tout de même ;
mettre la voiture sur cale pour que train avant et arr ne touche pas le sol
1 personne au volant et 1 qui tourne la roue avnt et 1 autre l' arr on tourne la molette de répartiteur a fond dans un sens et on compte le nombre de tour avt blocage puis on dévisse de la moitié de ces tours ( donc la rotule se trouve au milieu de la pédale) ( si il n'y a pas de molette on agit sur un bout de la vis directement en se glissant dessous !!)
Puis on freine doucement et les gars qui tourne les roues doivent crier stop pour le premier qui a sa roue qui bloque d'abord ; selon que c'est l’avant ou l'arr on essaie de trouver le moment( en vissant ou dévissant) ou les deux trains freinent en même temps puis arrivé à cela on met franchement ensuite deux tours " sur l'avant" et on teste avec les deux personnes , il doit y avoir une bonne différence de 2 à 3 secondes de décalage entre les deux "stop! criés par les gars !!
Façon plus course et Pro on trouve ( pas facile !!) deux tés de raccordement un pour le caliper avt un pour l'arriere qui permettent de monter en dérivation un mano avt et un arrière et on mesure les pressions pour un équilibrage correct il faut en général 65 à 70 bars à l'avt 50 à 55 bars pour l'arr
5/ De toutes façon pour faire une répartition correcte il faut aussi aller sur un circuit et faire des tours d'essai et de "peaufinage" car cette prédominance avt va induire un changement d'assiette à l'entrée des courbes et donc il faudra affiner en mettant 1/2 tour en moins ou en plus pour que la voiture devienne agréable à conduire ( plus de survirage ou sous virage du à une compression trop forte ou trop rapide induite par le coup de frein)
6/ pour aller plus loi dans ce réglage on peut aussi acheter des petits godets de peinture spéciale de plusieurs couleurs que l'on applique sur la tranche des disques , on fait quelques tour avec un certain set up de répartiteur puis on démonte deux roues et on contrôle comment les touches de peinture ont viré ( sur la boite des godets sont indiquées les couleurs conseillées pour un bon réglage de frein et une bonne montée en tempé des disques ) cela permet aussi lorsque l'on a déglacé les plaquettes et rectifié les disques de contrôler leur bon rodage en restant dans la bonne couleur ( elle aussi indiquée au dos de la boite )
Voila ce fut un peu long mais c'est un résumé qu'il faut connaitre et que l'on utilise lorsque l'on met sur route une voiture dont on a monté un pédalier neuf !!

 

[OliveR]

Bonsoir Michel et un Grand Merci pour toutes ces explications, c'est très clair et ça va sérieusement m'aider pour le réglage de ma répartition AV / AR.

Je t'avais envoyé il y a quelques mois un mail en me présentant, je ne sais pas si tu l'avais reçu ou non ??

Je vais m'occuper de ma belle ce WE et mettrai à jour ce post avec les résultats.

OlivieR

 

[Seymour Snerd]

Oliver --

You don't need to unpin anything to turn the cross shaft (unless your car has pins mine doesn't). On my car I can spin it with my fingers. The only thing that should prevent it turning is the lock nut on the right end. The pins are there to hold everything else still while cross shaft turns.

Also much easier access to pedals and cylinders by removing AC box and going in from above, not through footwell. No removal of seat, Steering wheel or console is needed.

 

[DaveM]

Wow Oliver, I admire your contortionist ability to work on the pedal assembly from inside the car! I've always done the work from the nose after removing the A/C evaporator, etc. Coincidentally I just replaced my clutch master for the second time recently. Don't know why this happens to the clutch but not the brake cylinders. My external slave never fails so I wouldn't think hot fluid was the problem. The clutch master doesn't leak fluid, but it starts to suck so much air that bleeding the system has no effect.

 

[OliveR]

Alan, Dave, I didn't know that I could access the pedal box after removing the AC Box ...

I'll try it next time or if I couln't adjust the cross shaft from inside the car.

Thanks again,

OliveR

 

[OliveR]

Alan, Dave, I have lock nuts on each side of the cross shaft.

Moreover the lock nuts and the cross shaft have been drilled in order to insert pin locks !!

That's why when reinstalling the system I didn't have any choices for the cross shaft position as holes have only one position for my lock nuts and for the cross shaft to insert the pin locks.

With that safety I cannot adjust the cross shaft so I'm going to remove the pin locks definitively.

OliveR

 

[Michel]

Hello
One good thing will be to install a cable with a button on the dash or below the dash to adjust correctly and easily that brake balance
If you do not want to have the button visible because too modern you can source a cable with a button which looks like arotor switch and be hiden in middle of your dash panel !( It's an UK manufacturer doing this cable)
Hope this helps

 

[OliveR]

Michel, Alan posted in May 2010 the solution he had installed in his car.

CNC, Inc. - Accessories

Alan, I suppose the adaptor on the cable fits perfectly on the cross shaft ?

OliveR

 

[Seymour Snerd]

Michel, Alan posted in May 2010 the solution he had installed in his car.

CNC, Inc. - Accessories

Alan, I suppose the adaptor on the cable fits perfectly on the cross shaft ?

OliveR

Yes, 3/8-24" is a "standard" for brake bias adjuster thread. In fact, I noticed that Howe Racing, who make the bias mechanism in our cars, also make a couple cockpit bias adjusters, for example: Howe Racing Enterprises - Wilwood Knob Style Adjuster so if I were doing it over I would get theirs.

I chose the CNC one because at the time it was available locally to where I lived.

There are other manufacturers as well, including Wilwood and Tilton:

http://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=brake%20bias%20adjuster

Also, on the subject of access to the pedals from above, here are some pictures and text:

http://www.gt40s.com/forum/superformance-gt40s/29204-changing-pedal-location.html#post270995

BTW Jim Craik discovered recently that how well the flexible air hose seals to the AC box has a strong effect on the performance of the AC system. As delivered it is simply pinned on by one or two self-tapping screws. Consider carefully taping and/or clamping it when you put this all back together to create a good seal.

 

[Seymour Snerd]

Moreover the lock nuts and the cross shaft have been drilled in order to insert pin locks !!

Thanks for explaining that. That certainly seems like an extreme reaction to the problem of the adjuster loosening. I think a single 3/8-24" nut would be sufficient, or a pair of thin lock nuts. But the cockpit adjuster is the best solution of all, in my opinion, since the proper setting would vary with tire choices, pad material, etc.

 

[Seymour Snerd]

The clutch master doesn't leak fluid, but it starts to suck so much air that bleeding the system has no effect.

Dave -- At the near certainty of thread drift, I'm puzzled by this. Do you still have the original reservoir-to-cylinder hoses? I ask because a friend who did his own install said when he bled his clutch or brakes for the first time the fluid came out black. It later occurred to me his was probably from the infamous deterioration of those hoses that ultimately leads to leaks into the foot well and has led a few people to install new reservoirs with Teflon hose, etc. etc.. I'm wondering if your MC is truly failing on its own, as opposed to the hose-to-MC seal deteriorates but you temporarily fix it by replacing the MC, or the deteriorated hose material is affecting your MC.

 

[DaveM]

Alan, thanks for the tip on the hose. Mine is the original and I have had black fluid when the cylinder failed. I'm wondering if material from the hose is destroying the master cylinder seals. Only thing is I still have the original hose on the brake masters too and no problem there. Anyway winter project is to change all those hoses to Teflon. Thanks.

 

[OliveR]

Hi Dave, Alan,

Here is a picture of my pedal box where you can see the lock nuts and the pin locks on both side of the cross shaft.



I've removed the pin locks and started to turn the cross shaft in order to move the cross shaft on the right and tested it on the road but it's the same the rear wheel stopped before the front wheel.

I'm going to adjust again the cross shaft and test it but if I still met the problem I 'll lift the car and adjust the cross shaft as Michel told me.

I'm going to check too if I have not some air bubbles in the front lines brakes even if I've checked it two times before...

Concerning now the remote cross bar adjuster (I've ordered the same as yours Alan) do you think it will fit as the left extremity of the cross shaft is very close to the clutch pedal ?

Thanks,

OliveR

 

[Seymour Snerd]

I'm going to check too if I have not some air bubbles in the front lines brakes even if I've checked it two times before...

Concerning now the remote cross bar adjuster (I've ordered the same as yours Alan) do you think it will fit as the left extremity of the cross shaft is very close to the clutch pedal ?

Bubbles on one side but not the other is a very good theory.

I attached mine to the right side of the shaft. I don't know if it will attach to the left. I doubt it because I think it would bend the cable too much. Here's a picture of mine, but that is all I remember. I haven't been "down in the tunnel" for a long time, thankfully. :laugh: That is the top third of the adjuster knob showing at the bottom of the picture, It ended up in a very nice position right next to my right knee, but otherwise out of the way.



According to my notes, the left master cylinder operates the rear brakes. In your picture the bias fulcrum is very far to the left (compared to my picture, where it was deliberately approximately centered), which surprises me, because I would expect the adjusted position to be somewhat to the right (most cars need more pressure to the front, all other things being equal, and the SPF GT40s front and rear brakes are identical). Of course it is possible I am wrong about which cylinder is which, so I think it would be important for you to verify that on your car.

I believe you said that before you replaced the master cylinders the balance between front and rear was normal, and after that the rear brakes locked too soon. Since the fulcrum position is determined by the lock pins, you must have put it back in exactly the same place, so the brake bias should not have changed. So I'm confused about what's going on. I really hope that bleeding your front brake lines clears this up.

By the way, not to change the subject, I am just curious why you changed your master cylinders. More specifically, how do the new ones differ from the original ones that came with the car? And I assume the two new ones are identical to each other. For example, if they were of a different cylinder diameter it would change the front to rear balance.