CSX 7000 Brakes

[Dan Semko]

Rick,
Who do you think Kris Kinkaid works for? None other than SAI. Kris has ALWAYS been owner supportative and informative.
I believe that you may owe him an apology!

[rdorman]

Like I said, I may have missed something! And I certainly did! I did not know that Kris worked for SAI. I still don't see any evidence of any real SAI involvement though. Not a slam on SAI in any way, shape or form. Just a point of curiosity. But, not really relavent to the topic.

My offer for help of course stands. Have you checked the pressure at the calipers with a pressure gauge? With what you have been through and the replacement of the master cylinder, this is an interesting one. And I am interested to know the resolution.

Rick

[427sharpe]

The way the tech describes the ease of turning the front wheel sounds like a pressure problem. If a new master didn't fix it, I would start checking each component individually to trace the problem. Hook a pressure gauge up to the master cylinder port, and have someone depress the pedal. Are you getting sufficient pressure? The Mfg will be able to give you a concise envelope of what should be acceptable. If pressure is ok, go to the next juction (probably the 'T' where the 2 front lines meet...and check EACH port for pressure loss. If the main line has a kink or restriction, it will show up here. If something has been trapped in the 't' you will find it. Then, check each side of the car at the inboard side of the brake hose. This will find a kinked or damaged hard line. Then check each brake hose....maybe one of them has collapsed internally. Finally, check for solid flow THRU the calipers and make sure that all the pistons are moving easily. Also check the BRACKETS to make sure that all attaching hardware is TIGHT and that the bracket itself is solid...if the bracket/caliper is moving too much, you will not get sufficient pressure applied to the rotor to stop the car.
I had a strange problem like this when I first began tracking my GT350...too much pressure required to slow under hard braking. In this case, it turned out to be the FIREWALL flexing! I found out thru a conversation with Walt Hane that he had the same problem with his R model, and how he fixed it. I hope the process above helps Jim fix his problem!

[tj1949]

I appreciate all your input into this problem but I want it to be clear that I have talked to 2 Shelby dealers, the one who built the car and Gary at SAI. I realize how hard it is to try and fix a car over the phone so I appreciate all of their suggestions and everyone elses too. This is the first Shelby that I have ever worked on or even driven so all input is greatly appreciated. Jim Maxwell has gone out of his way to try to help and I can't thank him enough.

Yes, I have checked for kinks in the lines, many times and even asked other people to look to see if I have missed something. Fluid flow out the bleeders is not a problem. With the car being as new as it is and with the good fluid flow that I have, I can't see the flex lines being a problem. I do know that with the master cylinders being so low that it can be very difficult to bleed the air out of the system so I have bleed the system several different ways using lots of fresh fluid to be sure that all the air is out.

The master cylinders are mounted one over the other with a non-adjustable balance bar. Both cylinders push in at the same time. I am presently working on a couple of other things and hope to resolve this soon. I have a lot of other work waiting.

[Excaliber]

.seems like pressure AT the caliper assembly would be fairly easy to test. Have someone MASH HARD on the brakes and open the bleeder. IF there is pressure there the bleeder valve will spew fluid like a rocket.

OK, not a great test you say? Well, what if the bleeder is only a trickle (you know, like a Gashole in the john)? That would mean you aint got squat for pressure!

Ernie

[Cobra75]

Originally posted by David Kirkham
Chris,
You stated, "The front circuit cylinder should be on the bottom of the pedal box as it gets actuated first, and the rear cylinder on top. If they are installed wrong, then the rear brakes will be actuated before the front."
Is Shelby still using the basic original design of the pedal box with a bias bar placed vertically between the master cylinders?
Thank you,
David

In the 4000 series, both master cylinders are .75" with the upper one feeding the front. Admittedly this may not be the same as the 7000 series. But if it is, possibly the lines were originally connected to the wrong master? (Also, on my car, the front & rear calipers are the same size both the Girling [original] and Wilwood [replacement].)

[wilf leek]

Tom - I have been thinking about your puzzle, and have come up with a possible scenario:

If the disc run out at the front is such that it is forcing the caliper pistons backwards significantly, it could be that you cannot achieve enough fluid displacement to get the fronts to grab the disc before the rear master goes "solid", and prevents any further pedal travel. Would the linkage system allow that to happen? Really scratching my head here.

If you disconnect (hydraulically) the rears, do the fronts work then?
Is the disc run out OK? Any pulsing through the pedal on the road?

[brentfenimore]

Tom,

I have been out of town on business for the last few days and was not aware of the problems you are having with the CSX7000 vehicle.

The system is the same configuration as the original as far as the mechanics however we have changed the master cylinders in size according to the manufacturers recomendations and testing that has been performed.

The system is the same on all three models of Shelby Cobras to include the CSX4000, 7000 & 8000 and has been in use for over three years and installed on over two-hundred vehicles. The larger bored master is for the front brakes due to the amount of fluid that needs to be transferred in order to actuate the two piston calipers as apposed to the single piston rear calipers.

It is not the system but rather a blockage (my first thought anyways) in the system which could be either pre or post master cylinder. We have seen a few instances in which the line between the resevoir and the master has become clogged when vehicles have sat for extended periods of time without use. The method to clear the line is to remove it from the master cylinder and then apply air pressure to the resevoir by removing the cap and using a rubber stopper around the nozzle of a blow gun. If this is the issue you will not see a good flow of fluid even with pressure applied. By increaseing the pressure it should clear the clog and you should see a steady flow.

If you have not resolved the issue prior to this post or if you attempt this inspection and the flow is fine please call the plant at 702-942-7325 and ask to speak with myself or Gary Davis so we can walk you through a few more steps that will help pin point the problem or simply post a response and I will give you the info on line.

Thank you,

R Brent Fenimore

Thank you for bringing this

[Tom Kirkham]

An easy and quick way to check and see if you have a restriction in your front brakes system is to open up the bleeder screw on the front caliper. It should bleed quite freely without pumping. If not you have a problem somewhere.

[aumoore]

Tom Jones the Mechanic not the singer

Have you tried swapping out the two master cylinders and putting the smaller diameter piston on the front? I am running the Wilwood dual master cylinder setup and they recommended 3/4 for the front and 7/8 for the rear. The smaller diameter piston will give more pressure and less voulme than the larger bore master. If you have a non adjustable balance bar then you have to get less presure to the rear than the front.

This may explain why the rears start locking up before the front as they are getting more pressure due to having the smaller bore master cylinder.

As for volume being a problem I doubt that would be a problem with disk brakes as they actually never stop touching the rotors. Drum brakes are a different story as they back away fully and it takes a little pedal movement before the brake shoes actually touch the drums. If the disk is warped enough to move the pads away from the rotor then they are warped enough to feel when stopping and need to be turned or replaced.

I would just swap out the masters and see if it helps.

[Anthony]

I think the relevence of the master cylinder bore diameter and pressure generated is not dependant soley upon the master cylinder bore diameter, but the ratio of the master cylinder bore diameter and the caliper piston total cross sectional area. If the front and rear calipers have different piston areas, then I don't think you can compare the master cylinder piston diameters directly.

[Tout]

After 6 pages of advice,not once has a pressure check been done at the caliper by the owner or builder. Where is the tech support from the builder?If possible take it back,have a professional look at this. Tout

[brentfenimore]

To all,

I have been told that the bottom line was that the brake pads were worn out and that the replacement of them has cured the problem.

By the way I also found out that this particular car was used in several race events prior to its sale to the gentleman that is outsourcing the repairs. I actually drove the car on the track myself a few years ago and it handled as well as braked quite nicely.

I am glad to hear it is repaired, please let me know if the information I recieved was incorrect and the system is not operating properly.

R Brent Fenimore

[KobraKarl]

ohfuChrissakes

KK

[Jamo]

hehehe....

[RACER X #99]

Good that it was only the brakes. Can you imagine if it was the engine that would not start.

Bill to rebuild engine, $7,500.00

On gallon of gas $ 1.50

Cranky

[Cobra75]

Originally posted by tj1949
Hello everyone,

I am the mechanic that Jim Maxwell is trying to help with this braking problem. .............................
I am still trying to resolve the problem. ........................................I could set here and type all night to tell you all the things that I have checked and done. And of course everyone that I have spoken to about this problem has never heard of it and are as befuttled as I am. I haven't given up and will update you soon.

There is a lesson here: "Never assume anything."
Did anyone else here "assume" that the brake pads were checked?

[Jim Maxwell]

Well, nothing like provoking a little controversy and some physics discussions! Sorry to all that contributed to the discussion for the solution to be so simple. The car only shows less than 500 miles.
I knew that the car had been raced, and my first suggestion to Tom was, "are the brake pads glazed?" I don't know why the pads weren't replaced early on in the investigation--Tom will have to answer that. Many thanks to all. The car is beautifully made, looks wonderful and drives incredibly. I look forward to the chance to drive it with brakes!

[coyled]

Cobra 75, I suggested replacing the pads in an earlier post. I am glad it was so simple but it usually is simple. Scott

[PatBuckley]

Sounds a little TOO simple - worn out brake pads are very obvious - they make some godawful sounds.....and you can feel the metal on metal grinding.