No problem at all, I think discussion is a great thing, ideas form and hopefully the problem gets solved.

 

As manifold vacuum decreases, ported vacuum increases...and vice versa...

and yes the booster is connected to manifold vacuum.

just for conversation.

James

 

I swapped out my brakes on my limited coupe to SRT brakes. I did calipers, rotors, pads and SS lines. In my opinion I had less brake peddle travel and quicker brake action with the limited setup.I ran two quarts of fluid through the system to make sure there was no air in the lines. Just my two cents.

 

I have often wondered if air had got into the ABS module on my car but the ABS works fine when tested on wet roads.
Your experience makes me doubt that assumption, bluecoupe reckons my pedal throw is greater than on his SRT.
It makes me believe that my pedal throw is greater than most SRTs.

 

Is there a difference between a dot 4 and dot 4 plus? Can I use either or should stick with the dot 4? Where I’m from there isn’t much options for the dot 4 fluid. I know that there is a generic penzoil dot 4 and also a dot 4 made for American cars and also a dot 4 for Honda and Acura etc. That was the selection from Canadian tire. If any of those won’t do perhaps I will have to go to Mercedes to get one from there??

 

This is from a website powerstop.com
DOT 4 is used in some euro and domestic vehicles. DOT 4 Plus is used in Mercedes and Volvo. DOT 4 Low Viscosity is used in some BMW models. Finally, DOT 4 Racing usually has an added blue color.
Just be certain you are using a glycol based fluid. I suspect the plus has some additives. NO silicone. It is best to use a pressurized tool to force the fluid through the system; Something like Motive Products POWER BLEEDER model0100 for European cars.

 

Dot 4+ has a higher temperature rating than Dot 4.

 

Good conversation and learning points, but is there any more idea's on the pedal throw. Like the rest of you, I feel like the pedal is going to hit the firewall before the car stops. Love to hear all the idea's.

Jim

 

I started this thread and still I have no idea why the pedal goes so deep. The brakes work great, no complaints there.

 

Regarding brake pedal going "deep". I owned a Pontiac Fiero for 27 years and only sold it as there was no room in the garage after I bought the Crossfire 3 years ago. I thought that my clutch pedal was also going too deep and eventually it got to the point that it was hard to shift as the clutch was not engaging. I mentioned this to my brother in law the hot rod builder. He got down, reached in and grabbed the clutch pedal and slowly pulled it back enough to notice. Clutch worked like new! Did some more checking and found that the original pedal would bend over time., The Fiero Store sells a stronger pedal so I got one as I was sure the original one would just bend again. Easy installation and like a brand new car again and it never did bend like the original

Just throwing this out there as a somewhat similar situation. From the Fiero Store website:

​​​​​​84-88 Clutch Pedal Most Fieros were equipped with clutch pedals that were a combination of aluminum and steel. Over time, that pedal will flex or bend, preventing full clutch disengagement. Our new all steel aftermarket pedal will last longer than the original factory design and will provide full clutch disengagement. Your Fiero will also shift and find gears more easily. We recommend that you change the two shaft pivot bushings (64358). This pedal does not require the master cylinder rod bushing (64900). This pedal is no longer available from GM. Pedal rubber (50160) not included.
Part # 66423 Price: $44.95

 

Good thought but the pedal travel is too long, it is a normal travel with the engine OFF but more than doubles with rather engine running.
The only place I can see this happening if the extra travel is somehow caused by the power assist unit.

 

I spoke with a top german mechanic,Klaus Von moron.He said the car was designed that way to make heel / toeing easier.Well my pedal was too high so I added just a little air to the system to lower it. Now I'm heel toeing all over the place.See,problem solved, next issue.

 

After six months with no advances to my problem and the car a month or so away from going on the road I have returned to the problem.
I have read that if the ABS module has a sticking valve then the pedal stroke will be longer than it should be.
I have noticed that with the ignition OFF the pedal travel is what I would expect with the engine running, turn on the ignition and the pedal drops considerably. I put this down to air trapped in the ABS module but as the peddle is rock solid in use l now think it is a sticky valve.
I have acquired a used ABS module from eBay, three cans of Motul 600 and plugs for the brake lines. I also have the DRB III Emulator just in case it can help somehow, it does not actuate the module to bleed it though.
Has anyone any experience in changing the ABS module and replacing it? Or activating the ABS valves so that any stuck valves would come loose.
I would be grateful for any help on this matter, there are others with the same problem.
I have also received the powered base from an SLK 320 to put in the car. I think I have more energy than the Eveready Bunny.

 

Great question. I’m looking forward to hearing the answers too.
I know there’s a lot of smart forum members that will know.

 

180 - Thanks for keeping this topic alive. I hope you have found the answer to our problem with long brake pedal travel. Like you, my car, with the engine off, has a very short stroke and a very firm feel to the brake pedal. As soon as I start the engine the pedal goes fairly far down, too far for my comfort, but is firm when it reaches the limit of it's travel. Some time back, noted above in the structure of the post, I wondered if the vacume chamber had anything to do with the problem. Still don't know for certain. I put on one of "Needswings" oil catch cans some time ago and wondered if it had anything to do with messing up the vacume on the canister. I must have taken that catch can system off and on three or four times, always asking myself if I overlooked something on the installation. It's just as instructed. Funny thing though, I never, and I mean NEVER, get any oil or gunk in the oil catch can. Seems funny that I have a lot of brake pedal travel, which depends on vacume, and no residue in the catch can that also depends on vacume. I'm wondering if there is a corralation (spelling) there? Please let me know your thoughts on this.

Jim

 

The vacuum assisted brake system is separate rom the ABS system. If the vacuum was totally lost the brake system would still work but a lot more pressure would have to be applied to the brake pedal.
I think that with the ignition OFF the ABS module is bypassed and the pedal travels the same amount as if their was no ABS system.
With the ignition ON the ABS module allows brake fluid to flow through it, somehow this causes the low pedal problem. I read a sticky valve can cause this problem. Or is it caused by air in the module, if it was air I think the pedal would be spongy.

 

I have returned to this problem, I have purchased a used ABS module and thought I would change them over. Second thoughts made me think twice about doing this, if by chance there was no air in the system then for sure I would introduce it when swapping the parts.
I have studied the workings of the ABS module and I cannot see why we have the low pedal if their is no air in the system, if there is air then I would expect a spongy pedal. I am at a loss as to the solution to this problem.
Has anyone got any ideas, if so please let us know.
It has been too cold to sit in the garage playing with the Micropod II setup. I wonder if that will be any help anyway.
A bit of history, when I purchased the car in 2011, I realized that the brake pedal went lower than my NA, thinking that the master cylinder was at fault I replaced the MC, no change. My deduction on the MC was wrong, I should have realized that at the start.
Obviously I did not let air into the system when I changed the MCs, if any was in there it was there before I did the swap.
I do not think that air is the problem, I think the fault lies in the ABS module, and that fault is a sticky valve(s).
The ABS system works that is the strange part, on a gravel or a wet road I can hear and feel it work when braking hard.

 

onehundred80, if the micro pod works exactly the same as a DRBIII then the ABS pump will run for about 2 seconds when the DRB III conducts a test of the system. Will a test show a sticky valve?
Mercedes dealers use a pressurized tool to flush/replace brake fluid.
As to replacing the ABS module it is rather straight forward. After disconnecting the electrical connection, loosen the two screws on the front of the ABS unit ( I think they are allen head) from the mounting bracket and the steel lines from the top; put new unit in place and reconnect lines and electric. It is very difficult to pull the unit out with the bracket attached. Those grommets are tight.
I have both a Limited and a SRT 6 in my garage and have just measured the diameter of the mastercylinder external and the two are identical at 31.3 mm. They are both marked with an H which I believe is a casting mark. Checking the part numbers at Mercedes I found both the master cylinder and the booster are the same part number, so it would seem that the longer travel on the SRT 6 is the result of the larger calipers on the front of the car.
Now, is the foot travel on your car longer and/or softer than other SRT 6. Pehaps a comparision with several other cars would be helpful; You should make a trip to the Dragon this fall and make the comparison.

 

That’s really great information

thanks for sharing

 

The pistons only travel a few thou, assuming that the NA and SRT travel the same amount the increase in area of the pistons would very little. At one point I calculated the increase in area and I came to the above conclusion.
The retraction of the piston is done by the seal that returns it to its previous position.
I am going to check the readings on the plug that goes to the ABS unit.
I will also try my Micropod II setup.
I have concluded that the problem is not caused by air as the pedal is not spongy.
I have had an NA at the time I purchased the SRT and noticed the difference, I have also compared it to another SRT.
The brakes work very well, and the wheels work as designed on slippery surfaces.
I will keep this thread up to date as I proceed.