Daniel_Mc

Hopefully someone can point me in the right direction.
http://forums.corvetteforum.com/c4-t...post1574317601

Thanks,

Daniel

BrianCunningham

what's the piston area compared to the stock ones?

any feedback from Wilwood?

94ZR1#444

From previous post:
"I have been having issues with the ABS on the Vette even since installing the Wilwood GN III calipers in the front. The brake bias spring has been changed to the DRM unit as well. The problem has been occurring during slow driving when coming to a stop the ABS will kick in and not allow the car to fully stop and now it is doing it under hard braking under slower speeds (autocross). I haven’t had the issue at any DE’s, which is what I usually run the car in, but I autocrossed at The Gathering and totally blew several turn ins because the ABS kicked in. Anyone know what could be causing this issue? The rear brakes are still stock units and the pads up front are performance friction SA01’s I do not recall what I have in the rear I will have to check my notes. I had a little scare in the pits this past weekend and want this fixed before I get in the car again." End of previous post.


Daniel,
I have the Wilwood GNIII's up front with the stock J55's moved to the rears. I haven't ever had the problems you are having. I changed out the original Master Cylinder that had a DRM bias spring to a 3/4 truck unit w/o the bias spring.

The only problem I was had was blowing the EBTCM behind the seat.
Have you checked for any active code set now or looked at the history codes? When you do, I'd erase all codes, take the car out in a empty parking lot as see if any codes are set. Good luck.

ScaryFast

Why the smaller bore MC? Do you still have the booster in there?

Aardwolf

No bias spring, did you put in an adjustable control?

FWIW I thought the ABS system was very poor, not at all like the C5 system. I removed it from my track car.

94ZR1#444

The stock M/C is 3/4" or 7/8", not sure. The 3/4 ton M/C is 1 1/4" I believe, so it's much bigger. Booster still in. The pedal is always high and hard.

Kubs

Yes the stock MC is 7/8". When I went to my C5 front brake upgrade I installed a 1" MC from a 4th gen F body. The pedal feels great but even with the 12.89" rotor and no input from my bias adjuster (plumed in the rear line), it is still over biased in the front, and the abs doesnt like it. I put the same pad compound in front to rear and it helped but I still need more brake in the rear.

Make sure you have the front to rear bias OK (sounds like you are WAY overbiased to the front) and I would second the vote to just pull the abs out.

Daniel_Mc

94ZR1#444,

Everyone I have spoken to about this has that same answer… Never had this issue…. I have changed the hubs, ABS sensors, and still no luck. The car is not throwing any codes what so ever so I am not really sure what direction to go. I may try putting the stock spring back in but when I spoke to Randy about it he didn’t seem to think that would be causing this.



Kubs,

I have the 4th Gen F body ready to install but want to correct this issuse first.

Daniel

Kubs

With keeping the rear stock you have LOTS of front bias. I think you are going to have the same issue even with the camaro MC. Those are big brakes in the front, the only way to correct the issue is to add more brake to the rear. You could put a bias adjuster in the front line but that would only make the big brakes as good as the stock setup. I would look into putting the old front brakes in the rear, or putting a good 4 piston caliper in the rear.

Daniel_Mc

Kubs,
I ran the idea of the 4 piston rear wilwoods by a few people and was told the $$$ associated with the parts would not be worth the gain... I guess i need to call DRM and get the rear set up and hopefully cure this issure.

ScaryFast

Ahhh, I misunderstood your post. You said the 3/4 ton truck MC and I read it as 3/4 inch MC.

The C4 MC is 22.2 mm, or 0.87 inches, so a 1.25" MC is significantly larger. How is your pedal effort? Much higher?

Thanks for the info...

ScaryFast

You don't need to spend any money on the rears, the stock C4 brakes are fine in back, even in their paltry little single-piston configuration.

I have big Brembos in front and stock rears and my rears lock up long before my fronts. It's a system setup issue. We need to work out the cause of this issue before throwing parts at it...

I vote ditch the ABS, though Tune the system without it. Lower the boost, increase pedal ratio, and play with MC sizes...

0Todd TCE

GNII is way more piston area than would be ideal for a conventional mc bore.
At 1.75 and 2 x 1.375 you're at 5.4" That's about 25% more than the conventional six pot kits.

Moving to the larger bore will improve the pedal fee for sure. But the bias will never come back to being right unless you also boost the total REAR piston area. Move your rears to some 4 x 1.375 and the larger bore master and things will greatly improve.

Right now you're basically working only the front brakes and the rears are along for the ride....

The down side of all that change is that in the end you'd be right back where you would have been with smaller bores on both ends and the smaller mc to go with it. You came full circle for the sake of a larger body caliper and bigger pad.

BrianCunningham

If you going to replumb it, you might want to think about separate master cylinders with a balance bar.

that would also take car of the master cylinder failure problems C4

94ZR1#444

When I'm going 140+ MPH in a C4, I have to apply a fair amount of pressure on the pedal. It's no more than before because before I did the changes, I always had to worry about a low pedal and a soft pedal after 6 or so hard laps on a stock brake system.

I for one, do not believe there is any big brake setup for a C4 this is not over biased front or back. It is all advertising smoke and mirrors. I have gotten used to ONLY braking in a straight line because I'm over biased in the front and when I brake in a turn, the rear will come around just enough to get my immediate attention. You just have to admit to the fact that you spent a boat load of money and it isn't perfect. I will work though. You just have to make it work.

Yeah, OK, flame on. I have thick skin. You who say they have a perfect C4 big brake system setup with ABS, let me drive your car on VIR. I say I'm talking 30 minute sessions doing hard braking.

I know this doesn't fix Daniel's problem but at least he's a bit more knowlegable in what faces him now. He has a unique problem and I can only wish him good luck because I had my fair share of problems getting the Wilwoods dialed in to where they are now. At least I don't have to change out my pads every weekend and my rotors every 3 events. I can now get 10+ events out of the 1 3/8" rotors and at least 5 events out of the pads. That is the real pay-off going bigger.

0Randy@DRM

Daniel,
At one point we had 5 chevy trucks in the employee parking lot that did the same crap. They would stop, the ABS rarely worked right and two of them including mine did the same 3 MPH ABS pump until you almost hit something. Mine ended up being a cut wheel sensor wire, the other one ended up crashing a few times and being sold with crappy brakes.

This is not a caliper, piston area, master, or anything like that issue. Check out the leads going to the wheel bearings very carefully.

Randy

0Todd TCE

No flames here, not my style but....

This statement doesn't really make much sense:
I for one, do not believe there is any big brake setup for a C4 this is not over biased front or back. It is all advertising smoke and mirrors. I have gotten used to ONLY braking in a straight line because I'm over biased in the front and when I brake in a turn, the rear will come around just enough to get my immediate attention. You just have to admit to the fact that you spent a boat load of money and it isn't perfect.

For one you cannot have a system that is "over biased" on both end of the car at the same time. It's either one or the other.

The movement of the stock calipers (forgive me I don't have bore data) is in part the reason you don't have 'his' problem so to speak as you have effectively boosted the rear piston area as I suggested above

However....your problem appears somewhat the opposite; from your own description the rear now has too much rear bias despite the additional front area also. And that makes sense to me as I'm guessing the front calipers (on rear) are far closer to 4.5sq" which would be now way too much area! If you cannot safely trail brake into a corner (we'll leave driving style out of this) without rear lock up that's a clear indication of too much rear bias.

I'll go out on a limb and say part of the reason you have a negative opinion on the discussion of bias is that you've never really had it right or had it explained to you thoroughly enough to understand that what you've done is not such a great idea. To balance this (dare I say messy) situation you need to either install an adjustable prop valve allowing you to set the rear bias to your needs and or put in a very low Cf pad that does not have a huge impact on bite. On the flip side a higher Cf pad up front would do the same but perhaps at the expense of excessive rotor wear also. My personal suggestion: get rid of those oversize front calipers being used on the rear.

1991Z07

Todd,
I think you misunderstood what he was saying. I understood him to say what I added in bold above.

What he said was there is no C4 (complete) brake system that doesn't have the bias either skewed to the front or the rear. Nothing is sold that is a "balanced" system for our cars. It takes lots of tweaking to get them to work correctly.

I have a feeling he has PLENTY of experience and knowledge on the subject...

The C5/C6 guys have it made. They have off-the-shelf systems that work right out of the box...no tweaking required.

It isn't fair...we've been around longer

But I think the right thing to do (in his case) is to add a bias adjuster into the system to fine-tune the brake bias until he CAN brake through the turns and NOT just in a straight line.

JMHO

0Todd TCE

I see what you're saying and agree. I interpreted this incorrectly, sorry 'bout that.

That being said, yes his time spent would prove a lot of trial and error no doubt there! I did get that part!

Still I would have to say that putting those front calipers on the rear even with the larger bore GNIII and his comments on handling (I'm reading that as tail happy under braking due to braking and not chassis here....) is indicative of too much rear bias still.

Aardwolf

What would be the best way to do this? I removed my ABS and plumbed the system together by the ABS pump. I would like to redo the lines at some point and have adjustable bias.