Vette-Dream

1998 w/o Active Handling
no CEL codes thrown

Symptoms: Hard Pedal, no rear braking.

My pedal has been hard for a long time, and when I register the car the I/M shop always says the rear brakes are barely doing any work. It's now at the point where they failed my inspection, so it's time to fix the issue.

Resolutions:
-Replaced the rear rotors and pads
-Replaced the master cylinder and booster
-Bled the master cylinder and all calipers
-Tried to activate ABS on a dirt road (low speeds) but only the front will pulse
-I have removed, disassembled, cleaned, and replaced the brake proportioning valve located just below the front line on the master cylinder that drives the rear brakes. Can I test this valve with compressed air?


Issues: Now that I've done this work I've made it worse. When I do a panic stop the front right brake will lock up. I drove for about fifteen minutes around the neighborhood (<35mph) and did lots of brake tests and the front right would always lock up. When I got back home the back brakes didn't even look like they had touched the new rotors. They were cold, easily touchable, where the front were radiating heat.


Ideas:
-pay a shop with tech2 to bleed the ABS (can I use HPTuner ?)
-use a lighter spring in the proportioning valve
-???

dadaroo

CEL light is not going to show you brake issues.

You need to pull your DIC trouble codes and see if you have anything EBCM related.

Maybe this will help:

http://www.bing.com/videos/search?q=...322207ED678C7D

Vette-Dream

Oh I didn't know that, cool! I've pulled the following, and from what I found online it appears that they are all historical (H)

I'll list them here in case one stands out, but I didn't see anything for the brakes jump out at me.

HO-LDCM
B2252 H Key Cylinder Switch Fault
B2282 H Battery #1 Fault
B2284 H Battery #2 Fault
U1255 H Generic Loss Communications
U1064 H Loss of Communications with BCM
U1016 H Loss of Communications with PCM
U1096 H Loss of Communications with IPC

H1-RDCM
B2283 H Battery #1 Fault
B2285 H Battery #2 Fault
U1255 H Generic Loss Communications
U1064 H Loss of Communications with BCM
U1016 H Loss of Communications with PCM
U1096 H Loss of Communications with IPC

HVAC
U1160 H Loss of Communications with LDCM
B0365 H Right Actuator Feedback Short to GND

H6-SCM
B0851 H Battery 1 Out of Range
B0856 H
U1255 H Generic Loss Communications
B2605 H Seat Front Vertical Position Sensor Failure
U1064 H Loss of Communications with BCM
U1016 H Loss of Communications with PCM

Vette-Dream

I went out this morning and bled the entire system once more. I noticed immediately that the pedal was MUCH softer than it has been in a very long time. I was worried at first that it might just be air, but after taking it out on the street I think it's how it was working when I first bought it years ago. YEAH! I finally have my booster working again.

I took it down a gravel road and also through a sandy lot to try and lock up all four tires to purge the ABS. I was getting lots of ABS activation, but when I took it afterwards to the shop the brakes measured exactly the same! The fronts are doing all the work, the rears are engaging from the test output but not enough to pass. The test results were literally the same as before.

So powered brakes... so nice! Not enough rear brakes, gah!!

At this point I can only think to order the Doug Rippie proportioning bias spring and replace it to see if that makes enough of a difference asap. I read somewhere that the spring is stronger than the stock spring, how does that work exactly.

http://dougrippie.com/products/drm-brake-bias-spring-3/

martysauto

When you bleed the brakes, do you get good fluid flow from the rear bleeders? If so, they should be working unless the replacement calipers are faulty.
How does the car stop? I have seen new cars flunk brake tests at state inspection, then run threw again on a different machine and pass.
Do you have a friend with a c5? Run both cars with similar driving conditions and measure all rotor temps with an infrared thermometer. If your fronts are hotter and rears cooler than the test car, something's wrong.

dadaroo

On your codes I agree there is nothing related to brakes.

Now that you have recorded what codes you had, clear/reset them so you will know if something comes back again in the future.

If you think you have an issue while driving pull your codes BEFORE you turn the ignition OFF. Most codes will only show H once the ignition is OFF so you don't know if it was a burp or if it is still there as a C.

Vette-Dream

@dadaroo Good tip, I didn't realize that about the H and ignition cycle. I'll clear them today.

@martysauto I get a good flow from the rears when using a vacuum bleeder. And the calipers seem to be clean and lubed well, they slide on the pins fine. I am so excited about having my power brakes working again, I was so used to the hard pedal for so long that it feels like a new car again. Sad it took failing my inspection to flush everything properly. But it's nice knowing the booster/master cylinder and all rotors and pads are new. I suppose I should have upgraded to SS lines while I was at it

I ordered the spring from Doug and if I still don't pass this coming week when it comes in then I'll just find a shop that doesn't use a brake pad test and just relies on brake feel ;-)

Though I really would love to see how well it stops when it's balanced properly...

One question though, during an earlier bleed session (not the final session where it's working) I tried to bleed with the car running just on the RR brake. When the car was running the fluid coming out was really frothy. I had my son holding the pedal that time, not hard but with the power running. Is that normal? I've never tried bleeding the car running and only did that one brake that one time like that. The frothy air and fluid had me worried so I stopped and did them all with the power off since then. As I said, I've flushed them entirely since that session so I don't have any symptoms from it, but was that normal?

dadaroo

Frothy means air is in the fluid. It should not have air regardless of how you bleed. Just bleed until the air is gone.

Bill Curlee

Hmmmm..

martysauto

Bleed it again. Have someone pump the pedal and crack the rear bleeder while they have pressure on the pedal. This will tell you what fluid is available to apply the rear brakes. Check the rotor temps after driving.
Let us know your results

Bill Curlee

Here is a schematic of the BPMV hydraulic valves and circuits from the master to all four calipers.

n8dogg

I highly recommend speed bleeders. You can crack open the bleeder and run a hose into a can and just keep pumping the pedal. It's one of the easiest and fastest ways to bleed brakes. I'd give each corner a good 30 pumps. Make sure you have plenty of DOT 3 or 4 brake fluid and DON'T RUN THE MASTER DRY.

If you still have rear braking issue then I'd consider replacing the proportioning valve.

The fact that you have a firm pedal tells me it might just be the proportioning valve. Any air will cause a spongy feel until you pump the pedal several times to compress the air.

n8dogg

I highly recommend speed bleeders. You can crack open the bleeder and run a hose into a can and just keep pumping the pedal. It's one of the easiest and fastest ways to bleed brakes. I'd give each corner a good 30 pumps. Make sure you have plenty of DOT 3 or 4 brake fluid and DON'T RUN THE MASTER DRY.

If you still have rear braking issue then I'd consider replacing the proportioning valve.

The fact that you have a firm pedal tells me it might just be the proportioning valve. Any air will cause a spongy feel until you pump the pedal several times to compress the air.

Vette-Dream

@Martysauto The rear brakes don't seem to warm up at all after driving around the back roads doing hard stops.

@Bill Curlee Thanks for the schematic, other than a TechII is there any other tool that will force the ABS to cycle? I have HPTuners from when I did my turbo build, but the last I checked he wouldn't touch ABS (not sure why, I can already change enough to ruin my car a hundred times over with the tuning, ABS shouldn't be left out IMO).

@n8dogg Lol, if I'd known at the start how many different times I would end up bleeding my brakes when I'd started this process I definitely would have put in speed bleeders. They aren't expensive, and are so easy to install, if anyone is reading this and hasn't started playing with their brakes... definitely install speed bleeders. I didn't know about the speed bleeders so I picked up a vacuum bleeder which works great as well to make it a one man job.

When I get the new spring in from Doug Rippie I'll put that in and test everything once again. I'm amost sure that will solve things.

I also got in touch with from Doug at corvetterecyclers.com and he has a complete valve in case it's not just the spring in my unit. I'm really hoping the problem is with my proportioning valve. They symptoms of not enough braking going to the rear while the fluid moves through the lines to the rear just fine during bleeding tells me that the issue is with that valve.

The real danger with leaving my car up on jack stands for this long is the temptation to buy more go fast parts and go crazy lol

Bill Curlee

Have you tried::

Jack up the rearend; put the drive train in Neutral. Have someone apply the brakes. See if you get any caliper clamping action on either rear wheel disk by trying to rotate the rear wheels.

NOTE! Both rear wheels will or should try to rotate together due to the limited clutches!

Just trying to see if either rear wheel caliper is applying at all. You can also press the pistons into the caliper and see if they extend back out.

Bill

Vette-Dream

I did have my boy press lightly on the brakes (car off) when it was up in the air. I could spin the rear tires with great effort, while I couldn't budge the fronts.

When I replaced the rear pads I used a standard screw type tool to press the pistons back in and they felt the same as the pistons on the front.

To be honest, if I didn't see the rears flowing so normally during the bleeding process I'd think nothing was happening back there.

On the skid test at Jiffy Lube their screen showed that the rears were engaging, but just not 'enough'. While the fronts looked like they were going over by 150% the rears looked like they were only filling up 20% on the graph.