Moridan

05 350Z, Tein Flex suspension lowered 1.5", 19x9-235/35/19 front by 19x10-275/35/19 rear

Problem: from as long as I can remember, whenever I was going hard into a turn and put some pressure on the brakes (yes, I know its the wrong thing to do but hey, it happens), it would feel like I lose some brake pressure and could hear a little grinding. Not such a big deal and have dealt with it over the years.

Recently, I ran over something in the road and ever since then... in the same situation as above but with the VDC on (I normally turn it off), my "SLIP" light will come on even though I am not sliding any, and various brakes will come on (I am assuming) and my car will get thrown around. This of course is very disconcerting as when this first happened it was raining and I was slowing down to go through an interchange on the highway.

So... thoughts? I had originally thought that perhaps since my car is lowered that when I was going into a turn, possibly a brake line was getting crimped and losing pressure to the brake. Also, it seems that whatever the problem is, it is now compounded when I have the VDC on (a small drop in brake pedal with a little grind turns into the car nearly losing control).

Thank you very much for any input you could provide.

dkmura

iTrader: (64)

My thoughts are that when you ran over something on the road, you might have damaged one of the wheel speed sensors. Besides sending erroneous data to the ABS computer, they are also used by VDC to determine wheelspin. These problem codes should be held in memory and using a CONSULT unit or UpRev's Cipher will allow you to examine ABS codes.

Another theory is that you might have bent a suspension component when you hit something in the road. If the car is crabbing (even slightly) down the road, it'll affect weight distribution, handling and braking. Have you had the car up in the air to inspect it thoroughly? Let us know what the outcome is.

Moridan

Ive looked underneath it and had a local speed shop look underneath it. Couldnt find anything "obviously" wrong (i.e. broken wire, ect).

For my original problem, what do you think? It seems that when I ran over something it compounded an existing minor problem.

Thanks for your input!

cow

iTrader: (21)

Check to see that your battery terminals battery is properly tied down & its terminals fully secured. I had a similar problem when hitting bumps, only to realize my battery tie down had come loose & when I hit a bump, the battery was moving.

Moridan

Not the battery, but thanks. 9-) The freeways around here are in terrible condition but I only have problems in the curves (even the smoothest) when breaking.

cow

iTrader: (21)

Ah. That's all I've got. Good luck.

Spike100

Hi Moridan… The symptoms you describe typically are a result of running incorrectly sized tires, but your sizes are right on (235/35/19 front by 275/35/19rear).

The grinding noise is ABS, apparently activated by VDC (I’m sure you already know this).

You mention seeing the SLIP light, but you don’t say if you experience a concurrent loss of power (that should always happen when the SLIP light appears). The SLIP light doesn’t activate ABS (which is accompanied by the grinding noise you hear) but it is linked to TCS which kills power.

VDC is just a coordinator that orchestrates TCS and ABS to keep your car going in a straight line to the direction of your front wheels.

I think all this information is familiar to you. It sounds as though your car’s safety equipment is faulty, and that would be very unusual. I’m not sure what is going on here. I wish I could be more helpful.

--Spike

Moridan

Thanks Spike. The SLIP light comes on when I have the VDC "ON", and I definitely lose power. I naturally let up on the gas some because when this happens its in the worst possible circumstances (cornering under braking).

Is it typical for when the ABS engages (grinding noise) that there is a loss of brake pressure? For instance, I am in a corner and apply some brakes. At the same time that I hear the grinding, my foot on the brake feels the loss of pressure (moves closer to the floor).

So the question remains, what could cause the original problem (ABS engaging when there is no reason to? And what could now be faulty to cause the TCS to engage (VDC on) when it shouldnt?

Thanks everyone!

dkmura

iTrader: (64)

There should be no drop in line pressure when ABS kicks in. is it possible you have some air trapped in your brake lines? That would explain why the brake pedal gets soft and drops lower when you're on the brakes. Have you done any brake work or changed your brake fluid?

Moridan

The grind/drop in pressure problem has been around for years. I just had all of my fluids checked/serviced (90K mile checkup) but I haven't actually had any brake work done or bled the system.

pro_350z

iTrader: (3)

05 350Z, Tein Flex suspension lowered 1.5"

Did you do the install yourself or have it professionally installed?
Depending on your answer I have a good hunch on whats wrong

Moridan

Well, both actually. I had the initial install done at the dealership but it didnt look or handle correctly. So I read all of the instructions and re-installed myself after adjusting things. Was 8 years ago so the details are a little fuzzy.

What are you thinking?

thanks!

zakmartin

I agree with the original response from dkmura. You can't just look at your ABS sensor and say it's fine if it looks okay. You need to hook it up to a scope and spin the wheel. Assuming you have a solid sine wave pattern for the full rotation, then your sensor is okay. It's a very simple test and it's really the best way to know if it's working.

Spike100

But, the ABS is working. dkmura's original message questions if the ABS is receiving faulty data/input from VDC (which I think is a possibility).

It certainly would not be foolish to check the ABS, but I’ll bet it tests OK.

There is something else going on here, and I’m thinking it’s related to the mods (but I’m guessing and not providing a certain answer).

--Spike

dkmura

iTrader: (64)

Back to my original suggestion: has Moridan checked ABS codes? With the problems he's had, if it can be traced to an ABS issue, theres sure to be a code in memory.

Moridan

Thanks dkmura, Spike100, zakmartin, and pro 350z for your assistance. I've been out sick for a long time and.. bleh.

Continuing on with the problem, I noticed the other day that when I had to brake hard in a straight line, dry pavement, I heard a very quick grind (ABS?). Even with VDC turned off. It seems that when I have VDC on, the problem is much worse.

I've had the car looked at by the local speed shop and they didnt find any codes set. They didnt have an O-scope to check the sensor, and I am not sure if they would have known how to regardless. 9-(

So... possible bad wheel speed sensor giving faulty signals to the computer? And that would only cause the problem when I am braking in a corner and not when I am driving straight? I guess I can see if the dealer has the equipment, but they would charge me almost the price of the sensor just to test it. argh