Hello Again , I'm at what I hope to be the last difficult and expensive fix on the 1986 Vette I got myself into . The Antilock light is on !
Here is what I know about it and the brake sys. Car Sat for some yrs
Prior owner bought it brakes were froze up . He replaced rotors /pads/
calipers /master cyl/booster asm. the car sat in a garage little over 1 year .I decided that my hip rehab was boring me and I needed something to keep me off the couch and rewarded myself with this car. So far I replaced intake gaskets /stat/rebuilt fuel rail /new injectors/fuel reg /egr /fuel lines /cleaned tank /oil /horns/ Now this
So one of the many things that failed by the time I got it home was the antilock light is on .(Clues?)I do notice that the brake pedal on this car is a bit stiff, takes a bit of effort to stop .(in comparison to my ranger or focus ) when restarted the light will go out then after moving the car at a few mph the antilock light will come on and stay on .
I read my shop man and it has reference to a device that is needed to check the sys .I don't have one !!
So If I check each wheel sensor with a ohm meter to see resistance to see if one is different /check continuity Or if I lift each wheel and have someone spin it would I get reliable info on a bad sensor ? Other than this what else can I check using a multimeter that will help locate the trouble . On my ranger when replacing brake lines the shop man warned not to allow the abs unit to get air in or it would have to be taken to the dealer to be reset is this sys similar ? .Can this have been caused when the po redid the brake sys? I have read a lot of info on cac on the antilock sys but it refers to using the gm test tool . Any advice on back yard testing on this is welcomed and appreciated Thanks in advance FT

 

Similar issue and anxious to hear replies. My ABS light was on when I bought the car two months ago. Brake has always seemed a bit stiff to me but I attributed it to 'just the way it is'. I looked at the wheel coonnections thinking I would see broken connections.of course all connections are present. There is a lot of grease on the front tires and corrosion from poor storage EVERYWHERE.

 

I did read that grease /dirt /metal fillings from bearing wear ,on the sensors can cause trouble .This car is clean but I might pull each sensor to see what may be on the tips ,I believe they pick up magnetic pulses from toothed rings on the wheel also need to check the rings teeth
I found some article's here and one refered to the corvette action ctr which had a very informative article on 86 to 92 abs but again it talks of the tester made for this as it won't throw a code on your ecm for early yrs.

 

I don't know of any way to test the older ABS without the Tech 1 scan tool and its cable. It could very well be that the professional scanners from SnapOn have adapters and can read it too. I have heard of dealers that no longer maintain their own set of scan tools for the older ABS too.

PM Agent86 and ask his advice or call the dealers in your area that have been there a while and ask what a diag fee would be.

If you simply bleed the brakes very well it just might solve the problem but this is a total guess. (although bleeding brakes isn't a bad thing to do anyway)

 

1st of all, welcome to world of corvettes !

brake pedal should NOT be very stiff. It should grab with a small amount of pressure. Booster is likely blown/leaking. Get under hood and listen for hissing when someone steps on the brake...engine tone will change also as a BIG vac leak starts when the pedal is applied.

ABS...
The lite can come on for a thousand reasons. Back then, the ABS was often a "one of" system and the scanner to read this system is as rare as a blond bigfoot...The 1st few yrs the system changed as it evolved.

ABS evolved over time to become part of the rest of the main ECMs system. Porsche, Mercedes and Cadillac also used this same system those years. Parts ARE available...just have to hunt. Wheel sensors are wheel specific...so IF you see a donor car that's got wheel sensors, BUY THEM !

The usual and most common issue is the ABS controller relays, or getting wet as water drips in from the hatch corner directly down onto the storage door to the ABS controller....
Also, any damage to a sensor will set codes. Ohms will NOT necessarily tell you if a sensor is bad or not...the sensor sits so close to the abductor ring that when a wheel bearing gets loose, that's enough to allow the ring to knock the tip off the magnetic sensor and that will set a code. Ya just gotta look at 'em all to know for sure....Sometimes they just get dirty with grease or mud.
The rings are made into the hub since its a replacement unit with no rebuilding for wheel bearings. Sensors mount into the knuckle of each wheel.

ABS will self test at every start up.. Sounds like your fails. Start the car, and roll. AT 3 mph the ABS runs a self test to see if all corners are reporting and if NOT or if there is trouble in the relay or module, it sets the code and drops out. Brakes are fine, just no ABS involvement in a skid. You SHOULD hear the growl of the ABS pump cycling during the test @ 3mph. 1-2 seconds either rolling back or forward. You can 'feel' the test in the brake pedal when it happens...

Dirty fluid CAN cause a lite or air in the brake lines. If the fluid is not crystal clear, flush it WELL and bleed. See if that doesn't help with the lite.

ABS is the most durable and most tested part on a car. They (DOT) tested for a decade before allowing car mfg to turn ABS loose on the public. Its a very durable system but the little things CAN bring it down. Fluid, physical damage, water etc...

Hope this helps.

 

I have a '96 which has differences but the following should really be the same for you. I had the light intermittently coming on and after doing everything I list, it has been off for a year. Try checking the abs fuse first (also make sure there is no corrosion on the fuse and holder). Next bleed the brake system. Take a turkey baster and pull old fluid out of the master cylinder - don't pull it all out but get to a low level. Then refill with new. Next, bleed at each wheel. I do the passenger rear, then driver rear, then passenger front and last driver front. I installed speed bleeders to make it a one man job. While at each wheel check the abs sensor for dirt and grease. If all else fails, using the Factory Service Manual find the ground for the abs module and clean it, then clean the electrical connectors for the module itself.

 

Thanks for all the interest , the master /booster /lines /pads /calipers /and fluid all new one year ago .fluid clear All is new /car only has 45000 mi spent its life inside barn and last 3 yrs in temp controlled garage . I did not bleed lines as I always associated soft spongy pedal with air in line not hard pedal . PO had this work done by a shop then stored inside heated garage since. very clean (actually seriously clean mechanicals)
I didn't consider re bleeding the lines but I guess it can't hurt trying .i'd feel better about the brakes if they weren't so stiff. I will pull all the calipers and check for stuck pistons check condition of sensor s and check with a multimeter ,bleed lines and see what I have .Just read a article saying a stuck caliper piston can cause problem (I do not have any brakes hanging up but can be stuck open ) .brake booster is new along with all other brake parts including rubber lines .As far as vacuum after replacing intake and everything on top I had to replace my pcv as the vacuum I now have causes it to chatter which it didn't do before went to a ac delco to stop it . .I also have replaced all the vacuum lines that looked rotted . vacuum is now over the top so not vac problem . Idle unchanged as brakes applied not a booster diaphragm issue but one would suspect as pedal is hard .I have to see if I can cross reference the master and booster to see if they are correct for this car .some work that was done to this car was wrong . !(found installed plugs for iron head not alumn heads big difference in length ) Bad weather coming to NE tomorrow so I won't be under the hood for a few days . I'll write back when I go over the above .Thanks Again

 

You might find this post of interest:

http://forums.corvetteforum.com/1570563275-post316.html

 

thanks Cliff, that is interesting .I have a docs apt this morn .the afternoon is bringing rain and snow showers here . maybe I should take out and finally have some fun with it . it has been nothing but money and despair since buying it . I might enjoy slaming the pedal a few times just to let off some steam .

 

The best / most resourceful post I have found that addresses your problem is linked below:

http://forums.corvetteforum.com/c4-t...questions.html

There are certain basic tests you can do at home with a DVOM and some time, but to get to the in depth stuff you need specialized kent moore tools.

But start with the easy stuff, first, that being each individual wheel sensor - clean those well (no debris or metallic shavings) and check them for resistance, should be 900-1500 ohms.

Good luck,

Matthew

 

Some more good info here:

http://www.corvetteactioncenter.com/...l#.UoJUASfXlp8

 

Thanks guys, I was hoping for some simple fix like a fuse or a simple relay .(I did check the fuses yeterday)I have been off recuperating from a hip replacement so I have had time to fool with things .So far this car has been my worst investment ever . I thought my wife and I would get to enjoy the fall riding in it while i'm off. instead I spend days repairing it and at this point frustrated .I over the years have bought old boats ,many motorcycles ,and junk cars to use for work as I put on 100 mi a day to work in a bad area so I don't use our good car or truck .Nothing I ever bought has frustrated me or cost as much just to drive around the block as this thing . (a little venting )
Well my shop is set up for motorcycles , I can fit the vet in for storage but its difficult to work inside .So I set up a barn tent in front of the shop and I will be spending my last week off tearing each wheel off to see what goes on . After that if I can't find anything Ill take it to another shop . If it was spring it would be out front for sale .at this point i'd be better off taking the loss as I keep throwing money at it just to find another problem and I have in twice what its worth now .I did get to drive it about 200 mmi since buying .a lesson learned the hard way!!

 

Sorry to hear about the troubles. Perhaps you should post in the local section and see if there are some local members willing to help you out.

 

well I removed each wheel /bled /checked pistons for movement /removed sensors cleaned with ele cleaner checked pads for signs of sticking .Everything is new even the bolts that hold everything together as the po stated . sensors were clean .pulled the plugs on the rear resistance 998 /999 ohms . I managed to snap one bolt on the front rt sensor and spent a fun afternoon removing the stud . I have to put it up on my ramps tomorrow to get to the plugs on the front to check them .I can't jack it up high enough to get under safely .I ran a quart of new fluid thru it but it was clean .Po had someone do a very good job on the braking sys. It had to be the easiest brake removal I ever did .I do seem to have a resistance to flow when bleeding the lines that I never felt with another vehicle .
I have to study the book tonight to see if there is some kind of proportioning valve somewhere maybe blocked up .

 

I kept getting the light. Finally traced it down to a broken sensor connector - by the K member. My 86 has the connector at each wheel and then there is another round connector by each leg of the K member. The connector was all grimed up and hard - it cracked and was showing an open circuit to the ABS unit - sensors checked out fine.
Fixed that wiring and no ABS light since.
Just a thought.

 

Completed cleaning sensors and checking brake hardware all is as good as it gets all new in working order ,ran near a quart of fluid thru bleeders while I was at it but fluid was new and no signs of dirt. Rear sensors 998 989 front right 989 front left 902 ohms
Can this front left sensor be a problem?????? its within900 ohms but is different than the rest
I cleaned all the plugs/connectors and used dielectric grease on them also.
None of this has solved the problem or have I found anything wrong with the components
Now this is a convertible according to the fsm there is a storage box behind the drivers seat that has the abs equipment .I have no hatch behind my seat like i''ve seen in coupes .i have boise speakers in the deck directly behind the seat and the rug runs under the grills .So to get at the abs equip do i have to rip all this out ??? I can see the box and brake lines running to it from underneath but fsm says not to remove from under the vechicle .
cgantner mentions another set of plugs besides the ones at the end of the pigtail for the sensor .by k member I don't see them .where should I be looking for them .I have to squeeze under this thing even on my ramps so its rough doing anything on the underside

 

Went out and followed the harnesses i think its the front pigtail plugs from the sensors that are mounted on the cross member on mine ?? I don't see any other plugs on mine . Going to see if the rug lifts out of the back of this . anyone knows verts give me a yell !!1

 

Having a problem with my ABS also, i have an 87 Z52
an aftermarket brake booster was installed by the PO, but it seems to have the same (repco) master cylinder but no sensor or wire going to it
i dont get any ABS light but it takes a lot of pressure for the brakes to stop the car, but they will lock up
i just installed new brake pads and bled and changed the brake fluid

any ideas?

 

Open the rear compartment behind the driver's seat. I think it is an odd size like 7mm. With the lid open listen for the pump to cycle its self test as you start and slowly drive off.

As to the pedal effort, is it possible the wrong bias spring is in the MC sending more power to the rear than it should?

Is pedal effort linear or is it squish and lots of travel then firm?

 

It was extremely spongey before i changed the fluid and pads, now it has some travel and then it feels somewhat spongey but more firm

also the pump makes no noise at all