Does anyone know what the AC specs should be on a 1987 for spinning the wheels and check what AC voltage comes out in milivolts?

I am getting . 600 on the backs at 4 mph
and .300 - .400 on the fronts?
are they supposed to be the same in the front and back?
They all go up and down with the speed
Should it be smooth like the speedo?

The dealer said it was the left front reluctor.
Not sure if they even plugged anything in because I learned there are no codes to get with the computer.

I am testing them by making jumper pins to a DVM and then either road testing them or jacking the rears of the ground.

 

i pulled ABS codes from my cars ABS computer. I have a 1996. Is you ABS light on? if so you have a code.

 

No codes are stored in this year. But the dealer said they got this from their computer. Left front reluctor missing or has broken teeth.

I took the hub off and all the teeth looked fine.

I checked resistance at each sensor and it was in the 900- 1200 range.
I fixed all the shorts in the wires.

I did an AC voltage test of the sensors by spinning the wheel and checking the voltage they produce in AC mili volts.
I don't know what the specs are.

Both fronts are similar readings and both backs are similar
The fronts are lower voltage than the backs.
Not sure what they are supposed to be.

GM doesn't answer me and Bosch said they don't offer tech support and to go through GM.

 

I had the abs light on my 87 years ago and I looked at the waveform with my oscilloscope from each wheel pickup and they all looked the same. The dealer that my mechanic works at had the computer that tests abs and we ran my 87 on it. It reported that the left rear wheel sensor was defective. Upon replacement the abs began working again. That wheel sensor was dented from some dufus that replaced the left outside universal on the half shaft. See if you can find a dealer with the abs tester computer.

 

It is great to know someone else got readings that looked good and it still was the sensor.

I brought it to the dealer
They said
"LF wheel either broken or missing reluctor ring"

I took the hub off and it looked ok

Then tested the wires goiing to the sensor plug and found a crack in the plug. It had resistance to. So i made a temporary wire to replace it but the light still goes on.

Could the shorted plug have damaged the sensor?

A parts guy said that there are two different sensors for the left front.
One has an o ring one doesn't.
Does anyone else have an o-ring on their sensors?

GMparts direct lists only two types

 

Shorting the abs wheel pickup coil and turning the wheel will not hurt the pickup. There is only one abs pickup coil on each wheel and if the dealers' abs tester reports your LF pickup is defective, I would replace it.

 

According to Gordon Killebrew, at 15 mph using a 10MegOhm Digital Volt-Ohmmeter the left front should read .65 millivolts AC and the right front close to the same. The rear sensors should each read 1.1 millivolts AC. If your reading is high it means the air gap at the toothed gear is too small. A lower reading would mean too much of a gap. If the air gap does not match left to right it could be caused by worn wheel bearings. If the readings are too low or too high, it will cause the 87 ABS light to come on. If the voltage readings are not close left to right, it will cause the 87 ABS light to come on.

The resistance across the 2 pins on each of the wheel sensors should read 900 to 1100 Ohms. They should also all be within 100 ohms of each other. If not in range, clean with WD40. If still not in range, replace the sensor.

I have found that the front wheel bearings have a minor amount of play in the way that they mount to the car. Once they are bolted in, they are in solid, but they can be mounted a tiny bit more forward or aft of center. Since the toothed wheel that induces the voltage to the ABS front sensors are on the front wheel bearings, and even a tiny difference in air gap has a pretty significant effect on the induced voltage readings; by adjusting the wheel bearing mounting, you can make a minor adjustment in voltage if your reading is slightly too high or too low compared to the other front sensor. This doesn't work for the rear bearings since the toothed wheel is not part of the bearing. A bad wheel bearing (front or rear) can cause the voltage to be off enough to set the ABS light. That was the cause in my case.

If the dealer test unit says "LF wheel either broken or missing reluctor ring" I'd guess that it is seeing an unstable or too low AC voltage. Since no teeth are missing, either the air gap it too great or the sensor AC voltage isn't being seen by the controller/test unit at the ABS controller harness. As the test unit did not find fault with the right front sensor readings, it doesn't matter if you test at exactly 15mph to read .65 millivolts AC, although that would be ideal. Just make sure that the readings are the same on the left front as at the correctly operating right front at the same wheel speed for both.

 

I ordered two new sensors for both sides from GM direct
They sent me ones with o-rings
here is a picture
http://www.automobiletest.com/servic...e/sensors2.htm

They don't fit without the o-rings and I can't imagine installing them with the spacer leaving a gap on the hold down plate.

Anyone know what the deal is?
I have to wait till Monday for an answer.

 

Only thing I can add,is be sure the abs fuse isnt blown and the relay good.Also be sure all the sensor tips are super clean.Years of grime and dirt can render them blind.Other than that,its a bit tricky to diagnose which sensor is bad.These bad boys arent cheap as youve seen.

Use some anti seize around the housing(not the tip!!) to slide the sensors back into the knuckles.I had one that was corroding into the aluminum.A good anti seize after clean up let it stay clean and removed next time with no problems.

 

JETSET, there are two part sensor types for the 86-87 ABS sensors. One used o-rings 1005226(1/2), and the other did not 1408407(7/8). You have recieved the wrong parts for your particular car. Here is the GM Dealer Parts info for 86-87 ABS sensors.

14084077 - SENSOR, SPD FRT-LH (1986-87) (*WITHOUT O-RING IN STEERING KNUCKLE.)
14084078 - SENSOR, SPD FRT-RH (1986-87) (*WITHOUT O-RING IN STEERING KNUCKLE.)
10052261 - SENSOR, SPD FRT-LH (1986-87) (*WITH O-RING IN STEERING KNUCKLE.)
10052262 - SENSOR, SPD FRT-RH (1986-87) (*WITH O-RING IN STEERING KNUCKLE.)

 

Mike thanks
14084077 - 14084078 are discontinued
they are for 86's
Everyone will have to retro fit the later ones. They are the same sensors except for the small are near the top where it is a bigger diameter and wont let it fit down flush. I will show pics on how i did it if anyones needs to know.

I have an 87 and the spindles were replaced with an 86 at one time
The 86 spindles don't have the countersunk hole
You have to machine out the top part of the hole to accept the 87 sensors. I used a brake hone and made it work with some small strips of sand paper. I only had to bore out the top part 1/8" down 25 thousanthds larger and then install the sensors without the plastic spacers. This seems to be the retrofit. They are the same length and fit nicely now.

but it wasn't the problem.
The ABS light is still on

got to check the cornering sensor under the dash
anyone know if that can that be done from the rear connector or do i have to remove it?

When the car is on jack stands and i apply the brakes the pump and motor kicks in so i know they work ok
I am wondering if a erear sensor may be bad
should the anti locks come on in that situation
the abs light doesn't go on when only the rear wheels are spinning so that is why i think the problem comes from the the front wheels
i replaced a wire that had some resistance to the left wheel but the light is still on.

 

On my '92, I test my ABS wheel speed sensors by plugging in my Vetronix Tech-1A to the ALDL connector under the dash, with the chassis cartridge, and driving down a straight road and comparing all four wheel speeds with the speedometer reading -- all five should have the same speed reading.
Doing it this way, you don't even get dirty.

Tom Piper

 

You have to remove it. It is under the A/C controls in the central dash area. To test you have til physically tilt it 90 degrees. It has a mercury switch that goes open or closed only.

The Tech-1A is an outstanding tool for all kinds of diagnostics on the C4, but even a Tech-1A cannot test the early 86-89 ABS systems. The pre-90 ABS system is very crude compared to the later C4 ABS systems.

For the 86-89 ABS systems there was a special Kent-Moore ABS controller test unit that available, but you have to find them used now. I bought one off of a retiring GM mechanic through eBay. Even that special test unit will not test the accelerometer under the A/C controls.

 

What model do you have
what adapter?

The early ones are a pain because no codes are stored. I have a brand new Snap On Solus and it only gives you readings to check out with a DVM. I did that and they come out in spec. I can't figure this one out.

I took off the rocker panel and found the wires were spliced from a previous body repair. They used crimp connectors to piece the wires back together. I am going to resolder them so they make a better connection.
The front connector where the sensor connector plugs in was damaged and shorted and I had to remove it. Then connect the new sensor with seperate wires because i can find those special connectors anywhere. I was able to solder pins so i could plug them in seperately with shrink tubing and replaced it to the splice. Ther other wire was ok. Now the short is gone but the light is still on soon as i roll.

I had to buy the newer style sensors and retro fit them in the older spindles. I have 86 spindles in my 87. I had to bore the top 1/8" or so of the hole 25 thousanths to accept the 87 sensor that has a larger diameter at the top.

This is how I did the retrofit
automobiletest.com/service/1987corvette/sensors.htm

Does anyone have a picture of the 87 hole?
Does the sensor fit all the way down flush on the flange with the black spacer going into a countersunk hole?

When the car is on jack stand and i run it up to 20 mpg the light doesn't go on. The front wheels aren't turning. Then when i hit the brake the pump activates with the anti lock system. Does this help in the diagnostics?

I would think the pump, relays and computer are ok if I heard them activate. Any ideas?

is there a way to check the acelerometer from the pins. The lights goes on right away so it must be sensing something i should be able to check. I wish it had ODBII

 

If I knew the software checks and sequence that the computer goes through at 4 mph it would help me diagnose the problem.

I have a Snap On SOLUS I tried to use but it connects to the ODB I plug and only tells me the specs and things to check with a DVM. So most of the ABS checkes don't work for these years.

The 87 service manual says to properly diagnose the ABS system use J35890 ABS Tester and the J35592 Pin Out box.

I am assuming they are made by Kent Moore for GM but I can find the unit anywhere.

I would buy a used one or a new one that connects the to ABS controller if I could find one.

 

Jetset,
Although this post won't help, I hope you solve this. My 87 although off the road at the moment has has the abs light on for a long time. I have had a few attempts, but never succeeded in rectifying it. Measuring resistance, changing relays etc. etc. It started with the light coming on after say 1/2 an hour, then earlier and earlier, until like yours, it came on as soon as I started to move. I hope you keep us posted and have better luck than I have had. I never removed the sensors, so can't help you with your question on the hole. I just hope the post bounces it back to the top of the list for more interest.

 

A lot of people have similar problems with this system.

This system should of been recalled from day one.