Brake Problems, ABS + Brake Light

Robert Kohlman

Registered User
Recently my 90 SC has developed a brake problem. The ABS Light and The Brake Light will come on and go off. Sometimes they will stay on for a while and other times for a short period of time.

This has been going on for a couple of weeks. I can usually hear and feel the brake pedal vibrating when the accumulator cycles. I haven't really noticed this too much lately. The brakes seem to go soft and then come back on. Sometimes they will work fine for an entire day and then back to the above symptoms.

I did notice that when the lights are on the ABS system does not work. I found this out in the snow and ice when I hit the brakes a couple of times. When the lights go out the ABS system works normally. Another thing that it is doing is that I have to press the brake much harder than normally when starting the car. Again, this does not happen all of the time but recently it seems more often than not. Another thing is that I thougt that I heard something buzzing before all of this started. I could not figure out exactly where it was coming from and it quit buzzing.

The brake resevoir is full of fluid to just above the full line.

Does anyone know where I should start? Is the accumulator going bad or is it possibly something else? I just don't know if the accumulator would cause the brakes to go that soft all of the sudden like they are losing all pressure.

Thanks in advance for any help.

Bob
 
Does anyone know where I should start?
Start by checking that the pump is running with the engine off and key in the run position. Press the pedal numerous times and listen. This validates your pump motor, pump relay and pressure switch if the lights go off.
Is the accumulator going bad or is it possibly something else?
It could be the relay.
I just don't know if the accumulator would cause the brakes to go that soft all of the sudden like they are losing all pressure
A loss of pressure will cause the lights to lite and then go off. If left to go, eventually you can loose all power assist and the brakes will get hard.
If you've never replaced the accumulator on the 90, its time.

Hope this helps.
 
Accumulator

This is a common "problem" for the Teves Mark II ABS (installed on SC's between '89 and '92). Our ABS used an accumulator to maintain system operating pressure between hydraulic pump cycles. The accumulator is a steel ball housing a dry nitrogen filled bladder. The bladder is compressed by brake fluid when the pump cycles. As the brakes are applied, the bladder expands and forces the fluid back into the system. This maintains the required pressure (approx. 2300 psi) on the pressure sensor/switch and in the lines to the calipers. When the accumulator bladder has expanded to the point it can no longer maintain the proper pressure, the sensor/switch triggers the pump relay and the hydraulic pump cycles again. The pump should only cycle about every 4th or 5th time the brakes are applied.
The accumulator is generally only good for around 10-yrs. After that, the bladder fails and will no longer contract and expand. This causes the pump to cycle every time the brakes are applied. The ABS control unit will sense this over-cycling and signal the failure by flashing the Brake and ABS warning indicators on the instrument panel.

Replace the accumulator ASAP or the constant over-cycling will cause the pump to fail due to overheating.

Accumulators are available from Prior Remanufacturing for around $100.00 (US). It is a quick & easy repair that will save you the $400.00 or so it costs for a rebuilt hydraulic pump.
 
Thanks for the replys so far.

I replaced the brake pressure switch in the fall because it was leaking and causing the suspension to stay in firm.

I have discovered a few other symptoms. The brakes have to be depressed really far for the brake lights to come on. When the brake is applied real hard it will not send the car into the firm ride mode like it used to. I looked at the sensor that is hooked to the brake pedal and it had a lot of fuzz on it. Also, it had a vacuum line directly above that looks like it might have had small amounts of oil seeping out becdause of a loose connection. I wonder if that could cause any problems. I'm going to have to take out the drivers seat so that I can get to the switch to try to clean it with electronic spray cleaner.

The noise that I heard sounded like and electric motor buzzing that would not go off. It would not even go off with the car so I unhooked the battery and it quit. I have not heard it do that since then. I hope that I did not burn anything up!!

Thanks,

Bob
 
The "vacuum hose" connecting at the brake pedal is probably the control for releasing cruise control. The cause of the "continously running hydraulic pump" is a bad ABS Pump relay (aka Brown Pump Relay). It will sometimes stick in the closed position and this will run the pump until the battery is disconnected, or goes dead. A replacement relay is available for around $15.00 (US), ask for a GP Sorensen MR120. The low pedal sounds like air in the system???? or there could be a pressure leak somewhere....
 
I just ordered an accumulator from prior. He said that I would have it in 2-3 days.

How much time does it take to replace and do I need any special tools. I figure that I can tackle it this weekend. I have a Haynes manual that is decent enough to get me through just about any problems that I have had thus far.

Prior also said that if the accumulator did not fix the problem that they I can send the unit to them for an entire rebuild for $540. They also said that they will give a $75 credit becuase of the new accumulator if it needs to be rebuilt.

Thx, Bob
 
The pump relay is located on the passenger side near the firewall under the windshield cowling. There are a couple of relays over there. The ABS pump relay should be marked and will be dark brown in color (Brown Pump Relay).

To replace the accumulator, you must depressurize the system.

With the key-off, pump the brake pedal around 20 to 30 times (until the pedal is rock hard).
Remove the windshield wipers and cowling. The accumulator (stock type) has a fitting for a hex-key/allen wrench on the top. I don't remember the size. unscrew the old accumulator and remove. (you probably will want to put the accumulator in a bucket because it will drain a lot of old brake fluid)

Be sure that there is a new O-ring on the new accumulator (Prior units have it), lube the accumulator threads with clean brake fluid and install. You only need to get the accumulator "hand-tight" (like an oil filter.

Turn on the key and listen for the hydraulic pump to pressurize the system. Fill the reservoir with fluid if needed.

Bleeding of the system is not typically required.
 
Here is a pic of the assembly.
You'll figure it out when you get the part.
absactuator.jpg
 
Thanks for all of the info. I help people out on the board all the time based on my experiences with things that I have had to fix on my SC's. I have not had any problems with the brakes until now so all of this info was great.

Tonight I pulled the car into the garage, turned it off and pumped the brakes until the pedal was hard. I pulled off the brown relay, cleaned it and put it back on. I checked the brake reservoir and it was full of fluid so I figured that the pressure had been relieved. I turned the key on and listened to the pump cycle until it went off. Then I pressed the brake pedal 3 or 4 times and heard the pump cycle every time that I pressed the pedal. This leads me to believe that the accumulator is the culprit based on what I learned from you guys.

I also have another problem. My brake lights will not come on until I am way into the brake pedal. Also, I am having to really depress the brake pedal to get the car to start. I took off the brake light switch, cleaned it and reinstalled it. I'm not sure what is wrong with it but what I did didn't seem to help any. It seems like it moves around upwards and downwards quite a bit. The switch on my 95 SC seems to be in a little different position and does not move up and down as much. I'm thinking that the switch is either broken or is not on the pedal correctly. Are the brake lights not coming on early enough and the car not started are related to the same switch?

Do you guys know anything about the brake light switch.

Thanks,

Bob
 
Replace the brakelight switch. They're cheap, $6 at Autozone. A faulty brakelight switch will cause your car not to start (for 90 model) and your brake lights not to come on.

Also, the hex fitting on the accumulator is 12mm. Do not use 7/16ths" or you'll strip out the fittting.. even though you are planning on replacing it, you'll not be able to get the thing off if it gets striped.

Also, in your case, you should bleed the brakes anyways. The low pedal is usually an indication of air in the lines. You can see if things are better once you have the new accumulator installed, but if you don't get a good pedal, bleed the brakes. There is an order for this, its RR,LR,RF,LF. And to bleed the rear calipers, you need the key on to keep the accumulator charged. You don't need to do this to bleed the fronts however. This is covered in the Haynes manual. Also, use clear tubing from the bleed screw into the catch can so that you can see when the air is out and good clean fluid is in the lines. I've found it to be much easier to just remove the wheel on the corner you're working with.

Hope this helps.. and also, how did you "clean" the relay? The sticky part is the contacts inside, so unless you pulled the case off, filed down the contacts, I'm not sure it will make any difference.
Hope this helps :)
 
Yes, I figured that I will bleed the brakes anyway just to be safe. I read the procedure in the manual and it looks pretty straight forward.

As far as cleaning the relay, I used a screwdriver to scrape away some of the crud on both the relay and the connector before I reconnected it. It seems to be working properly. I just wanted to try to make a few areas clean so that I would increase the probability of getting good contact when I put it back on.

I figured that the brake switch would be inexpensive because there is not much to it.

Thanks,

Bob
 
This must be on a auto transmission car?

I haven't ever looked at that part, but logic says one of two things could be the problem. Either the switch is requiring too much travel to trigger, or the switch is in a location that allows the pedal to travel further than it should to trigger it. I assume your cruise also doesn't disengauge until you really hit the brakes?

When it rains, it really pours huh?
 
You are correct. I have to hit the brake pretty hard to disengage the cruise control also. I usually would turn it off on the steering wheel. I wasn't going to bother repairing that little bother becuase my philosophy is "If it aint broke, don't fix it". Well, now it is broke so I guess I will have to fix it.

You are right about "When it rains it pours". I just put a radiator in it last month. I want to put new shocks on it too so that will be another $400 to $500. All in all for a 13 year old car I still don't think that any of the repairs are unreasonable.

My 90 SC is an automatic and my 95 SC is a 5-speed. I haven't driven the 95 since October when I bought it. So who knows what will be wrong with it when I fire it up for the summer. I do start up the 95 and get it to operating temp one time per week and roll it up and down my street one time just to keep everything in good shape.

Bob
 
I replaced my accumulator and the brake switch this month. The hex nut is 8mm. Once you replace the accumulator, your brakes will be like new and hence the old brake switch doesn't get engaged and the brake light doesn't come on and you will be scared that some one might rearend you. Change both the accumulator and the brake swithch.
I followed exactly the instructions given by LJGriggs and TbirdSCFan, thanks guys.
 
You're welcome.

I'll have to make a note about that hex nut size as, on second thought, 12mm does seem a bit too large. 8mm seems to be about right. Just remember to use the metric size, not the US.
 
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