240 "Brake Failure" light

1984 245

Replaced front calipers, pads and rotors over this past weekend and now have an intermittent brake failure light where heretofore I had none. Curiously, this light did not appear until yesterday, after nearly 200 miles of driving.

What trips this light?

System bled beautifully, good pedal, what gives?

Thanks.

There is a brake line junction block ( bolted under the car, above your left control arm ) in the middle of the block is a switch that's activated by an internal slider pin. When there is more pressure on one side of the pin, it move and sets the switch off.

You can re-bleed the brakes and crack open a line on each side of the switch on the junction. That usually works great. If you have any brake fluid leaking from what looks like the switch , you have to replace the whole junction block. Hope that helps

if you HAVE to REPLACE the junction block...don't CHEAP OUT....
buy the *real deal"...someone recently posted a problem w/the THREAD DEPTH
and SEALING ISSUES on the *economy* version of the block....

I have a solution for you. Reach up behind the cluster and pull out the bulb that illuminates that warning light. Problem solved. I did that some ten years ago and am glad that I did. It never comes on anymore. And my brakes work great.

coonmanx said:

I have a solution for you. Reach up behind the cluster and pull out the bulb that illuminates that warning light. Problem solved. I did that some ten years ago and am glad that I did. It never comes on anymore. And my brakes work great.

Click to expand...

not real smart

when you lose one side on these systems you can barely tell, it still brakes on three out of four wheels. that light is the only warning you're going to get if you drive the car lightly around town before the second half fails...

when my j-block failed it failed internally and leaked out of the switch port. if it's leaking there don't bother trying to fix it by replacing the switch, that won't cure the leak and the switch obviously works if the light is on

coonmanx said:

I have a solution for you. Reach up behind the cluster and pull out the bulb that illuminates that warning light. Problem solved. I did that some ten years ago and am glad that I did. It never comes on anymore. And my brakes work great.

Click to expand...

they are *just* brakes. ****...on this supposed enthusiast forum at least suggest the correct way before outright hacking it. Obviously you are in denial about driving a heap of a road going hazard and how much brake work it no doubt badly needs.

They finally figured it out in 1991...make the junction have no moving parts and put a float switch in the reservoir...like every other car company does it .

So yeah, I just swap them to the 91+ arrangement and make sure all the calipers, bleeders and master work right. Enjoy better pedal feel and never replacing that pita thing again or having it ruin the master or some such when it lets go.

Or just go ahead and put a stock oe one on it. The cheap one is not so great. If its leaking from the switch t must be correctly rebuilt or replaced.

The junction job is a pita.

coonmanx said:

I have a solution for you. Reach up behind the cluster and pull out the bulb that illuminates that warning light. Problem solved. I did that some ten years ago and am glad that I did. It never comes on anymore. And my brakes work great.

Click to expand...

I'll second the suggestion to not follow this advice. I did just this, and after a couple weeks, my brakes failed. I had ignored it.

If I had checked it out, I would've noticed a cracked junction block.

I didn't lose my fluid. The switch detected a pressure imbalance between the two circuits and eventually, the block cracked to the point that the brakes just wouldn't work.

yoshifab conversion gives that. all works fine, but it lies. i doubt thats the case, but heads up

Check for leaks at all connections.Then re-bleed the brakes again.There may still be air in the system or a loose bled screw somewhere.I had that light come and go until I bled the system with a borrowed mighty vac.Good high pedal,no more brake light issues.

When mine goes on, I turn it off by removing the rubber boot and spade lug / wire going to the junction block; then using a wrench remove the threaded plastic piece the spade lug mates to. When it is off, stick a narrow piece of metal into the hole to press down and reset (what I assume is) the plunger.

I've found this switch is capable of giving false alarm. That is, you can get a light even though it hasn't sensed an imbalance between the two brake circuits; the shuttle is still centered.

Assuming you are getting the light without having to step on the brakes, here's how you might find out if the shuttle is stuck to one side, or a small fluid leak in the switch is the cause of the warning light.

1. Disconnect the D+ from the alternator (small red wire). This allows you to disable lamp test mode without having to run the motor.

2. With key in KP-II, have someone observe the failure light while you disconnect the spade from the octopus and provide a solid, clean ground to the wire. If an assistant is impossible, an ohmmeter will get you to the same place without the need to test the lamp brightness.

3. If the light is just as bright connected to the octopus as it is directly grounded, the shuttle will be found to be stuck to one side. This would tell me I need a new one, and the conversion to 91 is my choice -- just be aware the correct float reservoir was only used on 91 non-ABS cars, as was the 8-port plain manifold.

4. If the light is brighter directly grounded, then you may be able to fix this by merely removing the switch and cleaning the rusty brake fluid from the cavity.

Note. When you remove the nylon switch body, the rust swollen first few threads in the block may make it a royal pita to re-install it. Chasing the threads with the flutes of an appropriately pitched tap will help.

Don't forget to reconnect the D+ wire as soon as you're done testing.

Excellent intel, Gents, thank-you. 'Flametrap you rock with the breakdown and illustrations, thanks man.

Will try to get under her this afternoon and hava look around.

Thanks again.

Sorry, I thought that you were talking about the bulb failure warning light and not the brake failure light. Yes, my advice would be bad in that case. I disconnected the brake light failure bulb which is just supposed to tell you when there is a brake light out, not if there is a problem with the brakes.

Apologies again. My brakes are in very good condition with new brakes all around and Super Blue in the lines. Stops great. I did have the brake failure light come on once when one of the flex lines failed on me (the guy who put in my front crossmember kinked that line badly). It is essential to have that warning light.

So many threads about the bulb failure light coming on. I should probably make sure that I am awake before posting.

Well. in paying attention to this, I will say this now, my brakes are fine, new pads, lines are in very good condition, only the bolts to the calipers are rounded off, from a poor attempt by someone else to bleed them, and ever since he... did them, that light had been stuck on due to him bleeding them wrong... I got sick of it, and I *did* pull the bulb out. I keep a watchful eye on my reservoir level every time I open the hood and it doesn't budge... Brakes work great, and I simply cannot bleed the brakes unless I farm it out to a shop and have them replace a caliper... funds which I cannot sanely expense... Thought I would just say.

Right on.

Considering how sensitive to pressure imbalance this system seems to sound, I picked up a new full set of brake hoses this afternoon and'll try to get them on this weekend.

Thanks again for your input, fellas. I appreciate it!

remove warning light and enjoy

Haven't been able to get back to this, the 740 tossed me a re-direct with a blown head gasket so I've been chipping away at that as time permits.

Thanks again guys.

Yes, I know this is an old thread...

Some of the previous posts mention bleeding the brakes...but how? I've never had a problem bleeding the brakes on other vehicles, but they also didn't have this "brake failure" (junction block with switch) feature. When you open the bleeder valve, pressure drops at that location. Won't that just set off the brake failure light again? Is there special equipment or a special process that must be used to bleed the brakes on this model?

I've never trusted Chilton or Haynes manuals because they never have enough detail. Is anyone here aware of a **paper** Bentley manual for the 1979 244DL? Is there any other repair manual available?

To bleed the brakes I use a vacuum bleeder. First I pull out as much fluid and dirt as I can from the master, add fresh fluid and then bleed the system.

I had a car recently where I bled the brakes and then after the brake warning light came on. I bled the system again and it went out.

Thanks. Bled the brakes. The correct order (https://www.brickboard.com/FAQ/700-900/Brakes.htm#BrakeBleedingSequences) begins with LR, but it wouldn't produce fluid. Noticed brake fluid puddling in the wheel. I'm guessing a blown o-ring in the caliper. Looking on https://www.ipdusa.com is looks like I can purchase a rear caliper or a caliper rebuild kit. Is the rebuild kit likely to meet my needs?

Other locations bled fine. I now have clean fluid through the system to 3 wheels.