Brake failure light on in my 75 Brave D21

[tbirdkeys]

Sent: 8/31/2008

I have recently acquired a 75 Winne Brave D21.  The brakes seemed a bit spongy when I got it but they stopped the rig ok as long as it wasn't an emergency.  But the brake light failure light is on and remains on constantly. 

Some info on this rig is I belive it is the M300 chasis.  It has a vacuum booster, MC, disc brake fronts, a proportioning valve and of course rear drums.  There is only one brake line running to each rear drum. 

I pulled the front calipers and I have brand new pads.  I found the fluid level really low in the rear brake reservior.  It might have even been empty, but I cant see into the stop of MC.  I filled up the MC and bled all the brakes.  Now it seems I have even better braking, but the brake light is still on.  I have not pulled the rear drums yet to see what I have going on in the back.  But I am fairly mechanicly inclined and I have worked on lots of brakes.   It seems that the brake light failure switch must be the presure switch in the proportioning valve.  And if I have the brakes bled correctly that should turn off the light correct??  I'm wondering if the switch might be bad.  The problem is I don't know how good the brakes used to be, to know if they are still not working correctly. 

Anyone have any comments on this brake light issue.  I read in the original owners manual that the MH is equiped with a dual braking system.  I don't know what this means.  Seems like a normal truck brake system to me. 

Thanks.  I'm new to RV's in general and this site is great.

[75Travco]

Sent: 8/31/2008

The brake warning switch is located in the proportioning valve.  If pressure is lost in one side of the system, a piston is forced off center which latches the switch into the "ON" position.  Once the system is repaired the switch should reset as soon as the brakes are applied - with equal pressures on both sides, the piston should be forced back to the center position putting the switch into the "OFF" position.

The master cylinder reservoir being low on fluid indicates a leak someplace in the hydraulic system.  Have you checked for the usual suspects - leaky rear wheel cylinders and leaks in the brake tubing?  The booster could be faulty, but that can be checked later after some simple causes are ruled out.

A fault in the wiring of the brake warning light circuit could cause the light to stay on.  Does the wiring look intact?  Over 30+ years the wiring can take a real beating.

[denisondc]

Sent: 8/31/2008

It was a normal truck braking system for the 70's. If there wasnt any problem with the brakes, the light should go out - after you had fixed a problem, and pushed the pedal down (fairly hard) with the engine running. i.e. it is supposed to re-center itself. If it stays on.....that is indicating you have incorrect pressure ratios on the two sides of the 'dual' system. It would be the same result due to having too much fluid displacement on one side of the 'dual' system compared with the other - which is what I think your situation is. The Service Manual calls the unit that turns on the dashboard 'brake' light a "Brake Warning Switch Valve and Metering Valve". As far as I know, the front axle (disc brakes) is one half of the 'dual', the rear axle (drum brakes) is the other half. All this info is in the service manual pdf file you can download from this site, if you have a broadband internet connection. Section 5 is 'brakes'. The file is about 178 megabytes.
My guess is that your rear brakes are where the problem is. If the self-adjusters are stuck and not 'advancing' the shoes, then the distance the wheel cylinders have to move when you apply brakes represents too much fluid displacement for the B.W.S.V. to be happy. If this is the case, fixing it requires removing the rear wheels and the hubs/drums to check on things.
Before you do that however, you might want to try bleeding the brakes while holding the 'metering valve' in its extended position. I dont have disc brakes on my Winnie, so I dont have that type of BWSV, and have not experience here. Good Luck.
Another possibility would depend on your Winnie being new enough that use of the parking brake also turns on the dashboard brake light. But in 1976 I dont recall they had thought of that yet; and my version of the service manual doesnt mention such a feature either.

[tbirdkeys]

Sent: 8/31/2008

AHHHHH, Dual brake system -- Front and back-----  Interesting.  I was thinking dual master cylinders or something. 

Thanks for the tips.  I am going to try and bleed the rears once or twice more before tearing into the rear brakes.  Thanks

[tbirdkeys]

Sent: 9/3/2008

Thanks for everyones help.  I bled the rear brakes again and the light went off.  Thanks.

[wcrowles]

Sent: 9/18/2008

We have the same make year and model Winnie and had the same brake problem. I think you better check the MC level frequently because your rear wheel cylinders are likely leaking slowly and may be stuck too. You should also check temperature of rear brake drums after driving the unit. I found leaky and stuck wheel cylinders and a broken return spring in the rear brakes.......after the rear brake overhaul I think fuel mileage shuold be much better since rear brake drums are now cool after driving but don't know how many MPG yet.