Jake Brake Install

[DoubleEagle]

Would it be logical (maybe legal as well), to have a amber light in the rear that comes on with the Jacobs brake? That way there would a two stage warning of braking action.

[richard5933]

Seems like this debate has been going on for decades - the book shows the brake lights being tied into the Jake brakes, but apparently few people actually starting doing that until recently when Jakes began performing more like the service brakes. At least that's what I'm reading online and gathering from the 'old timers' at the shop.

Tying into the brake light circuit isn't that difficult, according to the wiring diagram. Apparently there is already an unused wire in the OEM harness to bring the 24v signal from the Jakes back to the driver's electrical compartment. A short wire in the engine bay brings the signal to this wire in the harness, and then another short wire in the driver's electrical panel connects to the stop light relay to activate the stop lights.

Only question I have is which of the two stop light relays in the driver's electrical panel is used? There are two, one is labeled in the book as 'stop light relay' and the other as 'DD-3 brake stop lamp relay'. I'm guessing that they are talking about the one labeled 'stop light relay', but the diagram in the wiring diagram doesn't at all match the layout of the relay itself. Guess it's time to pull out the multimeter.

If I find that the Jakes provide actual stopping power, I'll connect the stop lights. I might add a toggle switch so that I can turn them back off for those long steep downhill grades where the Jakes do nothing but prevent acceleration so as not to have people think I'm riding the brakes all the way down.

[luvrbus]

When you are using Jakes about every truck or bus is doing the same,the transmission in our Trek will hold the same speed coming down from Golden Valley to Laughlin and that is 6% for 12 miles.This has always been just a option and not required by any law for years do what makes you happy .The newer buses have it or don't have it, none around here in Valley have it on these 6 % grades lol and I haven't heard of any getting rear ended,FWIW when wired to the stop light when the 1 way diode on the buffer switch blows and they do the Jakes will activate everytime you apply the brakes     

[richard5933]

...FWIW when wired to the stop light when the 1 way diode on the buffer switch blows and they do the Jakes will activate everytime you apply the brakes   

That's one thing I couldn't find in the wiring diagram - the diode.

My assumption is that something about going through the relay keeps the stop lamps from backing up into the Jake circuit and firing the Jakes. But, looking at the diagram I just don't see it. At whatever point the power feed from the Jakes hits the stop light circuit, there will also be power being fed from the regular stop lamp circuit.

Sounds like a diode belongs in that circuit somewhere.

UNLESS...

Perhaps the 'stop lamp relay' shown in the Jake wiring circuit is an additional one which is added specifically to allow the Jake's power feed to the stop lamps to remain totally separate from the one from the service brakes.

Thoughts?

[MagnoliaBus]

That's one thing I couldn't find in the wiring diagram - the diode.

My assumption is that something about going through the relay keeps the stop lamps from backing up into the Jake circuit and firing the Jakes. But, looking at the diagram I just don't see it. At whatever point the power feed from the Jakes hits the stop light circuit, there will also be power being fed from the regular stop lamp circuit.

Sounds like a diode belongs in that circuit somewhere.

UNLESS...

Perhaps the 'stop lamp relay' shown in the Jake wiring circuit is an additional one which is added specifically to allow the Jake's power feed to the stop lamps to remain totally separate from the one from the service brakes.

Thoughts?

From the wiring diagram you can see that when the engine brake solenoids are energized it also power the stop relay(terminals 3&4) wich close the circuit (terminals 1&2) for the brake lamps. With that setup, you don't need a diode.

As for blown up diode, one could put two in series hoping that they would not blow at the same time, but then...when would you know that one is blown and that now you're at the same point as having only one... I guess it would be better to replace the diode with one having higher watts rating.

[richard5933]

From the wiring diagram you can see that when the engine brake solenoids are energized it also power the stop relay(terminals 3&4) wich close the circuit (terminals 1&2) for the brake lamps. With that setup, you don't need a diode.

As for blown up diode, one could put two in series hoping that they would not blow at the same time, but then...when would you know that one is blown and that now you're at the same point as having only one... I guess it would be better to replace the diode with one having higher watts rating.

I understand how the Jakes make the brake lights turn on. What I don't get is what will keep the brake lights from triggering the Jakes?

If I'm connecting power from the Jakes to the same relay that the main brake light circuit uses, then wouldn't the brake lights be able to back feed into the Jakes without a diode? That's why I'm thinking that they intended for the relay in this circuit to be an additional one and not one of the relays already in the brake light circuit. The Jakes would trigger the new relay, which would then send power to the existing brake light relay (on the same terminal that the service brakes use to trigger the brake lights). By using the extra relay, the brake lights couldn't back feed. Or so I think...

[Geoff]

" I understand how the Jakes make the brake lights turn on. What I don't get is what will keep the brake lights from triggering the Jakes?"

Turning Jake switch to off.

[luvrbus]

All buffer switches have a one way diode on the switch or built it the switch to prevent back feed ,even with the switch off if the diode goes bad it will activate the Jakes wired through the brake lights     

[richard5933]

" I understand how the Jakes make the brake lights turn on. What I don't get is what will keep the brake lights from triggering the Jakes?"

Turning Jake switch to off.

The connection shown in the wiring diagram between the Jakes and the brake lights is rearward of the Jake switch. Heck, it's even rearward of the buffer switch. Apply 24v to that junction point it's going to send power to the Jakes, bypassing everything forward of that point. That's why I'm assuming that the stop light relay shown in the diagram is a new one installed specifically to isolate the Jakes from the existing brake light circuit/relay.

[luvrbus]

Makes no difference if wired with a 1 way relay the buffer switch will have a 1 way diode on if you look, I have replace a 100 of those diodes over the years on the snap type buffer switches like you have.Years back Jake sold a small capacitor to mount on the master and they would blow that diode in heart beat     

[richard5933]

Makes no difference if wired with a 1 way relay the buffer switch will have a 1 way diode on if you look, I have replace a 100 of those diodes over the years on the snap type buffer switches like you have.Years back Jake sold a small capacitor to mount on the master and they would blow that diode in heart beat   

I must be missing something - the wiring diagram from GMC shows the connection point between the Jakes & the brake lights to be between the buffer switch and the Jake solenoids. The buffer switch diode will not do anything to stop the Jakes from applying if the brake lights were to back feed 24v at the point they're indicating. I've circled it on this copy. With there being nothing to prevent the Jakes from being activated with voltage applied to this location, that's what has me thinking that the stop light relay itself must be the isolation point.

[MagnoliaBus]

From Jake troubleshooting manual, the diode seem to be only for protection. I guess that diode was not blowing when it was installed whit a capacitor.

The brake relay is an added relay. There is one in the DDEC II front junction box on my Prevost XL.

No need for a diode with this relay, stop lamps current cannot backfeed thru open terminal 1 or 2, since they are isolated from terminal 3&4 wich are connected to jake brake solenoid.

[richard5933]

From Jake troubleshooting manual, the diode seem to be only for protection. I guess that diode was not blowing when it was installed whit a capacitor.

The brake relay is an added relay. There is one in the DDEC II front junction box on my Prevost XL.

No need for a diode with this relay, stop lamps current cannot backfeed thru open terminal 1 or 2, since they are isolated from terminal 3&4 wich are connected to jake brake solenoid.

That makes sense - thanks.

[luvrbus]

The manual transmissions have a switch on the clutch too  there is a 101 ways to wire Jakes ,DDEC's Jakes are wired through the ECM plus the buffer switch shown is a early electronic type not what Richard has he has the snap type

[MagnoliaBus]

By snap type, do you mean this kind of switch ?