Any truckers in the crowd here?

[Rondar]

Our farm has had a Kenworth tandem truck for a few years with a jake brake that never worked, as we bought it used.  We got the truck worked on this year and got the jake brake working.  What is the proper rpm's to engage it or disengage it?  Or does it matter, just turn it on till you get the rpm down then shift gears again?  Its a cat engine if that matters, 400 hp.

[rpm]

The Jake is an ADDITIONAL brake assist. It's not a primary brake to slow down with. It chokes the exhaust valves to create back pressure and give some assistance when long braking is required, like down a grade. You can run a Jake at any rpm, but higher gives more resistance. It's just like gearing down, but with a little more resistance.

One thing, make sure the throttle cut-off switch works. You don't want a Jake engaged when you are under power, only when you are completely off the throttle.

If you run straight 6" exhaust, a Jake on a 3406 Cat sounds sweet.

[Shuffler]

Watch for signs regarding use of jake brakes..... some places frown on the noise.

[gyrene81]

rpm, the jake brake doesn't "choke the exhaust valves", more like it opens them slightly on the compression stroke to prevent ignition in the cylinders and it doesn't do all cylinders.

[doomed]

I use my jake going down long or steep grades so I don't burn my brakes off. Also if I'm heavy ill use it to help stop but the rpms don't matter it kicks in when you let of the gas. Downshifting take time to learn your trucks engine and what range you can downshift.

[Bronk]

rpm, the jake brake doesn't "choke the exhaust valves", more like it opens them slightly on the compression stroke to prevent ignition in the cylinders and it doesn't do all cylinders.

I could be wrong. I believe it opens the valve just before starting the power stroke so the compression stroke can be used as a brake. If it opened on the start of the  compression stroke little to no brake benifit would be had.

[Shuffler]

I could be wrong. I believe it opens the valve just before starting the power stroke so the compression stroke can be used as a brake. If it opened on the start of the  compression stroke little to no brake benifit would be had.

Yes the piston comes up on the compression stroke which the jake brake uses to help slow engine rotation as the piston reaches TDC the exhaust opens to release the pressure so it does not push the piston down with force. So the unit uses cylinder pressure on the pistons to slow rotation thus helping slow the vehicle or hold speed on steep down grades with clutch engaged and in proper gear.

[Bronk]

That is what I figured. Sounded funny to open on the compression stroke.

[Maverick]

Truckers running straight pipes make a lot of noise. That's the reason you see signs stating no exhaust brakes in town specific location. Pissing off the local population because some of the truckers don't feel "manly" without a lot of noise cost everyone the use of a good tool. The actual muffler of a semi isn't much of a restriction at all. I just swapped mine out last month. There was one swiss cheese cone shaped baffle across the opening of the pipe. The rest of the sound management was the series of holes surrounding a straight open tube to the outflow. It keeps the sound low but the "billy big rig" attention deficit folks who like to make noise dump the mufflers for straight pipes.

I use my jakes all the time except where restricted. It save the brakes on the truck and RV (5th wheel) on mountain grades. It also is a 3 stage jake. It will operate on 2, 4 or all 6 cylinders as needed selected by the driver.

[68ZooM]

I owned two trucks when i was hauling containers up and down the west coast for Sealand, My 78 Kenworth COE had the 350 Cummings bigcam 10sp with the Jacobs brake 3 way switch to either pop off 2, 4 or all 6 cylinders, the other Truck was a 86 Kenworth Ta600 Cat3406B-425hp 15sp with a Hydraulic Retarder, IMO the Retarder is the better way to go, just set the amount of hydraulic resistance you want and you hardly ever touch your brakes. jacobs brakes you still have some braking depending on the percentage of the Grade your going down and the gross weight of the load.

[68ZooM]

Our farm has had a Kenworth tandem truck for a few years with a Jake brake that never worked, as we bought it used.  We got the truck worked on this year and got the Jake brake working.  What is the proper rpm's to engage it or disengage it?  Or does it matter, just turn it on till you get the rpm down then shift gears again?  Its a cat engine if that matters, 400 hp.

After re-reading this here's some help, the operating range 1200 to 2200(governor) all your torque will be around 1400 without knowing the exact engine model# , your shift points will always depend on how much your weighing and gearing you have, but a safe range would be 1200 to 1800 rpms and never use the Jake to shift it drops the RPM's way to fast to hit the next gear, just ease back the pedal till you feel it slide out gear (little pressure), as your RPM's decrease then go for the next gear it will slide right in. just use the jake to get you into the right RPM range before you shift.

It's the opposite thing for up shifting to a lower gear going up a hill or preparing to stop instead of dropping the RPM's slowly you bring the RPM's up slowly and it will go right into the lower gear. i used my clutch for starting and stopping that was about it, but never use a Jake for shifting I've seen to many people either blow a shift or worse kill the engine while in the middle of a shift on a Hill.

[Tr1gg22]

The Jake is an ADDITIONAL brake assist. It's not a primary brake to slow down with. It chokes the exhaust valves to create back pressure and give some assistance when long braking is required, like down a grade. You can run a Jake at any rpm, but higher gives more resistance. It's just like gearing down, but with a little more resistance.

One thing, make sure the throttle cut-off switch works. You don't want a Jake engaged when you are under power, only when you are completely off the throttle.

If you run straight 6" exhaust, a Jake on a 3406 Cat sounds sweet.

Don't run it over 2000rpm... Builds to much compression and can blow top end of ur motor..A jake and an exhaust brake are two different things.. I hope u don't  drive anybody Else trucks Rpm .. Hopefully ur an owner operator if you even do drive truck..An exhaust bake by the way shuts a butterfly valve on the exhaust side of the turbo witch causes hold back kinda like putting ur finger over a straw. Jake's have way more hold bake than exhaust brakes do... I am no mechanic but my family owns a trucking outfit here in Idaho.. Anyway before you take any advice from people you don't no just ask the mechanic that fixed the thing.. A cat is pretty spendy.. Good luck

[Tr1gg22]

I owned two trucks when i was hauling containers up and down the west coast for Sealand, My 78 Kenworth COE had the 350 Cummings bigcam 10sp with the Jacobs brake 3 way switch to either pop off 2, 4 or all 6 cylinders, the other Truck was a 86 Kenworth Ta600 Cat3406B-425hp 15sp with a Hydraulic Retarder, IMO the Retarder is the better way to go, just set the amount of hydraulic resistance you want and you hardly ever touch your brakes. jacobs brakes you still have some braking depending on the percentage of the Grade your going down and the gross weight of the load.

If u can get a retarder and a jak then your sitting sweet!  I never drove a truck with a retarder ,but I heard there sweet.. There is a local guy who has a retarder and a jake set-up for his lowbay outfit.. Although he did reck his last one do to his forgetting about his retarder still being on when it was slick out..

[Buzzard7]

Cats will run happily between 1200 and 1800 rpm. Never jake above 2000 rpm. You will first stretch the head bolts then the poo really hits the fan. Give us the year and model if you can. 3046 B is a good reliable engine when cared for.
All of our power units are Cummins N14 rated at 435 horse 1800 rpm with 1650 ft/lbs torque at 1250 rpm. Some of the newer units are the ISX at 475 horse and about the same torque. They have all that emission garbage on them. Three of them have the diesel catylist on them. Pain in the hind end when you idle them for too long.
I pay no attention to signs telling me i need to heat up my brakes for some putz that doesn't want to hear my compression brakes.

[rpm]

Don't run it over 2000rpm... Builds to much compression and can blow top end of ur motor..A jake and an exhaust brake are two different things.. I hope u don't  drive anybody Else trucks Rpm .. Hopefully ur an owner operator if you even do drive truck..An exhaust bake by the way shuts a butterfly valve on the exhaust side of the turbo witch causes hold back kinda like putting ur finger over a straw. Jake's have way more hold bake than exhaust brakes do... I am no mechanic but my family owns a trucking outfit here in Idaho.. Anyway before you take any advice from people you don't no just ask the mechanic that fixed the thing.. A cat is pretty spendy.. Good luck

Just FYI. I was raised around trucks, too. My Dad also owned a trucking company and I drove OTR for 15 years and local for another 10 hauling oversize equipment until my eyes got too bad to drive at night anymore. I have more miles driving an overweight rig riding the Jake down Tehachapi, Cabbage Patch, The Grapevine, 9 Mile Hill, Morongo Canyon, Montrose Pass and 1000 other grades you've never seen than you have riding in a truck.

My first OTR trip was riding on the doghouse of my Dad's KW from Texas to California to Maine and back to Texas in 1966. That was truckin'! Hendricks suspension, twin sticks and no a/c or CB. I know the difference between a Jake and a Pacbrake. I might not know how to take one apart and put it back together again, (ok, I could take it apart but I'm a horrid mechanic) but I know when and how to operate one.

Most of the 3406's I drove turned between 2200 - 2350. They are (or were, I'm sure specs have changed since then) rated at 2500, but I wouldn't recommend running one that hard or you will get new vent holes in the block. We also tweaked the transmissions to get more speed out of them (swapping gears around) . It made that top gear hard to grab, but when you did you could get on down the road.

We ran Detroits for a long time. I sure miss hearing those old Jimmy's scream. I wish you could have seen Dad's '66 Diamond T. It had a 238 that turned 2400 with oversized injectors. More than one 290 Cummins and 318 Detroit were put to shame. It was the terror of I-45 between Dallas and Houston. He ran twin resonators on straight pipes and you could hear that old Diamond T from 5 miles away.

So before you think about schooling me with your vast background in trucks and trucking, you might want to research who you are talking to. I'm definitely old school when it comes to trucks. M'kay?