M813 Jake brake questions

[JungleBiker]

Okay, I searched for quite a while, but couldn't find any conclusive answers. Has anyone here ever successfully installed a Jake Brake on an NHC250, (standard M813 engine)? After our first road trip we're interested in installing a Jake Brake, (or something similar, I don't know what else is out there) on ours as most of the paved roads here are just 2 lane, lots of hills and blind corners.

Can anybody tell me which brake we need, (I've heard that we need a 425A), and where is the best place to get it? (Or I might settle for the cheapest place to get it!)

Thanks,

Andrew

 

[Hammer]

425A is the newer number, 25b is the older number.
If you want to install them on all three heads, you will have interference issues with the hood.
It has been rumored that you can install them on the rear two heads, and not have clearance issues.
This was my plan of attack, do the two rear heads, and if that isn't enough braking power, then I will worry about what I will do with the hood clearance issues with the third brake.

And finding them? Good luck, these are fairly old, and not always easy to find. Supposedly not that much money though.

 

[rosco]

Call a heavy truck shop and get prices. I can tinker with that stuff, but feel its money well spent, to have somebody that works on them all the time, do the job. They will know all the tricks/fittings/bolts to use, and more importantly, what not to use.

I'd put an air scoop on the hood, or whatever, so I could use full engine braking. I have often thought that the "Jake" is the best safety device that you can have. Once you have it, the rule will be, "stay off the brakes". They are just for minor speed adjustments - save them for emergencies!

Lee in Alaska

 

[area52]

My M816 has the Jake brake on it, the hood has been modified by the military to make it fit.

Can anyone explain how its supposed to work? I have not been able to get my air pressure up so I was thinking it might have to do with the Jake brake?

 

[rosco]

The Jake doesn't have anything to do with air with the trucks air system. But the Jake does work by compressing air to absorb energy, to slow the vehicle. On compression stroke at about TDC, Throttle off, a solenoid valve closes and uses engine oil pressure to open the exhaust valve/valves, dumping the air. The engine continues to be turned by the vehicles wheels & its forward momentum. Usually, there is a minimum engine speed cut out for the jake, so it won't stall the engine. That is especially necessary on icy conditions. When its real slippery, turn the Jake Off. Note: Compression is dumped, hence the characteristic exhaust noise. It/compressed air, does not have a chance to push the piston back down. In fact, after Mr. Cummins sold out, he continued to tinker, and conceived the the engine brake system. He went back to Cummins and they weren't interested. He did finally interest a forward thinking company that manufactured drill press chucks - Jacobs

Lee in Alaska

 

[JungleBiker]

I know I'll never look at my drill the same way again...

 

[raeme]

I put a jake on my m816 in the army and had to raise the front of the bonnet about 2 1/2 inches, so Iextened the legs on the bottom of the brush guard ,which could not be noticed behind the winch, and folded up 2 new side panels , no problemo.
raeme.

 

[bigelk50]

I know of a guy who has done body lifts to make the jakes clear. Looks pretty good really.

 

[wreckerman893]

According to FreightTrain( my long suffering side kick, chief mechanic, and now SS Banned Bad Boy) the Canadians had Jakes on their 250's. You might try that as a source.

 

[captw]

nhc 250 jake brakes

all CDN 800 series trks were speced w/j/brakes...wreckers, tractors and cargos...the hood has a piece cut out and another fibreglas molded piece attaches to it, leaving a 3">4" bump on the hood

 

[Evilone]

Here's a pic from an unknown source. It has the hump on the hood to allow it to clear the forward-most j-brake. Another member you could get some info from is Steamynachos - he has a sweet 813 with the setup.

 

[JungleBiker]

Yeah, I found some pictures of Canadian trucks with bumpy hoods in another thread. The sheet metal work doesn't bother me any, I just want to make sure that I order the right engien brake kit. I downloaded an application guide from the jakebrake website and it looks like the 425A fits 90% of the pre-1988 Cummins engines, so it seems like it should be hard to go wrong.

Evilone, I like your avatar--I'm a motorcycle mechanic by trade (but I'm really enjoying getting into heavy green iron) and I'd love to pick up some old brit bike sometime, preferably an ex-MoD Norton single or something.

 

[BIGdaddycatlin]

the only issue with putting jake brakes on the small cam cummins is that over time the jake brake will wear off the lobes of the cam wich is one of the reasons cummins went to the big cam engine

 

[JungleBiker]

That raises another series of questions--assuming good maintenance, how long will it take for a jake brake to wear out a small cam? 10,000 miles? 1,000,000 miles? Can a small cam be replaced with a big cam? What exactly is the difference between small cam and big? Is it the lobes or the bearings? If a big cam can be fitted to the NHC240 engine, is there any advantage to doing so?

 

[Steamynachos]

My truck came from the Army with the jake it has a switch on the dash to turn it off works great makes a ton of fun noise when it's on the rear two pods fit fine it's the front one that doesn't clear the hood so they just cut a hole in the hood and made a box around it. You can see the the hump in my pic and how the jake sits on the motor.

 

[BIGdaddycatlin]

im assumeing that your truck is more of a toy than a daily work horse so it could last quite awile. you can't put a big cam in a small cam block as the blcok is diffrent but they are almost identical engine so if you did want later down the road you could upgrade with not alot of difficulty

 

[JungleBiker]

Yeah, it's actually not a toy, we use it for getting around in the bush and for going places where most other cargo trucks can't go, (deep or fast water river crossings, rainy season boggy roads, etc., etc.), hauling building supplies, educational materials, hauling 5 tons of sweet potatoes to market for local growers, hauling coffee out of the bush for local growers, that kind of thing. At least, that's what we PLAN to do with it. Since we just got it a month ago and are still getting it all ironed out, we haven't done much with it yet.

But you are right that it will probably take us a long time to put a lot of miles on it since the longest trip that we are likely to make with it is probably less than 500 miles. (It's just not a very big or very wealthy country.)

Thanks for the info on big cam vs. small cam engines, that answers something I've been wondering about for a while.

I'll give this whole jake brake idea plenty of careful thought. Our engine only has 220 hours on it, it runs really well, I'd hate to wear it out prematurely, especially as parts take so long to get to this side of the planet.

 

[BIGdaddycatlin]

it sounds like you get to see some very interesting things but with your parts availibilty situation that has to make you a very resourceful person

 

[JungleBiker]

Hahahahahaha! You said it, bud. I like it though.

 

[BIGdaddycatlin]

well if you do decide to go with the jake brake make sure you post up some pics of the install