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tenfive0

ENDT-675 , 12 Valve Jacobs (Jake) Engine Brake

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Looking for a Jocobs (Jake) Engine Brake for a 12 Valve ENDT-675.

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have what your looking for in basement. Shipping from here to you would be expensive. Will get grand kids to take pictures if your interested. Email me.

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I got Jakes on the old wrecker with T675. I'm not so sure it was worth the expense and work. RPM has to be up around 2000 and the effect is not all that great. And it is adjusted to the "T" 

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Jakes are good for shifting up hill in lower gears.On a E6 your as well off to roll up both windows and hold the doors open. 

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I gathered up pieces and put them on my 237.   Noticeable function.  Not drastic, but for my truck/trailer it does hold it well on the hills I deal with.  No riding the brakes anymore.  Yes, cost effectiveness?  Eh, like mentioned, not great, but I'm happy enough with them.

If you find them, make sure everything is there.  Many of the pieces are NLA from Mack(like lash caps), especially the older large valve stem motors(like mine).  I had to go to Facebook and ask around.  I got the needed parts given to me from a random person.  Facebook can be a good thing.

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I know a Jake is not that effective on my specific engine but I'd like to have one just because. My truck didn't have a block heater and someone told me I don't need one, but I busted a nut adding a heater over last winter just because. My truck doesn't have an air dryer. I've been told by a few people I don't need one but I'm putting together the parts to ad one just because. All the older Mack's I've driven all had Jake's and some might say they really didn't need one but it just seems fitting my truck should have one too just because.   

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What tans does your truck have in it?

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Spicer 5 speed manual.

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Posted (edited)

I've only driven Mack Trucks during my career with either a straight 6 Maixdyne or Diesel Thermodyne. I have no other experience to share other than how effective a Jake is on either Mack Engines to draw a comparison from. All I can say is a Jake worked however ineffective they might be and the trucks I drove were better with them then without. Perhaps a Jake might work better on other engines but I wouldn't know. I think it’s worth the expense to at least entertain the thought of putting a Jake on my truck to hold it from running away downhill. I'm not looking or hoping to be put through the windshield I'd just like to avoid riding the brakes on some of the steeper hills here in Pennsylvania.

Edited by tenfive0

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The Mack is a small cubic inch, low HP, low compression engine, thus it has very little braking effect compared to a bigger Cummins or Cat.

My 673 had a block heater.  Never needed it, even when it was parked outside the first couple winters.  It would start, unaided(no ether) even at near single digits.  I was thoroughly amazed.  Yes, I had good batteries in it, and it would build some heat and fire off.  I removed it once I put the spin on filters(new mount was in the way).  It's in the garage all winter so it is not necessary to have one.  It was brutal to get that threaded plug out, took some heat and chiseling.

 

Do with the truck as you please.  You should hear the grief I got for putting an air starter on mine!!  OR air steering?  OR Jakes, or....(whatever I chose next).  Build it to your liking.

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Hard to argue with adding a safety feature like an engine brake, hopefully you'll never need it, but when you do...! I was driving a fleet truck powered by an L10 Cummins with no engine brake with only a 50,000 pound GCW when the Interstate was closed by an accident and traffic was rerouted onto the old two lane with a not all that long 6% grade but plenty of 30 MPH curves and a city with stoplights at the bottom. Speed limit was 55 MPH on 'til the road came into the city, but I came down most of it at 30 MPH with the engine wound out in lower gear and made it to the bottom with fresh brakes. Would have been nice to have an engine brake, especially if I'd had a full load!

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We had a Jake on our '79 endt676 up until last year when we had to delete it. Weak valve spring on one cylinder wasn't closing fast enough so the disk sitting on top of the valve kept popping out, resulting in that exhaust valve suddenly having way too much valve lash. I ran the truck pretty much every day for 6 years here in southeast PA. The truck shifts gears twice as fast using the Jake. Which means climbing a hill you wind it up to 2100+ and when you shift you're still in your powerband with the perk of still having your turbo spooled up. I've driven the truck over blue mountain a couple times, that's a nice hill. 

Don't let anyone here dissuade you from a Jake on your Mack. Its completely worth it just for climbing hills alone. And a properly adjusted Jake brake works well on these motors, you just need to ride it around 2100 rpms.  When I retire my '79 I'll likely restore it and replace the valve springs and put the Jake back on.

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