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Joseph Pickarts

'79 Mack 235hp Jake Brake?

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I have a 1990 rb with a '79 235 motor. The tag says its an etz 675. It's not stock. Has an air to air, bosch injection pump and mated up to a 13spd. Just kind of wondering what these had for Jake's and whether it would be a dynatard or Jake Brake. Also how to tell if it's a 2v head. I just can't find much about it on the internet.

Thanks

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a 675 could have either a Jake or dynatard.Easiest way to tell a 2 valve head is the injectors go in the top.

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So my next question would be what is the best way to tell the difference. It has some setup that doesn't work. Has the 12v running to the valve covers and has the electric selenoids under which I would assume runs off oil pressure?

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If it is a jake it would have a spacer about 2-3" under the valve cover with a wire going thru the plate, if dynatard it would have a wire on top of valve cover. a 2 valve will have a stamped steel valve cover.

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A Dynatard is nothing more than a noise maker, a Jake on a E6 Mack is a little better. Watts sells Tecbrake same as Jakebrake. you might give them a call, they can get some hard to fine parts.

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So I did some investigating. From what I gathered most motors equipped with a factory installed dynatard had a b in the engine model. And it takes a special cam to work the dynatard. So if my engine is stamped etz675 does that mean it doesn't have that cam and the dynatard was added later in the motors life?

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A safe way to check is pull a valve cover and have some one turn the engine slow while you check valve clearance on a exhaust valve.If it has a dynotard cam at some point your going to have about a 1/8 lash.If you never find that lash it may not be a dynotard cam.

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Okay so now say it does have a dynatard cam. And I have power to the valve covers. What would my next step be. Replacing the selenoids and seals under the valve cover?

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Have you check to see if you are getting current to the wires on the valve covers?

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The pull the covers and when running apply 12 volts to each selnoild to see if they are working.Also look for oil leaks on the rocker shaft.

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If memory holds correct, when we would buy an new dynatard switch for the 2 valves it always came with a spacer ring about 1/8" thick, every truck we pulled apart did not have the spacer ring in it. It seem like we had found some under the solenoids when they wasn't working good and we took them out and they worked better. I assume some of the first ones used, but I never seen one that did, it came with a new one and I guessed people just put it in there. We found a lot of solenoids that would come loose where they thread into the rocker arm. You might try a valve adjustment. It's doubtful but you might ck and see if mack still offer's mack remack dynatard rocker arm for the engine.

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