Jacobs 675 swapping from one engine to another

[Full Floater]

I have a complete and functioning set of Jakes on a 675 that is in a truck that's no longer going to be on the road.   I'd like to take the jake setup and install on another 675 engine with nothing on it, not even a dynatard.

Im assuming there will be some orings that I will need to replace?  Are those something that's available from Jacobs?  Is there anything else (aside from valve cover gaskets) that I will be needing before I tear into it?

[Freightrain]

Should bolt on.  You can still get full kits for them....just real pricey.   I went through mine when I bought them used(old and unknown condition).  Bought everything through local Mack dealer.

[davehummell]

Freightrain If memory serves didn't jakes for Macks have two different size disks that went on the valves? It's been a couple of years ago that I put the jakes on my engine. I remember working in that fleet garage all Mack tractors and adjusting the dynatard brake system that was about 40 years ago, so my memory is not good. 

[Freightrain]

Yes, the early valve stem was larger and took a different disc.  My 237 was like that.  That disc is NLA.  The later, smaller stem is available.

[Macktruckman]

Do you happen to know what is considered earlier or late years? Like possibly what year the break is?  I’d like to find some jakes for mine and it’s a 2 valve and I am thinking the engine is a 1980. Was originally a EM6-285

[davehummell]

Macktruckman your year engine is the same as mine and I needed one disc and I bought it from Cook brothers my local Mack parts dealer. I think I paid about 70.00 for the part it was about four years ago but I can be wrong on the price.

[Macktruckman]

Thank you very much sir.

josh. 

[Macktruckman]

Any leads on a complete or mostly complete used set up?

thank you. 
Josh

[Mean Green]

a lot of Jacob's parts are the same internal wise I tuned mine up and the spools and springs solenoids were all the same as parts for a jake for a cat 3406 e I had a broken power lash adjustment screw and I did have to buy it from mack 80 bucks lol they said it has been on the shelf since 1985 if they had to order one it was 120 . the spools have been updated I think newest have the flat bottoms will work in an older brake

[Macktruckman]

Good to know 

thank you much. 
Josh

[Full Floater]

Thanks for all the input fellas.

Also, on the engine that I am removing the jakes from.  It's a running engine, it just won't be leaving the yard anymore as it's not road worthy.   So i'd like to have it as a runner still after the jake heads are removed.   Im assuming this will be straight forward or would anything have been modified or changed on the engine to accept the jake heads?

[Freightrain]

I bolted jakes on my 237, no problems.  I'm trying to recall it used longer head studs in certain locations?  Heck, been 5? yrs so I can't recall.  But if you are swapping between engines, then you should have everything to do it and have two running engines.

[davehummell]

Make sure when you replace the valve covers you pay attention to the wires that activate the solenoids. I am guilty of trapping a wire under the cover. 

[Full Floater]

And slightly off topic, but not really.   I imagine that a Dynatard set up transfer from engine to engine to?   Both 675s

[Macktruckman]

My understanding is that the dynatard equipped engine actually has a different camshaft. I do not know if it will interchange without a cam change but I’ll bet someone will be along that will be able to tell you for sure 

[davehummell]

Dynatard works on a different camshaft if I remember correctly, I haven't worked on one for almost 40 years. On the flywheel it is marked for setting the dynatard I think you would need the corresponding flywheel.

[mechohaulic]

on the jake swap; 

the exhaust rocker  adjusting screws need to be changed also. mack adjusters are screw driver slots. when a jake is installed no access with screw driver. the adjusters are changed to a 3/8 or 7/16 head ?. i have found if you take a small center punch and punch marks on the valve cover or jake spacer, the rubber gaskets don't slide out and leak.

basically the jake is an add on;; the dynatard is built in.

[Full Floater]

On 8/11/2022 at 5:14 PM, davehummell said:

Dynatard works on a different camshaft if I remember correctly, I haven't worked on one for almost 40 years. On the flywheel it is marked for setting the dynatard I think you would need the corresponding flywheel.

This engine is a "B" family which I think represented Dynatard capability, but not sure.    

[Macktruckman]

I believe that is correct 

b was for dynatard as I understand it 

[davehummell]

I was rooting around my favorite truck junk yard when I found my jake on a 675. On another 673 setting there it had a double over triplex. I went right home and rounded up some tools and went right back and ripped off the jake and the yard guy Jay helped me get the trans off with their forklift. I took the owner for a ride in my B model, and it has brought me a very good standing when I go looking for parts.

[Full Floater]

On 8/9/2022 at 6:24 AM, Freightrain said:

I bolted jakes on my 237, no problems.  I'm trying to recall it used longer head studs in certain locations?  Heck, been 5? yrs so I can't recall.  But if you are swapping between engines, then you should have everything to do it and have two running engines.

I have noticed that the tall bolts for the rocker housing are longer, to accommodate the jake assembly

[Full Floater]

Does anyone know if this O-ring on the adapter fitting for the oil feed to the jake assembly thru the rocker, is still available thru Jacobs?  Looks like a specific square style oring.  I'm reluctant to reuse it

 

According to the parts list on their site, its a .365IDx.07W   

Edited January 11, 2023 by Full Floater

[Freightrain]

Don't recall if it was square?  You would think a regular round one would suffice.  Even if not available from Jacob, you should be able to come up with something online.

Measure the bore that it fits into and work backwards.  

[Full Floater]

1 hour ago, Freightrain said:

Don't recall if it was square?  You would think a regular round one would suffice.  Even if not available from Jacob, you should be able to come up with something online.

Measure the bore that it fits into and work backwards.  

Yeah maybe it started off round I guess