Altering jakes on a 12.7

thomasinnv · April 02, 2018, 03:41:51 PM

The 12.7 that is on its way to replace my 11.1 has full jakes on it, the 11.1 has partial jakes becuase of interference with the floor. The 11.1 has older style 760A jake heads, the 12.7 has newer 795 jake heads as it is a newer year model. The official word from jacobs is that the 760A heads from the 11.1 cannot be used on the newer 12.7 without catastrophic results. I am assuming that I can simply remove the rear jake head from the 12.7 and replace those 3 rocker hold down bolts with standard detroit hold down bolts. Since one solenoid will be eliminated will it require an ecm reprogram or throw any codes or lights? I am getting conflicting answers from the ones that are supposed to be in the know. Anyone? Clifford maybe?

Before anyone tells me to just keep the full jakes and modify the floor, that was an option before i had to switch shops. Not going to be an option at this point.

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buswarrior · April 02, 2018, 05:07:10 PM

Not altering the floor, that's a shame...

Can you not do something obscenely expedient, and clean it up later?

You will really like the difference 6 holes make, vs 4...

Happy coaching!
Buswarrior

thomasinnv · April 02, 2018, 06:23:33 PM

Actually it would be 3 holes. The 795's service 3 holes each. I have decided to go ahead and chop the hole and I will pretty it up later on. I really would much rather have all 6 holes on the brake. Looks like its going to be a few days before the shop can start anyway.

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luvrbus · April 02, 2018, 06:30:20 PM

There not much involved in modifying the floor on a DL with the 12.7 for a full set of Jakes mine is modified , you will love the 3 setting on the Jakes with a 12.7 if you go that way lol even a 1/2 set of Jakes on series 60 is better than a full set on a 2 stroke.Did you buy a EGR engine ? those are the only 60 series I saw with the 795 heads

thomasinnv · April 02, 2018, 07:38:51 PM

No it is a non egr engine. The jacobs guy said 795 but maybe they are the 790. The 790 or 795 are just 2 stage arent they? Just one solenoid in each jake head? The 760 series on the earlier engines cover 2 holes each for a total of 3 solenoids for a full setup.

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luvrbus · April 03, 2018, 05:15:50 AM

Mine are just 2 stage but a buddy has 3 stages on a 2000 series 60,after a little research I found out the 795 will work on the 11.1,12.7 and 14L premium series 60 ,man they have a lot of variations for Jakes on a series 60 what is up with that ?

chessie4905 · April 03, 2018, 05:21:49 AM

question..... with engine in place, can you remove valve covers to replace leaking gasket, adjust jakes or valves?

lostagain · April 03, 2018, 07:27:18 AM

IIRC, on the '95 D3 I used to look after for the hockey team, you lifted the hatch under the back seat and the valve cover was right there accessible.

JC

thomasinnv · April 03, 2018, 08:49:25 AM

Quote from: chessie4905 on April 03, 2018, 05:21:49 AM
question..... with engine in place, can you remove valve covers to replace leaking gasket, adjust jakes or valves?

On the earlier ones with partial jakes you can remove the upper rocker cover for maintenance access, but the lower rocker cover remains in place as there is not enough clearance for removal, which makes replacement of the lower gasket a real bear you have to drop it in and thread it around all the valve mechanism. Later models with full jakes have increased floor clearance so no issues there.

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thomasinnv · April 03, 2018, 08:59:05 AM

Quote from: luvrbus on April 03, 2018, 05:15:50 AMMine are just 2 stage but a buddy has 3 stages on a 2000 series 60,after a little research I found out the 795 will work on the 11.1,12.7 and 14L premium series 60 ,man they have a lot of variations for Jakes on a series 60 what is up with that ?

From what i understand there were several changes and revisions to the rocker assemblies in a short time, and also the elimination of the additional cam lobe for the jake activation replaced by a new style injector rocker with a "dish" on top. I am told that the older style 760 series began phaseout late 99 to early 2000 and went to the 790 series for the upgrades. I believe the older 760 series can be used on later models but it requires changing the entire valve mechanism. (Rockers, shafts, bolts, etc.)

I have conflicting info on the last part so not willing to take the risk personally. Only takes a few seconds to end up with a 3k pound hunk of scrap iron.

So many "experts" on google, let them pay for the trial and error, not me.

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buswarrior · April 03, 2018, 11:11:46 AM

Yeah, online experts...

If it isn't written in the manufacturer's documentation...

Pretty much nobody ever gets back on the Internet with the results of misadventure, so the gaining confidence thru only half the story is folly...

And how many authoritative social media posters actually own a wrench, or a bus...

Stick to BCM and BNO says I.

Happy coaching!
Buswarrior