Jake brake 25A vs. 25B & their use with a pulse manifold

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US6x4

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I'm to study up on jake brakes and turbos for the small cam NHC 250 and I have 2 questions bundled together here, but i think they're related.

1. What are the differences between the jacobs 25A & 25B compression brake? What I've read so far suggests the 25A is iron? and the 25B has an aluminum rocker box, but are there other important differences?

2. Can these older Jake's be used in conjunction with the newer dual port outlet pulse manifolds?
 

ross165123

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Exhaust manifold will have no efect on the Jake brake. The difference between the old and pulse is as follows.

"This is an updated design exhaust manifold that can be used to replace the old style manifold, part number 3801322. The old style manifold used sealing rings between the end sections and the center section. The sealing rings were prone to failure during prolonged exposure to extreme heat cycles. The new version 3801915 manifold system does away with the sealing rings entirely. It was designed with a tighter, slip fit between pieces where no sealing ring is required. You can confidently replace your 3801322 manifold with the 3801915 design for a superior product."
 

WillWagner

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A pulse manifold can have effects on brake operation as well as turbo turbine housing. A pulse manifold has smaller ports, increasing velocity thru the manifold and into the turbine housing. If you use a divided entry turbo with a pulse manifold, the autolash screws might need to be installed or changed to a different type. Pulse manifold was introduced at an emissions change year, IIRC 1986? This was to get turbo speeds up to get rid of something ARB or whoever thought was necessary so we could all have better air. Later in life the exh ports took on a change from the big ports to ports the size of the pulse manifolds, again to speed up exhaust gasses. There were multiple bulletins from Jacobs and Cummins about the different lash screws on different models of brakes and what could happen if the wrong components were used with each other. I will dig around an see if I saved any of it, I had a binder full.
 

US6x4

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Will, these are the aspects that I was trying to recollect from an older post of yours - thanks for responding! For the record I currently do not have a turbo exhaust manifold or a turbo so I do have the flexibility to choose the correct combo. I plan on adding 25B jakes.
 

WillWagner

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I'll still dig through my pile of paperwork to see if I have anything left. I think I might have given it to somebody before I left.
 

US6x4

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I found some info on the PACBRAKE website regarding the single vs divided entry turbos and they call out special adjusting screws for divided entry turbo applications. I don't know anything about PACBRAKE but they use Jacobs same nomenclature on things. Maybe some of there parts are interchangeable? Basically it looks like the 25B jake brake is for single entry turbos and the 26 is for divided entry and the 25B can be converted with the addition of the adjuster screws.

Jake brake parts-pg. 5.jpg
 

simp5782

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Pulse and N14 manifolds are divided entry so it really shouldn't matter on that part as you will have a divided manifold regardless. The n14 and pulse flow more air. If you want to get even better turbo spooling swap to the BC4 heads but you have to upgrade the injector hold down hardware. I have run both divided and open on the n14 manifold on the NTC400 and not changed a thing.
 

US6x4

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Do you guys think that a divided exit manifold combined with a divided entry turbo would not require the special adjusting screws?
 

WillWagner

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No, IIRC it requires auto lash, or hydraulic type adjusters. I did look for books, but they are MIA, I don't remember what I did with them as well as some other books I am looking for. PAC brakes were horrible, alot of failures seen with them. They came out when the pat. on the "jake"design expired. the next best were the C brake that Cummins produced until they bought the Jacobs patent. Funny, Clessie Cummins invented the engine brake after he was no longer a major share holder or involved in Cummins. He offered it to Cummins but they decided it wasn't needed. He sold the idea to Jacobs engineering, hence the "Jake" brake.

History back. Everything marked, everything membered.
 

US6x4

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No, IIRC it requires auto lash, or hydraulic type adjusters.
Ok, so here's another question. Can jake brakes with the auto lash adjusters be used on an NA engine safely? I will most likely have the jake heads installed a year before I get the turbo put on.
 

WillWagner

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I don't know. In the literature there are warnings in bold red that warn of mis match parts and engine damage. I have been looking, but a box of books is still MIA.
 

US6x4

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I found some more info from the Jacob's literature-not Cummins- and it warns of no 25B with divided entry turbo and also when I load the CPL 0026 the application guide points to model 425A which has no warning about turbo entries which makes me think the 425A is more versatile.
20190811_081307.jpg20190811_081320.jpg

So would a pulse manifold with a single entry turbo mounted to it behave like a divided entry turbo?
 

WillWagner

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The exh gasses passing thru the manifold are sped up, I think that is why the TT autolash screw came into play. As engine designs were changed to meet emissions, cam/injection timing changed and this effected the brake operation. There were a few brakes that could not be used with twin entry turbos, IIRC, 25, a, b, 30. I am still looking for the books, it is complicated when it comes to upgrading brake components. The paperwork I have/had, gave part numbers of the lash screws for the different housings and what components....log, standard and pulse manifolds as well as T46/A and Holset turbos. I think I remember the lash settings changing with different component configurations.

Still looking
 

Lonnie

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Could anyone shed some light on the Model 25? Mine does not have an A or B suffix.

I wanted to use the Jakes off of a '78 NTC350.

Any issues I should be aware of?
I searched extensively & there is very little data that I could find.

i'm using a pulse manifold off the NTC350, with single entry BHT3B turbo.
 
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