Description

Jacobs 455B, 455C, 455A Installation Manual

I have been turning wrenches for 28 years. When I see a manual that came direct from Jacobs Engineering, I pay attention.Jacobs 455B, 455C, 455A Installation Manual is one of those. It is 16 pages, no filler, no generic aftermarket guesswork. If you are installing a C Brake on a Cummins N14 Plus, this is the paper you want on your bench. I have used aftermarket copies that skip the slave piston adjustment step – then you get a brake that either drags or doesn’t engage. That costs hours and parts. This manual keeps you from making that mistake.

Safety Precautions – Why They Matter on Install

Page 2 lists the safety symbols. That may seem basic, but I have seen techs ignore the warning about exhaust gases and moving parts. The manual states plainly: “The C Brake by Jacobs engine retarder is a vehicle slowing device, not a vehicle stopping device.” That is not a liability disclaimer; it is a functional truth. If you treat it like a parking brake, you will have a bad day. The manual forces you to read those precautions before you touch the engine. I respect that.

Tools Required for 455B/455C/455A

Section 1 lists exactly six tools. A 7/16″ 12-point socket for the housing mounting screws, a 0.023″ feeler gauge (Cummins P/N 3871534), a 3/4″ socket for the solenoid, a 7/8″ crowfoot for the Robo-Lash adjusting screw nut, a 3/8″ hex for the adjusting screw, and a 7/16″ hex for the master piston capscrew. That is it. No special dealer tools, no proprietary adapters. The manual even notes: “No engine conversion parts are required for Model 455B and 455C installations on N14 Plus Cummins engines.” That saves you the phone call to the parts counter. You have the tools, you have the parts – now get to work.

One critical application note: These models are for Cummins N14 Plus engines only. Check your engine CPL with a Cummins dealer before you order. Misapplication voids any warranty and can damage the valve train. This manual tells you that in bold on page 3.

Engine Preparation – What the Manual Doesn’t Skip

Section 2 covers engine preparation. It is short but specific. You need to set the engine to top dead center on the compression stroke for the cylinder you are working on. The manual does not tell you to “eyeball it.” It tells you the exact procedure using the timing pin and barring tool. I have seen DIY guys skip this and then fight with slave piston clearance for an hour. Follow the prep steps exactly.

Brake Housing Installation and Slave Piston Adjustment

Pages 5-6 are the meat of the install. The brake housings go on with the 7/16″ bolts torqued to factory specs – the manual gives those values in the text. The slave piston adjustment requires a 0.023″ feeler gauge between the slave piston and the exhaust valve crosshead. Too tight and the valve never seats. Too loose and the brake loses efficiency. The manual shows the adjustment sequence cylinder by cylinder. That is the difference between a brake that works and a brake that sounds like a rock tumbler. If you have ever had to re-do this on an N14, you know the value of a correct spec.

Electrical System Installation – Wire It with the Diagram

Section 4 covers the electrical system. The solenoid valve wiring is straightforward: power from the dash switch, ground through the ECM or a dedicated ground. But the manual includes a wiring diagram that shows the correct relay and diode placements. I have seen installs where the diode was omitted, causing the solenoid to stay energized after the switch was turned off. That burns out the coil in a week. The diagram is on page 7. Use it.

The solenoid valve itself is a standard 12V unit. The manual says to torque the solenoid mounting bracket bolts to 30 ft-lb – not guessed, not “tighten firmly.” 30 ft-lb. That matters because the bracket sees vibration and can crack if under-torqued.

Engine Brake Operation Check and Bleeding

After installation, Section 5 tells you to bleed the engine brake housings. Air trapped in the hydraulic system will make the brake sluggish or non-functional. The procedure: crack the bleed screw on each housing while the engine is running at idle, wait until oil flows steady without bubbles, then tighten. Do it in the order listed. The manual says to run the engine for two minutes after bleeding to re-check. That takes ten minutes total. Skipping it costs you a comeback. I have seen it.

The operation check requires you to cycle the dash switch and listen for the solenoid click, then verify that the slave pistons move. The manual describes the audible and visual checks. No guesswork.

Maintenance and Theory of Operation – Why It Works

Section 6 covers maintenance and theory. The theory section explains exhaust blowdown: how the solenoid controls the control valve, which opens the master piston, which hydraulically pushes the slave piston against the exhaust valve. The Robo-Lash adjusting screw is a mechanical lash adjuster that compensates for wear – no periodic adjustment needed. That is a feature you want to understand when diagnosing a noise. The manual explains slave piston and master piston rebuild procedures on pages 13-14. If you ever have to tear one down, those pages save you time. Parts like the O-rings and seals are common, but the manual gives you the exact cross-references. That is something aftermarket manuals never do because they copy from the same source and miss the details.

Need the correct solenoid valve part number? It is listed in the electrical section. Need to verify the control valve clearance? Page 10 reads: “0.001-0.003 inch.” That is a feeler gauge measurement, not a guess.

Related Manuals

• Jacobs 401A 401B 401C Installation Manual
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• Jacobs 317E, 317F, 336A 1995 Troubleshooting Manual – OEM Brake Specs

For general knowledge on how a manual transmission interacts with engine braking, see this article on Manual Transmission operation. Also, if you are working on a vehicle with a manual gearbox, check the Manual Transmission section on our site for maintenance schedules.

Does this manual cover the 455A model?

Yes. The manual title includes 455A, 455B, and 455C. Installation steps are identical for all three, with notes on specific model differences where applicable.

What page has the slave piston adjustment spec?

Page 6. It shows the 0.023″ feeler gauge procedure. If you lose that page, you will waste time. Get the manual.

You need the correct procedure and factory specs for this install. Do not rely on a PDF someone copied from a forum. Get the original 16-page Jacobs manual. Access the Factory Manual from AutoRepairManuals and put it on your bench. Your engine brake will thank you, and your wallet will too.