Author Topic: engine brake lag time  (Read 241 times)

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Offline Charlie/Susie

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engine brake lag time
« on: October 27, 2019, 08:17:30 PM »
Just got back from 5 mos in Maine. No real problems but I have a question about the lag time between pressing the engine brake and the time it takes to activate the compression and down shifting. During emergency braking this led to some heart stopping moments while also standing on the brake peddle. Is this lag time normal or is there an adjustment that can cause a quicker activation? Oh yea, its a 2005 cummins-allison 6 speed air brakes. Also , what is the minimum brake pad thickness before replacement is necessary? Again, thank you for ant info. Charlie. 
Charlie and Susie
2005 Fleetwood Bounder 38N 5.9 cummins
2014 Corolla toad

Offline Brett Wolfe

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Re: engine brake lag time
« Reply #1 on: October 28, 2019, 06:20:24 AM »
So, what is the lag time between turning on exhaust brake (or having it on) and removing foot from throttle?

Is there lag time between switch on/foot off throttle and Allison shift pad going from "6" to whatever the preselect gear is-- usually 2nd or 4th?

OR does that happen immediately and then there is a lag before the downshift?

OR does the downshift happen immediately and there is a lag before the exhaust brake closes/adds its braking HP?

Offline Charlie/Susie

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Re: engine brake lag time
« Reply #2 on: October 28, 2019, 04:23:50 PM »
Hi Brett, some of the braking had more warning then others. At times I would brake first then use the exhaust brake, that would take about 3-4 seconds to kick in. If brake is on already lifting foot from accelerator brake would engage immediately. With emergency braking both exhaust brake and foot braking happens at same time, lag time seems excessive maybe 3-5 seconds. Trans shifts from 6 to 4 then soon to 2. Depending on how fast we're moving ( 60mph to 64mph) those few seconds can be scary. Thanks Brett hope the info helps. Charlie. 
Charlie and Susie
2005 Fleetwood Bounder 38N 5.9 cummins
2014 Corolla toad

Offline Brett Wolfe

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Re: engine brake lag time
« Reply #3 on: October 29, 2019, 06:15:19 AM »
Sorry, I don't understand. Appears these two sentences are in conflict (immediately vs 3-5 seconds):

" If brake is on already lifting foot from accelerator brake would engage immediately."


"With emergency braking both exhaust brake and foot braking happens at same time, lag time seems excessive maybe 3-5 seconds."


If you would, go back to my post above and let us know at which step the delay occurs or break what is happening down into steps in your own words.

Thanks.

Offline David.e.atherton

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Re: engine brake lag time
« Reply #4 on: October 30, 2019, 10:06:29 AM »
Charlie, Brett, the Response time is almost instantaneous with the compression brake application however there is question as to what speed you are traveling when compression
brake is applied. Reason for that question that many misunderstanding the compression
Brake application at speeds more than 45 mph the exhaust pressure from engine will over
Take the pressure on the flapper the is controlling by the air cylinder. Speeds lower than 45
and below compression brake will effectively do its job . Second question with the compression
brake the arm that the air cylinder can be sticking and delay in movement. This delayed
movement also can be from the activation solenoid ( electric to air ) location on clip at rear of engine head. Dirty connection , short in wire or coil on solenoid going bad. Your last question
air brake shoes replacement, in center of brake pad there is a v notch that is the indicator for
replacement if you cannot see that notch with inspection dust cover removed time for brake
replacement.  Ask Dave, Dave Atherton Retired Cat Mechanic

Offline Charlie/Susie

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Re: engine brake lag time
« Reply #5 on: October 30, 2019, 05:15:54 PM »
Thanks for your questions Brett. The immediate braking part I mentioned was low speed braking for sudden traffic or stop lights. Higher speed braking IE. down hill or being cut off in heavy traffic at 50-60mph is where the lag time gets scary.  Also thank you Dave for suggesting some items to look for on the exhaust brake itself. I bought the unit used and don't really know how well it was maintained so I will look into the maint. procedures on this. Also time for new brakes. You guys and this forum are life savers.
Charlie and Susie
2005 Fleetwood Bounder 38N 5.9 cummins
2014 Corolla toad

Offline Brett Wolfe

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Re: engine brake lag time
« Reply #6 on: October 31, 2019, 06:07:17 AM »
And, if a PacBrake brand exhaust brake, the DO require lubrication:

https://pacbrake.com/product/c18037-superlube/

Offline David.e.atherton

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Re: engine brake lag time
« Reply #7 on: October 31, 2019, 07:42:33 AM »
Brett, thank you .I have had problems at that location , delayed response from dry pivot on Actuation Arm on air cylinder.  Dave

Offline Brett Wolfe

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Re: engine brake lag time
« Reply #8 on: October 31, 2019, 07:45:45 AM »
Yes, either the air cylinder piston or the flap in the exhaust itself can stick if not lubed.

And, if it/they happen to stick CLOSED you will not go anywhere!