Failed Coast Clutch - Am I safe to drive In mountains? - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #1 of 11 (permalink) Old 09-11-2018, 09:47 AM Thread Starter
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Failed Coast Clutch - Am I safe to drive In mountains?

Hey All, I have a 99’ F250SD 7.3 with a very recent HD upgraded rebuild (under 5k miles) on my 4r100. This week during my first trip into the Sierra Mountains in California, my coast clutch has failed completely. I called my tranny shop and am under warranty, but I’m up in Lake Tahoe, headed down 395 to Mammoth and then to SoCal. There are at least 3 mountain passes that I’ll need to make that exceed 7k ft. I’m carrying a properly loaded truck camper for my truck (~$2500lbs wet), gross payload is near max. My concern is using all brakes down these passes and risking the possibility of damage/failure there also given the load. Need some advice or ideas on best way to get from A to B? (Note; I’ve read multiple posts on the issue already and have confirmed the failure diagnosis with my mechanic). Thanks
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post #2 of 11 (permalink) Old 09-11-2018, 10:03 AM
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I would think you would want to avoid using the O/D lockout while going down hill.

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post #3 of 11 (permalink) Old 09-11-2018, 10:38 AM Thread Starter
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Agreed, though at this point it wouldn’t help anyway. If I lock out O/D, (electronic) or drop into 2 or 1 manually (via hydraulic pressure), the engine drops to idle and the truck free falls down hill, regardless of the gear. Concerning.

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post #4 of 11 (permalink) Old 09-11-2018, 01:19 PM
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Back when, I burned out my coast clutches going down the mountains in first gear in North Carolina...
I first noticed the problem when backing up a small hill..
I got 'chatter' when backing up...
I called Brian at BTS transmission, and scheduled an appointment in 2 weeks...
He told me NOT to use 1st gear and Reverse..at little as possible
I don't know about 2nd or 3rd..though....
Maybe Mark will chime in and comment for you....
Did you check the color of the tranny fluid ??????
Before you do anything, I would go for a transmission flush,
To get all the black stuff out of the tranny..

XS_SUV
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post #5 of 11 (permalink) Old 09-11-2018, 09:23 PM
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Quote:
Originally Posted by Graupp View Post
I got 'chatter' when backing up...
The coast clutch doesn't do anything when you're pressing the accelerator pedal in reverse. If you're coasting in reverse I could see how it would chatter.

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I called Brian at BTS transmission, and scheduled an appointment in 2 weeks...
He told me NOT to use 1st gear and Reverse..at little as possible
I don't understand why. Once again, in reverse the coast clutch is only doing something when coasting. If you're in first gear with the OD OFF light not illuminated the coast clutch isn't even applied.
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I don't know about 2nd or 3rd..though....
Same as first. If you don't press the OD OFF button the coast clutch isn't applied. It isn't doing anything, it's just along for the ride.

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post #6 of 11 (permalink) Old 09-12-2018, 12:09 AM
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Good info.
Dumb question, does reverse even have a coast clutch?

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PHP HYDRA, 6637, 3-4 DP TO STRAIGHT 4 BEHIND THE TIRE, 1.0 EXHAUST HOUSING, DIY D66 TURBO, FUGA E-FUEL, EBPV DELETE. Cooper discoverer AT/3'S.

2010 VW JETTA TDI DSG Kerma tune. Hankook ventus v2 concept 2.


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post #7 of 11 (permalink) Old 09-12-2018, 10:08 AM
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OK Mark;
Admittedly that was 15 yrs ago ,and maybe my memory is failing me..
BUT, I do remember putting the shift lever in LOW, and going down the mountain, and it would
flip out of low gear as I descended the mountain and I would be coasting down the mountain..
It would hold and then just release....
I really didn't understand what was happening, until I backed up the slight hill in my driveway...
And that's when I realized that it was 'chattering' on me, and my transmission was malfunctioning...
I checked the tranny fluid, and it was black...
That's when I called Brian at BTS, and he told me NOT to use low gear, and use reverse sparingly...
I also remember that coming down any sort of steep hill, when taking my foot of the accelerator in OD,
the RPM's would drop to idle, and I would be coasting down the hill...
SO!!! What type of clutches are we talking about here ????

XS_SUV

Last edited by Graupp; 09-12-2018 at 10:15 AM.
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post #8 of 11 (permalink) Old 09-12-2018, 05:57 PM
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Quote:
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Good info.
Dumb question, does reverse even have a coast clutch?
No, reverse doesn't have a coast clutch. Either does any other gear. Only the coast clutch has a coast clutch.

The coast clutch is applied and active when coasting in reverse. Maybe that's what you mean.

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I really didn't understand what was happening, until I backed up the slight hill in my driveway...
And that's when I realized that it was 'chattering' on me, and my transmission was malfunctioning...
I checked the tranny fluid, and it was black...
That's when I called Brian at BTS, and he told me NOT to use low gear, and use reverse sparingly...
You had one or more failing clutches. The coast clutch cannot make reverse shudder.

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I also remember that coming down any sort of steep hill, when taking my foot of the accelerator in OD,
the RPM's would drop to idle, and I would be coasting down the hill...
SO!!! What type of clutches are we talking about here ????
When in overdrive (fourth gear) there is ALWAYS coast braking. The coast clutch is NEVER applied in fourth gear because that causes a tie up. A tie up is when the output shaft is locked to the case, which makes the rear wheels stop turning RIGHT NOW.

If it dropped to idle while coasting in fourth gear the transmission had a major mechanical failure, not a clutch failure. It likely would never be able to move the truck again. So I suspect you really were not in fourth gear when this happened.
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post #9 of 11 (permalink) Old 09-12-2018, 07:03 PM
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Ah, now I see. The coast clutch is separate. Not attached to any gear in particular.

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PHP HYDRA, 6637, 3-4 DP TO STRAIGHT 4 BEHIND THE TIRE, 1.0 EXHAUST HOUSING, DIY D66 TURBO, FUGA E-FUEL, EBPV DELETE. Cooper discoverer AT/3'S.

2010 VW JETTA TDI DSG Kerma tune. Hankook ventus v2 concept 2.


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post #10 of 11 (permalink) Old 09-12-2018, 07:44 PM
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If it dropped to idle while coasting in fourth gear the transmission had a major mechanical failure, not a clutch failure. It likely would never be able to move the truck again. So I suspect you really were not in fourth gear when this happened.
Well, on this 'particular' point I have to disagree with you...
I am "ALWAYS" and ever driving with OD in the "ON" position..with light NOT lite...
I NEVER EVER drive in 3rd gear [OD light lite] "" PERIOD""
And I always distinctly remember going down hills and having the engine drop into the idle mode..
And this I have done ALL the time......
Admittedly, my ""THIRD"" transmission doesn't seem to be activating the same way...
SOOO !!! Just maybe the ""ORIGINAL" transmission was a piece of crap coming out of the factory...
""DEFECTIVE?"""

XS_SUV
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post #11 of 11 (permalink) Old 09-13-2018, 09:08 AM
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[sarcasm]It must have been defective. The gears came out of mesh when coasting in overdrive, then magically fixed themselves when you went power on again.[/sarcasm]

What you're saying is analogous to saying your engine's connecting rods are only connected to the crankshaft power on, but they disconnect when coasting. Then when you go power on again they reconnect.

Coast braking is ALWAYS active in fourth gear. It isn't created by the coast clutch, the arrangement of the powerflow in fourth gear ALWAYS has coast braking. There is no way it can remain in fourth gear and not have coast braking.

You can disagree with me if you like. One of us understands how power is transmitted through the transmission, and one of us does not understand.

What you may have had is a torque converter that had a higher stall speed than the one you currently have. A higher stall speed will allow the engine speed to drop further than a low stall converter.

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