Help Narrowing Down 1988 F-250 7.3 IDI N/A Slipping Clutch Cause

rempfer

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On two occasions, after many miles on long trips pulling a loaded trailer, at full throttle in 5th overdrive at 65-70 MPH I have observed the engine accelerate several hundred RPMs due to the clutch (or ???) slipping. On the first occasion I backed out of it immediately and dropped down a gear to lessen the load on the engine and the slipping stopped. On the second occasion I stayed on the throttle a few seconds before backing off and could smell the clutch (or ???) "burning."

Here's what I can report from observations so far.
1. While I have done the modification to the clutch pedal push-rod (getting rid of the fakey plastic bushing), the modified rod is the correct length and is NOT preventing the master cylinder from retracting fully whether the vehicle is hot, cold, or possibly binding in a turn. There is always 3/4 to 1 inch free play in the pedal due to a slight gap between the push-rod and the master cylinder piston when the clutch is engaged.

2. I do not "ride" the clutch pedal.

3. The clutch disc does not feel as if it's worn out, since the clutch begins to engage with the pedal about 1/3 of the way off the floor and therefore has a lot of pedal travel between where the clutch fully engages and where the pedal reaches its top position.

4. So I believe there's plenty of thickness left to the clutch disc, that the clutch linkage is not causing the problem, and therefore that it must be an issue either with the clutch having gotten wet/oily or most likely a weak pressure plate.

5. Possible argument/exception to #4: I've read some stuff here on the forum about "dual-mass" flywheels -- whatever those are -- that makes me wonder if the flywheel could be slipping internally or ???. (I would remind you all that if allowed to slip for 2-3 seconds, one does get a slipping clutch smell.)

As far as I know, this truck is all original/unmodified from the factory. What flywheel would it have?

If not a weird flywheel issue, or oil on the clutch disc issue, what parts (clutch disc and especially pressure plate) should I buy and install to ensure that this problem won't happen again?

Your thoughts and advice, please?

Thanks,

**** Rempfer
Elma Washington USA
 

Randy Bush

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On two occasions, after many miles on long trips pulling a loaded trailer, at full throttle in 5th overdrive at 65-70 MPH I have observed the engine accelerate several hundred RPMs due to the clutch (or ???) slipping. On the first occasion I backed out of it immediately and dropped down a gear to lessen the load on the engine and the slipping stopped. On the second occasion I stayed on the throttle a few seconds before backing off and could smell the clutch (or ???) "burning."

Here's what I can report from observations so far.
1. While I have done the modification to the clutch pedal push-rod (getting rid of the fakey plastic bushing), the modified rod is the correct length and is NOT preventing the master cylinder from retracting fully whether the vehicle is hot, cold, or possibly binding in a turn. There is always 3/4 to 1 inch free play in the pedal due to a slight gap between the push-rod and the master cylinder piston when the clutch is engaged.

2. I do not "ride" the clutch pedal.

3. The clutch disc does not feel as if it's worn out, since the clutch begins to engage with the pedal about 1/3 of the way off the floor and therefore has a lot of pedal travel between where the clutch fully engages and where the pedal reaches its top position.

4. So I believe there's plenty of thickness left to the clutch disc, that the clutch linkage is not causing the problem, and therefore that it must be an issue either with the clutch having gotten wet/oily or most likely a weak pressure plate.

5. Possible argument/exception to #4: I've read some stuff here on the forum about "dual-mass" flywheels -- whatever those are -- that makes me wonder if the flywheel could be slipping internally or ???. (I would remind you all that if allowed to slip for 2-3 seconds, one does get a slipping clutch smell.)

As far as I know, this truck is all original/unmodified from the factory. What flywheel would it have?

If not a weird flywheel issue, or oil on the clutch disc issue, what parts (clutch disc and especially pressure plate) should I buy and install to ensure that this problem won't happen again?

Your thoughts and advice, please?

Thanks,

**** Rempfer
Elma Washington USA
I would suspect the dual mass flywheel is the problem. When you tear into it buy a kit with the replacement style flywheel.

Sent from my KYOCERA-E6790 using Tapatalk
 

rempfer

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If it's only the friction slipping in the DMF (I don't get any of the idling-in-neutral rattle I've read about when the DMF's springs are failing/breaking), am I in any danger of continuing to drive it this way until this winter when I can do the SMF conversion?

Has anyone posted a video of the R & R procedure?
 

Randy Bush

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Because I pull heavy with mine once it did it I changed the clutch and flywheel . I suspect if it start doing it more often One better get it done as it might leave you stranded.
 

IDIBRONCO

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As far as I know, this truck is all original/unmodified from the factory. What flywheel would it have?
What year is the truck?
3. The clutch disc does not feel as if it's worn out, since the clutch begins to engage with the pedal about 1/3 of the way off the floor and therefore has a lot of pedal travel between where the clutch fully engages and where the pedal reaches its top position.

4. So I believe there's plenty of thickness left to the clutch disc,
While you may be able to get a close guess this way, I don't believe that you can tell how much material is left on the clutch without actually looking at it.
 

catbird7

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Friend neglected to repair a small fuel leak on main return line on top of the intake. When the line completely failed it absolutely hosed down everything under the hood and firewall. Fuel line was repaired and truck worked OK till he hauled a load, then the clutch slipped. Apparently over the years a mixture of fuel & old motor oil caked on engine block ended up soaking into his clutch disc. Had to replace the disc.
 

rempfer

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So if I'd like to go to the single mass flywheel, exactly which product should I buy? Is anything made in the USA anymore? Or if overseas-made, I'd like to install the best design & quality. Help on making the best choice for SMF, please.
 

onetonjohn

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The other thing that can make it slip although there is plenty of clutch material left is a leaking front seal on the transmission. You should be able to remove the inspection cover and see if it's wet in there.
 

IDIBRONCO

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A lot of people have used the Luk brand SMF kit. I've had mine in three different vehicles and it still works great.
 

typ4

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With hydraulic clutch actuation there is no way to tell disc thickness, hydraulics keep it as "zero" all the time.
When you do this clutch swap if the shift tower boot needs replaced make sure it has a vent cut in it or it will build up case pressure in trans and push oil past the front seal.
I found this out the hard way.
The replacement boot is for the later ZF -6 that has a vent in the case.
I have used LUK kits and when I did the all night trans swap in 2018 in Calvins shop driveway I put in an autozone clutch, has been as good as the luk so far. and its had some work.


https://www.oilburners.net/threads/psa.82634/#post-984373


https://www.facebook.com/photo.php?fbid=2122149644469751&set=pcb.10160286124675644&type=3
 
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catbird7

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My kit came from Advance Auto. Flywheel, disc, pressure plate, throw-out, & alignment tool.
 

rempfer

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Thank you. Will go with the LUK option. One last question -- I'm old enough now that I can't bench press a transmission anymore. What transmission jack will work/fit the best for the ZF in my truck? I do not have a hoist in my shop, so truck will be at ground level.
 

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