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Slippage? - Advice needed - Transmission, Differential, or Engine?

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Old 06-12-2017, 10:41 AM
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Question Slippage? - Advice needed - Transmission, Differential, or Engine?

I've been noticing some slippage recently, and need to figure out how to determine the root cause so I can address it before i get stranded somewhere. By "slippage", I am referring to what feels like a load-related slight and sporadic shuddering in the drive line.

Context - 291K miles, 2WD, stock transmission (never been flusuhed), and stock rear end (never been flushed). The two scenarios described below are the ONLY times I ever feel slippage. I don;t tow/haul anything, so the slippage is with an EMPTY truck.

Scenario 1: Going up and EXTREMELY steep hill from a stop at the bottom -- If I crawl up at almost zero mph, making sure to never get out of 1st gear, I only begin to feel some slight evidence of slippage as I reach the top at about 0.15 miles of travel distance. Alternatively, if I sort of just drive up the hill trying to stay in the 10-15 mph range, I feel a lot of slippage.

Scenario 1: After a long 4-5 hours drive late last week, lots of interstate and county highway roads, I land in Destin, Fl (FLAT), come to a stop, and make a hard left turn from a standstill and feel something (very slight slippage, or very mild shudder or chatter). If its a mild turn, no symptoms at all.

Scenario 3: NO slippage for straight ahead driving even after long drives. NO slippage on even extreme grades while driving at 30-50 mph. No slippage at any other times.


I had been thinking that it might just be time for the transmission at 291K until I had the Destin scenario late last week. I began to think it might actually be the differential because of the significantly different side-to-side wheel RPMs while making such tight turns. Maybe it's both the transmission AND the rear end?


QUESTIONS:

1) What can I do to further diagnose this issue?

2) Can AE be used for any of this diagnosis on the tranny?

3) Would fluid change in either or both components be advised/helpful?


UPDATES (You can read the remainder of the thread for details):

06/13/2017 - Differential has been ruled out because I was mistaken in thinking that the differential could experience slippage

06/14/2017 - Differential may be back on the table as one of my issues due to it being a Limited Slip rear end

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Old 06-12-2017, 10:51 AM
Walleye Hunter Walleye Hunter is online now
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I can't imagine it being the rear differential. Those are direct gear driven and if it was slipping it would be completely dead. If it was a LS and the LS was going bad you'd just have an open rear. Do you have trans temp gauge? Does your trans oil smell burnt? Other than that trans is out of my league.
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Old 06-12-2017, 11:06 AM
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Haven't smelled the fluid yet. I'm just digging into this with this thread. I don't have a temp gauge installed.
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Old 06-12-2017, 03:45 PM
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I would change the fluids with fresh appropriate fluid and see what happens from there.

As a matter of fact, this might be a waste but it was peace of mind for me. When I bought my truck it had 228K miles on it. Because I was confident the truck was maintained, but not sure how well I changed every fluid you could on the truck. The major parts like engine, transmission and differentials I ran the new oil for about 200 miles then changed them all again.

Since I did that, the transmission was out recently after nearly 20K miles of towing and the fluid was as red as the day I put it in.

You have to ask yourself, what is $75 in fluid going to hurt if that fixes your problem? If it doesn't, then you can dig deeper.
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Old 06-12-2017, 03:59 PM
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I've been thinking the same thing, Sous. I have the high dollar fully synthetic Schaeffer fluids for the both changes, but I'm thinking I might just purchase and use some of the lesser expensive (but good) fluids through the systems and see what happens. That way, if that makes things better, I can wait for a while and then replace again but with the better fluids I have.

I've already prepped the wife for this, and the question is "Just how deep do I go if I have to do the BIG job on the tranny?". I've wanted to swap to 4WD, and if I have to do the transmission... that might just make it worth it to go back in with a 4WD capable transmission... I think.
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Old 06-12-2017, 08:22 PM
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I checked the trans fluid when I got home, and it has a "well-used" brownish tinge to it but no burnt smell at all.
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Old 06-12-2017, 09:29 PM
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Differentials can't slip, period.

If the transmission is slipping the RPMs will go high.

My guess is that you're getting misfire.
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Old 06-12-2017, 11:41 PM
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Pete, could you be getting air in your fuel? Have you done the hutch mod? Sometimes extra load on the engine can expose a lack of power. Does your oil get changed on a regular basis?
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Old 06-13-2017, 12:04 AM
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Hmm... misfire? Could be, I guess, but why only on the extreme step hill at low speed? I've punched it hard a number of times getting on the interstate with no sign of misfits then.

As for air in fuel or oil issue ..I'm doubtful. Hutch and harpoon were done over 9 years ago. Fuel pump replaced about 18 months ago. Fuel filter has less than 10k miles on it. Racor PS120 and new suction hoses installed over a year ago with no evidence of air entrainment.

Oil still has low mileage. I need to check the level, I guess, but that doesn't explain the feeling of slippage on level ground during a slow sharp turn, either, especially after sitting at a light for 3 minutes.
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Old 06-13-2017, 12:06 AM
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OK... I conclude from the input thus far that I can rule out differential "slippage". Thanks for the education on that point. I'll drive my attention to the transmission and/or engine.

I'll admit, too, that I've been fooled by fuel flow issues in the past which masked themselves as transmission issues on steep hills (broken pickup foot with pieces of plastic plugging the pickup line, trash in the fuel plugging the inline strainer, and weak fuel pump). I was also fooled in a very short term by a dying IPR, but that was quickly diagnosed and resolved as it had a fairly quick death. I also know that I have one or two very tired injectors which require some warm up time before they fire properly, but once the engine is at temperatures, I have observed no other symptoms for problems with ignition/firing aside from a very rare and very slightly erratic idle. UVHC's were replaced about 3 years ago (Motorcraft), as were the GP's, GPR, IPS, and IPR, and the CPS is only about 15 months old.

I'll try to repeat the slippage scenario and watch the RPM's, and will hook up AE to watch for misfires, and will double check my oil level.

UPDATE:
Oil level is about 2 quarts low (a hair below halfway down the hash marks) which is not low enough to cause any running issues. I'll be topping it off this weekend, though, just for good measure (literally).

The AE watching will probably wait until this weekend as well, given that the "slippage" events take place all the way on the other side of town where I do not travel during the week.
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Old 06-13-2017, 03:02 PM
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Do you have a limited slip differential? My F150 started shuddering from a stop around corners once in a while once the differential heated up. It got worse and worse until I thought I broke it and took it to Ford. They laughed at me and changed the differential oil and it was perfect afterwards again.
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Old 06-14-2017, 08:42 AM
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Not being certain, I just went out to the parking lot to look, and the door sticker confirms that I have a limited slip differential. Picture of the sticker is below.

That being said, could it be that what I have felt in the turns after long runs recently may indeed be slipping clutches in my LS differential? I'll change the rear differential fluid (and friction modifier) in the next week or so (this weekend is promising a lot of rain), and will see if that resolve that particular symptom.

NOTE: What I had earlier called "slippage" in reference to the rear differential could also be called a very slight shudder.
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Old 06-14-2017, 04:05 PM
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Pete, in regards to the friction modifier I would not put any in if you plan to use synthetic gear oil. Some of those oils have friction modifier in them. Just put the oil in and take the truck out for a test drive doing a couple of sharp turns at low speeds. If there is some chattering/noise, put a bit of modifier in, then keep going until the differential is quiet.

I used Amsoil gear oil and did not require any modifier.
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Old 06-14-2017, 04:20 PM
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For me it started as a slight chirp from the tires and vibration once and awhile when turning from a stop. It became obvious later that it was differential because of all of the binding and tire scrubbing from the back of the truck. The dealer said my symptoms were common when the friction modifiers break down. I also remember it costing a small fortune for the synthetic oil and friction modifier from them. It scarred my memory so badly that I practically ran back to the dealer when the pinion seal started leaking because there was no way I was going to pay to replace all of the oil again only 6 months later.
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Old 06-14-2017, 04:53 PM
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Yeah, Sous, I don't believe the Schaeffer oil I have will require the modifier either because it has a decent dose of molybdenum disulfide built into it. I'll give that fluid change a shot at solving that issue sometime within the next week or so, as weather permits.
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