For those with the 2-1 “bump”

[JExpedition07]

I’ve often read on this forum it’s a software glitch......not in my case. On the F-150 most attribute this to slip yolk. Many added grease fittings so it can be greased more often. The bump has disappeared since I put in new shaft assembly that came greased......I get a light “clunk” sound but no more bump.

I’d recommend greasing the yolk splines for something to try.

 

[crector080862]

What is this in reference to just wondering

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[iimagine]

What is this in reference to just wondering

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Transmission bump.

iimagine

 

[08navigator]

Could you explain this a bit better? I have a 2008 with the downshift from 2-1 bump/clunk.

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[Trainmaster]

Ford recommends their blue silicone grease for this. I believe the yokes come with a Teflon coating, but this wears off and needs to be greased. It worked like a charm on my 2000. I didn't know the 3rd Gen cars had the same ailment.

 

[JExpedition07]

Could you explain this a bit better? I have a 2008 with the downshift from 2-1 bump/clunk.

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Sorry I missed your reply, haven’t looked at this thread. I’m referring to the downshift bump/clunk that sometimes occurs where it almost feels like getting hit lightly from behind coming to a stop. Sounds like you have it. This is documented on early 6R75&80 transmissions in the Expedition and F-150. Many F-150 owners attributed this to the slip yolk lacking lubrication on the splines. I recently replaced my driveshaft assembly which came with a new greased slip yolk and the bump occurs much less frequently, if at all. My old one had no grease inside, the new one came with a lot on the splines. The slip yolk is what goes into the Transfer Case or Transmission depending on drive type, it allows the driveshaft to move forward and back with changing load and the older ones stick up.

Here is a slip yolk:

 

[JExpedition07]

Here is a good video that explains it:

 

[crector080862]

I'm confused why would the expedition have this problem since the rear end of the vehicle never goes up and down so the slip yoke shouldn't ever move that much to cause a bump

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[08T1]

The rear diff does not move. Maybe a smidge here and there...

I had a 12 F150 it did the clunk.

I also drive a 07 F250. It clunks but it’s the 5 speed.

If I put my expy in neutral and role to a stop I can get it to clunk.

Not sure.

CJ

 

[JExpedition07]

Guys if you could sit under your truck while it’s under way you’d see the slip yolk does a lot. Every time you accelerate or brake your rear suspension is going up or down, and the diff is moving. The driveshaft has to move in or out to compensate. When your driving the rear suspension is under varying loads, and that load is changing depending what you are doing.

I’m confused, are you guys suggesting the F-150s diff and rear suspension moves under various acceleration/ deceleration loads but the Expedition does not? If so, how is this possible?

My old driveshaft, like the original F-150 shafts, relied on a nickel coating. The new yolk (like the newer F-150 yolks), had fords special grease in it instead of relying on the nickel coating. At some point Ford acknowledged there is a problem with the old driveshaft. They also sell repair kits with a new yolk and grease for the old one.

 

[08T1]

The F150 has axle warp. That yoke will get used a lot.

I’m not saying the expy does not move... just very little compared to the F150.

Unless we’re talking about the first gen expy with a solid rear axle?

CJ

 

[JExpedition07]

The F150 has axle warp. That yoke will get used a lot.

I’m not saying the expy does not move... just very little compared to the F150.

Unless we’re talking about the first gen expy with a solid rear axle?

CJ

Agree to disagree I guess, when I was under my expy I can see a line where the yolk goes and and out against the rubber seal on the T-Case and I can tell you it moves generously.

 

[08T1]

Yes sir I could be very wrong. Not worried about being wrong.

Just wanting to learn to be less wrong.

CJ

 

[08navigator]

Well I only have the bump when coming to a stop so mine must be software related. I guess I could take it to Ford. Not sure if it will damage anything.

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[JExpedition07]

Well I only have the bump when coming to a stop so mine must be software related. I guess I could take it to Ford. Not sure if it will damage anything.

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Yes mine occasionally bumped on acceleration as well esp at low speeds. Likely won’t cause any form of damage, esp if it’s been doing it since 2008 like mine.

 

[JExpedition07]

Yes sir I could be very wrong. Not worried about being wrong.

Just wanting to learn to be less wrong.

CJ

I could be the one that’s wrong. There are so many variables on an automobile something could have changed around the same time I replaced the yolk. I also changed the T-Case fluid, maybe that’s related? This was just my best guess.

 

[08navigator]

@JExpedition07 we just bought the navigator with 125k miles on it. The bump isn't crazy but it's there sometimes. I'll be dropping the pan, changing the filter and filling with fresh mercon sp so hopefully that will help smooth things out. Thanks for the replies!

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[5150 pops]

I’ve often read on this forum it’s a software glitch......not in my case. On the F-150 most attribute this to slip yolk. Many added grease fittings so it can be greased more often. The bump has disappeared since I put in new shaft assembly that came greased......I get a light “clunk” sound but no more bump.

I’d recommend greasing the yolk splines for something to try.

Curious if you're possibly experiencing this, or if you have ever seen this?

 

[JExpedition07]

Curious if you're possibly experiencing this, or if you have ever seen this?

Could be, I almost replaced that diff mount but I’m hesitant because I don’t get that surge shown in the video when putting it into gear. I do have a light clunk occasionally in reverse though, almost feels like warn out rear diff part.....waiting for it to get worse but it hasn’t so far. The 2-1 bump has pretty much been alleviated for me after changing T-case fluid and new yolk.

I can’t figure out the reverse clunk. It doesn’t occur from reverse to drive just park to reverse. Seems the noise doesn’t occur until load is on the rear end (powertrain force being applied) and it sounds like it’s coming from the very back of the expy.

I’d think I’d get the shudder and jump in drive like in this video if it were the case. It isn’t that loud, likely me trying to fix things that don’t need it as usual. Seems I chase a lot of ghosts.