klutchdust
Orange, California
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enblethen wrote:Sounds like the rear end is wrapping up. This happens when too much torque is applied. When brakes are release, the rear suspension twist is released. Common area is center bolt in spring, shackles, torsion bars and spring perches.
Old school:
When a u joint is in question we would put the vehicle in gear, hold the brake down firmly and push the throttle down slightly to apply pressure to the joint and listen for a click.
Also effective when checking motor mounts to see if the engine lifted off the broken rubber mount
Is this what you refer to as wrapping up?
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RambleOnNW
Pacific Northwest
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Did you have the A/C on? The A/C cycling on will kick the RPMs up. Anyway if you feel the jolt again quickly look at what the RPM gauge is showing.
I had this same thing happening on an older AWD car occasionally. Could have sworn someone was tapping my rear bumper. But concluded the power output was fluctuating for some reason. Perhaps related to how during a cold start the vehicle RPMs are elevated for a short time until partially warmed up. Pressing the brake harder prevented the increased power from overpowering the brake pressure. Or put the transmission in neutral at stops.
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VQ74
California
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Something mire intense from the rear.
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klutchdust
Orange, California
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VQ74 wrote:Something mire intense from the rear.
So has it done it again or was this an isolated incident. If it is doing it regularly I would have an experienced mechanic take a ride with you to help out with the diagnosis.
keep us posted.
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Grit dog
Black Diamond, WA
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^To his point, if you intend to diagnose this for free with help from your internet friends (nothing wrong with that, it’s a great resource and convenience of this 21st century technology) then you need to help. IE see how repeatable it is. Same conditions different conditions. You’ve added nothing other than it did it twice, in a row and then you apparently parked it. And a buddy looked underneath and said nothing looks broken.
It doesn’t feel unsafe to drive and you’ve also confirmed that it drives fine.
So please go try to repeat the condition. Pay attention to all parameters. Does it do it cold, or only after up to temperature, or directly coming off of a highway speed run, etc.
We’re trying to help but this is not the time to be of few words.
And while possible it’s something structurally wrong or something worn out. It’s highly unlikely given the age and extremely low miles. (Which some of the respondents aren’t considering).
Oh also, brake system. Is it just a standard vac or hydro boost? Not electric over hydraulic? Presume so since it’s a class 4 chassis (or 3 can’t remember if you said 350 or 450). Also unlikely but throwing it out there
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Lumpty
Greater Gotham City
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My guess is something driveshaft related, either the slip yoke at the transmission connection, or on many long wheelbase trucks there is a constant-velocity joint in the center, or a carrier bearing there, that may have some play.
Rob
Too Many Toys.
- '11 E450 Sunseeker 2300
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klutchdust
Orange, California
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Lumpty wrote:My guess is something driveshaft related, either the slip yoke at the transmission connection, or on many long wheelbase trucks there is a constant-velocity joint in the center, or a carrier bearing there, that may have some play.
I have experienced that on my 2500 GMC pick-up when towing my trailer. I removed the driveshaft and lubed the splines and it's been good for many miles. I had a clunk sound when moving from a stop.
The OP hasn't said much regarding his experience with all things mechanical so hopefully something said here helps.
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Grit dog
Black Diamond, WA
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OP seems to quit wanting help from the brain trust here, but again, as new/low miles as it is, structural chassis issues and driveshaft issues are highly unlikely and also largely not commensurate with the symptoms as described.
Thinking a bit more, could be a late downshift back to 1st gear after coming to a stop.
Could explain how to try to diagnose that but the words are seeming wasted without input from the guy who asked for help.
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VQ74
California
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VQ74 wrote:klutchdust wrote:try this. Start vehicle. put in neutral. release foot brake. Apply foot brake and put transmission in drive. Is this what you felt?
Ok Will try. If I do feel a jolt from the rear what does that mean. Transmission problem.
Did try this no jolt from rear. Just forward movement.
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Grit dog
Black Diamond, WA
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VQ74 wrote:VQ74 wrote:klutchdust wrote:try this. Start vehicle. put in neutral. release foot brake. Apply foot brake and put transmission in drive. Is this what you felt?
Ok Will try. If I do feel a jolt from the rear what does that mean. Transmission problem.
Did try this no jolt from rear. Just forward movement.
No, that would be a u joint or a lot of slop in the ring n pinion.
Gotta ask why you only respond in little bits n pieces or not at all, if you’re looking for help to diagnose it?
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