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Discussion Starter · #1 ·
Hi, does anyone have any idea what this is? When reversing normally at slow speed, like out of a parking spot, never noticed anything. But then yesterday, I had to reverse half a block, and pressed the gas pedal to get moderate - aggressive acceleration, and felt a bump bump bump feeling, like you had a cone stuck under your car while driving.<p>The wierd thing is it only seems to happen when I press the gas moderately, so if I go a constant 10 or 15 MPH I don't feel it, but then as soon as I accelerate quickly, I feel the bump bump bump during acceleration.<p>I thought at first could it have something to do with the 235/50R18 Pirelli Scorpion Zero Asimmetrico tires that aren't meant to roll backwards, since they are meant to roll in one direction? But if that was the case, then why is it at a constant speed in reverse I don't feel it, and only under moderate to heavy accerleration?<p>What could it be?
 

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I'm not a mechanic, but could it be a speed or RPM limiter? Since cars are not meant to go very fast in reverse, perhaps the bump feeling was the engine trying to limit backwards acceleration. I think you can rule the tires out. At a constant speed in reverse, the engine will not be trying to limit the RPMs.
 

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Discussion Starter · #3 ·
Re: (Cabot)

No unfortunately, I doubt it. I could accelerate just from 0-10, and feel the bump bump during acceleration. Then go at a constant 10 MPH for a while, and feel nothing, but as soon as I accelerate to 15 MPH, feel it again. Those aren't high speeds anyway.
 

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Re: (Lotus99)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Lotus99</b> »</i></TD></TR><TR><TD CLASS="quote"> Those aren't high speeds anyway.</TD></TR></TABLE><p>I would be interested in knowing how many revs your engine is turning going 15MPH in Reverse. REMEMBER, Reverse gear in most cars tends to be significantly higher numerically than first gear going forward.<p>In other words, its not unheard of for a car to be doing considerably more RPMS at a given speed in Reverse than at the same speed in First Gear
 

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Discussion Starter · #5 ·
Re: (V70 Brad)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>V70 Brad</b> »</i></TD></TR><TR><TD CLASS="quote"><p>I would be interested in knowing how many revs your engine is turning going 15MPH in Reverse. REMEMBER, Reverse gear in most cars tends to be significantly higher numerically than first gear going forward.<p>In other words, its not unheard of for a car to be doing considerably more RPMS at a given speed in Reverse than at the same speed in First Gear</TD></TR></TABLE><p>Sure, I'll try to see if I can do another test and tell you for curiousity's sake. Though it has nothing to do with the issue I'm reporting, since from standing still even, when you accelerate, you feel and hear this bump bump bump.
 

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Re: (Lotus99)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Lotus99</b> »</i></TD></TR><TR><TD CLASS="quote"><p>Sure, I'll try to see if I can do another test and tell you for curiousity's sake. Though it has nothing to do with the issue I'm reporting, since from standing still even, when you accelerate, you feel and hear this bump bump bump.</TD></TR></TABLE><p>The point of this is that I'm wondering if you're hitting the rev limiter.
 

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Discussion Starter · #7 ·
Re: (V70 Brad)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>V70 Brad</b> »</i></TD></TR><TR><TD CLASS="quote"><p>The point of this is that I'm wondering if you're hitting the rev limiter.</TD></TR></TABLE><p>Again, I'm getting the bump bump when accerlerating from a stop = ZERO speed. It's one thing if I was feeling it from 15 to 20 MPH and up only, in which case the rev limiter might be the issue, but that's not the case here.
 

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Re: (Lotus99)

I have gotten something similar when my traction control activates. See what happens if you deactivate it...
 

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Discussion Starter · #9 ·
Re: (V70 Brad)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>V70 Brad</b> »</i></TD></TR><TR><TD CLASS="quote">I have gotten something similar when my traction control activates. See what happens if you deactivate it...</TD></TR></TABLE><p>So you mean if you accelerate too fast going in reverse and your wheels start slipping, that's when you feel it? I'm not accelerating anywhere near that fast, and it was dry pavement, and I didn't feel the wheels slipping, but I'll give that a shot.
 

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I'm young enough that I still enjoy doing burnouts at lights. <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/biggrin.gif" BORDER="0"> I get a similar sensation when I do them UNLESS I turn off the traction control...
 

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Discussion Starter · #11 ·
Re: (V70 Brad)

So as I suspected, traction control (it's actually the anti spin control you're referring to, you can't turn off the traction control) had nothing to do with it - on or off, it still vibrated. As I wasn't getting any wheel slippage when accelerating either, this wasn't related to it.<p>Hitting the rev limiter is a non issue as well, since I wasn't going that fast. 20 MPH in reverse is still only about 2500 RPM. In drive, 1st gear, going the same speed you actually have a higher RPM of around 3000.<p>So the dealer checked it out and their best guess is that it's a problem with the drive shaft, so they're ordering me a new one. Wow. New drive shaft after just 4,000 miles... should I be overly concerned?
 

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Re: (Lotus99)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Lotus99</b> »</i></TD></TR><TR><TD CLASS="quote"> Wow. New drive shaft after just 4,000 miles... should I be overly concerned?</TD></TR></TABLE><p>Kind of a wierd thing to happen, which is probably why the idea was missed here. <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/rolleyes.gif" BORDER="0">
 

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Discussion Starter · #14 ·
Re: (rovermark)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>rovermark</b> »</i></TD></TR><TR><TD CLASS="quote">Lotus, off topic: I wonder, are you happy with your car? Would you buy a Volvo again?</TD></TR></TABLE><p>Wow, that's a tough question! There are certainly things that do bug me about this car, which I do not expect considering what I've paid and the quality the car claims to be. I've only got 6 months and 6,000 km's under my belt, so it's kind of early to be having these issues IMO.<p>As you've probably been following my posts, the car's had numerous software bugs (did I buy a Windows based OS system? <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/tongue.gif" BORDER="0"> ), which at least they seem to have fixed now, the car stalled for no reason at all, but luckily started right after, and I've been told the software was the problem and they upgraded it, and now the drivetrain needs replacement.<p>By contrast, my BMW 335i with the same mileage and a few months older hasn't had a single real issue. Knock on wood!<p>The fact that the cars also weigh about the same (the 335i's only 200 pounds less), and have about the same HP, but the Volvo still does dismally in fuel consumption gets me too. My 335i is rated at 12.3L/100km in the city and gets 15L/100, but that's b/c I drive it like I mean it, while the Volvo's rated for 13.7L/100, is driven mainly by the wife, and still ends up getting almost 18L/100!<p>Overall though, I'm still really happy with all the extra features I got like the car's collision avoidance system and adaptive cruise, the various other safety things built into the car, tons of cargo space, and it drives very comfortably and quality inside is pretty good so far, and there's 4C so I can stiffen it up a bit when I want.<p>So for our needs right now, with a 2 and a 4 year old, I still feel I got the right car, as utility, space and safety are the priorities over driving feel. I'm just hoping it won't let me down in the next few years... <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/embeer.gif" BORDER="0">
 
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