Hydroplaning & Handling ???'s

[DeeVeeEight]

A few weeks ago I got caught in the rain on the Atlantic City Expressway while in the 'Vette. I noticed that when I took my foot off of the gas pedal the car would momentarily get a slightly unstable feel to it (in the rear), like I was temporarily hydroplaning.
What are the forces at work here, why does the feeling only occur when transitioning from pulling to coasting?

New tires, smooth road surface (asphalt), moderate rain, speed about 65 mph.

 

[lars]

You might want to check out your rear end for bearing and bushing tightness - When you go from power-on to power-off, any looseness in the rear end changes the toe setting from toe-in to toe-out. The sensation becomes more noticable under reduced traction conditions, such as rain and snow. I don't think you're hydroplaning - I think your rear end alignment is shifting.

Lars

 

[mrvette]

Every car with a locked driveline....auto/lockup or stick does it, damn if I know why......my work vans do it, my huge Pontiacs back when did it, the '72 did it, so did my '87 vette....:surrender:

And what Lars said makes sense too....but why a solid axle car do it??? my old automatic 455/400 turbo '73 Grandville even did it.....ONE thing all my RWD cars have had since forever now, is POSI, wonder if that contributes to the 'happening'......

 

[greg75vette]

With what Gene is saying I think that has to deal with the engine applying a 'braking force' when lifting off the throttle. In a manual car, when you lift off the throttle and leave it in gear, the engine will begin to slow the car down, as we know. That braking force will only be applied at the rear wheels of course. This could potentially be enough drag in order for it to be a little uneasy.

A thought I had was throttle-off-oversteer, or rather something to that effect. Throttle off oversteer is when the weight transfer of the car causes instability in the suspension, usually in a turn. Porsches were known to do this back in the day, I believe. Basically how it works is when the car is under acceleration there is significant weight transfer to the rear wheels in order to maintain stability. However, when lifting the throttle, that weight transfer is reduced, or placed forward, thus reducing grip on the rear wheels enough for them to loose traction and cause oversteer. Usually this is when the tires are taxed already being in a fast corner where the throttle is needed to maintain traction. Unless you were really accelerating in the rain, I don't know if this could be the issue.

For your case, not sure. But now you have three possibilities :nuts:

 

[DeeVeeEight]

Thanks to all here. Yes it does feel like possibly the rear end is shifting a bit when getting on/off the gas pedal. I guess it's time to get the checkbook out. The trailing arms, bearings and bushings are about the only thing I haven't replaced yet. I'll have them checked and see what's up.

Funny, every time I get a few bucks put away the 'Vette sniffs them out.... :flash:

 

[DeeVeeEight]

The money....

You know, the more I play this game of being a C3 owner and think of all the time and money I have put into this car in the last 5 years I can't help but wonder, wouldn't a newer 'Vette have made more sense?

Yeah, I know, Hindsight is always 20/20..... :surrender:

 

[mrvette]

You know, the more I play this game of being a C3 owner and think of all the time and money I have put into this car in the last 5 years I can't help but wonder, wouldn't a newer 'Vette have made more sense?

Yeah, I know, Hindsight is always 20/20..... :surrender:

Well, I dunno what you farm out, and what you do yourself....I do it awl myself, or give up the car, :gurney:.....as if any 'newer' old vette would NOT have even more problems??? mainly electricals/electronics which I feel are the ultimate death knell of most new cars as they get over ten years old....enough with a simple 2 dzn wires on a engine computer, they get nutz with ABS and ASR, and security, then active shocks, and then a body control computer....

sorry but there simply has to be a limit to computers and cars, I call it quits with a simple engine controller, the rest bring almost nothing to the table....

and most here don't even want FI....I maybe antiquated but not THAT far back yet....

:gurney::hissyfit:

 

[boeing46]

A few weeks ago I got caught in the rain on the Atlantic City Expressway while in the 'Vette. I noticed that when I took my foot off of the gas pedal the car would momentarily get a slightly unstable feel to it (in the rear), like I was temporarily hydroplaning.
What are the forces at work here, why does the feeling only occur when transitioning from pulling to coasting?

New tires, smooth road surface (asphalt), moderate rain, speed about 65 mph.

I went to a driving school for track racing many years ago and was told to turn into the skid and give it a lil gas. Ya do the same thing if ya get a flat on the front. Turn in the direction the front is going no matter how back ackwards it seems. What ever ya do don't touch the brakes and backing off the gas would be just about the same thing continuing the hydroplane.