When i leave my car in first, second or any gear i can roll the car, that is w/o the parking brake. Now that to me is a bit conspicuous. My shop teacher told me it would be a lack of compression which keeps the engine from rolling over, but that was in relation to a piston engine.

Could it be that possible my clutch master or slave cylinder is giving up? I don't really have any problems while shifting, i do get the 2nd gear grind when cold but thats about it.

I'm Confused

 

When the car is started and all it runs ok and shifts ok within the gears ?? The best you could do is probably get a compression test .. If my memory is acurate you should have arround 25-30 psi per rotor side...

 

It would not be the cylinders as the clutch disk is against the flywheel without the hydraulics. Sounds like your clutch is slipping, but you would notice that driving as well. Does the clutch slip when you are driving? Does the engine turn when the car is in gear and rolling? It's hard to imagine how your compression could be so bad it would make a difference in the rolling resistance and yet not notice any performance problems in driving. How long has this been happening and has it gotten more pronounced?

 

that's kinda what I was getting to aswell. *USUALLY* , and I meen this also with piston engines, the car should have at bare minimum , enough compression to stop u from pushing it while in gear. I rememeber when I blew my engine, I had 0 compression in the rear rotor and there was no way in hell I was gonna push that thing. Probably has something to do with your clutch, or tranny because even at 0 compression, I had a hard time pushing my car. cosmicbang made a good point by asking if the engine turns while u push it... Check and see if the fan's turning a bit ... Get back to us on this one... I'm curious to know what the matter is

 

And since rotaries don't have any compression at super low engine speeds, it is entirely normal for the car to rill when in gear.

In fact you should be able to turn the engine by applying light-medium pressure on the alternator's cooling fins.

So to recap: You have no problems. Use your handbrake, don't leave it in gear.

 

Slight Hijack: Why don't rotaries have compression at low engine speeds??

On topic: Does it do this in gears other than 1 and 2? I usually park mine in 5th or reverse depending on the slope.

 

Mine rolls down hills.

But it does it unevenly, which makes me think it's the engine in my case.


Park in 1st or reverse, not 5th, nevarmore.
When you're in 5th it's easier for the engine to turn then when in 1st or reverse.

 

Open the hood and see if the engine turns when the car rolls. If the engine doesn't turn the clutch is slipping.

 

Of course it can roll to a certain extent with the engine turning if you park without the handbrake. And obviously it will be easier to turn a rotary with 3 moving parts than a big-*** V8 with pistons and camshafts etc. It sounded like he was saying there was some kind of problem and it was rolliing more than it should be. Such as the clutch slipping.

Earlier today I experimented with 4 cars in my driveway: first gen with excellent compression, third gen with ok compression, first gen with good compression, first gen with low compression one rotor none on other rotor. I did not find any observable (eyeball) correlation between compression and rolling resistance, ie coefficient of static friction. There may be a difference, but the effect of other drivetrain and brake parts makes it hard to isolate. The owners manual says to apply the hand brake and put in" P" if auto and "R" if manual transmission. I put it in 1st if facing uphill.

 

Easier to just adjust the e-brake lever with a just a few turns and always park it in gear.

 

listen, to answer your question, no. thats why no matter where you park make sure you use your e-brake. if not you never know, your car might get away from you.

 

It does it in any gear. 1st/Reverse would have the highest resistance to motion because mechanical advantage works just the opposite when you're putting power through the gears backwards - IE to have the easiest time turning the engine put it in 5h gear.

The reason there's little/no compression is because it is just about impossible to seal a square-edged volume. The method employed by Mazda works admirably well, but at super low engine speeds it is insufficient. This is why if you have a poor battery/cables/starter and the engine cranks over slowly, it is easy to flood the engine. Not spinning fast enough means poor compression means you flood the engine. (So having a good battery and cables is ESSENTIAL to happy rotoring)


Plus, there is no valvetrain to cause resistance as well. Much of a piston engine's resistance to turning is due to the valvesprings. Try turning a boinger over with and without a cambelt installed - big difference eh? Then try turning just the camshaft.

One time I left my car in Reverse while checking the backup lights, and went to push the car forwards (never shut off a cold rotary!) and I was like, what's that puffing sound underhood?

 

Other thing that could be causing the problem is the transmission. If you push or something pushes on the car, and it pops out of gear. This would explain your symptoms. Maybe another car parks behind yours and pushes it knocking it out of gear even though you think you left it in gear. I do not think compression make a difference, how much it rolls, if you are still driving the car. So do not worry about compression causing the roll.

 

Please inform if the engine moves when it rolls and if the car remain in gear before and after you push it. Also asking how long has it been happening and has the problem changed?

 

The car will roll down even a slight incline if it's in gear and the handbrake is not set.

Heck my GSL rolls down hills even WITH the handbrake set. Stupid useless disc brakes... A coupld days ago my neighbor was knocking on my door. "You know your car is in the street?" Sure enough it was. My driveway isn't steep, it's not even shallow, it has maybe 4 inches of rise over its 100' length. Some quality time with an air hammer removed the calipers, more quality time with rifle brushes and a drill allowed the slides to move again, now I have rear brakes again for a few months. (Seriously considering converting to drums)

 

This is true. All know the car can roll somewhat which is the normal condition. My car always will roll if parking without handbrake and many others even with piston engine roll also. However if in gear there should be "some" resistance to rolling. If the car is out of gear it is easy to roll, whereas if in gear the the car should be hard to roll because the engine must turn.

Here is a test: Put car out of gear and push it. It should roll easy and engine does not turn. Then put the car in gear and push. It should feel harder to push and you may hear the engine rotate. If the car remains easy to roll, and the engine is not turning, then you have a problem. I say possibly the transmission has slip out of gear, or the clutch is slipping. Another cause is oil spilled or leaked onto the flywheel to make the clutch slip.

 

Thanks for the tip. I was working under the (logical) assumption that it'd be a bitch to get the car moving if I started off the line in 5th thus parking in 5th will make things the hardest to move. Now that I've thought about leverage (wheels are just continuous levers) and gear ratios I consider myself lucky to have an operational parking brake and a flat parking spot.

 

Wow, didn't know i was going to get so many reponses. I haven't looked to see if the engine is moving when i roll it. I thought the clutches had something to do with it but i guess i'm wrong. I do for Some reason only have one parking brake hooked up on my calipers *just noticed*. Now i have had this happen the whole time i've had the car, but i replaced my clutch about a month ago. So that doesn't make sense in response to that portion. I guess the best response to this is to rebuilt my back brakes.

 

^^^ I need to rebuild my drum brakes too..... I'm not sure that they're working at all
I need to also replace the cables for the ebrake.....
Another project for this spring, I suppose....