Hi everyone,

I picked up my '05 RX-8 a few weeks ago and when I started to drive it, I noticed it "bucks" when I shift gears. I saw that there are a lot of issues with the engine mounts and I took it to the dealer. They supposedly changed the L and R engine mounts and the car idled smoothly and was easier to get into gear.

But now when shifting it feels like its bucking again? is this normal in this car. It always happens when I get off the gas completely and get back on the gas. ITs driving me crazy:Eyecrazy:

Take it back, the mounts are under warranty for atleast 12k miles after they are put in

also if youre still under warranty, its covered

is your CEL light on? or does it blink during occurance? I don't know what detonation is like for a Rotary?

is it the Engine bucking? or does it feel like slack, then 'shockload' during clutch engagement?

you could have driveshaft play that will do this.. if there is enough play between the drive shaft and the transmission... You really should provide a consistant reproducable method, and have the mechanic take it for a drive... especially if it's under warrenty.

are you resting your hand on the shifter?

no CEL light on, most time it occurs from 3rd gear on and right after shifting or when off the gas/coasting for a couple seconds and then getting back on the accelerator. it feels almost like when letting go of the clutch too fast, but it happens even after the car is completely in gear. does the 8 usually have these driveshaft issues?

are you resting your hand on the shifter?

no way :eek:

yeah, my best guess is driveshaft play. Did you have bad engine mounts for a while? i've seen busted engine mounts cause transmission bearing wear on automatics if they sit cockeyed from load...

How many miles Scrapin? What rpm's & mph are you at when this is occuring? under 3k rpms? I've noticed a persistant pitched wine if rpms are to low and i'm in a higher gear, 4th gear +, below 3k rpms.... haven't done it since.


the shockload should also occur in the lower gears if it is drive shaft play. you should have it looked at, since these are carbon composite shafts..... on a bright side i believe it should just shatter to pieces instead of trying to carve you in half if it goes as it slices through frame like a boogie monster trying to get you while your laying quite.... asleep and relaxed being the big spoon or little spoon ... (I don't know you :) )

later!

no CEL light on, most time it occurs from 3rd gear on and right after shifting or when off the gas/coasting for a couple seconds and then getting back on the accelerator. it feels almost like when letting go of the clutch too fast, but it happens even after the car is completely in gear. does the 8 usually have these driveshaft issues?Try getting on and off the gas quickly--does it buck still?

How many miles on your car? Try replacing the coils.

I replaced the coils *and* the sparkplugs recently (at 56K miles), and I can't be sure which one was responsible, but I noticed that I have a lot less hesitation getting on and off the gas. The power-back-on after shifts is smoother, with less bucking.

But I'm suggesting the coils because I read somewhere else on here that worn coils can cause hesitation.

yeah, my best guess is driveshaft play. Did you have bad engine mounts for a while? i've seen busted engine mounts cause transmission bearing wear on automatics if they sit cockeyed from load...

How many miles Scrapin? What rpm's & mph are you at when this is occuring? under 3k rpms? I've noticed a persistant pitched wine if rpms are to low and i'm in a higher gear, 4th gear +, below 3k rpms.... haven't done it since.


the shockload should also occur in the lower gears if it is drive shaft play. you should have it looked at, since these are carbon composite shafts..... on a bright side i believe it should just shatter to pieces instead of trying to carve you in half if it goes as it slices through frame like a boogie monster trying to get you while your laying quite.... asleep and relaxed being the big spoon or little spoon ... (I don't know you :) )

later! I rpm have 15K on the car, and this happens at around 3000 rpm and its very noticeable around 30 mph in 3rd gear, but its there pretty much in every gear.

Try getting on and off the gas quickly--does it buck still?

How many miles on your car? Try replacing the coils.

I replaced the coils *and* the sparkplugs recently (at 56K miles), and I can't be sure which one was responsible, but I noticed that I have a lot less hesitation getting on and off the gas. The power-back-on after shifts is smoother, with less bucking.

But I'm suggesting the coils because I read somewhere else on here that worn coils can cause hesitation.

Yes it still bucks when getting on and off the gas quickly. The car has 15K on it, and its not really hesitation but a moving feeling when on and off the gas. I feel the car move back when getting of the gas and when I get back on it, the car bucks forward like 3 times until it starts to go smoothly.

Make sure the current flash in the PCM is up to date and all the maintenence, too. What RPM are you shifting at?

Make sure the current flash in the PCM is up to date and all the maintenence, too. What RPM are you shifting at?

the dealer updated the pcm last week, and i usually shift at like 3500 rpm (+/- 500 rpm)or so when just cruising.

I have solid mounts and I get a little bucking from time to time when I shift at those RPMs but that is usually 1-2 and 2-3 where the gear spread is larger.

it feels like the car is about 30 years old. I go in my other car its very smooth, and actually all my other cars were smooth, this car is so frustrating. I will take it back to the dealer and see what happens.

Maybe the shocks are going?

it feels like the car is about 30 years old. I go in my other car its very smooth, and actually all my other cars were smooth, this car is so frustrating. I will take it back to the dealer and see what happens.I wonder if it's the rest of the PPF mounts... it's like, OK, your engine mounts are new, but what about the rest of that power plant frame.

it feels like the car is about 30 years old. I go in my other car its very smooth, and actually all my other cars were smooth, this car is so frustrating. I will take it back to the dealer and see what happens.

Let me know also... My car has been doing this as well..

I rpm have 15K on the car, and this happens at around 3000 rpm and its very noticeable around 30 mph in 3rd gear, but its there pretty much in every gear.

that is the test for bad motor mounts... as in. mazda describes that as how to test for bad motor mounts.. maybe another dealer?

beers :beer:

Is it possible he has a light flywheel and he is unaware on how to drive a car with one?

Is it possible he has a light flywheel and he is unaware on how to drive a car with one?

i doubt this car has a lightened flywheel, as it is bone stock in every way. Also, I had 2 240SX with lightweight flywheels and this is nothing like that. I have been driving manual cars for about 10 years and this is my first experience like this.

that is the test for bad motor mounts... as in. mazda describes that as how to test for bad motor mounts.. maybe another dealer?

beers :beer:

yeah I know, its just like that, but they changed both mounts and I have noticed the rough idling go away right after picking it up, but it still bucks.

I wonder if it's the rest of the PPF mounts... it's like, OK, your engine mounts are new, but what about the rest of that power plant frame.

i was thinking the same thing, and since I am still learning about all the issues about this car I can't rule this out either

To check that, focus on the PPF where it bolts to the rear diff.

To check that, focus on the PPF where it bolts to the rear diff.

Can you be more specific? :) What are we looking for?

There are 4 nuts AND one cross-bolt that hold the rear of the PPF to the differential housing.

The way that I always re-installed my PPF, and have never had any problems, was to hand thread the 4 nuts on to the point that the PPF is properly engaged on the shoulders of the diff mounting location, install the cross-bolt and torque it to spec as THAT is what properly locates the PPF to the diff, then tighten the 4 nuts to spec.

How to check for problems w/o rebolting everything together?

Try and look for signs that the PPF was/is shifting such as worn paint marks on the rear of the PPF where the nuts are located.

There are 4 nuts AND one cross-bolt that hold the rear of the PPF to the differential housing.

The way that I always re-installed my PPF, and have never had any problems, was to hand thread the 4 nuts on to the point that the PPF is properly engaged on the shoulders of the diff mounting location, install the cross-bolt and torque it to spec as THAT is what properly locates the PPF to the diff, then tighten the 4 nuts to spec.

Interesting.. I'll have to try it this way..

Remember, I had 8 years on an assembly line working a lot of different jobs in different plants and I have a lot of experience with ISO and Kaizen processes. That is one area where I differ with regard to other shops/techs.

I have an appointment for Monday, I guess we will wait until then to see if the dealer finds out whats wrong, but if it is driveshaft play that is causing the problem, what are the fixes?

Is it the PPF mounts or something else?

well I took it to the dealer and as I guess they could not duplicate the problem at this time. I was unable to stay at the dealer and show them exactly whats wrong, but I told them exactly how to get it and they are like I should come down. I picked it up after hours and was able to replicate it on the way home.

It only happens in 3rd and 4th gear, and when the car changes weight to the rear (off gas) and then gas again, it bucks. I am starting to hate this car and its only been 3 weeks with it.

Since you can repro it, and they can't. Get a mechanic to ride along and show them.... If you think they're sidestepping the issue (trying to not validate the claim by your repro steps) you maaay want to find another Dealer to service your car. :(

i was at the dealer and they were able to duplicate it and said it was normal. They drove me in an automatic 8 and it was not the same feeling but similar. they said its because of where the torque is delivered. I guess...its still not a smooth car overall, but I'll deal with it or sell it and get something else like a S2K or something. But it does seem to be how these cars are.

BTW the dealers don't care about cars overall, but we should know that. they took that automatic car cold, and reved it out to like 7K and then just parked it back up after about 2 minutes of driving. That's what I hate about taking my car to a dealer, they just really don't care about your car.

Just to add my 2 cents worth... I drive my 8 hard and the dealer has replaced the motor mounts twice within 25k miles. There was a dramatic difference with this problem both times. When I bought the car, the power train was tight as could be... so I know the car was not built with the looseness it suffers when the mounts are bad. Changing the mounts didn't get it back completely to the like new feeling, but did get it pretty close.

Aside from driving at 3k rpms and getting on and off the gas to make it buck (cuz it doesn't sound like this method positively identifies the problem), is there a way to see if the mounts are bad by jacking the car up and looking? I haven't tried yet, but I'm hitting the end of the warranty period so it's going to be on me to fix it in the future.

Also, I see people talking about solid mounts. That sounds like a pretty extreme fix. Does anyone know if there are middle of the road mounts available that are stronger, but not solid?

IIRC the solid mounts actually change the location of the engine.. Plus the NVH will likely drive you crazy. A better option would be to fill them with urethane as MM suggested. I might try that the next time mine fail.

As for checking them, you can take off the wheel and look for any noticeable cracks. Mine were bad without any visible damage, though..

I don't see the post you are referring to from MM. Can you either direct me to it or elaborate on the details of filling with urethane.

What is urethane & where do I get it. Is it the same as silicon? Do I need to (or is it recommended to) remove the mounts to fill them?

You would have to cut out the bottom of the mounts, empty them if they didn't leak completely, mix up some urethane and pour it in.. I'll try to track down the details, he actually provided a link to the exact compound to use

Here's the post in question:

http://www.rx8club.com/showthread.php?p=1234858&highlight=urethane#post1234858

He also mentioned in another thread with the "80 shore" might be too hard and suggested trying 60 shore.