Car Judders when throttle off, Why ?

[C J R]

Hi Guys,
Drove my new RX for the second time yesterday, I have noticed that when slowing down, ie; just before changing down a gear, with the throttle off, the car starts to judder through the transmission system and if I do not dip the clutch it becomes quite violent, through the gearbox and through to the diff. Its as if the engine is trying to push the car forward.
The engine is producing 450bhp (low boost) and 540BHP (high boost) with a single plate clutch.

Is this just a matter of learing to drive the car and changing gear quicker, http://www.mazdarotaryclub.com/forums/images/icons/icon11.gif or does it suggest worn transmission parts ? http://www.mazdarotaryclub.com/forums/images/icons/icon9.gif

Any advice is welcome.
Thanks
Chris

[interloper393]

do u have a diff brace fitted? might be the diff mounts..

[clive]

Always difficult to diagnose down the internet but I would get the car in the air and check the propshaft joints and flange bolts then for broken engine mounts and then powerplant frame for cracks and bolts missing,

With any of the above a car would seem o/k when the power is taken up but the go can crazy when lifting off

If it's none of these things I would then consider pulling out the box to see if the flywheel to counterweight bolts or main center nut has come loose,

One thing is for sure, you do have a real problem and I would not advise driving the car until checked for safety's sake


Hope this helps,

[David Nock]

Yes, I would second that - you should get it up in the air and check the drive chain.
On a more hopeful note, if you're not used to driving a rotary, and I can only speak for the 1st Gen FB here, all our 3 cars exhibited a form of backlash judder which means you have to dip the clutch early.
I have a test report from the early 1980's which warns of this characteristic on the FB. Our present one still does this and has done it from new.
However, as Clive, if your symptoms are bad, it could well be something serious and not just a characteristic. Remember as well the FD may have had this old problem sorted out at the drawing board?
I'm in South Yorks and would gladly give you a run in the FB to compare the backlash I'm talking about if you think you could get here safely.
PS I'm probably doing 90 BHP with no boost anywhere!

[strange_days_uk]

I used to have pretty much the same problem, and still on occasions

These engines can run quite lumpy low down

3 things I found that helped a lot

Diff brace
Engine torque damper
Finely tuned map

[C J R]

Thanks for your advice guys,
I checked the drive train from under the car and can confirm, no broken mountings, no loose bolts (didn't check the flywheel), and the backlash in the propshaft/diff/drive shafts is what I would expect.

So, I have ordered a diff brace and shall learn how to drive the car !!! http://www.mazdarotaryclub.com/forums/images/icons/icon10.gif

I took it out for a drive yesterday and managed to avoid/reduce the effects by dipping the clutch earlier and changing down sooner.

Hopefully the problem is down to me http://www.mazdarotaryclub.com/forums/images/icons/icon11.gif and not the car.

Thanks
Chris

[Dr-Rotor]

What gear are you in when you back off and let it slow down? Also what speed are you doing when it starts to jerk and you are still in that same gear.

I can tell you this...rotarys are affected buy the rotation of the engine...your car will slow down but that rotor still has enough energy to effect it if you are not in the right gear. A slack gear like 4th with no throttle behind it and slowing down to less than 50kp will start to jerk as the rotor can pulse that gear due to it beeing a higher gear....some fine tuning will reduce this as we have done it on my girl friends FD...we just leaned it out off the gass under costing conditions...this helps the rotors slow down as there is less fuel to burn & less pressure...but it will still jerk if you let it go to long in that slopy gear.

I bet if you rang out 2nd to about 80kph then backed off and let it coste to 20kp it wont jerk...because 2nd is twice has hard as 4th and wont let the rotors bully it..in fact it will slow them down quicker. Have you ever heard of gear braking? When i slow down I always push in the clutch, rev it up to match the speed for the lower gear, put it in & let out, the car will be smooth & slow down quicker with no jerk, once you approche slower speeds, repeat, clutch-rev-change-release & slow down. Smooth all the way.

I have only ever driven my FD. Its my first car & the car I learnt how to drive in. I guess you just need to listen to what your car wants you to do with it. You cant drive these cars the same as piston crap.

All the people I take for a drive are always amazed at how I rev before each change down & how smoothley the car slowes down without jerking. They always ask do you always drive like this? Haha...o yea, thats the fun of driving a rotor. Ofcource you can slow down normaly just change down sooner....I dont think you are used to the rev range & gear range of your FD. You dont drive it everyday do you? The more you do the better you will get.

[logicalChimp]

Hmmm - I have to say, I get a tiny bit of judder under engine-braking (on a stock motor) - but only if I let the revs dip below 1k or so... As a result, I try to always downshift at or just below 2k rpm. As a side benefit, this means I don't bog down when it's time to start accelerating again...

Dr-Rotor - i've been trying to match revs on each downshift - when i get it right, it works well - but it's harder than it looks :D

[Dr-Rotor]

heheh...not when you been driving one for 4 year solid every day....its great. Dose help to have a race spec engine with a light flywheel that revs stupidly fast.

I have noticed that it is a little more tricky for me to do it with my girl friends car. As her flywheel and clutch are stock. She dose it on her car better than I can & I do it on mine like a champ. Scares the **** out of everyone on the motor way in traffic & wakes up all the day dreamer drives. People never know if im droping gears to race or slow down....very funny to watch when your car is loud. Iv caught out a few would be racers thinking that I was droping a gear to race.

Dont let the revs drop below 2k....1st gear is 2k range. When slowing down from 80kph in 4th to 2nd it goes like this. Cruise at 80kp....light up adead goes red.... 80kph,clutch in--rev--3rd--slow for a bit use brake if traffic--50kph,clutch in--rev--2nd--slow to 30kph--clutch in & neutral--brake and stop. Some times when going to fast I will only down shift to 3rd then brake & slow down to 50kph..clutch in & neutral...no time for 2nd gear. As you get to this point when you are on the brakes in nuetral approching the lights & they go green you simply clutch in--rev it up--hook 2nd & bugger off.

Not sure about you guys but 1st gear only goes in at a stand still. This is why I coast to lights in 2nd from high revs and speed anywhere from 40kph to 60kph or more depending on traffic, theres no jerk & the power is waiting, more often than not your on the brake due to traffic but only lightely as we are in 2nd & gear braking...remeber 2nd dose 115kph with a 4.10 final drive. Most manual FD's should have a 4.10.

Do be carfull going to 2nd with a rev not high enough for the speed as you will lock the diff...then its a whole new world of fun.

[logicalChimp]

Do be carfull going to 2nd with a rev not high enough for the speed as you will lock the diff...then its a whole new world of fun.

Ahhh - so that why it sometimes tries to put me through the windscreen! :D

Sounds like i use the same timings / technique as you - just need to get more practice :Tongue1

[Dr-Rotor]

Hehehe.....yea like I said....a whole new world of fun.

Yea seems to be the way these cars like to be driven.

[RedRummy]

I try to do this too, but am always a bit scared of wearing the clutch out too soon, by revvings while its pushed in...

I've got the single plate Exedy Organic clutch - will this stand up to this kind of daily driving?

[RemarkLima]

I try to do this too, but am always a bit scared of wearing the clutch out too soon, by revvings while its pushed in...

I've got the single plate Exedy Organic clutch - will this stand up to this kind of daily driving?

By heel & toe'ing (the name for all this blipping throttle malarkey!), you're doing less damage to the clutch.

The clutch is basically the same as brake pads, that attach to the flywheel... If you just shift down, and use the clutch to pull the revs to the same as the gearbox then it's the friction material on the clutch doing the work.

If you blip the throttle before you shift down, so the revs match then there's no friction (well, some but minimal) on the clutch as they're both spinning at the same rate IYSWIM.

Have a read of:
http://en.wikipedia.org/wiki/Heel_and_toe

And an article written by one of my old track buddies (she really can drive!):
http://www.mr2.net/trackdayqueen/heelandtoe.htm

HTH,
Mark

Edit to add, next have a look at Left Foot braking, now that's hard! First time you try you'll headbutt the steering wheel!!! :D

[RedRummy]

yeah, have tried left foot braking... its amazing how different it feels... LOL
I didn;t think we were talking about heel and toe here, just blipping the thottle... which is done with the clutch in, no?

surely blipping the throttle with the clutch in isn't good for it..?

will those articles now LOL

[RemarkLima]

yeah, have tried left foot braking... its amazing how different it feels... LOL
I didn;t think we were talking about heel and toe here, just blipping the thottle... which is done with the clutch in, no?

surely blipping the throttle with the clutch in isn't good for it..?

will those articles now LOL

Yeah, you blip with the clutch pedal down, and therefore the clutch disengaged... I can't see how this would be bad for the clutch? It's not touching anything at that point, just free spinning on the release bearing.

And blipping with the clutch engaged is tantamount to suicide ;)

[RemarkLima]

Oh, just another thing I remembered, when I was racing at Pembray (BTW, we did give our cars absolute hell!), there was the final corner that it was better to just mash the clutch for... Basically coming at it in 4th full throttle, then just dump it into 3rd with no heel and toe, and bring up the clutch as fast as possible, this basically locked the rear wheel with the transmission just for a bit but meant you could back onto full throttle straight away :D

I'd neven say do it to a car you like ;) But as you can easily lock the driven wheels with the gearbox it shows how important heel & toe can be!

[Dr-Rotor]

Oh, just another thing I remembered, when I was racing at Pembray (BTW, we did give our cars absolute hell!), there was the final corner that it was better to just mash the clutch for... Basically coming at it in 4th full throttle, then just dump it into 3rd with no heel and toe, and bring up the clutch as fast as possible, this basically locked the rear wheel with the transmission just for a bit but meant you could back onto full throttle straight away :D

I'd neven say do it to a car you like ;) But as you can easily lock the driven wheels with the gearbox it shows how important heel & toe can be!


Hehehe...sounds like what I used to do on a paticular corner of a track going from 3rd to 2nd with no blip, locking the wheels for a few seconds as the car slid into the corner & you stand on the gas then bang your out of there and off down the straight. Now I just hold it in 3rd and hang on for the ride & hope it dosent slide out into the wall. HAHAhA....much faster way around this paticular corner as I have learnt. Racing teaches you some crazy ****.

About the clutch and bliping the throttle or heal toe, It dose not do a damn thing to it at all. How do I know for sure...well heres how. When I bought my car on 48,000km Id say it would have still had the same clutch as when it had left the factory. The car had never been moded, it was bone stock. Now as I was learing to drive my dad had shown me this method of gear braking to increase the life of the brake pads. So I practiced it with my car and discoverd that it drove alot more smoothley this way & also alot more interesting that the conventional method.

I drove it this way for 30,000km before I had the block removed & all the work done to it. When the rotary mechanic replaced the clutch with my new twin plate crabon D core from Exedy he said, "your old clutch has bugger all ware on it & can be used as a replacement for another car" I looked at it & saw it was still in pretty good nick, pretty much no heat marks or anything.

The only thing that free reving the clutch will do is work out your bearings. Aside from that & sharp blip to select a lower gear wont do a thing to the friction plates.

[probedb]

Mine used to do this quite bady, fitted an engine torque damper and it's all but gone! Really didn't expect it to do this but it did :)

[Dr-Rotor]

That will be because the engine cant move when you drop the gears & make the clutch play catch up...& as the car slows down it wont be abel to vibrate as much so it wont jerk your lighter gears around in the wrong rpm range.

As said before this can also be reduced with finer tuneing. This past week we have just done it on my girls car. The car will come right down from 3500rpm in 4th to around 1200rpm without jerking....but why the hell would you want to drive like that anyway. Also since the new tune it now revs alot quicker for the blip clutch change down....its lovely...soo smooth.

[gmogle]

Mine does this also, I find myself coasting a bit to stop it. Do try to do the heel and toe but it isnt easy as the pedals are close together and have to use the side of my foot. But its much smoother when shifting down.

Wil bear that in mind probed, tempted to get one at some point.

[Dr-Rotor]

You dont need to do heel toe to do this blip thing that Iv been talking about. More a matter of adjusting your driving style & beeing more aware of the distance you have to stop in. Yes you can do it heel toe but its not essential.

Hmmm ok let me put it this way....the way i drive is wired. I do not travel right behind people...I keep about 3 to 4 car lengths away. When I have to slow down I blip for the change down before I brake as I am not at the brakeing point so therefor no need for heel toe. If I need to slow down quicker I will still blip before brakeing, but brake harder and usualy just go to neutral if I have to stop.

Due to traffic I cannot always drive like this & do need to just slow down and have to wait for the right Rpm so I can change down. Sure you can heel toe but I wont take that chance of sliping off the brake and accelerating into the car in front.

[Timmy]

I think dr rotor is saying because he's not raceing he's slowing down well in advance without braking so he doesn't need to heel and toe. I often do the same.
Say your comeing up to a corner and you know you need to shift down you lift off well in advance and with your left foot on the clutch and your right foot covering the accelarator dip the clutch blip the accelrator and change gear all without touching the brakes and by than you've lost enough speed to go round the corner.

[Dr-Rotor]

I think dr rotor is saying because he's not raceing he's slowing down well in advance without braking so he doesn't need to heel and toe. I often do the same.
Say your comeing up to a corner and you know you need to shift down you lift off well in advance and with your left foot on the clutch and your right foot covering the accelarator dip the clutch blip the accelrator and change gear all without touching the brakes and by than you've lost enough speed to go round the corner.

:D Haaaa exactly what Im trying to say...thank you Timmy. :cool

[RemarkLima]

Ah ha, I see what you guys are saying now, and yeah I quite often do the same thing, if you only need a dab of brakes, or just need to lift off then just blipping the throttle is the way to go :D

Hehehe...sounds like what I used to do on a paticular corner of a track going from 3rd to 2nd with no blip, locking the wheels for a few seconds as the car slid into the corner & you stand on the gas then bang your out of there and off down the straight. Now I just hold it in 3rd and hang on for the ride & hope it dosent slide out into the wall. HAHAhA....much faster way around this paticular corner as I have learnt. Racing teaches you some crazy ****.


I think a big difference is that we were racing old Mk1 MR2's, 1.6 short-stroke NA engines, and with basically zero torque, so unless you were ringing it off the limiter they had no real guts to pull you out... We ended up doing the same thing pretty much as it was the only way to keep it right on song! Oh, happy days and good fun... Shame I ran out of money :/