Bent my Drive Shaft again

[620Z]

Well the trip down to Tassie certainly tore into my Drive Shaft. About 8 months ago I set up all new bracing for my R200 diff after which I realised I had a fair bit of vibration. After much searching and expense I insisted on getting a new drive shaft made up even though everyone told me it wasn't the problem since it was balanced etc etc. Well to cut a long story short it did fix the problem. I got it made with a stronger shaft and a bigger uni on the front. The rear already had an extra large 1310 size "U" Joint and uni. Anyway before I went down to Tassie I got a new set of "R" spec tyres. This extra grip didn't give way like my old 4 year old set which would often giveway to a burn out. So Tassie was the first real time since the new DS instalation that it had a serious work out. Anyway over the course of the week a small vibration progresively got worse and Symmons plains really finished it off. Whilst not breaking, something definately was bent. Anyway I am in the progress of getting an even bigger one made up at the moment a 1350 same size as the V8 Super cars use including the same uni's so let's hope my 750nm of torque won't screw this one up. Will keep you posted once I get it in.

[C.A.R.]

Where has it actually bent, Craig?

[zr240]

Hi Craig

 

Are you sure its bending from tourque and not a problem somewhere else.

 

The reason I ask is I run std r200 shafts and even though I didnt have the same power as your v8 I run slicks (285s) and I have never bent a shaft. I think the loads on mine would be higher? I have broken the bar that holds the diff in (along the back of the diff) before but still not even damaged the half shaft.

 

Thinnks might change now with the higher touque of the rb25det??

 

Anyway be interested to find out whats doing it (if not the motor).

 

Ash

[620Z]

Yeah I cracked a rear moustache bar 7-8 years ago. It's a funny one because no one can tell me where the problem is. A few people had looked at my old drive shaft and said there wasn't a problem with it and wanted me to spend another 2.5K searching in places I didn't think were necessary. After several re balances and cutting and re aligning. I insisted they make a new one at my expense despite advise to the contrary. But I figured I know my car better than them since I was driving it. Anyway to cut a long story short. The new DS fixed the problem. Anyway 8 months later and with the new tyres before Tassie giving me more grip (I was breaking traction a lot before that) the vibration through the car got progressively worse over the week in Tassie. With the last day at the track being the final straw. So there is no doubt, I repeat no doubt it is the drive shaft.

The problem is locating the part breaking down. Is it the uni's, is it the U-Bolts or is it the shaft it's self. (The old one had the Uni's replaced but still same problem). All of which the experts have viewed and insisted were all OK. So I guess going to a 1350 Universal joint I am eliminating two of these things and the only other is the shaft which was increased in wall thickness last time. So my conclusion is that the Uni's can't take my torque. V8 Super cars use 1350's and I am not that far off torque wise, further off HP wise. So I am guessing this is the way to go. I have made some enquiries for a Carbon Fibre DS in the States but haven't got a response yet. I might call them tomorrow. But I have Rob Creighton on the job sourcing some good quality parts. Either way this should (I hope) fix the problem happenning again. The last DS was only $250- but the next one will probably be $1,000- to be done properly. The only problem is trying to keep the weight down but maintain strength.

I hear what you say Ash but I think the torque in my car is the problem. It's huge and at full noise it must be straining something in the DS. Maybe it right's itself when it is not under stress? Not sure.

[24OZ]

just a thought and you have probably already looked at these,may be worth checking the diff flange for concentricity(long shot but easy enough to do)

also the alignment of the engine conversion angle...there is not much margin for error before the unis start chopping out

i have seen driveshafts twist like spaghetti and unis go bang with slicks/hookup but gradual deterioration(emerging vibration) strikes me more of a geometry issue....keep us posted on the resolution

[Zedman240®]

Is there a way to check the alignment of the g/box - diff with a laser made for sight alignment for rifles etc. I'm just guessing but 240Z made a valid point. I've heard about drive shafts not in alignment, and how important it is to get it right. Maybe when you make a stronger DS, I hope you don't find something else weaker in the chain that will break! Take Sinisha's car for example, that's putting out approx 500Hp and I don't think anything has let go...yet! I know its DS is a bit shorter, if that has anything to do with it tho..hmmm

[aegean]

And maybe look at installing a flex disk rather than a univeral. At least that way the flex disk will let go and not transfer all the load.

[24OZ]

Is there a way to check the alignment of the g/box - diff with a laser made for sight alignment for rifles etc. I'm just guessing but 240Z made a valid point. I've heard about drive shafts not in alignment, and how important it is to get it right. Maybe when you make a stronger DS, I hope you don't find something else weaker in the chain that will break! Take Sinisha's car for example, that's putting out approx 500Hp and I don't think anything has let go...yet! I know its DS is a bit shorter, if that has anything to do with it tho..hmmm

 

i think Hybridz has an article on making a speccy laser pointer device to go on the end of the gearbox splines

i would think you could do a quick check by removing your tailshaft,sticking one of those laser pointers(from the $2 shops.....tape it up so the light remains on) into a big ball of blue tack and adhering it to the end of you gearbox output shaft

now down the diff end,again with blue tack(no i don't work for 3M ) stick a sheet of cardboard(as big as will fit,eg A4 size) onto the diff flange

now roughly square up the laser pointer so it runs true with the output shaft(ie in a straight line)

see where it points on the cardboard

with the rear of the car on stands and in gear,get a friend to turn the engine over by hand(may be easier with plugs out) while you watch the laser dot transcribe a circle on the cardboard,the smaller the circle,the closer the pointer is to being aligned correctly with the gearbox output shaft

keep adjusting the pointer in the blue tack until you get just a dot when it is turning with the motor

this dot(or very small circle) should show the alignment of your motor/box in relation to the diff

mark this point on the cardboard

measure from "the dot" to the center of the pinion nut

now with the assistance of trigonometry work out the degrees off center that the universal joints are spinning

i can't remember the maximum you can run before asking for trouble,i think it is only 4-5 degrees,but best check with someone like a driveshaft or bearing company

hope it works out

keep us posted

paul

[sco_aus]

Just a thought, but maybe to reduce the length of piping thats unsupported, perhaps having a centre bearing?

[620Z]

Thanks for all the ideas and advise guys. Yeah the alignment has been checked quite a few times. We tried it either way up and down from the point where we reckon it was exactly right. No difference.

With the new diff coming I am getting a new rear flange made up as well to suit the new larger bolt holes and flange.

I guess the thing to remember is the the problem went away imediately after I put this new drive shaft in. That tells me for sure that this was the problem. Since it is reaccurring again (after some real hard driving) I can only assume that one of the 3 main components is giving way in the Drive Shaft. So seems, larger it will have to be. You have to remember my car isn't a turbo or a straight six so the torque from my motor is greater than everyone seems to think and is on for much longer than a turbo car which has a spike on the dyno. Where as mine is on pretty hard from 3500-7000 rpm. I will keep my fingers crossed that the new one will do the job.

Will give you an update when I get it made up. Cheers

[24OZ]

Thanks for all the ideas and advise guys. Yeah the alignment has been checked quite a few times. We tried it either way up and down from the point where we reckon it was exactly right. No difference.

 

what about left to right aspect?

can't help thinking there is misalignment somewhere,there are plenty of big hp/torque/traction cars that don't have any problems in the tailshaft area,if the unis are not strong enough they usually fail catastrophically not incrementally

needle bearings are very good at spreading load due to the increased bearing to race contact area but don't function well if there is any sideways play....bit like rattling a stick in a hole ....only gets worse with time irrespective torque more to do with RPM and harmonics

[620Z]

We didn't try the left and right aspect. But why was the problem fixed when the new Drive Shaft went in. Drove perfect for months even at high rev's till it got a number of hard work out's. Well when the new Drive shaft goes in and the problem goes away again it will only confirm where the problem was. If it's still there then I know to keep searching. But I am presuming it will go away again only, hopefully not return since it will be beefed up more than the last one.

Actually I finally found some statistics matching HP to U-Joint sizes and they say 500bhp is the max for a 1310 U-Joint. Since I have 530hp and more torque than most motors with the same HP due to the config of the engine and cam, I reckon that is my problem. Not quite enough to break it, just bend it a bee's dick. Mmmm

[24OZ]

OK

[620Z]

I went and saw all the components to make up my new DS this arvo. Looking good. All forged steel 1350 fittings with titanium uni's plus I am going from a 1.9mm to 2.4 wall thickness on the shaft as well. Should be unbreakable or bendable this time. Rob has got some "experts" welding it all up to make sure it is aligned and then balancing it in 3 places. So this better fix my problem.

[C.A.R.]

You 'had' 1.9mm wall tubing!? No wonder it bent/warped...

[620Z]

The first one, before that was 1.6mm wall. The guy increased it to 1.9mm (After I suggested it) and said it should be more than enough. But as usual the so called experts wouldn't have a bloody clue what they are talking about. Aparently the guy Rob spoke to said it sounded like the tubing since it was getting progressively worse which is supposed to be a tell tail sign. But I will stick with the stronger fittings so I should be right when I add another 250hp one day. 

[Zeddophile]

Aparently the guy Rob spoke to said it sounded like the tubing since it was getting progressively worse which is supposed to be a tell tail sign.

 

Seems logical, as you give it a hard time the whole length of tubing starts to deform and twist a bit, then as it gets worse it gets the uni's out of alignment and chews them up too....  Must be getting to be a pretty heavy tailshaft by now though!

[Zedman240®]

I think if that one fails, try some solid steel rod! a bit weighty but should never twist!

[620Z]

Yeah I think these mods should do it. But I agree it is starting to get heavy. I have already gone from 4.5kg to 5.5kg. I am guessing this one will take me to 7kg which will drain some of my HP. I am figuring the Dyno might show 10-15kw less next time. Still not much I can do about it. I wouldn't mind so much if it was dead weight in the car but this is extra weight in the drive line. 

[24OZ]

can you get chrome moly in suitable sizes,it wouldn't have to be as thick to be as strong

[nat0_240_chevZ]

SOLID ROUND BAR WILL NOT INCREASE TORQUE TRANSFER (Sorry bout the caps!)  nor will it twist less (much anyway), its the outer most fibres of a round section which transfer all the load anyways hence they way driveshafts are made already.

 

what increases torque transfer capacity is the wall thickness and the Overall diameter of the tube not making it solid.

 

I would highly recommend ditching the unis joints all together and opting for the expensive route of CV joints instead, they have a much higer torque transfer and do not change rotational speed depending of angle as compared to unis. also they allow much more angle of mis-align before starting to overstress them.

 

craig i still feel you tranny and diff output/input alignment exceeds that allowable for a uni, i also have a SBC in one of my Z'z and i feel the geometry is not ideal, so i made my own tranny crossmember to lift the trans output a lil.

 

I understand your torque output is considerably high than what mine is outputting, but ever since ive had no dramas dropping R to D for stupid burnouts etc etc, but the only thing the prev owner said ever broke was a moustache bar mounting pin which attaches to the body, only woble i get is from the tyres delaminating and causing vibration there.

 

feel free to hit me back with more info Q's etc.

nato

[620Z]

I will have to ask about the chrome molly tubing for the shaft. I haven't heard much about the CV diff Nato. But I figure if the V8's don't have them nor most cars then I should stick to the conventional.

As said previous the diff and G/Box seem to be in alignment. So I will know for certain when this DS goes in. Remember it temperarily fixed the probelm when the other new one went in.

[C.A.R.]

Craig, I just dropped Rob's Tassie tapes back to him & I had a look at your new bits...

Rather large I must say!

If this one moves at all, I'll be surprised...

[nat0_240_chevZ]

craig, have you had the rear bearings on your trans / g/box loked at??

 

im not sure if your familiar with the vl auto problems with that small vibr to begin until its gets worse and worse esp under load???

 

DS cv's are very common, look at all comonhores they have a centre bearing which is essentially a constant velocity joint.

thing is with a uni, your only able to transmit what that small + shaped centre can withstand under shear / due to torsional loading, also the endcaps of the unis tend to wriggle a bit underconstant abuse which then lets the DS sit slightly off centre and when you can it you feel the 'offcentre' vibr, all it needs 0.1mm play /slack/ lash side to side and youe will begin to feel it.

 

Also the speed variation @ a given angle is detrimental to other drive components, ie when a uni is transfering torsional load @ any angle other than dead straigh it actually speeds up and slows down in respect to its drive to driven counterparts.

 

CV's are the modern version of the uni joint, yes the uni is still used but this is more of a case of minimising production cost. have a look @ all late model nissans with their rubber triangle front uni type joint, a cheap and rreliable method of transfering torque with a built in cush drive assy.

i personally would exhaust all other option before replacing something which was probably never the cause in the first place. as unis will wear and fail, just like all other items that are deemed to have a limited service life. Yes cvs do to but just do a giggle search for maybe a beter alternative, but all thins aside it may not be the uni's and shaft causing the problem

 

try this link http://www.conbear.com/PT%20Shaft%20Couplings.htm

or http://www.conbear.com/CVJ%20Industrial.pdf

[620Z]

Well looks like someone has taken up the challenge and done some home work Nato. Thanks for the heads up. Those CV's look interesting I notice they are rated to about 6,000 rpm. Look more like for use in machines. Also the speed variation theory makes sense and hopefully this new DS will eliminate that.

Anyway we are now well underway to making this new DS so I will stick with the original plan. Rob is getting me some good prices (compared to what it could cost) so I guess once it's all in I will know for sure if it fix's my problem. Yes they are pretty big Lurch. But that's the next size up from the 1310 uni joint that is only rated to 500bhp. So I have to go to the next level 1350 even though I am just over. These 1350's are significantly bigger and made of titanium so no chance of breaking or wearing in the near future. I also need to plan for the future so I don't end up having the same problem later down the track if I increased the power to another level.

The way I see it if the problem get's fixed I can always work backwards and get another DS built only with thicker shaft only and see what happens. This would save 1-2kg if I still use the 1310 uni's. But one thing at a time.