RWD rear end and pinion angle q's

[rolleraction]

I was told to set the angle at -6deg for leaf. I did on my race car and worked very well, no tramp etc no noises . fyi
Steve

[RobertoX]

Just a thought but could it be do do with having the diff welded? Maybe something like a small amount of splatter on crownwheel or similar problem (maybe have a look at the welding diffs thread to see common problems)

[oldcorollas]

So the issue is that I was just adjusting the drums and put the car in first and started to accelerate with it on the jack stands and it had a constant shudder like...donk...donk...donk...donk... not like donk,donk,donk,donk until the speed was up but it is speed dependent. Other info. which may be required is that the diff is welded and the axles had to be shortened about 9mm each as the fella who welded it welded the plate too close to the axle holes. The shudder is definitely from the rear and happens with the brakes on or off. There didn't look to be any movement at the flange of the tailshaft.

put a piece of tape on one of the wheels and one on the driveshaft.
with car on stands and in first gear
let it run at idle and if the "donk" is there, then check if it happens in time with wheel position (one donk per tape revolution), or if it is according to driveshaft (one donk per tape revolution).

if it is the uni joint, then it should have two donks per tailshaft revolution, maybe 4.
if it is the pinion, it will be one.
if it is the crown wheel, it will be one per wheel rev.

welding spatter could be it.

[chris davey]

Good idea. WIll do that tonight also.

If it is I am NOT going to be happy after I could have got a relly to do the welding but decided to take it to a "pro" instead.

[The Real Roadrunner]

you should run as little angle as poss to get quick times.
i would set it up with adjustable upper arms and set the arms with the diff fully compressed
ie no springs and a jack under the housing then leave a 20 - 25mm gap between diff flange and body that way as the bushes tourqe up the flange still wont hit.
the angle on your shaft doesnt look to bad .
id hazard a guess to say that its spatter on the crown or notchy bearings.

[Robbos_Toyotas]

have a look at a hilux 2wd rear half of the tailshaft chris, and it will re-assure you yours will be fine....dont forget the hilux is also rated to tow one tonne!

[chris davey]

Ok, did some testing.

Firstly, had the wheels on and mounted. The noise is more like a constant vibration as speed increases. We were testing in 3rd gear. Firstly, we found that the left rear wheel had quite a bit of up and down movement in it like it could be a bent axle or rim. So we pulled the wheel off and checked the drum and centre of axle but it appeared to be round. This leads me to believe that the rim is bent.

However, this was not the cause as the vibration was exactly the same with no wheels on. I did what oldcorollas said but it was impossible to determine as the noise became more constant even at very low speeds. (3rd gear was only 30kms) I had a good feel around to try and pinpoint it and the axle tubes had slight vibration but you could feel it very easily from the rear of the diff and from underneath (near tailshaft).

The tailshaft "looked" to be ok so at this stage I am thinking that it is the diff. We pulled the drums off and the tailshaft and spun the diff flange by hand and it is very smooth, no notchiness, easy to turn and VERY minimal backlash (less than my old diff I think). I did notice that one of the drums was fairly tight whereas the other one wasn't so could this be an option? Also it seems the tailshaft bolts aren't a perfect fit so I am going to get bigger ones but the tailshaft has a locater on it so it can't really move off the diff flange and the bolts are only used for clamping pressure not locating.

So at this stage, I will get new bolts for tailshaft, refill diff oil, fit tailshaft and run it with no drums and see if it vibrates.

Also, I believe pinion angle looks pretty normal now.

[allencr]

Pinion angle isn't important, unless it's too big or zero.
What is important, is that the angle of the rear u-joint is close to, if not equal to, the angle of the front u-joint.

Please search for some driveline sites. They're mostly 4x4-offroad stuff, but except for the transfercase & front axle, it applies the same with whatever you've got.

[chris davey]

It appears as though the main culprit for the vibration was one drum being set tighter than the other however I think I should be sorting this pinion angle stuff anyway. So the plan is to get some the top mounts on the diff lengthened so that the angle is more like the second pic in the first post and also have them adjustable so that I can then bring the pinion angle back up about 4 deg to get minimal operating angle on the unis.

From http://www.drivetrain.com/driveline_angle_problem.html

Ideally, the operating angles on each end of the driveshaft should be equal to or within 1 degree of each other, have a 3 degree maximum operating angle and have at least 1/2 of a degree continuous operating angle.

RPM is the main factor though in determining maximum allowable operating angles. As a guide to maximum normal operating angles, refer to the following chart:

DRIVESHAFT RPM
MAX. NORMAL OPERATING ANGLE

5000
3.25º

4500
3.67º

4000
4.25º

3500
5.00º

3000
5.83º

So as I intend on revving to 8000rpm in 3rd gear, 1:1 then I think I need it to be less than 3% operating angle.

The yoke on the box appears to slope to the back of the car by 1deg and the diff appears to slope to the front of the car by approx 4deg. (need to check it better yet) But that gives 5deg operating angle.

[Sam_Q]

there is some info on this topic in my old thread

http://toymods.net/forums/showthread...=rear+geometry

[chris davey]

Thanks Sam

Well, for those interested I have found a pretty awesome little program here. It is through excel and looks pretty fancy. http://www.race-dezert.com/forum/showthread.php?t=9502 First post.

Do some reading on wiki about antisquat as well. I don't understand all of it but means lots of stuff to learn. Also, performance trends do something similar for $80US so this is good for free

100% antisquat means that the body will not move up or down when the clutch, transbrake or brake are released. Less than this means that the body moves down. More than this means the body moves up and the tyres therefore move down and plant into the ground.

I did some estimates of mine in the program and this is what it came up with.

-28% antisquat! Will do a more accurate one but that sucks! Possibly one of the worst suspension setups possible I would think. Solid, 4 link rear ends are only as good as they are setup. I would think a typical IRS setup would be a lot better than my current setup.

Another good read
http://www.procarperformance.com/bud...ink_tuning.htm

[chris davey]

current
antisquat: 54.83%.



I have 8" of clearance above the top control arm to the floorpan but I am unsure how much it will drop when under compression. I wouldn't think 8" though.

So say option 1 to increase the height of the top control arm mounts on the diff by 1". This gives us antisquat of 125.26%, roll axis angle of 1.04deg and the IC intersects above the CG by a little but it is very far away. So you said that as this is far away it would be more of a gentle transition rather than a hit even though the antisquat is above 100%?



Option 2 is to do option 1 and also drop the lower control arm at the diff mount by 1". This gives antisquat of 175.76%, roll axis angle of 1.95deg and brings the IC closer to the rear. Would I be correct in saying that this would be a more aggressive hit than option 1?



But as far as I can tell, either of these will be better than what Muz showed in diagram a as a "typical" setup. It just depends on how aggressive a hit I want.

I think if I was to do both mounts and get the rods made adjustable length and then give both a go that would be ok. And then at that time I will adjust the rod lengths to get the pinion angle correct also.

Does this sounds like a good plan?

And just about any setup should be better than what I have now.

[Mr DOHC]

*cough* 4 link 9 inch *cough*

[chris davey]

*cough* already have 4 link 8 inch *cough*

[chris davey]

Well well well

I just fitted the lowered king springs from my other corona onto the yellow car. How it turned out was the diff pinion angle has gone from.

before
engine: 1deg to back
tailshaft: 3 deg to back
diff: 3 deg to front
pinion angle: 6deg

engine: 2.5deg to back
tailshaft: 1 deg to back
diff: 2.5 deg to front
pinion angle: 3.5deg

I am a lot more happy with this as I can definitely see this being close to 0 under acceleration

At the same time, lowering the car has lowered the mounts on the car for trailing arms by 1.75". Top has gone from 17" to 15.2" and bottom has gone from 10.5" to 8.75". The net result of this is antisquat going from 43.21% to 57.26% and roll axis angle going from 4.77deg to -3.8deg.



As you can see from the pic the top mount is now facing down by 2.5deg and the bottom is facing down by 1deg. (both to the front).

I checked clearance below the bottom mount on the diff and I can have enough room to put another mount in about 2" lower. If I was to do this antisquat goes to 156.26% and roll axis angle goes to -1.98 deg. This brings the IC back a lot closer to the diff which should mean a lot harder hit on the launch and planting the tyres into the ground.



Also, talking to my mechanic yesterday. He gave a simple analogy. Push someone and they will move back. Push someone with a soft spring between and they will not move, the spring takes the pressure instead. This is what can happen if you try to promote weight transfer via soft springs. The weight will naturally transfer but the antisquat properties mean that the body is still trying to move down also which means the tyres are relatively going to be moving up. The opposite being a high AS where the body will move up and the tyres will be planted down.

Think of an extreme example where the top mount is facing down a lot like this


When the diff trys to rotate up the body is obviously going to be lifted as it is under tension. The further up this mount is the lower the force is trying to pull the body up. For ref sake this setup has 734% AS. Probably a bit too far

New Tailshaft angle