Ujoint play on Corvette suspension

[John]

I've been trying to solve a vibration problem on my KVA GT40 - it has C4 Corvette rear hubs. The ujoint on the left side shows a small amount of play on the drive axle and the spindle. Is this normal or should there be no play. The left side shows no play. The inner shafts are connected to the Porsche transaxle by way of CV joints and these are rock steady.

Anybody have any suggestions and could this play cause the vibration - I get the vibration while accelerating between 2K and 4K RPM's? I get no vibration when just reving the engine so it seems to be drive train related!

John

[Big-Foot]

It's time for a new hub John. There should be no play at all in that hub assembly.

[chuck smith]

try tightening the hub nut first, it might be the problem

[Larry]

John,

My KAV seems to have the same thing. I am still sorting out the car since I have no history. I do know thru the research that it is the corvette uprights. If you have the part numbers for the brake pads can you please forward! Will save me the trial and error at the auto parts store. Or at least give me a place to start.

I am checking the wheel nuts on the rear this p.m.

Thanks

Larry

[John]

Originally Posted by Big-Foot

It's time for a new hub John. There should be no play at all in that hub assembly.

Randy,

I've already replaced the hub - there are two tabs on the spindle where the ujoint seats. These are supposed to seat the ujoint in its proper position when the ujoint is bolted in .However, there is about a couple mm space left over when the ujoint is installed which allows the ujoint to move slightly to each side.

Is that normal?

John

[John]

Larry,

The last set of rear brake pads that I bought were made by Albany Brake shoe company, P/N MKD295 - sku 090037 - they are semi metallic.

Do me a favor, grab both half shafts near the Corvette uprights and try to move them in all directions to see if there is any play in the ujoint! You may have to rotate the wheels and try it several times.

What kind of transaxle do you have?

John

[John]

Originally Posted by chuck 1

try tightening the hub nut first, it might be the problem

Chuck,

The hub nut is torgued to specs - no movement there!

John

[BruceLambo]

Two people with similar problems of vibration in a particular part of the rev range on the same vehicle?? John, does the car have the vibration while static in that rev range? I mean just crusing in say, 5th at 3000rpm or only under accelleration?
Id check your engine mounts or how the engine/gearbox is mounted eg: the steelwork mount design is not rigid enough.
I have had this on a similar car years ago, vibration through a point in the rev range. It was found that the engine mountings on the chassis were flexing. Cured by placing a solid brace between the two mounts. This is on the steel of the chassis Im talking about.
And to add, another car had again a similar thing, vibration during accelleration, found to be a buggered Ujoint on the gearbox end.

[John]

Bruce,

I get no vibration when the car is sitting still through that rpm range - indeed, I don't think I get it in 1st gear (I'll recheck). I only seem to get it when accelerating in 2nd or higher gears (I have a four speed Porsche 930 transaxle)

John

[Ian Anderson]

Do you have enough side play in the length of the shaft to allow for full droop to full bump? As you say vibration under acceleration I would think the snag would be on bump.

It could be the geometry causes the shaft to "streach" or compress a little too much and thus bind. With a UJ this bind would cause a vibration.

The reason I mention it is the DAX ended up breaking a roll pin holding the adaptor in place as it "tensioned" the unit on the right side - I thought I had tested during build but it snagged. - The left side did not have the same problem.

Of course this could be a wild goose chase but worth checking.

Ian

[Big-Foot]

Ian is correct in that the side-play of the shaft within the CV joints is important and there is a tolerance (specs are uknown - I've always gone by feel).. If the CV Joint is either bottomed out or stretched to the max - it will cause you heartburn. I noted that the GTM builders on the ffcobra.com website had similar issues.. You may also want to check there in that they use Corvette driveline parts mated to P-car transaxles..

[Wayne M.]

I have a differrent car that has a similar rear hub. There is a spacer between the bearings on the stub axle inside the rear hub. If the spacer is too long or has not been crushed to the proper length there could be some play causing the u-joint to move in and out.

[John]

Randy,Ian, and Wayne

I have CV joints on the transaxle side of the half shafts - I assume this allows enough in and out play. My problem is up and down play (vertical) on the ujoint. The distance from the end of the ujoint end caps seems a hair too small - perhaps a couple of mm. This allows the ujoint to move vertically in the half shaft and in the spline. There are two tabs on the edge of the spline into which the ujoint fits - these are a little too wide allowing the ujoint to move slightly here. Also, on the shaft end, the distance between the retaing rings is a hair too long allowing the ujoint to move slightly here.

I've measured the distance between the edges of the endcaps and this is about 92 mm. I've stopped by several auto supply places to see if they had ujoints with a larger distance between the edges of the ujoint caps - no luck!

John

[Big-Foot]

Originally Posted by john_douglass

Randy,Ian, and Wayne

I have CV joints on the transaxle side of the half shafts - I assume this allows enough in and out play. My problem is up and down play (vertical) on the ujoint. The distance from the end of the ujoint end caps seems a hair too small - perhaps a couple of mm. This allows the ujoint to move vertically in the half shaft and in the spline. There are two tabs on the edge of the spline into which the ujoint fits - these are a little too wide allowing the ujoint to move slightly here. Also, on the shaft end, the distance between the retaing rings is a hair too long allowing the ujoint to move slightly here.

I've measured the distance between the edges of the endcaps and this is about 92 mm. I've stopped by several auto supply places to see if they had ujoints with a larger distance between the edges of the ujoint caps - no luck!

John

Hmmm.. I'm lost without pictures.. Okay - I understand that on the inboard side of your half-shafts that you have CV joints to the trans. On the outboard side, no CV joints but U-Joints.

First off I have to say that this is the first time I've ever heard of that combination being used. I know that if you phase two U-Joints wrong that it will vibrate like a b@stard - I can't tell you how to phase CV's to U-Joints.. I'm certain though that you'd have the same type of malady..

Now in terms of trying to get the slack out where your U-Joint fits in the yoke (presuming that I know what you're talking about when you reference "tabs") - I have swiped an image from the www and modified it slightly (see attached)..

If you have too much slack between the end-cap of the u-joint and the retaining tab, you could be a little creative in removing the cap and doing a quick tack-weld to a washer up against the backside of the cap where it seats against the tab (see image). Of course you'd need the proper thickness washer. Might require a touch-up with a flat b@stard file..
This is all (presuming) that you cannot find the appropriate joint.

[John]

Randy,

Thanks for the picture of the yoke - the old adage that a picture is worth a thousand words sure holds true. The welding of a spacer to make up the gap is an option, but I'd rather find a ujoint that is a few mm wider. Also, on the shaft side of the ujoint there is a little play - so the welding approach would require the use of spacers here. I might not have to weld here as the retaining spring would likely keep the spacers in place. Also, equal spacers would have to added on both sides to keep the ujoint centered.

The gap is so small ( a few mm) I'm not sure how you would weld to a paper thin spacer.

One question I'd like a comment on is whether a little play here is really a problem and is it really the source of the vibration.

John

[Peter D]

Hi John,

I had exactly the same end-play problem on my uni's - if we made sure that the end-caps were hard out against the circlips, we could rattle the internal cross-piece about 0.5mm back & forth between the end-caps.

The problem was totally resolved by replacing the cheap Taiwanese uni's with genuine GM parts - no end-play at all !

Big-Foot has raised the other major concern : Uni's vs CV's.

- With a single Uni & a steady input rotational speed, you will get a sinusoidinal variation on the output side rotational speed - the greater the angle between input & output, the greater the output rotational speed variation.

- With a drive shaft set up with 2 x Uni's, they are phased so that the sinusoidal rotational speed variation of the intermediate shaft is cancelled out by the 2nd Uni joint => constant speed in / variable speed on the intermediate shaft / constant speed out (assuming that input & output shafts are parallel).

- A Constant Velocity (CV) joint is effectively a collapsed version of the above assembly - constant speed in / constant speed out (all in the one unit).

- So, I suspect that there could be problems when a CV joint is used at one end of a drive-shaft, & a uni at the other end : no compensation for the variable speed induced by the single uni ?

The last price I saw for a set of Corvette spindles to suit CV's was around AU$1300 - so it would be probably a lot cheaper to look at a pair of sliding-spline drive shafts with uni's at each end ?

Food for thought.

Kind Regards,

Peter D.

[Ian Anderson]

Hi John

Accepted that this is not the "play" that you were asking about but still worth checking if you have some slack / play along the length of the shaft on bump, droop and neutral - you only have 1 CV and hence only 1/2 the potential "expansion / reduction" capability.

Ian

[John]