Lack of Drive Shaft Endfloat

[ArthurH 5]

I am aware that the cause of our lack of endfloat is almost certainly due to a problem with the shell/body/chassis, but I have posted this deliberately under Drivetrain.

 

Our 1.6GTI was already suffering from a lack of float when we bought it in 2017, with extreme vibrations as the DS bottomed out.  From memory, the standard figure is between 10 and 16mm on each side.  (lets call it a nominal 13mm). we spent a lot of time (100s of hours) unsuccessfully trying to find what was bent so we could straighten it.  Measuring between tooling points and comparing with known 'good' cars, swapping out subframes, driveshafts, lower arms, nothing helped.  In desperation, we moved the engine towards the O/S and achieved 11mm on each side.

 

A touch with the Armco at Pembery lost the endfloat again, moving the engine meant we now had 8mm on each side.  Two years later a small prang at Donnington and we are down to 4mm.  This is too low; the driveshaft destroying vibration is back.  We don't want to invest more valuable time into the existing shell, and have bought a new shell, but that won't be ready until next year.

 

So our last 'roll of the dice', to get through this season, is shorter driveshafts; I am looking for ones that will fit the 1.6GTI (BE3, standard 1.6GTI hubs so 24T/21T/M20) which is approx 9mm shorter than the standard length.  OR any specific brand where the overall compressed length is that much shorter than standard.

 

Or any way of reliably shortening one ( I very much doubt we can afford custom-made ones)

 

I have tried the SKF website, but although the interface is one of the best I have seen, sadly the data it is returning is flawed (it is offering 25T/24T/M24)

 

TiA

[petert 554]

I’d first of all change to the larger, later CV’s which have 34 splines. These were fitted to Series 2 Mi16, GTi6 and probably many others. There are solid and hollow versions of the driveshafts, which are far stronger than 205 or 1.9L Mi16 versions. You could then shorten the driveshaft to the required length by sleeving etc. I’m sure if done properly, they’d be strong enough for your application.

[Tom Fenton 1,526]

28 minutes ago, petert said:

I’d first of all change to the larger, later CV’s which have 34 splines. These were fitted to Series 2 Mi16, GTi6 and probably many others. There are solid and hollow versions of the driveshafts, which are far stronger than 205 or 1.9L Mi16 versions. You could then shorten the driveshaft to the required length by sleeving etc. I’m sure if done properly, they’d be strong enough for your application.

The 1.6 GTI uses a smaller joint and wheel bearing etc over here in the UK Peter. It would be an involved job to change them, uprights, drive flanges, wheel bearings etc

[petert 554]

3 minutes ago, Tom Fenton said:

The 1.6 GTI uses a smaller joint and wheel bearing etc over here in the UK Peter. It would be an involved job to change them, uprights, drive flanges, wheel bearings etc

I know, but it opens up the options and has to be cheaper then custom driveshafts.

[welshpug 1,626]

Surely it would be far cheaper to get the shell on a jig and pull it straight again, like you said its not moved far.

Edited April 25 by welshpug

[ArthurH 5]

We couldn't find anyone with a jig that was willing to do so without charging us many £100s; so as a new shell also will address some other issues, that plan is now already underway, but I won't have it ready in time.  I have just 3 weeks until the next two races at Silverstone.

 

The regulations of Classic Stock Hatch are very much focused on the 'Stock' element, so we can't change the carrier or hub or upright.

[petert 554]

I'm a little perplexed on this, after giving it more thought. Isn't the end float controlled by the wishbone lengths + subframe width? ie if the engine is securely located by the lower engine mount, the end float must be fixed and constant. Movement in the body would only marginally effect this. As the top of the strut position changes, there would be changes to camber & caster, and less so end float. What sort of lower mount do you use?

 

Or mushy wishbone bushes?

Edited April 27 by petert

[ArthurH 5]

Hi Peter, yes, we can not see any flaw in your logic at all.  Hence the swapping out of the subframe and the wishbones with known good ones.  In the case of the subframe, not only did fitting it make no difference to the end float, but it fitted effortlessly, indicating that all the subframe mounting points in the chassis rails were exactly where they should be.  I didn't mention before, but although the wings are a bit battered now, the bonnet fits square to the windscreen and the wings square to the bonnet, so no indication of any trapezing.

 

But the empirical evidence is that we are losing a few mm of end float each time a wing gets bent.  In fact, if we assume a start of 26mm in total, we have now lost 17.5mm

We have to run the standard 205 lower wishbones, uprights, hubs, and flanges.  The current set of wishbones, including the bushes, are brand new.

 

Regarding the drive shafts, I am aware that each manufacturer must meet certain design aspects that are 'important' to the function, e.g., overall length, journal diameters etc.  But I was hoping that the overall compressed length (the point where the tripod bottoms out) may be left to the manufacturer's discretion.  And out there somewhere, someone is making ones that would work for us....

[petert 554]

Surely the 26mm has to remain constant? ie 13 + 13, or 6 + 20, as the engine moves?

 

Is there a strut brace fitted?

Edited April 28 by petert

[ArthurH 5]

It may help if I take you through a typical incident.  I should first say my son (aka James) is a very clean driver in a non-contact formula, normally 12 or 14 races per season, but occasionally cars touch each other.

At the penultimate race of last season at Donington, the car James was battling with had to take sudden avoiding action from the cars further in front and James could not avoid him.  Both cars carried on, James with a broken headlight and a slightly crumpled off-side wing.  For the rest of the race, James could feel the now all too familiar bottoming of the near side driveshaft on right-hand corners.  Note in this instance it is the opposite side to the prang.  This is true 80% of the time, it seems counterintuitive, but perhaps its a clue.  Back in the paddock, we see the inner boot has split, this happens 90% of the time, I have no idea what causes it, but we have fitted many boots from many different suppliers.  We check the end float, and find 2mm left on the NS DS (not enough).  We fit another driveshaft,  move the engine towards the OS, and balance out the end float.  We now have 4.5mm on each side.  In the final race of the season on the following day, we discover 4.5mm isn't enough for the fast right-handers and bottom out another drive shaft, (and another split boot).

 

The engine moving is achieved by slotting the upper engine mount, its crude, but the only solution that has allowed the car to keep racing, when you look at the photo, remember we have to allow room for a socket.  We also have to fit a spacer behind the battery tray.

 

 

So the original 26mm of float has dropped in stages, each time balanced out, to the current 9mm (4.5 + 4.5)

 

The regulations forbid any strut brace.  https://750mc.co.uk/ugc-1/1/1/0/2024_final_regs_-_classic_stock_hatc.pdf

We do keep a close eye on the camber, this has never been affected by any of these incidents....  This aligns with the fit of the bonnet.

 

I now have a plan to shorten a drive shaft, but need to strip it down completely.  I am baffled by the strange circlip on the inboard joint, rather than 'eyes' it just has two 'horns' , The circlip moves very freely, which is good, but I'm finding it much more awkward to push those horns apart.  I've struggled with long nose pliers, but still can't slide the spline.  Am I missing something?

 

 

[ArthurH 5]

I thought I'd better include a picture of the circlip 'horns' I was trying to describe.  Is there a particular technique for holding these open?  While drifting out the spline....

 

 

[Tom Fenton 1,526]

11 hours ago, ArthurH said:

I thought I'd better include a picture of the circlip 'horns' I was trying to describe.  Is there a particular technique for holding these open?  While drifting out the spline....

 

 

 

I'd try a pair of external 90 degree circlip pliers and try to open the clip up with those.

 

[ArthurH 5]

Thanks Tom, I did as you suggested and it made all the difference, I had the shaft out within a few minutes.

 

Any idea as to how I remove the ballbearing 'cluster' from the housing?