Quaife ATB needs longer crownwheel bolts

[MikeB]

Folks

Just bought a Quaife ATB to put into my 915 'box, I have noticed that the flange that you bolt the crownwheel onto is approx 3.5 to 4 mm thicker, it means that the bolts only have about half the tread depth compared to the std diff. Has anyone dealt with this issue before, did you fit longer bolts, if so where did you get them?

[Nine One One]

Mike Bainbridge can probably answer this question with ease?

[knapmann]

Not sure if its related to this issue but there are 2 types of diff in the 915. The early 7:31 R&P diffs are different from the later 8:31 R&P diffs, the ring gear is offset between the two. Do you have the correct diff for your gearbox?

[MikeB]

Quaife only do the one ATB diff casing for the 18T and 32T drive flanges, my box is a 78MY one. The diff fits fine, even the bearing spacer settings are pretty much the same as the std 911 diff. I have sourced slightly longer bolts and will make up lock tabs to suit.

Another requirement is slightly longer bolts to hold the drive flanges into the diff, the std "elastic" ones only engage with the last two or three threads, so have ordered bolts that are 5mm longer (80mm long)

[BILLY BEAN]

Although you have found a solution when I purchased a Quaife for a 915 box they had two offerings. One for the early mechanical speedo and one for the later electric speedo. Whether this accounts for any significant difference in the length of fixing bolts I don't know.

[MikeB]

Yes, mine was set up for the electric speedo, but not sure if that changes the crownwheel mounting flange thickness, as it is at the other side of the diff, so to speak. Certainly, they only have one drawing on their site for the 915.


Just looked on their site and the Pre 74 diff has slightly different dims for the depth of the bearing seats, to compensate for the lack of the magnet wheel on the electric speedo, bit for my query , they ironically have an even thicker CW flange at 14mm tck !! Maybe earlier diffs have longer bolts? Yet Design911 list the one bolt fits all diffs from 65-83 !!

[MBEngineering]

HI Mike

which CWP have you in the box, 7:31 or 8:31, is the diff fine spline or corse,

if you have a 7:31 CWP you will need longer diff bolts and a spacer for the CW, or cobble it with diff shims to set the bearing pre-load and back lash,

if you have fine splines, the shafts should fit in and be the correct length, if you have corse spline shafts, you will find they will be to short and when you bolt them in the diff WILL be locked with the flanges

you will need 22mm long diff bolts from a 928 ( 928 332 276 03 )or a 968 ( 928 332 276 06), lock tabs are ( 901 332 285 01 )

a spacer will be needed to remove the speedo disc or cobble it with a stack of diff shims

Spacer's are the only way to go, or you may end up with the diff off-set to one side in the box with one drive shaft flange further out and further in against the oil seal with the poss' of oil leaks

regards mike

(just to let you know I can receive E-mails at the moment, but cannot reply, for some reason?) if you need some more info

[MikeB]

Mike

Thank you for your comprehensive answer, have got the diff shimmed up and first measurements taken, it’s an electronic speedo drive, so kept the magnet disc. I’ll give you a call next week to cover the issue with my 18T drives, as I assume I need to make a spacer to fit behind the end of the splines on the drive to push it out and ensure no interference with the diff flange.

[MBEngineering]

HI Mike

yes, you will need a spacer for the end of the shaft into the diff, check the length of the shaft and the inside of the diff, I think you will find it is around 5-6mm to get some clearance

I have taken this up with Quaife, and thay seem to be NOT intrested

regards mike

[jwhillracer]

Is that the same length as the stub shafts for the ZF diff?
JW

[MBEngineering]

HI JW

yes it is the same as the N.L.A. ZF LSD out-put flange/hard to find/lots of££££ when found

Quaife have made the 911/914, 915 diff case the same and as beeing in a engineering/cost cutting, did not look any further than the end product that will only fit the SC/3.2 915 box with no prob' (well maybe??) and did not look at the sizes/fitment to the early box's,

this diff (in your hand) will only fit a 915 box with a 8:31 CWP and elec'speedo and the 3.2 oil pump drive, (this needs to be checked VERY carfully when fitting the Ally gear on the diff)

if you have any of the other early box's, you have fitment issues

regards mike

[jwhillracer]

Hi Mike,
I have two of the original ZF output flanges, if you know anyone who needs them. We broke enough of them over the years to contribute to their rarity and expense! We had a couple of batches of uprated ones made that definitely take a lot longer to break!
We stayed the night before last in Tebay, but sadly didn’t have the time to stop off and say hello, maybe another time.
Cheers
JW