Differential Failure

[CBUEB1771]

How long are the special ARP bolts ? Does Burtons stock them ? I could not find them on the ARP or Burtons web site?

Very good question, you might drop Tony Ingram a line:
http://www.lotus7.com/Home.html
Among his ARP fastener kits is a set of studs, washers and nuts for the English axle side bearing caps. I didn't see anything for attaching the crown wheel to the diff though. You might also ask Stuart at TTR what he uses when he builds diffs. It would also be worth looking at NAS fasteners which are supplied in 1/16" inch length increments. Of course these are normally used with nuts and the threaded section length might not be right for a bolt with the optimum overall length. Oh and I assume these are UNF thread form.

[promotor]

I did some measuring of the various components to check the required CW to diff centre bolt lengths

Original diff centre flange thickness = 7.3 mm
Quaiffe diff centre flange thickness = 10.3 mm

depth of tapped hole in CW = 17.5 mm
depth of tapping in hole = 14.5 mm ( the hole does not appear to be bottom tapped)

Original diff bolt length = 19 mm (3/4 inch)
thus for original bolts
Depth of thread engage with original diff centre = 11.7 mm
Depth of thread engagement with Quaiffe diff centre = 8.7 mm

If you went to the next standard bolt length of 25.4 mm (1 inch) for the Quaiffe diff centre
then depth of engagement would be = 14.1 mm
This is very close to the tapped depth in the crown wheel so you would probable want special bolts about 22.2mm / 7/8 inch long or cut off 3 mm (1/8 inch) from the standard 1 inch bolts.

How long are the special ARP bolts ? Does Burtons stock them ? I could not find them on the ARP or Burtons web site?

cheers
Rohan

Rohan,

Do you have a standard T/C or crossflow 6 bolt crank flywheel bolt? Try one of those in the all of the crownwheel bolt holes to see if when it/they are fully screwed in to the LSD mounting face the crownwheel will be clamped nicely.
If they will work then the ARP bolts will be fine also - Burton stock ARP crossflow flywheel bolts. These are the ones my brother and I use when putting LSD's into diffs (usually 3J driveline ones) :

http://www.burtonpower.com/arp-flywheel ... pfw01.html

I don't recommend using use any bolts other than those unless they are original genuine Ford spec'd ones. The OE type replacements have lead to failures in my brothers (expensive) experience. It's either original Ford flywheel bolts, or the ARP ones only.

[promotor]

Any update on your diff Rohan?

[rgh0]

Pulled the Quaiffe LSD apart today to clean out any metal bits. i have everything needed including ARP bolts for the crown wheel and will start reassembly next week. The spine on one of the diff output shaft needs a little cleaning up as its a very tight fit into the diff centre, i looks like the end has a few rough bits on it that need a little fettling, Not sure what caused it as I dont remember it being tight when I fitted it many years ago

cheers
Rohan

[promotor]

Have you kept the diff output shafts "handed"? Have they ever been swapped over from one side to the other?

For info I have just built a diff using a new 3.54 CW&P and the shim ended up being 0.133" despite the dummy pinion saying that it should be 0.135". Have you worked out the shim you think you need or are you planning on putting the same one back in?

[rgh0]

Yes I marked the output shafts and will keep them on the same side. i have got a replacement cast iron diff nose also as the original one was gouged when the pinion bearing failed. I have got a complete set of new shims also as the original one had welded itself to the pinion.

I am using the same tool that I use for measuring the valves position in the head. This spans the diff carrier bearings and enables me to measure with a depth micrometer down to the pinion bearing seat. I can then calculate the shim thickness based on the depth measured and the measured bearing dimensions.

cheers
Rohan

[promotor]

Yes I marked the output shafts and will keep them on the same side. i have got a replacement cast iron diff nose also as the original one was gouged when the pinion bearing failed. I have got a complete set of new shims also as the original one had welded itself to the pinion.

I am using the same tool that I use for measuring the valves position in the head. This spans the diff carrier bearings and enables me to measure with a depth micrometer down to the pinion bearing seat. I can then calculate the shim thickness based on the depth measured and the measured bearing dimensions.

cheers
Rohan

Sounds like a good way of checking for shim requirements.

How easily did the pinion head bearing come off? Any signs of micro welding to the pinion? The pinion that i've just removed had a bearing failure and I can't pull the inner race off (looks melted) so it's going to have to be chiselled off to get the shim out - hopefully that won't be scrap too!

[rgh0]

The pinion end bearing race came of very easily, It had overheated and distorted and was actually relatively loose on the pinion shaft. Came off with a bearing splitter and puller with little effort.

cheers
Rohan

[gus]

Wondering how much horsepower you are pushing through that

Curious at what point the diff mechanicals become the weak point

[rgh0]

I am putting about 180 hp. A friend of mine who races with a Seven is putting about 190+ hp. The diff is certainly capable of these levels for many years without failure. My diff was the original one in the car and has had about 40 thousand road miles with a standard engine and then around another 40 thousand race miles with racing twincam engines and lots of drop the clutch starts overs the years.

The only reason it failed was the bolt heads on the crown wheel to carrier bolts failing in fatigue and jamming in the gear teeth. I am building the new diff with ARP bolts and it should be good for another 40 years

cheers
Rohan

[elansprint71]

Interesting thread, Rohan; I think if you have had 20 years use out this diff you have done well- especially considering the amount of racing. A most unusual failure.

[rgh0]

Finally found some time to finish the diff rebuild after collecting all the bits.

The new Burton pinion was at the top end of the tolerance on the mounting diameter for the pinion bearings. i had to press on the front pinion bearing to the correct bearing pre-load as I could not pull it up with just using the nut on the input flange as it was to tight on the shaft and the Burton collapsible spacer is also a lot stiffer than the Ford original.

Everything finally came together OK and the tooth contact pattern was OK first time. I have the Australian Lotus Clubs national meeting and track day in South Australia in 2 weeks and a race meeting about 4 weeks after that so need to get this finished in the next couple of days and the diff run in.

cheers
Rohan

[seniorchristo]

Rohan
I have a question on rebuilding the diff. As I understand it, the proper amount of shims are required to set the pinion depth. Once this is achieved, pinion bearing preload is set using either shims or the crush washer. The two operations are independent of each other. Correct?
Thanks
Chris

[rgh0]

Yes the shim under the pinion is used to set the engagement depth with the crown wheel. Once that is set it is fixed and it is done first. The crush spacer is used to set the pre-load on the back to back taper roller bearings that support the pinion. That is set by measuring the pinion rotational torque and you torque up the drive flange nut according to the manual. With the Burton components I found I needed a press to set the pre-load and then tighten the nut. The setting of the pre-load does not affect the established pinion engagement depth.

Once the pinion position and pre-load is set then the crown wheel position and pre-load on crown wheel bearings is set to get the correct tooth contact

Its a relatively simple 4 step process but it does require some precision measuring tools and practice at using them

cheers
Rohan

[seniorchristo]

Informative as always. Thanks Rohan.
Chris