3.92 Diff

[Guest salty_monk]

After my "running for 500 odd miles with no oil" experience the Diff is pretty noisy. (except on overrun which I believe is standard for a worn diff on these..)

 

Talking to a guy last night who reckoned the half shafts are softer than the diff & that it would be these which have worn so I should get away with just replacing them.. What do we reckon?

 

Tried some "Molyslip" in it yesterday to see if it quietened down... no real difference :boohoo:

 

Doesn't seem to be affecting perfomance though

 

Also - off subject, When I boot it in the higher gears (say from 2k in 5th) I get a distinct smell of petrol wafting up from the exhaust, is this normal or does it indicate that perhaps timing is out or it's out of tune?? (I have the standard distributor with points but no vacuum advance)

 

Planning to get it off for a rolling road session some time in the near future, anyone have any recommendations down my way? I Know Bob has used Sanspeed with success, just wondered if there are any others that people have used...

[Longboarder]

I think there is normaly much more diff and gearbox noise in a seven compared to almost none in your average tin top. Wait till your next meet and drag a few experienced hoodies round the block as passengers to see what they think. It is very very unlikely that the diff will just break and leave you stranded or in the hedge.

Far more important mod is to find yourself a Bosch inductive distributor, electronic coil and six wire ignition module off an 85 or earlier sierra and fit that. Gives far more accurate ignition timing over the whole rev range and wiring it in is dead easy. Then get it rolling roaded.

 

Nigel

 

Looks like this.

[Guest salty_monk]

Was planning to put an Aldon ignitor in there before I had it rolling roaded... Is the ignition system in your pic better than that or just a cheaper alternative?

The distributor is brand new (guy who built it bought it, have receipt from Demon Thieves says "Vacuumless distrubutor suitable for tuned Pinto 2.0l or similar on the receipt) so would rather not junk it...

 

Diff has definitely worn because the whining started pretty suddenly (so much so that even my girlfriend noticed & said "what's that? Didn't make that noise yesterday..." but that's what I'd expect from 500 or 600 miles with no oil!!

 

Not planning any drastic action on the diff at the moment just trying to work out the various lines of attack available.... Will wait till the winter before I do anything as long as this one keeps going!

[Longboarder]

Bosch induction gives cheap reliable accurate sparks. A new vacuumless points dizzy with the right mechanical advance curve set up for a tuned pinto with the points replaced with aldon/magnecor/lumenition innards and a decent coil will be better.

 

Nigel

[Guest salty_monk]

Pretty sure this one has the modified advance so I'll go the Aldon route. The coil is brand new as well (although only standard spec I think...).

Will get a flamethrower if necessary.

 

Thanks for the tips!

 

P.s. The donor was an injection model, Haynes tells me they were all 3.92. How can I check??

I've been offered the diff from a G reg Sierra Estate DOHC. Will it fit? Is it the same ratio?

If anyone wants this car as a donor & can pick up from Leicester region I'm sure it could be arranged. Failed MOT on steering bushes, steering rack play or something I think...

[Guest wmc]

If you've run the diff with no oil for a while, it's probably done more damage to the bearings than to the gears themselves. The pinion bearing in particular will have suffered badly from oil starvation a) as it's running 3 times faster than the crownwheel bearings and because it relies heavily on oil splashed up by the rotating crownwheel to lubricate it.

 

It would be worth checking to see if the pinion has any excessive float in it, also check the bottom of the case to see how much glitter/debris is there. A little is normal, if the 1st bit of oil comes out like silver paint it's rebuild time!

 

If it's an LSD or you've been doing a lot of wheelspinning it definitely worth stripping it as it will need it.

 

The half shafts shouldn't have worn as there is little or no movement between the side gears and the shaft i.e. no plunging or potential fretting, so I'd discount that.

 

If you're still worried, pull the back case off and have a look at the adjustment of the crownwheel to pinion, it should be fairly snugg, but not tight and there shouldn't be any scoring or pitting on the face of the teeth.

 

Diffs are notoriously difficult to get to run quietly, ask any Land Rover owner. But it shouldn't sound like a jet fighter either.

 

Good luck.

[Guest salty_monk]

Ongoing saga here Diff Saga

 

Pic of teeth on there, they are marked & have almost like small serrations on them... did expect the bearing might be the culprits. The diff certanly feels a bit "tight when you turn the prop flange by hand.

 

Anyway, another diff to fit (thanks Jim ) now so I'll get that in and report back.... the one that was run dry was getting to the stage where it was louder than the exhaust at times & very high pitched. Very annoying!!