Problem removing differntial cover

[mnicoop63]

As the title says I am having a problem with removing the differntial cover on one of my gearboxes. I have removed both side covers and all the nuts and tapped the cover to break it loose which it has except for the lower corner on the speedometer housing side. There are two studs that have 1/2" nuts and the outer one seems to possibly be seized to the cover. I can't get it to budge. The rest of the cover has split from the case but that corner is giving me problems. I dont want to ruin any part of the gearbox because its an original 22A363 box from a 997 cooper. Has anyone had this problem before with a diff cover being seized to a stud? How did you get it to break loose without damaging anything? I dont want to just start hammering on the thing in fear of having either the case or remote diff cover cracking.


Brian

[Oneball]

Throw some penetrating oil down there for a few nights then have a go at unscrewing the stud.

[Jason]

Hi Brian
Had plenty of these over the years, the 5/16 steel stud reacts with the aluminium causing galvanic action. Some release easier than others.
I remove all the other 5/16 & 3/8 diff housing studs. Lock two nuts on the offending stud, then warm up until orange and allow to cool. Apply wd40 or something similar and keep repeating until it starts to free. Once you are clear of the housing dowels you can unscrew the complete housing with the stud and remove from the gearbox, then drift the stud from the diff housing.
If the are really bad, I have had to drill the stud out completely.
Plenty of patience required, good luck.

Jason

[mnicoop63]

Hi Brian
Had plenty of these over the years, the 5/16 steel stud reacts with the aluminium causing galvanic action. Some release easier than others.
I remove all the other 5/16 & 3/8 diff housing studs. Lock two nuts on the offending stud, then warm up until orange and allow to cool. Apply wd40 or something similar and keep repeating until it starts to free. Once you are clear of the housing dowels you can unscrew the complete housing with the stud and remove from the gearbox, then drift the stud from the diff housing.
If the are really bad, I have had to drill the stud out completely.
Plenty of patience required, good luck.

Jason

Jason I will remove all the other studs but the stud that is next to the offending one will only unscrew so far before it hits the remote type diff cover. if i am able to raise the cover far enough to be able to get it past the locating dowels how am I supposed to unscrew the cover with stud still in it with the differential, output shafts and bearings still inside the box? Won't they be in the way of it spinning?


Brian

[Dearg1275]

I have found heating the diff housing itself and then shocking it with cold water has worked for me. The corrosion holding the stud will act as a thermal barrier so most of the heat will go into the alloy and not the stud causing it to expand away from the stud. It might take several goes. If still no joy walk away and try again the next day.

Go luck.

D

[mnicoop63]

Hi Brian
Had plenty of these over the years, the 5/16 steel stud reacts with the aluminium causing galvanic action. Some release easier than others.
I remove all the other 5/16 & 3/8 diff housing studs. Lock two nuts on the offending stud, then warm up until orange and allow to cool. Apply wd40 or something similar and keep repeating until it starts to free. Once you are clear of the housing dowels you can unscrew the complete housing with the stud and remove from the gearbox, then drift the stud from the diff housing.
If the are really bad, I have had to drill the stud out completely.
Plenty of patience required, good luck.

Jason

Jason I misunderstood you and realized after heating and breaking loose the stubborn stud that it would spin and raise the differntial cover. Not the cover spinning itself. I was able to get the cover off and wanted to thank you. I unfortunately just bnroke a tooth on my laygear and 2nd gear trying to get the nut off the end. I am beyond upset with myself as both were in great shape and fear I'll never find another 22a350 laygear as nice as this now broken one. I have the oppoortunity to purchase a NOS cone to baulk ring conversion kit and am curious if maybe you know if they were all for the 850? It comes with a used but good condition laygear but its for the 850. I was wondering if it was possible to use the 22a350 laygear in order to have the original gear ratio but that isnt an option anymore if it were even possible with perhaps a differnt gear or two. I am obviously not very knowledgeable about gearboxes.

[Jason]

Glad you have managed to get the diff cover off Brian. Unfortunately damaging 2nd gear and the corresponding teeth on the laygear is a common occurrence if the correct gears are not locked together when removing the 3rd and 1st motion nuts, the use of impact guns to release stubborn fixings can also cause this. Also there are some workshop manuals out there with incorrect instructions!
The 22A350 laygear and associated gears on the mainshaft were a cone synchro set unique to the early 997s if my memory is correct. Other forum members may shed more light on this for you. The cone to ring conversion set was for the 850 and gives you a standard ratio gearset. Before giving up hope drop Simon a message (251 ENG), he has a lot of early gears and may be able to help you out or supply you with an alternative later type 3SYNCHRO close ratio set.
All my A and B type 3synchro gear stock is standard ratio.