Does anyone know of any issues in using 3J alloy diff casings??
Ive heard mixed reports but no real specifics??
Does anyone know of any issues in using 3J alloy diff casings??
Ive heard mixed reports but no real specifics??
I'll apologise in advance that this is not directly about your particular brand of casing.
However, from my experience of aluminium cases (I can't remember if I've built any 3J ones though) alloy cases are a pain to build - the housings for the side bearings are tighter than cast iron (when cold) due to slackening off when warm (aluminium rate of expansion) to keep the required grip on the bearing shells. This causes issues getting the bearings to slide while moving the crownwheel over to get the correct contact patch while setting up a cold diff.
I do know that in the past (not sure if it's still the case) 3J didn't have any figures for what the cap-spread should be on their casings. Aluminium cases tend to deflect more than cast iron for any given bearing pre-load when setting them up and thus needing more cap-spread than cast iron.
Personally I don't see the point of fitting one : if it's for saving weight it's also usually the case that the car is going to have quite a lot more power than a standard car. More power equals giving the basic design more strain in use, and if it's aluminium (in my mind at least) it's not doing as good a job as cast iron at keeping the teeth meshed and bearings pre-loaded correctly. I appreciate aluminium is used for all sorts of motorsport items but most are designed from the start to take into account aluminium's properties with strengthening etc in all the right places. I don't usually see that in aluminium diff noses - they look a very similar design to cast iron ones.
I've used a flotech one (remember them) for years, built up by a very good gearbox man!, and never had a problem. In a light car mind which always helps
Thanks for the ffedback, the 3J ones have additional stregthening webs, cap spread was my thoughts too but wanted to confirm, as far as the thoughts behind using one - im on a big weight savings mission, its for a hillclimb car with 196hp Pinto.
This is the one i have, they also do a magnesium alloy version :
https://www.3jdriveline.com/webshop/...-diff-carrier/
Ok, try getting 3J to give you a specific cap-spread figure for that diff casing.
Thinking about the last alloy one I did I seem to remember I measured what the cap-spread was after setting the complete total running torque figure (after first setting the pinion pre-load) - if memory serves me rightly the cap-spread - based on the desired running torque - ended up @ approx 0.020".
Excellent thankyou, i will drop 3J and email tomorrow and ask.....you sound like you could build it for me! ive only ever done cast ones. I guess the process is the same just with different cap spread values.
I don't touch alloy ones if I can help it! Not a fan!
Sometimes you have to leave the bearings caps just loose enough to allow the bearings to move when setting up. It can mess with your settings though when you finally torque the caps down so you have to compensate for that or re-adjust as necessary.
You can lighten the std cast diff housing by quite a bit if it's just for weight saving issues
Ive been in touch with 3J they say the only issues are with the magnesium alloy ones...they have given me cap spread measurements and offered to build the diff for me also if i have problems. At the end of the day, most diff housing are alloy, Cossie included.
The material isn't the problem as aluminium is a wonder metal. It's the design that can be a problem as with any re-manufactured item.
As an indication I've heard that some of the reproduction Atlas axles (cast-iron) are so bad that correct mesh is problematic if not impossible in some cases.
What cap-spread measurements did 3J give you?
0.020'' as you said, i had a good chat with the guy at 3J today who was very up front about the previous issues, the early castings were a bit suspect and he said they had problems with the magnesium alloy ones, so they have stopped making them, but he said the new aluminium alloy castings are very good and they've built them for a lot of race cars, westfields, Escorts etc. without issue.
Glad to hear you're sorted, and cheers for the details.
3J used to outsource their diff-building as they didn't have anyone who knew what they were doing. Glad to hear it sounds like someone there may know their way around diffs.
What were the previous issues with the alloy and mag castings?
Not 100% sure as i dont know anyone thats had one, spoke to a few guys in Ireland that use them in Westfield race cars and theyve had no issues so think i'll go with it. Nothing ventured nothing gained and i have a casing so worth a go.
Keep us posted how you get on with it.
Will do
So how did you get on with it?
Maybe he'll get a notification. He left this one on a cliffhanger!
Sorry, yes. That’s what I was alluding to. If he’s not actually on the forum he’d get an email (notification) telling him someone has quoted him on a thread.
Still running a 3j alloy housing. No issues at all
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