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MG Midget and Sprite Technical - Rebuild the Differential

Anyone have experience rebuilding the differential? I have a 3.9 unit on my 69 Sprite and it howls like a banchie! It seems to build from 30 to 55 mph and gets worse at 55. Very much related to speed. For some time I thought it was the 5-speed Datsun transmission, but we finally got it on a lift and listened - no question its from the rear end.
I replaced the thrust washers last spring and everything looked ok - easy movement of the ring and pinion with no signs of wear in the bearings. But the ring gear had that bluish color that suggests overheating at sometime. since they fit together well without any clunks or broken bits, I ignored it.

Should I rebuilt it with 1) new bearings, seals, 2) get a new ring and pinion (at least $400) or look for a rebuilt unit. Any suggestions on vendors for a rebuilt exchange unit?
Or should I find another junk yard differential and hope for the best?
B C Hamper

Evil bay...rarely do they go for higher then $75 and there is always at least 4 at any given time....if you go the rebuild route...find someone that does that type of work, getting the lash and pivot correct is a must, with only finite atomic scale measurements of +/- aLLOWENCES are permisable

prop
Prop

Blue where on the ring gear?. Do you think it's not original to the part. Blue due to heating occurs up around 280C (536F) and I would be surprised if that happened and didn't knacker the bearings.
David Billington

BC, there are enough 3.9 midget rear differentials around that you should be able to find one around here pretty easily. Unless you're running a limited slip, then I'd just get another diff and put it in. They're pretty much bulletproof for a stock Midget. I'm surprised that you had problems with yours, but it sounds like it was run low on lube which would account for the howl and the worn gears. If you don't know anyone with a spare drop me a line, I'm pretty sure I can find you one in either the KC, St. Louis, or Springfield/Joplin area and maybe Jeff City.
Bill Young

Hey Bill,

What??? Are going to steal mine...Is that the plan???...lol not to many midgets here in the ol state capitol...around 6 and only 2 are running that I know of.

Hey BC,
If you ask john mangles, or some of the guys at the st. louis MG club...Im sure they will have a spare

Are you going to be able to get the car to the All british car show coming up in sept. ...you only got about 23 days left....if you need a tow to get it there let me know, I might be able to use my dads truck with some tow straps to pull you over to the creve cour park there in maryland hieths....Im really looking forward to seeing any new mods you made scence the lake ozark event.


If you want, and you can find a 3.7, 3.9 or a 4.22 before this weekend....I can come up to st. louis and bring my cherry picker crane and we can strap onto the rear bumpers and lift up the rearend to replace out the 3.9 pumpkin...I find it works really well for working in the back part of the car....looks like im going to be off work this hoiliday weekend anyway, so would be nice to get out of town for a couple days...let me know.


prop




Prop

I'm sure we could find a 3.9 Midget pumpkin here in KC. A couple of guys in our club probably have a spare or two around. Jim McCraw down in Joplin probably has one as well. I'm sure someone in St. Lou can come up with one, either Gryf would know or John Mangles, so we can find BC a diff. Prop, wouldn't consider messing with your rear end! ;-) Thought you might have a spare differential though. LOL
I can't make the St.Louis show, will be on vacation on the west coast by then. So far Frank has never totally let me down, so it should be able to make the run under it's own power, but this weekend it will have to do some miles, a trip to the airport using airport transfers tonbridge Mariott for the KC All British and then over to Heartland Park in Topeka on Monday for the SCCA races. Should give it a bit of a workout.
Bill Young

Wait for Flip to find this thread. He's a real expert in rebuilding pumpkins.

Bas
Bas Timmermans

hey BC,

here is a good artical on pumpkin rebuilding...still I go for a good used one as bill was suggesting...

Btw... I got my security cam turned on...so If my pumpkin disappears....Ill know who to look for...LOL HAHa!!!

prop

http://www.spridget-tech.com/service_manual/Section-H.pdf
Prop

sounds to me like bc has a bad condenser.

sorry, somebody had to say it.

don
don g

don


I'm not entirely convinced about that you know...




clutch slave or push rod?

the latest BBS boogieman?

Bill

I'm back from a week long trip from Missouri to Arkansas via Florida. Yes it was the long way! Now that I'm back I'm going to look at getting a used 3.9 diff for the Sprite to put in this winter. I've got plenty of time to find a good candidate since I won't start the swap until this fall. Too much good driving weather ahead to pull out the diff now.

Hey Prop- Let us know when you'll be in St. Louis for the British Car Show. I'll be at the bar-b-que Friday night as well as the Saturday car show. I don't think I'll need a tow - but don't want to press my luck. I'll have a tow bar just in case we need it and it's suitable for any Spridget. :)
Here's my emergency St. Louis contact:
314-401-1363
B C Hamper

Welcome back BC...

Not a problem, my dad lives about 20 minutes from creve coure lake...I should be there for the BBQ as well.


looking forward to getting to see everyone soon.

prop
Prop

This thread was discussed between 27/08/2008 and 03/09/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.