Does this sound like the rear end gears are done for? Fixed!

[Dino]

Funny we were just talking about the 741 being the weakest but not all that weak and here I am , likely with a busted 741....  

I was driving it into work this morning, it was raining pretty hard so I was taking it easy.  I was on the road for not much more than 5 minutes when I took off from a stop sign, at a very normal pace, when I felt and heard a thud and the car started making a bunch of noise in the back and started shaking rather violently.  

I pulled into a parking lot and stuck my head under the car but I didn't see anything out of the ordinary.  Mind you, it's 7 am, it's dark and it's raining pretty steadily so I'm not spending a whole lot of time looking here.

I decide to drive it back home at about 30 mph and the car is trembling all the way home, steering wheel is shaking, deep bass rumble going through the cabin.  The engine is fine and the trans shifts smooth so my guess is that the whine in the rear end changed to a small explosion and there's a few teeth missing in there.

As I said it's a 741 case and it has 2.96 gears.  The u joint is a universal type and I did have to mess around with it a bit to make that thing fit last year.  Maybe the u joint got busted?

I'll put the car on stands this weekend so let's assume the u joint is fine and there is no visible damage, it should be the rear end gears right?

[bobs66440]

It's VERY unusual for the gears to just break. Especially under a light load. Maybe something came apart. Is it an open rear or sure grip? Maybe a u-bolt/strap worked it's way off the u-joint. Are the brakes working ok? One of the rear brake assemblies may have also come apart and the parts may be getting ground up between the shoes and drum. 

[Dino]

I took  a quick look a minute ago alas without a flashlight but the u joint looks fine, nothing out of the ordinary under there but I'll confirm soon enough. The gears always had a whine under load so I was assuming something went wrong in there.  It drives fine at walking speed but not a whole lot faster.  When I put it in gear there's a thud and a light shake.  A bit worse in reverse.  The brakes work fine so unless the driveshaft is bent I think I need a new pumpkin...and it's not easy finding 2.96 gears in anything but a 741 case.  Andthat's not so easy either.

[c00nhunterjoe]

Drop the driveshaft and spin the wheels.

If it turns out to be the 741, scrap it and get a 489 or 742 with 3.23s. Very plentiful and I will bet you won't tell a difference from 2.96s to 3.23s

[Dino]

Drop the driveshaft and spin the wheels.

If it turns out to be the 741, scrap it and get a 489 or 742 with 3.23s. Very plentiful and I will bet you won't tell a difference from 2.96s to 3.23s

I don't think I'd want to go lower than 2.96.  I have a set of 3.55's and they are not going back in that car unless there's taller tires under it and a 4th gear in the trans.  3.23 will be better but 2.96 was perfect.  I don't even think they put those in anything but a 741.  Now if I find a 3.23 for a good price I will try it.  If it's not my thing then it'll be an easy sell or I can keep it for when I do change the trans.

The only one in my area (over an hour and a half away) is a 741 with 3.23 for $75.  I think I paid $25 for the current set.  Came out of a 66 Coronet if I recall.

I'm sure there's a few members here that have what I need but those things are so heavy shipping is out of the question.  Anyone close to SE Michigan drop me a pm though or let me know in this thread.

[John_Kunkel]

The rear end noise is most likely the spider gears in the differential, the cross shaft wallows out the housing and the gears eventually fail; even under light load. Ring & pinions usually don't fail by themselves, some collateral part fails first.

[Dino]

Alright, jacked up the car and had a better look yesterday.  Turns out one of the caps on the u joint is mia making the driveshaft bang around.  I don't know if the damage is limited to the u joint or if the gears got hit but we will soon find out.  That is if I find a u joint.  Autozone and advance auto don't seem to carry them so I'll have to get the same precision brand as I just ruined.  Ironic name since the last one was 2.19" wide instead of 2.125"   

[Troy]

I have a couple on the shelf but I forget which yoke they are for. I'm nearly positive they are the larger ones as all I have are 489 and 742 cases. However, I may have purchased these for the Barracuda so they might be smaller. I'll look if you need me to.

Troy

[Dino]

Thanks T but I just found one at Napa.  Picking it up tomorrow and this time I'm bringing a caliper so I can make sure the 7260 end is less than 2.13" wide.

I don't know what the rule is with which u joint goes on what yoke.  My 3:55 gears are in a 741 case but it has a 7290 u joint.   

Tomorrow night I shlould know how the rear end gears are doing.  I hope they survived this ordeal.

[Dino]

Update:  I went to napa to pick up the u joint.  It was the same box as the last one I bought, Precision #347, but when I opened it, it had different caps.  Last time I installed one of these I had to grind two of the posts to make the thing fit (likely why it failed).  These caps are different sizes, unlike the old u joint, and there were two thin clips and two thick clips.  Again the old u joint's clips were all the same so I must've had a messed up one as this u joint went in without a hitch and fit like a glove.

Took it out for a test drive and not only are the rear end gears okay, the whole thing whines a little less than before as well!      

[cdr]

very good

[Troy]

Troy