Rear end - two questions

[Trip59]

Ok, so in checking everything out on my new acquisition (72 GMC 1/2 ton, 5 lug 12 bolt rear end) the pinion seal is leaking and slinging BAD. The rear cover is leaking, piece of cake there, but I've never done a pinion.

How bad are they? Is it tricky to get things set, difficult to complete yet easy to screw up?

Second question - installing a 4 speed next week, 2 line Saginaw, ratios:
3.11
2.20
1.47
1.00

Right now with the stock 307 (had a 3spd manual from the factory) but putting in a '67 327c.i. this summer.

What rear end should I have?

Trip

[Wrenchbender Ret]

Easy. Remove the drive shaft from the yoke. Mark the pinion nut with a punch so you can put it back in the same place. Remove the nut. The yoke should tap off with a small hammer but sometimes you need a puller. Dig out the old seal & install the new one. Put the yoke on & the nut. Use threadlocker on the nut. If there is a little up & down play after you tighten it to the previous mark you can go a little further to remove it. If there is excesive play you are needing new bearings.

[Trip59]

I thought it wasn't safe to do it that way... That process sounds like a piece of cake!

Trip

[hicktownhotrodder]

what are you going to do wiht the truck? daily driver i would say a 3.21 to 3.08 for more pulling a 3.73 up to a 4.11. in the middle would be a 3.55

[Trip59]

Mostly around town, pulling would be rare, if ever, and not too heavy/short distances if I did.

I'm pulling the cover off this weekend to see what's in it for sure, I tried counting rotations, but my math didn't add up...

Trip

[hicktownhotrodder]

if its an open rearend you need to block one wheel so it wont turn. then check your rotations. if its a posi unit you dont need to worry about it.
i have a 3.21 in my truck and i absolutely love it, but i have granny low to get a load rollling though.
how tall are your tires? that makes a difference too

[Trip59]

It's either not a posi, or is broken, as the wheels spin independent... I lifted one side and marked the shaft in 1/4s and the tire for a full rotation. Rotating the tire once around had the shaft rotate 7/4+... just under two rotations. That seems waaaay low for me, shouldn't it go around 3x+?

I've driven trucks with a granny low, but what is that in real numbers? Just for reference...

Trip

[69GMCLonghorn]

The granny gear on an SM465 or the NP435 is in the 6 range. The SM420 up to '67 had a 6.90 or something like that. If you're not pulling much or ever, just go with a standard 4 speed if you have that option. Or better yet, get a 5 speed with an OD and you can go with a little lower rear end gear.

[Trip59]

Originally Posted by 69GMCLonghorn

The granny gear on an SM465 or the NP435 is in the 6 range. The SM420 up to '67 had a 6.90 or something like that. If you're not pulling much or ever, just go with a standard 4 speed if you have that option. Or better yet, get a 5 speed with an OD and you can go with a little lower rear end gear.

4 speed sitting on the floor of my shop... 2 line Saginaw, ratios:
3.11
2.20
1.47
1.00

Great deal, new kit, machined flywheel, clean bell, and a $250 Hurst tight as the day it was installed... All within my limited budget (or else I'd have gone with a 5...)

Trip

[69GMCLonghorn]

Sounds like a winner to me! Also, I'm a big fan of the 307's... I know, there's bigger and badder out there, but I've had 2 of them, one in a Chevelle and one in a '69 C/20. They both were beat on (by me!) like a step child and just came back for more...

[Trip59]

My 307 leaks like a seive... I'm upgrading to a '67 327 within the next few months. Dollar for dollar, it'll actually be cheaper, I'm buying a nearly complete 327 with all machining done, just the heads are left to rework. I was actually going to go to a stovebolt (my favorite) but I had to do the math and go with the one least likely to force me to sleep on the couch

Trip

[hicktownhotrodder]

Originally Posted by Trip59

Rotating the tire once around had the shaft rotate 7/4+... just under two rotations.
Trip

i ran into that problem once too. turn the driveshaft and count it that way. i think it has something to do with the spider gears? not sure on why that is

[Trip59]

I'll give that a shot, going to pull the pan this weekend too, it's leaking like a Harley... Once I know more about it I'll decide what I'm going to do, fix, replace, pay someone...

Trip