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I got the differential off and 'cleaned it'... Now I'm thinking of changing the gear ratio... I read some threads here and there.
Don't know what gear ratio I have now. Probably standard for a 77 L48 w. auto?
I never done it, and to be honest I don't understand it... Could somebody give a small explanation?
1) Is it worth changing? 2) What will I need to do the job? (parts and special tools 'not part of your standard mancave') 3) Do I have to remove the pinion seal? 4) Do I have to remove the side yoke seals? 5) What are the springs etc in the diff case? ... Is it something to be scary about when working on it for the first time. 6) I saw some people putting yellow stuff on the biggest gear. Is this to see if it's worn? What is that stuff?
Search for writeups by GTR1999, there are a bunch, and they are very detailed. You will get a feel on whether or not you can do this from his papers. Here's one:
Since you have the case open, you can count the teeth and determine exactly what gear you have, as there's been plenty of time for some PO to have swapped gears.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Please don't take offense but just by reading your questions, I think you'd be in way over your head doing work on your diff. What are you trying to achieve? More performance or better gas mileage? If all you needed to do was change out worn side yokes, you could do this very easily but beyond that, it gets more complicated.
I got the differential off and 'cleaned it'... Now I'm thinking of changing the gear ratio... I read some threads here and there.
Don't know what gear ratio I have now. Probably standard for a 77 L48 w. auto?
I never done it, and to be honest I don't understand it... Could somebody give a small explanation?
1) Is it worth changing? 2) What will I need to do the job? (parts and special tools 'not part of your standard mancave') 3) Do I have to remove the pinion seal? 4) Do I have to remove the side yoke seals? 5) What are the springs etc in the diff case? ... Is it something to be scary about when working on it for the first time. 6) I saw some people putting yellow stuff on the biggest gear. Is this to see if it's worn? What is that stuff?
1). Depends. Most typical reason folks change ratios is they aren’t satisfied with what they have. Example - I want better acceleration and I have a 3:36 so I want a “deeper” ratio ( like a 3:70).
2). Rebuilding a differential is not a job for everyone. It does take a lot of special tools but more importantly, it takes a lot of knowledge and experience to do it correctly.
3). To change ratios, you need to change both the ring and pinion gear so the short answer is yes.
4). Technically no, but you’d be a fool not to with the unit disassembled.
5). Those are the posi clutch preload springs. Knowledgeable folks don’t reinstall them. Instead, they “tune” the posi unit. I wouldn’t classify working on them as scary.
6). That paste is applied to the gear faces to determine the contact pattern between the ring and pinion.
My recommendation for you at this juncture is to pull the cover and measure the gap between the axles and the posi cross shaft. The axles, if original, are likely heavily worn. Look at the outer edge of the ring gear and look for the tooth count that is stamped in. On the bottom aft most edge of the case are a series of letters and characters stamped in a sequence. Post some pics and we can continue the conversation.
Here in the states, the entire carrier can be swapped-out for a rebuilt unit all set-up and ready to go with maybe 4 or 5 different choices of ratios.
However, your old unit must be put on a pallet and shipped back as a core charge. I believe those units run around $1100 + shp both ways.
That's not going to help you in Europe though, sorry.
Your 3:08s are doggy, designed for good MPG, highway ratio. You would likely enjoy a 3:70 if possible.
Well when I first read this I wasn't sure if it was for real but then read you were in Europe so probably have little exposure to this work. Getting quality work here is difficult between con men and those inexperienced in custom work. An exchange diff here is a crap shoot and it must be unrealistic outside the USA.
So you should think out your goals. If the diff is in need of service- which an original C3 diff will need, then you have to learn if it's something you can do and if not if there's anyone you can trust. If you just want better mileage forget it because it's not going to work, if you want more performance or want to make it stronger for more engine power then that's different and you're back to deciding who will do the work.
Today with supply chain issues, part back orders are common. Add in the fact that good parts are getting more expensive or have been obsoleted already, and as mentioned finding experienced, really experienced guys is getting harder since we are retiring or dying. DO NOT believe what you see in some catalogs, web sites, or advertisements- some are good many are not. Some have excellent web sites and it's all a con, trust me on this with certain placed and individuals.
Since you are in Europe and most likely want to make weekend trips in the car, I highly recommend that you keep the 3.08 rear gear. It will serve you well for getting better fuel mileage. And with the fuel prices you have over there, your wallet will appreciate it.
If you want better performance, spend your money on engine component upgrades....
Make sure and check the stub shafts for wear while it's out. I think with a TH350 transmission 3.08 ratio is not a bad choice if you drive at highway speeds much. Changing gear sets is pretty big job and takes some skill to get it right.
I wouldn't change the ratio unless I did the engine with more power. What kind of gas is available. Gary above is the guy. I, with a HP engine would like a 370, but if you just want to drive, then you are already set up. If you want stop sign to stop sign then take a look at your engine and fuel availability.
77 change diff gear ratio
