Ronnie Brennan

ok so I have a 10 bolt with(what I assume to be) 3.23's 'was almost 3 1/4 turns of the drive shaft per 1 rotation of wheel' I hear that the 10 bolts are notoriously bad when under stress from higher HP engines. I pulled my 305 HO out this winter and am replacing it with a 400HP 350 build engine(originally built for race car). my fear now is that my weakest link in the drive train for my car now is the 10 bolt rear end.

I know the dimensions on the 10 bolt(researched here on TGO) is
"Approx. 57" from backing plate to backing plate and 62" from axle flange to axle flange."

Anyone know what the dimensions of the 4th gen rearend are?? I would consider putting a 4th gen rearend under my car but it cant be much wider than the 3rd or my tires will stick out TOO far... they stick out enough as it is lol!!


Also I know the 12 bolt rearend is a bit better than the 10 bolt but still not sure how much better it would be.

jrz28

iTrader: (6)

I dont know for sure, but if I remember right I think the 4th gen rearend is about 2 inches wider per side than a 3rd gen rearend.

BlackenedBird

iTrader: (5)

Correct.

93-97 = approx. 4" wider, 2" per side
98-02 = approx. 3.5"/3.75" wider, again half & half (1.75"/1.875" per side)

What wheels do you have now? If they are the 16" stock wheels, they'll line up just under the fender lip but not stick out past it. If you have the stock 15" wheels, they will set out past the fender lip.

EDIT:I just saw your sig pic & it looks like they stick out as it is now. So yeah...They'll be WAY out there with a 4th gen rear unless you change wheels. I'd change the wheels you have now myself, but it your car. Only you have to like it. Not me or anytbody else.

Ronnie Brennan

Unfortunately due to my current setup a wider rearend would not be good. here's a pick that shows my current setup. albeit a bad picture at that...

Ronnie Brennan

this one actually gives an idea on how my setup is.
Still not the greatest picture of what I am trying to show but maybe I can get out to the garage and get a better picture but between these both you get the jist haha

AlkyIROC

You just need rims with more backspace to tuck the tires back under the fenders.

As for strength, a fourth gen diff is the same strength as a 90-92 third gen. Update your 82-89 diff with 28 spline axles and posi and it also becomes the same strength. Upgrading to a fourth gen diff gains very little other than the ability to use a newer disk brake setup.

Upgrading to a 12 bolt or 9" is a big jump compared to the tiny 7.5" 10 bolt.

89blackbird89

Sorry to just throw this in here but I'm buying a posi rear end with disc brakes from a 2002 and I know that 4th Gen rears fit in our cars with little to no problem but I can't seem to find anything about the ones from the 2000's I know that the only things that really changed in those years were cosmetic. So would it still fit?

BlackenedBird

iTrader: (5)

98-02 same. The 5th gen is an IRS design & would require a complete custom fab to fit.

89blackbird89

Awesome! I've read on here people saying that its a straight swap besides bending the brake lines and relocating the e brake but some ppl are saying there's more to it. So here's basically what I'm doing the rear end is out of a 2002, I'm ordering new 3.73 gears and disc brake set up, will I need to change anything going from drums to disc and is there anything else I need?

AlkyIROC

Strength wise, the fourth gen diff is no stronger than a 90-92 diff and the 82-89 10 bolt diffs can be upgraded with 28 spline axles and posi to make it just as strong. Third and fourth gen f-body 10 bolt diffs all use the 7.5/7.625 ring and pinions.

The only real advantage to installing a fourth gen diff is to get a newer disk brake system and getting a posi with less miles on it and probably in better condition.

BlackenedBird

iTrader: (5)

The e-brake cable will need some splicing or pull the entire e-brake assembly & lever from the donor car.

Drum to disc.....You might want to swap out the proportioning valve under the master cylinder. I say put the rear in first & see how you like/dislike it before doing the prop valve swap.
If you have a EARLY 3rd gen, 82-86 iirc, the brake line threads are SAE not Metric & I dunno how those are handled. I know I put a 84 rear into a 90 years ago with no problem, yet that shoulda had the same thread problem but it didn't.

gtaward

sorry for changin the topic guys.... but i have the 9 bolt borg warner in my 87 gta right now and gears, seals everything is gonna bend me over in price and availability...i found a 10 bolt out of 91 gta...would she bolt right in?

BlackenedBird

iTrader: (5)

Yes

gtaward

thanks, the guy doesnt know if its posi, as far as i know they never made a gta that wasent posi correct??

BlackenedBird

iTrader: (5)

After 21 years, there is no guarantee it is even the stock rear end that came with the car. So I'd personally check it regardless.

sofakingdom

iTrader: (1)

Wrong. Un-"know" that. Posi was an option with that particular trim & appearance package, same as it was with any other trim pkg.

If you want to know what's in a rear end, take off the cover and look.

If you lack sufficient motivation, as LOTS of people who come on here after using all the different "guessing" methods and coming up with garbage seem to, and all you want to do is P&M about how "hard" it it, think about when the last time you changed the rear end fluid was. How many miles ago did you say? Oh.... did I hear you say NEVER? Well don't you think it's ABOUT TIME??? So while you're catching up on the overdue scheduled maintenance you've been putting off about 3 times its recommended interval, make a point of LOOKING AT the parts.

gtaward

if you actually read it you would have noticed i said im looking at BUYING it, hence the reason i asked the question buddy. would you drive 2 hours to take the cover off and realize its not posi? didnt think so.

JamesC

iTrader: (5)

To avoid that waste of time, perhaps you should ask the seller to drop the cover and snap some pics for the sake of verification. The pics posted here would get you the answer you require (if you're uncertain). You could also ask him to verify the ratio.

JamesC

sofakingdom

iTrader: (1)

Only if I thought it might be.

In your case, get him to take the cover off and snap a pic for you. Buddy. I wouldn't buy one without some kind of proof... I'd accept a pic in lieu of seeing it with my own eyes, prior to the drive; I'd then want to see THE OBJECT IN QUESTION itself, using my own eyeballs. There's just no substitute for LOOKING AT THE PARTS.

And then of course, I'd put new fluid in it.

krisner89

hell with changing the fluid. Id rather **** a big loaf, pack it full and slap the cover back on before I put 1 penney into a weak *** 7.5 rear. Mine blew out soon as i hit the nitro.

p.s. ya I just changed the fluid a year ago

89blackbird89

OK so i got a rear end from a 95 z28 instead and its in but the e brake cables are a pain in the #$$, so if I get the set up from a 4th Gen what is different? Is it longer or something so it will hook up easier?

Ron U.S.M.C.

Ronnie,
A 400hp to the ground engine with sticky tires/posi. and hard launches will not allow the 10 bolt to live very long. Even one that has been modified. On the other hand there is a man here that says his modified 10 bolt is holding strong with 530 ft. lbs torque with street tires and never seeing the track.So there is a trade off. Ether baby the 10 bolt or pound on a 9in. or 12 bolt with confidence.

Ronnie Brennan

For now.. I'm probably going to run as is and start pounding on it next fall b4 I put it away. If it breaks or shows signs of weakness, I'll probably upgrade. This summer I'm going to be short on cash as I have landscaping to do around my house and thats going to eat up a huge chunk of change lol!!

midias

At minimum grab a TA girdle or a similar item to make it a bit stronger. Later they sell used fast for not much off what they go for new.

Yea I understand my wife always makes me spend my money on **** around the house.

Nathon

I just did the swap in my 83. the brake line fitting is slightly different at the bracket at driver side wheel well. took the old fitting and line off original rear and put it on new rear. good to go.

Brakes seem to be fine without proportioning valve. make sure to bleed everything well.

While i had the rear out i swapped in a new exhaust system. shorties to 3inch flowmaster catback i got for 100$.

One issue you might want to look at with either rear end and aftermarket rims is clearance with rear calipers. I Had to grind the hell out of my to clear the rim.

Got my rear for 175$ from craigslist. also got fresh rebuilt vortec heads for 160 from same guy.

Tires do stick out quite a bit on the rear bout 1/2 to 3/4 an inch.

blackroc68

iTrader: (2)

I know a guy witha 81 malibu and a 540 and a 10bolt 390 gears.ANd he has about 100 passes on it he runs 10s. 10 bolts can live

AlkyIROC

The 81 Malibu probably has an 8.5" 10 bolt diff, not the tiny 7.5" that third gens have. Big difference in strength.

Trevmust

if I get a 12 bolt will any year work? cuz I figure it would be cheaper to buy a used one and rebuild it if need be. (as far as I know 12 bolts came from C/K series trucks and muscle cars?)

BlackenedBird

iTrader: (5)

You'll hafta find one the width that will fit with your wheel choice & you'll hafta convert it from leaf sprung to the coil spring/LCA fit ours aer, or a 4-link if you are tubbed & "Pro Street".

Or just buy an off-the-shelf 12-bolt from Moser.

Trevmust

well theres a guy selling a 1970 lemans non posi for 500...

JamesC

iTrader: (5)

Pass on it.

JamesC