4th gen rear in a 1st gen f-body ????

[SamHatco]

I've been working on my 69 firebird convertible and have been researching disk brake options, gears and limited slips. Mine is a 10 bolt with open diff, 2.73 gears and drum brakes. I know allot of guys are swapping ford 9" rears and the such, C5 brake conversions or big brake kits from wilwood, bear, and other manufactures, but that can really eat up the budget, so I was looking at possible alternatives. I believe the rear on my firebird is 60.1 inches and the 4th gens are 60.5 inches. Am I wrong?

I have seen some really good deals on 4th gen rear ends complete all the way to the disk brakes with and w/o traction control, with limited slip and pretty decent gears, i.e 3.42 or 3.23. Some as low as $50.

So...... the question is has anybody tried this swap?? What would be the pitfalls and is this a doable deal? Your thoughts, comments, suggestions, criticism welcomed. Go easy on the last part, please.

Thanx,

Sam

[TA219]

I didnt know the measurements but i do often see good deals on 4th gen rears and wished i could make it work.

I guess if the size didnt affect the way your wheels fit in the wells you could just cut off all of the mounting points for a 4th gen and pick up something like the adjustable leaf spring pads from DSE
http://www.detroitspeed.com/productp..._pads_prod.htm

I have never seen anyone do this so i guess you could be the pioneer !

[SamHatco]

That's my thinking. You could use more back spacingg on the wheels to make up any difference on the greater width of the 4th gen rear. Use the DSE brackets to weld up new spring perches. Thanx for the reply Wayne.

Anybody else with some thoughts?

Sam

[zman1969]

I'd say its a waste of time. a 2nd gen f-body is same width as your 69- the perches would need to be moved -alot of 8.5 posis are cheap for them and still easier to modify+swap and stronger than the wimpy 7.5 4rth gen. id recomend a 72-78 nova 8.5 - its pretty much a bolt in- except for springs- some are mono - most are multileaf in novas except for 72 and some 73s which are monoleaf and rare,75 and later there are 7.5" so avoid those- came behind 6 cyl cars. the 8 cyl novas after 75 are the 8.5" variety, gears and posis are plentiful and theyre near bulletproof for 95% of the cars being built.The nova is also 1" narrower than a first gen firebird and same width at early camaro , good luck if you need one let me know - I build alot of 8.5" rear ends

[SamHatco]

Appearantly the 4th gen is fairly solid because they are running pretty good hp #s on those ls1 motors. I know it isn't as strong as 8.5", 9" ford or 12 bolts, but I was looking for a complete package that would be fairly easy to swap.

Sam

[Project69]

Appearantly the 4th gen is fairly solid because they are running pretty good hp #s on those ls1 motors. I know it isn't as strong as 8.5", 9" ford or 12 bolts, but I was looking for a complete package that would be fairly easy to swap.

Sam

As a member on LS1tech also i can safely say...the 4th gen rears are crap. They cant handle alot of power for a period of time. Yes guys are putting down 450-500 at the rear on stock 10 bolt with gears and girdle, but couple weeks later there saving for a 12 bolt. just go with a 10 bolt 8.5 gear, or 12 bolt if you want.

I have a 10 bolt 8.5 rear sittin on the side of my house if your interested it in. Its out of a 78 Z28.

[tumper93]

I have a set of 4th gen rear disc brakes with new GM rotors I will sell that will fit your 10 bolt, I don't have the calipers for it but it has the park brake shoes with all the pieces installed. I had two sets and used one set so I need to get rid of one set, let me know if you would be interesrted

[Ralph LoGrasso]

Unfortunately, the 4th gen rear is very weak, and as such, lots of guys break 'em with stock power (~300rwhp). I wouldn't waste my time with the swap.

[Project69]

Yup what Ralph said. My friend blew his at the track with just a 3400 fuddle stall and minor bolts on with slicks, he had 38k miles on it.

[MonzaRacer]

No doubt the 4th gens are crap, you put any power to them and you will break them, if your lucky you might hear a whine or moan before it blows but for the work forget it.
Besides doesnt Kore3 make adapter plates for the 10 bolts/12 bolts.
Besides any 8,5 or 12 bolt can be made to fit very well and be mucho stronger.
The only way I would use a 9 in is with the centerthat uses 12 bolt gears, 9 in rear take A LOT of power overthe GM diffs.
If you build a rear the strongest(yet heaviest) is a Dana 60.
But if some of the 10.5 crews can make 8.5s live then your certainly not gonna break something unless you try to put 1000 hp to the ground and put 9 billion miles a week on it.
I hope to find a 8.5 from an S10 4wd to build after I validate the fitment for my Monza well enough to source better wheels for it.
Since its gonna be under 3000lbs I figure the 7.5 will live for a while.