i wanna put a set of 4.10s in my 3 series 12 bolt .. the gears i bought are for 4 series .. should i sell my new gears and buy 3 series gears (pain in the *** to sell) ?? or just buy a cheap spacer and run the 4 series gears in my 3 series diff ?!

 

I am not so sure there is another carrier for the higher gears other than the 3 series. There may be, but one does not come to mind. The old 12 bolts I ever dealt with could handle anything with a 3 series gear to a 5 series without a carrier change.

 

umm .. yeah shoebox .. there is .. usually gears lower than 3.90 go on a 4 series carrier .. but u can get 4.10s and 4.56's made to fit the 3 series (they have a "think" ring gear) .. OR u can use a 4 series ring gear + a spacer on a 3 series posi ..

 

From the looks of your times with the M6 your pushing that 12 bolt to the limit. Without question, I'd get the correct gear set for sure.

Steve

 

thanx for the response .. me and u have almost identical setups looking at ur sig i have all the mods u got .. + some ported LT4s

how much torque did u get out of that cam with stock heads ? I wonder .. cuz my torque #s were LOW LOW

 

Well, I guess it was too long ago.

 

My torque peaked at 331 ft-lbs at about 3500 to 4000 rpms. I've just put a set of Lloyds heads on now and will dyno next week hopefully. I'll post some numbers if they're not too embarrasing.

Steve

 

Pushing the 12-bolt to the limit with an M6? What is "the limit"? I've seen 12-bolts take 750HP in an M6/4,000# convert without any problem.

I agree, get the correct gears. Did you make certain you have the 3-series? My Strange came with 3.73's and the 4-series carrier.

 

my invoice says 3 series written on it in several spots ... so i am to believe it has the 3 series carrier !!!

 

Steve's formula for a practical limit on a 12 bolt has nothing to do with FWHP or FWTQ.

M6 Transmission
+
Heavy car
+
ET Streets
+
5000 RPM launch
+
Rigid Suspension
+
Street Twin Clutch with steel flywheel (rotating mass)
+
Well prepped track
+
10 passes per week

=

You breakie parts sometimes. I've been through 4 R&P. I even had a set that blew to smitherines on Launch #1. 12 bolts can break on 275HP stocker!

All that aside, my point was that If your building or rebuilding a rear, the spacer deal can't be good. You'll risk having more runout, The bolts are longer (lower spring rate and may loose clamping load under dynamic conditions plus more bending load). Plus, the 4:10 Richmond 4 series is about the cheapest gearset in the book. $146 the last I looked.

Fred
Was George running street or pro gears? I know both you and he had very good luck with your 12 bolts. I've not been quite so successful however.

I've thought about trying some pro gears but I don't think their lifespan on the street is too swift, but they may survive the shock loading a tad bit better.

Steve