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 3.08 vs 3.42 
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Post 3.08 vs 3.42
So, I am beginning to work on my '76 TA and it has the stock 2.44 drum brake rear end. I have been weighing some options and right now I can pick up a 3.08 disc brake rear end with an adjustable proportioning valve. I had been thinking about getting a 3.42 disc brake rear end, but I haven't found anything. So the question is, do I settle for a 3.08 disc rear end, do I try and find a 3.42 disc brake or should I just upgrade the existing rear end with 3.42's. My engine is a 400 Pontiac that will be upgraded, so it will be around 300 hp mated to a rebuilt TH350 with shift kit. Anyone have any thoughts or experience in this area?

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1990 GTA
1987 TA (gone but not forgotten)
1976 TA (project)
1995 Z -28 Camaro
1982 Firebird ( my 1st )


Sun Feb 01, 2015 6:59 pm
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Post Re: 3.08 vs 3.42
If you're prepared to buy new gears and install them in your existing differential. Why not buy the disc brake diff and install new 3.42's in it? You can inspect the posi and bearings at the same time. That way you know what you're getting.

Or be patient and wait for a 3.42 disc to come along.

Both upgrades are worth having.

If I had to choose only one? It would be the 3.42's with drum brakes. But that's just my opinion.

Good luck! Nice car! Lots of torque to spare!

Cheers,
Ken

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1996 Z-28/SS

Previously - 1996 Z-28, 1989 Pontiac GTA, 1985 5.7 IROC Z-28, 1976 Camaro LT, 1974 Trans Am 455HO, 1974 Z-28, 1967 Firebird Sprint,
1967 Camaro 230 cu-in 140-hp "Blue Flame" straight six with a 2-speed powerglide.


Sun Feb 01, 2015 7:33 pm
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Post Re: 3.08 vs 3.42
Normally 3.42s are better but those Ponchos make big torque and keeping the tires planted is difficult. That and the missing overdrive will make me want to stay with the 3.08s. Torque curve of those Ponchos usually nosedives at 4500 RPM IIRC. The highest revving 400 that Ive seen with the stock rotating assembly and 455 heads made less power at 5500 RPM than at 4800 RPM. My 2 cents


Mon Feb 02, 2015 3:41 pm
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Post Re: 3.08 vs 3.42
Do they make 3.42 gears that will fit on the 3.08 carrier? (ie 2 vs 3 series?).
If they do, I'd get the 3.08 disc rear and try it first..

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Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH


Tue Feb 03, 2015 4:30 pm
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Post Re: 3.08 vs 3.42
^ No but you can get a shim. Regardless with a 3 spd transmission if you want to drive the thing anywhere 3.23 is as low as I would dare go. RPM spins too high otherwise and you'll guzzle fuel like mad. I like the 3.08 for a 3spd its a driveable ratio and the big torque from that Poncho and those cubes will still keep it snappy down low. A good stall converter is gold when it comes to auto builds though. GOOD one. If it costs less than $500.00US its probably junk.

Coan, Art Carr, Pro Torque, PTC, are a few that rank high. Hutch down in London is one heck of a good guy who wont steer you wrong plus hes local.

http://hutchtrans.com/

Remember fellas, those serious race cars dont run much different stuff than street machines do, but its the tolerances, the parts used, and the way its allllllll assembled and matched up perfect that turns ho hum cars into wild rides!

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1987 IROC ww 99 LS1,TR224/112, STG2 heads ported by American Speed, P Gold springs, LS6 intake, SVO 30's, Ported TB, Comp Cromo Push rods, Katech Rod bolts, LS6 oil pump, T56, SW LT's, 8.8 hybrid rear 3.73, 275/40/17 MT ET streets, lots more
12.1 @ 112 mph 1.69 60'

89 R7U 1LE Players Challenge car all stock.


Wed Feb 04, 2015 2:20 pm
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Post Re: 3.08 vs 3.42
Thanks guys for the info. I guess that 3.08 is still alot better than the 2.44 drums that the car has now. They guy is also going to throw in a dial adjustable proportioning valve as well. Lotsatas has purchased some stuff from the guy and he says he was very reasonable. I know he is with the Londion Trans Am club as well...he has quite a bit of 2nd gen parts. I will see if he actually has a torque convertor. How big of a convertor should I go with?

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1990 GTA
1987 TA (gone but not forgotten)
1976 TA (project)
1995 Z -28 Camaro
1982 Firebird ( my 1st )


Wed Feb 04, 2015 2:55 pm
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Post Re: 3.08 vs 3.42
IMO a good converter needs a very detailed discussion with the man who is building it. Even then a lot of times to really sort it out it may need a restall pending data after the build. Its all about time and effort and how baddass you want the package to be. But for simple NA street builds like this? 3000 or so is plenty, 2800 maybe. Any tighter than that is hard to get a stall that will still flash on launch. This is where the multiplication factor of autos really can turn a ho hum ride into something fun and inspiring.

Im sure most here know what its like when you get in a ride that has just the right stall for the package and BAM every time the gas is touched it just lights the car up with energy. If it feels like boooooooahhhhhhhhhh or boggy its too tight and if its flashing up too high and is tricky to drive around slow or part throttle is mush its too high.

Stall speed is relative to horse power so thats why its so key to build the entire car first, then do the stall right at the end after discussing with the builder.

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1987 IROC ww 99 LS1,TR224/112, STG2 heads ported by American Speed, P Gold springs, LS6 intake, SVO 30's, Ported TB, Comp Cromo Push rods, Katech Rod bolts, LS6 oil pump, T56, SW LT's, 8.8 hybrid rear 3.73, 275/40/17 MT ET streets, lots more
12.1 @ 112 mph 1.69 60'

89 R7U 1LE Players Challenge car all stock.


Wed Feb 04, 2015 3:05 pm
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Post Re: 3.08 vs 3.42
Seems like sound advice....

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1990 GTA
1987 TA (gone but not forgotten)
1976 TA (project)
1995 Z -28 Camaro
1982 Firebird ( my 1st )


Wed Feb 04, 2015 5:16 pm
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Post Re: 3.08 vs 3.42
I think worry about the converter once you decide what kind of can you're going to end up with. This is when dyno/track time is helpful. TC depends on can,gearing weight and torque curve. What's hood about TH350s is that its a popular tranny and TC are cheap for it.


Wed Feb 04, 2015 7:14 pm
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Post Re: 3.08 vs 3.42
As said above things need to match. Until you have a cam/heads picked out you cant get the correct stall

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Wed Feb 04, 2015 8:00 pm
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Post Re: 3.08 vs 3.42
Forgive the spelling..autocorrect,fat fingers plus no glasses..

To add -the job of the stall is to keep your motor at its sweet spot


Wed Feb 04, 2015 11:04 pm
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