The Stovebolt Site Forums The Shop Area Engine Shop 2.41 rear end t5 transmission will it ever get rolling

It turns out the 79 firebird rear end I have is 2.41. The t5 has
3.97 1st, 2.34 2nd, 1.48 3rd, 1.10 4th, .72 5th. From what I can tell it should take forever to get off ot the line but should top out at the speed of light. All of this is behind a stock 235 so maybe just short of the speed of light. 90% of of my driving is at 55 mph on a straight flat road. I am hauling light loads of lumber every now and then. About 6 times a year I drive 200 miles on interstate at 70 mph. I think I would be better off with at least a 2.73. Gas mileage is a high priority, I am looking for an old man driver not a race truck. Should I Bother with the 2.41 or is it not going to be as bad as I think.

Thanks Neilroy

Over gearing can kill milage as it will use too much throttle to maintain speed...look for a diff in the 355 ot 370 range...doc

doc41 has the right idea those 2.41s are too high 3.00 to 3.55 with a 28" tire would be great 3.73 if you have taller tires.

This site will help with gear ratios and speeds:
http://www.onlineconversion.com/bigger_tires.htm

What is your tire overall diameter?

My guess is that you could not pull the 2.41 rear and an OD with the 235 unless a strong tail wind with a good down hill.

2.41 could be about right if you had the SM420 4 speed, then you have a low gear to start with, and the 2.41 is effectively an overdrive once you get to 4th.

Grigg

I tried to run a IROC-Z 3.08 with a .72 T5 in my 235.....worked great as a 4 speed but wouldn't pull in 5th gear. I switched to an 88 Camaro 3.42 (62" wide) from behind a 2.8L V6 with a 28" tall tire and I cruise effortlessly at 70 mph in 5th@2000 rpms and still has plenty left. Can drop down to 45 mph in 5th gear and accelerate with traffic without needing a downshift. If I need to pull a trailer I can run at 65 mph in 4th gear at 2600 rpms. If most of your driving is at 55 mph a 3.55 or a 3.73 would also be good options.

Dave

Using the tire diameter calculator at angelfire.com looks like 205/75/15 which would be close to stock works out to 27.1". I will assume that it would be cheaper to find a new rear end than to swap out the gears. It looks like 3.42 to 3.73.

thanks neil

Swapping for a 3.42 or 3/73 would be cheaper for the diff. However, the third generation Camaros/Firebirds (62") are 5 bolt and you may/will be faced with buying rims. I scouted the yards for some used 15" rims with 4" backspacing and found they are few and far between let alone finding 4 matching rims.

Secondly, the Camaro diffs have 2-5/8" axle tubes, not the standard 3" so you have to add some straps if you want to use the 3" U-bolts. The U-bolts/perches are available from the trailer section at most Tractor Supply stores. The up side is that they are plentiful in the 3.42's behind the 2.8 V6's.....I couldn't find a 3.73.

I'm running 255/70/15's on the rear and 235/70/15's on the front with 15X8 and 15X7 rims respectively, and have no clearance issues with a 5 bolt front disc conversion.

I really love my gearing setup as most of my driving is on the open road at 4 lane speeds. However, it was by no means cheap when you consider you're going to be springing for 4 new rims. Just thought you should be advised of some of the issues involved with using the Camaro/Firebird diffs.

Dave

I feel better now. 65 degrees, not a cloud in sight in East Mississippi. Dropped the top on the 1960 mga and drove around in the country, contemplating my rear end. I guess maybe I should say the truck's rear end. I am not sure which I will be concerned about if my wife gets wind that I am about to spend more money.
I measure 61" mounting surface to mounting surface on that 1979 firebird. It looks like that year they also had a 3.23 and 3.42.
it has a 5 bolt 4.75 bolt pattern. Will that extra inch make the rim quest any easier? Maybe I should have kept the 15" GTO rims that were on it. I didn't think they were good for the truck. I sold them and that leaves me $75 in the hole on the rear end.

Going with the Camaro/Firebird 2nd or 3rd generation diffs, along with the 5 lug disc conversion on the front, saves you from having to spring for the $100+ special vendor roller bearing sets for the front and lets you use a wheel bearing/rotor/hub that's readily available from your local parts house, but you wind up needing the 4" backspacing.

I liked the idea of getting a diff which was readily available, with lower mileage, and being able to get replacement parts locally, without having to wait along the side of the road for a 5-7 working day delivery from UPS.

In your case you might be better off to scout up an open drive diff from a later model pickup and be able to use some available 6 lug rims. Some of the other guys who have done this swap might be able to offer some better suggestions. My experience is limited to what I had to do on my 54 to get her operational.

Dave

Well if your really after gas mileage - once you put a bit more gear in - say 3.08/3.23 the biggest jump will be to convert to TBI.

If your running the OEM carb your can expect 15% increase in mileage by converting to TBI. 90% of the needed parts are readably available in the wreckers.

I think worse. You'll stall at every stoplight and you'll kill the 235 if you're loading it.

Found a 3.42 rear end from a 78 firebird that is 61" wide and life looks better. the TBI conversion is on the menu. Thanks for all of the info guys.