I have a 68 RS/SS with a Tremec TR3550 5-speed. I was told it originally had an automatic tranny. Anyway, the rear end is a 12 bolt posi with an eaton 3-series and a set of richmond 3.42 ring and pinion gears.

I drive it mostly around town with few highway miles. I would like a good combination of performance and driveability. Might take it to the track sometime, but mostly just local car shows and being able to beat most of what I come up against at a stop light off the line.

I'm considering changing the rear axle ratio from a 3.42. Any suggestions?

Thanks

acceleration will be increased with 3.55 3.73 3.90 4.10 gears indeed. As far as beating all on comers...it will take more than gears to get that job done. TRACTION is always the big issue. If you use slicks at the drag track that equation is a no brainer. When you are street bound you will have to pick the right size tires and compound and actually drive the car carefully to get the most from it.

Gears will help... but only so much before suspension and tires traction gives.

3.73 is a very popular gear...3.90 might be the little advantage that most do not go for that you need over the next car on the road. Good luck with the choice. Jim

Your tr3550 has a 3.27 to 1 low gear, that adds up to 11.21:1 overall in first.
That puts you into second before the centerline in an intersection now, or before the 60 ft beams on the dragstrip.

I run a tko500 with that sam first gear, and am very happy with it with a 3.08 in the back, tho if I had 3.42 I'd probably be happy with that too.

Exactly what are you looking for that you don't have now?

Thanks for the suggestions. Just FYI everyone, the TR-3550 gears are:

1st
2nd
3rd
4th
5th
Rev
Torque Rating
TR-3550
3.27
1.98
1.34
1.00
0.68
3.00
425 ft lbs


Tires are P225/45ZR17

Nothing really "wrong" it just seems to rev out sooner than I would like. I may end up keeping the 3.42.

There is a small issue that there is no tremec speedometer gear for a 3.42 ratio so the speedo reading is wrong.

This guy is looking for some 3.42's.
http://www.camaros.net/forums/showthread.php?t=164987

I think the lowest you could go with the 3 series carrier is 3.08. That would still give you 10.07:1 effective first gear ratio. It wouldn't rev out so quickly but would still be good off the line.

The 3.42 is usually the most popular ratio. It's hard to find a good after market 3.08. If you can get a US Gear 3.08 the it will probably be good. Don't get a Richmond 3.08. They make more noise that you can cover up with open headders.

Nothing really "wrong" it just seems to rev out sooner than I would like. I may end up keeping the 3.42.

There is a small issue that there is no tremec speedometer gear for a 3.42 ratio so the speedo reading is wrong.

I wouldnt bother swapping - not worth the money- that gear and a O/D should be good. Maybe they have a speedo gear for a 3.31 or a 3.55 both would be close enough to live with IMO

Nothing really "wrong" it just seems to rev out sooner than I would like. I may end up keeping the 3.42.

There is a small issue that there is no tremec speedometer gear for a 3.42 ratio so the speedo reading is wrong.

I have a TKO600RR, 3.42s, and approximately 27 inch tall (245/60 15) tire, and my speedo is dead on (checked with radar). Is the 3550 that different, or do you have some odd rear tire size?

If the 3550 uses the same Ford speedo gears as the TKOs, if you tell us what size tire you have someone can guide you to the right speedo gear.

And as far as recommending a ratio change, we'd have to know more about the engine (specifically what the cam specs are and anything else that affects where the torque curve begins). I know with my mild BBC (over 400 ft-lb starting below 2,000 RPM), I can take off in 2nd (1.89 2nd) without lugging the engine on anything but an incline, so I could use a little less gear and am watching for a good set of GM 3.08s for my 8.5-inch. But if you have an engine that makes power and torque higher up the RPM range, then it might not like the overdrive gear at "normal" highway speeds.

If you decide to change I would be interested in purchasing the 3.42 gear set, If you like a 4.10 we could swap or change carrier assemblies. Keep me informed.
Steve

I found a used GM 3.07 gear for sale if you decide that is what you want.

The tires are Tires are P225/45ZR17 (about 24.5 inches tall) These are the speedo gears I am looking at:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=260324779036&viewitem=&sspagename=STRK%3AMEWAX%3AIT

Could I get one of them to work with my tires and the 3.42 rear end?

I plugged your setup into the calculator at Forte's ( http://www.fortesparts.com/SpeedoCalculator.htm )
and came up with you needing 19.3 teeth on the speedo drive gear.

That translates to the pink, 19 tooth gear in the ebay link, so you can just take that part number down to your local Ford dealer.

19 Pink C0DZ-B

Full part number (if the one above doesn't work) is C0DZ-17271-B.


For what it is worth, I ran the calc above with my combo and the results came out with the 18 tooth yellow gear, which is what I have. As I said, mine is dead on.

Just a reminder, as I see people saying lower when they mean higher and vice versa.

Going from a 3.42 gear to a 3.08 gear, is going to Higher gears. You are going lower numerically, but you are going to higher gears.

Going from a 3.42 gear to a 3.73 gear, is going to lower gears. You are going higher numerically, but you are going to lower gears. This can be also known as deeper gears. The lower you go, the faster the acceleration.

Example : The TR-3550 we are talking about, has a 1st gear of 3.27 and a 2nd gear of 1.98.

1st or LOW gear is a 3.27 2nd or HIGH gear is 1.98. Make sense ?

The 3.42 gears should be perfect as they are !

For 1st gear you want a total ratio of about 10. 3.27 x 3.42 = 11.18 ! any lower will be too low !

Higher gears like a 3.08 x 3.27 = 10.0716

With 11.18 effective in first, he's already up there above a muncie 2.20 first with a 4.88 rear! That's 10.7 And with 24.5" tall tires, No wonder first gear doesn't last long.

I've got 9.55 in my car and that is plenty for me with 26" tall tires. Knocking his down to a 3.08 rear would be nearly equivalent to a muncie 2.20 and 4.56 rear if it was on stock height tires.

Thanks guys, so it sounds like the 3.42 isn't such a bad ratio after all. I was thinking of changing for two reasons one was the speedo gear issue, but sounds like I can get pretty close. I could use some advice on the second reason.

The second reason I have the whole rear end out of the car is because about a week ago on a side road, I heard a bang, then a dragging sound. I pulled over and looked under the car. The weld that holds the passenger side leaf spring saddle to the axle let go! (Its a mono-leaf setup with t-nuts and no u-bolts)

So, after getting it towed home, I thought this was a perfect opportunity to address a few other rear end issues. One was the axle ratio we discussed, second is new shocks, leaf spring bushings, and changing from mono to multi leaf springs (and maybe some traction bars!)

Anyway, my question is what to do about the broken weld. I would like to just get a new axle, but I can't really afford that. I was planning to have the leaf spring saddles replaced with new ones for multi leaf springs. My local shop however said that since the axle tube is hardened steel welding to it is not reccomennded is that true? What do you guys think I should do?

Thanks

Find a new shop. If you are going to switch to multi-leaf springs, I would have multi leaf perches welded on, and use U-bolts !

Axle tubes are NOT hardened steel. They are mild steel, jut like the rest of the car. They can be easily welded. I have welded hundreds of axle tubes.