I need some input. I've got a stock 400sbc in my '53 and I'm using an 80's camaro 7.5" rear with 3.73's or a 70's firebird 8.5" rear with 4.55's. I plan on cruising the car regularly and maybe taking a few road trips. I have no idea on tire size yet, but most likely close to what was stock for the car. I have an m-21 with a hurst straight line shifter and I have a friend with a rebuilt 700r4 for cheap. Dollar for dollar the stick shift is cheaper and will get me going faster, but will it hurt my engine at cruising speeds with the gears I have? UPDATE post #13
Easy enough yes.... 4.55's will be tough even with OD. 3.73's would be liveable with OD. The M21 with a the 3.73's could be ok depending on the tire size chosen.
***uming a 25" tall tire the 3.73 with the M21 will give you 3259 rpm at 65, the 700r4 drops to 2216 rpm With the 4.55 the M21 is an unbearable 3975 rpm at 65 while the 700r4 is a decent 2705 rpm
Most of my life I was a 4-speed fan but running a 4.56 posi got old fast. Yes it was great from stop-light to stop-light but let's be honest those days of "spontaneous speed compe***ion" as the highway patrol calls it when they write the ticket are gone for the most part. (Ha HA - don't ask how I know that.) These days I prefer an automatic overdrive. That 400 of yours has plenty of low end torque and the 3.06 first gear of a 700-R4 has all the stop-light showoff I would need with the bonus of a quieter, more economical cruising speed in overdrive.
Wasn't the 7.5 camaro rear end originally designed for the 4 cylinder Vega? If I recall, it's only good for about 200 hp. If I were you, I'd consider pawning that 7.5 off to a member of the local mullet club for about $200, and using the $$$ to put "perfect" gear into your 8.5
I donno 'bout vega but my 80's El camino has lunched a couple with an uncammed mildly built 305, figuring i'll need some extras for when i get this warm 283 going in it
Go 700 and send the ol'leftover M21 my way. I'll dispose of it for you! I need and extra for project 2. Hehehehe
With a 3.73 and a 1:1 ratio m-21, the final drive ratio is 3.73:1. With a 4.56 and a 1:1 ratio m-21, the final drive ratio is 4.56:1. The 700r4 having an overdrive ratio of 0.70:1 would give you a final drive ratio of 2.61:1 with 3.73's and 3.19:1 with 4.56. The 3.06:1 first gear in the 700r4 and the 2.20:1 first gear in the m-21 could also be a deciding factor. I'd choose the 700r4 because of it's ability to get off the line and wind high quickly with the 3.06:1 first gear ratio. It is fun grabbin some close ratio gears though. Hope this helps
Thank you for all the input. I've been pondering the idea of selling off that 7.5" for a while, it came from the same car my original t-5 was plucked from (that trans didn't last long behind the 305). I think I'm going to start looking for a set of 3.73's for my 8.5" rear and call it a day with the m-21. I don't like any of the shifter options for the 700r4 and I don't like the fact that it will be difficult to hook up a TV cable when/if I drop my TR1X manifold on there instead of the 2-barrell. What size tires look good on '53 chevy/pontiacs and will work with 3.73's? I'm not very handy with metric tire size calculations and I don't know much about the old tire size ratings either.
With a stock 400 I would be looking for some 3.23 or 3.31 gears for that 8.5 rear. A stock 400 and an M-21 will pull that just fine. 3.73 would be too much cruise RPM for it. As to tires, a 225/70 radial is probably the same height as the 6.70-15's that came on the '53's. Hope this helps.
put the 700r4 in it and try it. i bet you will like it. dont worry about the rear breaking unless you plan on really hammering it.
update: someone stole the 4.55 8.5" housing on me I picked up a 2.41:1 ratio 8.5" rear from a firebird shortly after this happened. Is this going to be decent gearing with the M-21 and a 400 with a 2 barrel? I was planning on getting a 700r4 for $200 and using my smaller rear with the 3.73's but this 2.41 rear fell in my lap at the right time. It's a little stronger but the gearing leaves a little to be desired. I've never driven anything with a 2.41 rear before, what do you think?
I had a 2.41 in a Formula Firebird with a 400/th350. A little slow off the light but good highway cruising. If I remember right it was about 2,000 rpm at 70. If you gave me 2 new 700r4's I wouldn't use them. They usually break and never shift right. I know guys will argue different but I've had 3 break in different vehicles. I would use the 8.5 rear as is and if you don't like it swap the ring & pinion later.
That's what I thought, then I remembered I have a 650 horsepower monte carlo in the driveway that pulls wheelies. The delivery is just for cruising... but the 2.41 rear does have a posi if I want to break 'em loose.
Thank you for the insight, I couldn't find much in the search about 2.41 gears being usefull for much other than paperweights. I plan on a lot of highway cruising. Some trips may be in the 1200 mile range.
I have a Monte Carlo with 3.73 and a 700, very freeway friendly and the deep 1st gives you stop light performance, good combo while you save up for a TKO.
They do require a little more setup than a th350, I had several go bad before the trans shop gave up, turns out the tv cable adjustment is important. They aren't in business anymore. I want to use a 4l80e which doesn't need it, just a little converter box. Easy enough to hide, but costs$ up front.
yeah what he said! go with the T56 its like a 4 speed plus two overdrives! you can pick em up for around 800 used bob weir makes a bellhousing kit to make it work for around 600.00. ive had one behind a 500 horse 406 since 97. bullet-proof so far! 700r4s just plain **** behind anything with nads
My T700 ****** has a large number "14" on the p***engers side of the outer housing. What does this tell me??? Is it good or bad news??? <!-- / message --><!-- sig -->
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