Highest (lowest numerical) rear gears you've seen?

[55Test]

Seems like stupidly tall rear end ratios were a thing back in the late 70's and early 80's. I was just reading a brochure for the 1982 AMC vehicle lineup and some of those were available with a 2.21 rear end! Why did parts like that exist? I suppose it could have possibly saved some fuel on perfectly flat ground at cruising speed but I would have thought the engine would be working that much harder trying to get the car moving, not to mention having to deal with hills. Must have put a lot of strain on torque converters. My old 93 Crown Vic had a 2.73 which was fine on flat ground but would get shifty on long hills on the highway, moreso out in the country at speeds around 40-45 mph. I just can't imagine having a 3600 pound car with 120 hp and a 3 speed automatic driving in hilly terrain with rear gears so tall

 

[SteveSRT8]

My 78 Firebird Trans Am had a 400 cubic inch V8 with 185 hp and a 2.56 rear gear.

Went through the traps in second gear. Big V8's love to work hard so tall gearing worked well in the days before overdrive became common

 

[skyactiv]

I think 2.41 was common on mid-late -70's large GM land yachts with large engines.

 

[DriveHard]

Rear end ratio is only one part of the equation. It is the OVERALL ratio from the engine to the tires that matters. If the gears in the transmission are super low to offset the high read end ratio, then it is a wash. The better question is what is the highest overall ratio you have ever seen? I think today's cars with 8+ speed transmissions are running overall top gear ratios much higher than in the 80's.

 

[SHOZ]

Could be worse and have too low of an overall ratio. My FIL had a 60's International Scout that top speed was around 55 mph due to gearing. I had Triumph TR 7 4sp that would top out in 4th gear around 110 mph per red line of 6500 rpm.

 

[Chris142]

My 79 LTD had 2.2x rear gears. On the other hand my peterbilt had 6.14 gears in it. Every gear after 4th and direct was an overdrive.5th and over was basically Basically 4 overdrives.

 

[Chris142]

Originally Posted By: SHOZ
Could be worse and have too low of an overall ratio. My FIL had a 60's International Scout that top speed was around 55 mph due to gearing. I had Triumph TR 7 4sp that would top out in 4th gear around 110 mph per red line of 6500 rpm.
The Scout could be ordered with 4.88 gearing. My 68 scout had 3.73 and my 1210 pickup had 4.30. The 4.30 was actually pretty good with 33 inch tires.

 

[SwampSurvivor]

Here's a question - why do we have overdrive transmissions?

Why have a 4 speed Overdrive with lower (higher numerical) axle ratio instead of a 4 speed direct with higher (lower numerical) axle ratio? Overall ratios would be the same but the transmission would be more simple.

I may have calculated wrong, but with the bigger tires I have changed my effective gearing to somewhere around 2.9. Jeep 4.0L engines just can't lug like that.

Going the other direction I know a few people who put 5.38 gears in Jeeps. Between that and a transfer case doubler, talk about gear reduction!

 

[440Magnum]

The lowest I've personally seen were civilian 80s Chrysler M-bodies (Diplomat / Gran Fury / 5th Avenue) that were something like 2.26:1. Chrysler didn't have a rear-drive 4-speed (O/D) transmission at that time and in the Iacocca years there was exactly no budget for any new rear-drive tech, so they developed the A999 version of the A904 3-speed. It had a "deep" (higher numerical ratio) FIRST gear so that they could put a 2.26 rear end out back, effectively turning 3rd (direct) into a pseudo-overdrive and using convertor slip and the deep first gear to keep the cars from being complete and total pigs off the line (they were still painfully slow). But that setup could return mid to high-20s MPG in a fullsize 3-box v8 sedan with a very reliable 3-speed automatic setup and a brutally strong ring/pinion set- I've seen a lot of them with over 200,000 miles and no transmission work at all (a far cry from Chrysler front-drive automatics of just a couple years later!) So it was making the best of a bad situation. The cop-spec M-bodies could be had with that same deep first gear and a 3.23 rear end, which actually made them launch surprisingly fast for only ~150 horsepower.

 

[supton]

Originally Posted By: Miller88
Here's a question - why do we have overdrive transmissions?

Why have a 4 speed Overdrive with lower (higher numerical) axle ratio instead of a 4 speed direct with higher (lower numerical) axle ratio? Overall ratios would be the same but the transmission would be more simple.


My recollection was because of design reuse, the parts back then got weak(er). I think the ring gear got too thin, as they couldn't just (quickly) redesign for the now much-larger pinion (couldn't kick the ring gear out further from the diff case etc). Also, the driveshaft and u-joints have to sized to handle more torque, as the rear gears aren't contributing as much as before, for torque multiplication. I also suspect that the transmission may get too larger, since it has to size its gears to handle the output torque. Thus, everything was a balance, looking for the best compromise. OD and lockup (since what red blooded American buys stick?) meant the older gearsets could be reused.

But technically it'd be lower loss in top gear if it was direct drive. Then again, today, since we have many many more gears than before, there may be some wisdom (at least in trucks) to have a couple of overdrives, so that when the engine is actually working, it's in a direct drive application with the least losses.

 

[440Magnum]

Originally Posted By: Miller88
Here's a question - why do we have overdrive transmissions?

Why have a 4 speed Overdrive with lower (higher numerical) axle ratio instead of a 4 speed direct with higher (lower numerical) axle ratio? Overall ratios would be the same but the transmission would be more simple.


I used to have the same question, and the answer I was always given was "packaging." To make 1st, 2nd, and 3rd gears "low" enough (numerically high) to match the same overall ratios with a"tall" (low numerical) rear end as you have with a typical O/D trans and more normal rear end, that means that either an input gear in the transmission has to be really, really tiny and therefore prone to wear out, OR some driven gears have to be too large to fit in the existing cases and transmission tunnels. It all "fits" easier if you put some O/D in the transmission and then offset it with a higher ratio in the rear end. And you hit a similar problem in the rear end- not all rear end housings can take a pinion big enough to get much below 2.7:1 or so, either. At least in the case of a rear end, a big pinion (low numerical ratio) is typically very strong.

Furthermore, its about the same amount of gear friction loss either way. Yes, the direct gear is always a *little* more efficient, but its very very small numbers. The one noticeable downside to a lot of overdrive and then a high numerical rear ratio is that driveshaft speed can get really high, and so the U-joints and driveshaft have to be light, tight, and well-balanced.

 

[ShotGun429]

My 1980 Mustang V8 (255") Cobra

I bought new (still have it) has a 2:26 rear end ratio, C-4 automatic (Non overdrive) Not fast at all but gets great highway mileage, nearly 30MPG.

 

[FlyNavyP3]

Lowest gears in a commercially purchased vehicle (non medium or heavy duty) I've worked on was my Grandfathers old Dodge 1972 W300 225 Slant 6 Granny Gear 4sp Dana 70 F/R with 7.17 gears. It would pull absolutely anything. Just not fast.

 

[Robenstein]

My Nova had a 307 small block with a 2.56 rear end when I got it in 1999. Minivans were faster than that.

Swapped it out with a 1970 LT1 with brodix heads and a 3.42.

 

[CarbonSteel]

There were GM cars with 2.29 ratios (I saw a 1980 Firebird with one) and my 1980 Trans Am had a 2.41 gear in it. I deep-sixed it in favor of a 3.23 posi-unit from an earlier model T/A.

 

[SubieRubyRoo]

2006 Odyssey has like a 4.46 final drive, a little higher than Subaru's 4.44. It's the highest I've seen.

 

[SEMI_287]

My 93 Z28 auto had a 2.73 and my 300C has 2.82. A 2.29 is ridiculous!

 

[spasm3]

I had a 76 buick regal with the turbo 350 trans and a 2.56:1 .Shifted into third at 90mph at wot.

 

[TiredTrucker]

Originally Posted By: SEMI_287
My 93 Z28 auto had a 2.73 and my 300C has 2.82. A 2.29 is ridiculous!


Think that is ridiculous? Try that the commercial heavy truck drive axle OEM's are now offering 2.28 ratios in axles rated for 40,000 lb to be put on commercial semi trucks. I have 2.64 Meritor diffs in my semi truck. I just looked up on the Meritor axle website and saw they are offering 2.28 now. Lowest I had seen before was 2.47. Those 2.28's obviously are being offered for those that are buying into the major engine down speeding concept. Some of those setups have 13L engines only turning 1100 RPM under full 80,000 lb load. Wouldn't work at all for what I use a commercial truck for. I'll leave that kind of nonsense to idiots who sit in cubicles and spec fleet trucks and don't even know how to drive them across the parking lot, let alone with 46,000 lb in the trailer and dealing with major grades.

 

[02SE]

The tallest gearing I have experience with in a rear end, is in the 1.6:1 range. This is in a blown fuel LSR Streamliner some friends run at Bonneville.