A guy at work is telling me that if I go from the 2.73 rear end to the 3.55 then it will throw off the speedometer and that the transmission won't shift gears at the same speeds that it does with the 2.73. Is that true? Will I need to change a lot with the transmission if I go to the 3.55 rear?
87 Cougar XR7
You should only have to change the speedo gear to get it to read right. I'm not into AOD automatics much but I'd think that after the speedo gear change, the trans would shift like it should. I'm quite sure someone with more knowledge with the AODs will chime in.
The new ratio will cause the governer on the output shaft to be spinning faster at any given road speed, since it does it's job by centrifugal force, your shift points WILL be affected, but if you're anything like me you won't mind once you've driven it. They're generally be a few hundred rpm higher, especially on WOT upshifts. Ever had your foot on the floor and your AOD shifts to 2nd at like 4800rpm? That will go bye bye. I've swapped my 2.73 with a 3.73 and if I had to do it again, I'd go 3.55, additionally, I replaced the mechanical internals with those of a 4R70W, giving me the wide-ratio kit you can't get anymore (used the thinnest available forward clutch piston, too so that I could run 2 more steels and clutches) which also got me lighter stronger stamped steel parts to replace all the brittle and heavy cast iron parts, a 2 inch OD band, and more steels and clutches in the direct clutch. I've still got the AOD valve body, but I pulled the lower 1-2 accumulator spring, and enlarged a couple holes in the separator plate. The wide-ratio work brought my upshifts a little higher still. I can hit 2nd at 6500rpm on the WOT upshift, and I chirp the tires almost every time.
The transmission is affected by engine speed....these cars don't care what speed your wheels are turning.
In Short, if you change the drive gear in your trans to match the new ratio, you'll not notice anything...except the easier acceleration.
Accelerating faster than you could before will affect the governor, which will affect the shift point. Try and see. Output shaft speed correlates statically to engine speed, but when you change the ratio of the final drive, you cause the engine and, by proxy, the output shaft to be spinning faster at any given road speed, faster output shaft speed, more centrifugal force acting on the governor, higher shift point. This is a desirable thing anyway, at least with an aod, so it's not a problem.
This could explain why my TV cable would not work. The original vehicle my trans came out of is unknown. I got it out of an 89 mustang that was originaly a standard. Had to use a Locar cable to get the shift points right. My speedo is about 10 miles an hour off.
My crownvic with 3.55's and aod shirts from first at 35mph, with the 2.73's in my bird, it shifted at 42. You will gain a couple hundred rpm's on freeway crusing. Should get better city, worse freeway. Best I can squueze out of my wagon is 22 freeway.
When I went from 2.73 to 3.73 and was still auto, it did not negatively affect the AOD transmission in any way. As others have stated your RPM's in overdrive will obviously be higher than before. Your speedo will be off by quite a bit but all that requires is a speedo gear change.
Just swap to a 5 speed and you won't have to worry about it! ;)
What RPM is your 1-2 upshift at WOT? What was it with your 2.73?
My shift point is where ever I want, lol. I have a 5 speed now...I honestly can't remember how the shift points were affected on the AOD.
The point I was trying to make with the OP is that if he re-gears there will be no harm done to his AOD. I drove my car for 7-8 years with 3.73's and the stock 180,000 mile AOD with no problems at all.
I didn't say there would be problems, just that lowering the final drive would lift the max rpm where the trans will upshift at Wide Open Throttle. This is a good thing, because stock, most of them WOT upshift at less than 5000 rpm.
I have about the same set up. An 1986 Cougar with a AOD transmission and a 5.0 engine and 2.73 gears. How much will it effect your top end when you went from 2.73 to 3.55? Our freeways are set at 75 mph. Which means that half the traffic goes at 85 mph. I don't have an rpm gauge on my Cougar, so I have no idea what my rpm's are at 85 mph. If I were to go to 3.55 would that change about 5-10 mph?
This is kind of an interesting question. The answer may not be as straight forward as you might expect.
It's highly unlikely there would be a difference in "top end" with such a mild gear change with this combination.
Top end is a function of horse power as well as gearing:
There is a difference between being drag limited (the amount of horsepower is not adequate to overcome aerodynamic drag) and RPM limited (having enough horsepower to over come aerodynamic drag and mechanically top out the engine RPM).
A
stock S/O V8 Cougar is
horsepower limited on the top end with 2.73 gearing (we're talking a whopping 140 hp here). This combination will likely reach it's max MPH in 3rd gear (maybe even 2nd, depending on the current power of the engine as well as the AOD's acceleration killing 3rd gear lock up feature, which eliminates the torque multiplication of the converter).
The car may even slow down after pulling to it's top speed and shifting into the next higher gear (either 3rd or O/D) as it may fall so far out of the power band it no longer has enough torque to accelerate the car against the aerodynamic drag.
The 3.55 gear
will increase cruise RPM (there are plenty of calculators on line to get an approximate RPM per mile an hour change), but it won't limit this combinations ability reach it's max MPH or to maintain highway speeds, particularly in OD. It'll still pull enough MPH to get a healthy ticket on the highway!
A 3.55 gear will provide greater leverage to utilize the torque and HP the engine does have (shifts will occur quicker, putting the engine back in the "meaty" part of the torque band ), which provides quicker acceleration.
Guys have been swapping 3.55 & 3.73 gears into Fox bodied cars for three plus decades as a first modification because it offers two of the biggest clichés in hot rodding in just one step!: "seat of the pants" & "bang for the buck"
The 3.55 and 3.73 is a perfect street gear with an AUTO. Ford thought the same thing as they equipped the 3.55 with a 5 speeder on the Turbo Coupe. And the 3.73 on the auto Turbo Coupe. Hay who can argue with those BLUE OVAL ENGINEERS!!!
Sounds like 3.73 rear gears w/351 Cleveland, AOD transmission might be a good set up for me. Who knows, I might go with a 5 speed.
3.73 on the left and 2.73 on the right. I exclusively use ford gears on all my 8.8 builds. They are easy to set up and they are QUIET. Good luck
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A crush sleeve eliminator is mandatory.
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Everything has to be CLEAN and a good quality TORQUE WRENCH IS MANDATORY!!
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And you need dozens of shims to set it up correctly
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And all bearings AND RACES MUST BE REPLACED!!
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A special torque wrench is needed to set up the pinion pre-load
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Just posting for discussion on the change over!!
good pictures Tom! Good incite on this procedure, I am pondering changing gearsets in the future.
Thank YOU
Proper way to remove ring GEAR
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Remove the bolts and use a flat punch with the HOG IN A VICE. use a heavy towel to not mess the gear up if you plan on REUSING IT!!!
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Installing the ring gear is best dun with pulling it on. Here is a ring gear from my TYPHOON being installed with long bolts backed up with nuts. I thread the bolts in the ring gear all the way and use the installed back up nuts to pull the gear on the HOG. Some final drives have left handed threads so make sure when you remove the bolts you are in fact not tightening them!!! Then install the proper bolts with RED LOCK TITE and torque properly in a 180* pattern. Also make sure the ring gear and hog are free from nicks debree and gouges. Any dirt or material that winds up in between them will make the gear not sit flat together. And do not use oil or lubricants. It will fill the blind holes and you can break the bolts with HYDRAULIC LOCK UP.
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Also always use FACTORY BEARINGS AND SEALS!!!!
Here is a bearing from an axle that the customer bought a rebuild kit from the aftermarket. Note the lack of roller bearings compared to the factory one. I never use aftermarket or store bought bearings and seals. Other than GENUINE TIMKEN. Note the difference in the bearings and the number of rollers.
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Also always pack the back side of the pinion seal or any seal for that matter. It prevents the GARTER SPRING FROM POPPING OFF WHEN YOU TAP IT IN. Ask me how i know this. The grease holds the spring in place nicely. I think i INVENTED THIS!!!
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Also make sure you have the proper tools to install the races and seals. Never install a seal without the proper driver. Tapping around a seal with a hammer is a NO NO. Us the proper tools
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Good pic set. They taught us in school to pack the back of the seals with transgel, but I've seen lots of guys use vaseline for that.
Like I said, I always learn a lot from this forum. Thanks, for the pictures! I have only watched a friend work on the differential on my jeep, I've never done one yet.
Nice pics Tom, I was taught by a friend out in Chehalis Wa how to rebuild diffs. He did the vasiline trick as well. Like you, he was extremely buttstuff about cleanliness, proper tools, and proceedure. That rubbed off :D
Tom, this subject would make a terrific in-depth tutorial to share your vast knowledge. Thank you for the pics, could you post more about the proper setup, tools, etc? Perhaps even recommendations as to where one might obtain the necessary tools and consumables like shims, dial indicator, seal installation tools, etc.
Thanks!
Sure RANDYS RING AND PINION has tech support as well as tools and shims. You can access the web site by typing ringpinion .com. I probably set up more gears than most. Been doing it for many years. One thing you must understand is the 8.8 is a final drive that cant be spread. Case spreaders are a must on big axles but the 8.8 does not have the provisions. I made a home made one and it does not really work that good. The carrier shims must be selected and tapped in so it is a little more involved. Normally i do not use vasoline for garter retaining as it is to thin and does not hold as good as heavier grease. I actually have a 5 LB can of long fiber grease to hold cluster gear bearings and seal garter issues. Personally i think Vasoline is to thin but what the HECK!!! Thanks and i am glad you like the write up.
I have just one thing to add. If you do a lot of freeway, I think the 2.73 gear is perfect for a commuter car. Around town, I think 3.55's or 3:73's are better.
The overall drop in economy is probably close to loosing your overdriver gear, at freeway speeds.
Drive around in "d" instead of od if your thinking about a gear swap.
My wagon with 3.55's shifts first at 35, second 55-60ish, and not sure on third, probably over 80mph.
The birds/cats I've had with 2.73's shifted at 42, second at 65-70, and again, not so sure on 3rd, for wot automatic shifts.
In a 75mph zone, the wagon requires a bit more throttle, and I would guess 600-800rpm's higher engine speed. My bird, if I drove 62mph over a 50 mile freeway commute, I would average 30mpg or higher. If I did 77mph(highway was 75mph, 77 was where the car liked to sit), mileage dropped to 25-27ish. If I did 75mph in drive(simulating 3.73 gears), I averaged 22mpg, which is what I get out of my wagon with 3.55's.
I hated doing less then 75mph though, because I would constantly get passed and have cars ride my rear end. 62mph was a good speed because then I could just cruise with the big rigs, and pass them on the uphills and overpasses.
First thing is shift points are determined by line pressure and throttle opening. When line pressure equals throttle pressure the tranny shifts!!!
With that here is the tables on MPH @ RPM With a 28" Tire and a .68 OD!!!
2.73 @ 80 MPH 1782 RPM
3.55 @ 80 MPH 2317 RPM
3.73 @ 80 MPH 2435 RPM
Drive around in "d" instead of od if your thinking about a gear swap. NOPE!!!!
In drive the transmission would not lock out the converter adding another 300-350 RPM to your thinking!!!
So going to a 3.73 would increase mileage overall other then on the highway that is a given. But the overall fuel usage would be comparable
Engineers are designing transmissions with more gears to get better mileage. But with the parameters of the transmissions you are talking about just dont make it. So either stay with 2.73 which in my opinion are ATROCIOUS for overall performance and loss of acceleration and overall performance. Or change out to a 3.73 and bring that engine in to it's peak performance RPM BAND. YOUR CHOICE!!!
Using drive instead of OD 28" tire
@80 MPH 3.55 3708 RPM
@80 MPH 2.73 2921 RPM
this is one to one no lock up!!!
In the AOD the direct clutch engages solidly to the torque converter housing (lockup) so whenever you shift into 3rd the connection to the motor is solid. And since 4th is just the further application of the OD band, 4th is a solid connection as well. With my setup, my WOT upshifts are about 6200 rpm or so. Before the gear change and the trans work my WOT upshifts would come around 5000 rpm.
My car has 3.73 and a .7 overdrive (a result of the wide-ratio mod), and I've got about 3000 rpm at 80 in 4th. I've got the full digital cluster, so that's as precise as I can get.
According to B&M the converter they sell eliminated LOCK UP. I am not an auto guy by any means but releasing lock up is accomplished how in an AOD. Once again i am not an auto guy but their must be a way for lockup to disengage when applying the brakes. Please advise as once again i do not excel in auto transmissions. 6 speeders is my thing. With a 6 speeder i can run gears as tall as 4.88 on the street if desired. Just saying!!
Note driving an AOD as i remember had a distinct lock up. But it has been a very ling time since i have driven one. I will take you word for it FOE. Either way a set of 2.73 gears are best used as an anchor for a DINGY.
A shop I worked at years ago had a horseshoes pit in the back they made with a pinion gear welded to a pipe and driven into the ground. The owner said he used the ring gears because in his book close was good enough for hand grenades, but didn't buy into the idea that close was good enough for horseshoes.
As far as the AOD goes, they can't lock in 1st and 2nd, and you're not likely to stop in 3rd or 4th. once you put your foot on the brake and start slowing, you downshift to an unlocked gear before even getting close to stopping. AOD, AODe and 4r70 are the only trans I ever heard of that are like this, anything else has an electro-hydraulic lockup clutch.
I'd love to have the cash to have a 6M, or even a 6A, I'd even like to have the money for a 5M swap. Unfortunately I'm stuck with a column shifted slushbox. All I can do is make what I have work as well for me as it can.
Just spoke with our Auto tranny guy. Here is what he said True fourth is locked up except the electronic units. But other than the electronic units third gear is as follows according to jim
Third gear is 70% locked, fourth is 100%.
Thanks FOE i did not know this. That is crazy how third is a slipper and was told by jim never keep it in DRIVE fore extended periods of time. The 30% slip creates to much heat according to JIM my tranny guy. Live and learn. Slush boxes are not my thing. Just me Thanks i learned something today about the AOD. It has 30% slippage in drive.
He also told me he has converters without lock up. Strange as he tells me in third the tranny is in fact slipping to an extent and looses 30% He also told me the tranny is not that strong unless it is built to the hilt. Single piece input shaft and no lock up is mandatory according to HIM.
The direct clutch in the AOD and AODe is junk. One of the reasons I put a complete 4R70w stack in mine. I ended up with a total of 6 additional clutches and steels AND lighter and stronger internals, which I'm thinking is good for somewhat lower drivetrain losses. My original direct clutch and it's cast iron drum were reddish black from all the heat when I pulled it out. Kind of like a brake rotor that's been really really hot.
Good info foe!!!
I didn't even know AODs had a converter clutch. I thought that started with the AODE. GTK. 2.73 is just too high. Even if you drive on the highway a lot, the in town mileage just sucks so bad you would not gain anything with 2.73. One needs to have at least 3.25, but 3.55 is even better. From what I hear, 3.73 not too bad either.
They don't, at least not in the converter, the inner shaft(3rd & O/D) is splined directly into the front hub of the converter... The non-lockup converters for dual input shaft(aftermarket) have the inner shaft splined into the turbine... Those cannot be locked, period...
If you have a engine with a slightly rumpy cam, no less than 3.73 is mandatory, at least that's my opinion and is what I have in my Bird(stock gears for '87 & '88 TC automatic)... If I ever change gears it would be at least 4:10 & maybe 4.30...
As far as need this, have to have that, I have nine years, approx 35K mi(additional, already had 45K when I bought it), 700 drag strip passes(some with a 150 shot) on a STOCK AOD with only a Trans-Go kit and hardened input shaft as modifications(I did bust the orig shaft)... Internally, they aren't as fragile as some lead us to believe...
BTW this trans is from a '89 Super Coupe and is supposed to be one of the best versions, but that's only because it has the larger "A" O/D servo and 7 tooth output shaft... Some of the F & E Series versions used a wider O/D band but I ain't racing in O/D...
BTW #2 I've only used Type F fluid in it since it was installed...
Thanks for the clarafication. I understand now.
If you have much of a rumpy cam, gas mileage is not much concern. In that case 3.73 would be mandatory. It all depends on how you drive the car. Track time or highway time. I wouldn't put 4.10 if it is mainly driven on the highway. For this guy's engine, I would put 3.73. That would be just awsome.