will new gears throw off speedo??

matteo

Registered User
im putting 3.73 gears in my car that currently has 2.73s (i think), i would assume this might throw off my speedo or something. will it? and if it does, how do i adjust it to correct the problem? thanks.
 
You don't want 3.73s. I know you've prolly heard this a lot but you should sit down and do the math and see why...

Compare the T-56 and M5R2.

T-56 1st ratio is 2.66
M5R2 1st ratio is 3.73-ish on '89-'93, and 3.42 on '94-'95

That's a big difference. Now then, say the T-56 car has a 4.11 rear gear ratio, so the total torque amplification in 1st is roughly 10.9. If you even put a 3.55 in your 5-speed the tq amp will be about 13.2. You WILL NOT get traction without wrinkle-wall slicks, and if you do you'll be shifting into second at 15 mph. Not a worthy thing to pursue. With a 3.27 and your tranny it's STILL nearly 12.2. I would not even consider any gear numerically higher than 3.27 for drag racing on an early model 5-speed.

Just my $0.03. ;)

NOTE: I used the T-56 because of it's popularity and it is often used with steeper gears such as 3.73-4.30.

If you change gears your speedo will be inaccurate by a little bit, depending on which gear you go with. To get the speedo on the right track again you'll need to buy a corresponding speedo gear.
 
Last edited:
David Neibert said:
What he said.....go with 3.27s and a 21 tooth speedo gear.

David

I have 327 and can't imagine wanting a lower gear.First is a little short w/ 327s so I went to a 235/60-16 to get a little back.
 
DriftingThunder said:
You don't want 3.73s. I know you've prolly heard this a lot but you should sit down and do the math and see why...
I understand (and appreciate) your concerns, but this isn’t my daily driver it’s just a fun car to dick around with. Turns out the junk yard differential that I got to put my 3.73s in had 3.55s in it. So if I find 3.73 is too much, I’ll drop down some. But I won’t know if I’ll like the 3.73s unless I give it a shot, right?

So since I’ve already bought the gears, what speedo gear do I need for 3.73s, where can I buy one, and where does it even go? Is the gear around the speedo or the diff or somewhere in between?
 
matteo said:
I understand (and appreciate) your concerns, but this isn’t my daily driver it’s just a fun car to dick around with. Turns out the junk yard differential that I got to put my 3.73s in had 3.55s in it. So if I find 3.73 is too much, I’ll drop down some. But I won’t know if I’ll like the 3.73s unless I give it a shot, right?

So since I’ve already bought the gears, what speedo gear do I need for 3.73s, where can I buy one, and where does it even go? Is the gear around the speedo or the diff or somewhere in between?


I love people that don't listen,they get to do stuff 2 or 3 times.
 
matteo said:
I understand (and appreciate) your concerns, but this isn’t my daily driver it’s just a fun car to dick around with. Turns out the junk yard differential that I got to put my 3.73s in had 3.55s in it. So if I find 3.73 is too much, I’ll drop down some. But I won’t know if I’ll like the 3.73s unless I give it a shot, right?

So since I’ve already bought the gears, what speedo gear do I need for 3.73s, where can I buy one, and where does it even go? Is the gear around the speedo or the diff or somewhere in between?

Since you have 3:55's, try them first. There are a few 5-speeds running 3:55's. Plus trying them would only cost you some of your time. If you still want more then you could put 3.73's in your 2.73 pumpkin. Then sell the 3:55 pumpkin. This would also save you a few bucks. Just a thought.

Michael
 
j rick kirby said:
I love people that don't listen,they get to do stuff 2 or 3 times.
There’s no reason to talk *****, I'm not telling you to put the gears on your car, I want to put them on MY car. And I appreciate and respect the SC guru’s opinions, that’s why this is the first place I go with questions. But this is my first car that I’ve bought just to have fun with and I'm teaching myself how to work on it while I go. And if I make mistake and if I should have listened, oh well, lesson learned I’ll take it back apart. And isn’t that what it’s all about, having fun working on your car? Not being a dick on forums.


And Michael, that’s a good idea, I should have thought of that. Maybe I’ll put the 3.55s on first, and go from there. Thanks for your help.
 
matteo said:
There’s no reason to talk *****, I'm not telling you to put the gears on your car, I want to put them on MY car. And I appreciate and respect the SC guru’s opinions, that’s why this is the first place I go with questions. But this is my first car that I’ve bought just to have fun with and I'm teaching myself how to work on it while I go. And if I make mistake and if I should have listened, oh well, lesson learned I’ll take it back apart. And isn’t that what it’s all about, having fun working on your car? Not being a dick on forums.


And Michael, that’s a good idea, I should have thought of that. Maybe I’ll put the 3.55s on first, and go from there. Thanks for your help.

Thanks

I just purchased a 3.27 pumpkin to put 3.77's in it. I have an auto.
 
90blkbrd said:
Thanks

I just purchased a 3.27 pumpkin to put 3.77's in it. I have an auto.
what i want to know is how you pulled 14.6s with only those mods listed. i have all that and more (well i dont have my IC fan on yet) and i was nowhere near your time. i did have bald tires, but that wont make up for an entire second.
 
Most of the people on here with 3.55 gears have the late model M5R2 tranny with the wider first, second, and third gear ratios, it nearly evens out. I was considering a 3.55 for my car, but I decided against it partially because I already have a 3.27 ring and pinion in my garage.

90blkbird can run 14.6 with those mods in part because his car is an auto I would think.

The previous owner of my car calimed 14.2 @ 96 but I have yet to try it at the track myself. Even so, I don't think I can go that fast. I'd be happy with 14.5.
 
matteo said:
There’s no reason to talk *****, I'm not telling you to put the gears on your car, I want to put them on MY car. And I appreciate and respect the SC guru’s opinions, that’s why this is the first place I go with questions. But this is my first car that I’ve bought just to have fun with and I'm teaching myself how to work on it while I go. And if I make mistake and if I should have listened, oh well, lesson learned I’ll take it back apart. And isn’t that what it’s all about, having fun working on your car? Not being a dick on forums.


And Michael, that’s a good idea, I should have thought of that. Maybe I’ll put the 3.55s on first, and go from there. Thanks for your help.

The spedo gear goes in the same place as just about any other car around, the trans tail shaft. Just so you know you just can't drop a set of gears in a pumpkin and be done with it. They will need to be set up properly, if not they will howl or worse, break. A shop will usually charge about $200 to set up a pumpkin if you bring them the parts.

Jeff
 
J57ltr said:
The spedo gear goes in the same place as just about any other car around, the trans tail shaft. Just so you know you just can't drop a set of gears in a pumpkin and be done with it. They will need to be set up properly, if not they will howl or worse, break. A shop will usually charge about $200 to set up a pumpkin if you bring them the parts.

Jeff
trans tail shaft, got it. thanks for the info.

I’ve got a couple ford technicians putting it together for me at work in their free time. It helps to have friends who work at ford otherwise I’d never be able to keep this car running on my own. :eek:
 
matteo said:
what i want to know is how you pulled 14.6s with only those mods listed. i have all that and more (well i dont have my IC fan on yet) and i was nowhere near your time. i did have bald tires, but that wont make up for an entire second.

I got lucky, I have what is called a factory freak. I was also running 10 year old bald tires when I ran the times.
 
FYI no one makes a 373speedo gear for 5spd. I'm going to be doing a 5spd swap on my sc which already has 373s in it for the auto but I'm gonna give it a shot and if I don't like it probably gonna do 355s
 
matteo.....have you ridden in an SC with 3.27 in a 5 speed? Or have you even been in an SC that taller gears besides the factory setup? I would suggested finding someone that has 3.27, and have them take you on a ride, its plenty enough gears for the 5spd! Trust me, I'm running 3.27's and it's a big jump from 2.73s! 3.55 or 3.73 are way too tall IMHO for a 5spd.
 
FearThis SC said:
matteo.....have you ridden in an SC with 3.27 in a 5 speed? Or have you even been in an SC that taller gears besides the factory setup? I would suggested finding someone that has 3.27, and have them take you on a ride, its plenty enough gears for the 5spd! Trust me, I'm running 3.27's and it's a big jump from 2.73s! 3.55 or 3.73 are way too tall IMHO for a 5spd.

Calvin,

Several people have already tried to tell him that...but he doesn't want to hear it because he has already bought the 3.73s.

David
 
Anyway, here's the link to the speedo gear calculator on this site:

http://www.sccoa.com/faq/speedgr.html


If you feel like pulling the tailshaft of the trans., there is a 7 tooth M5R2 drive gear available from the F-Series applications. I don't recall the p/n off the top of my head, sorry.


cheers
Ed N.
 
David Neibert said:
Calvin,

Several people have already tried to tell him that...but he doesn't want to hear it because he has already bought the 3.73s.

David
Yeah....I see! Amazing that a wealth of knowledge gave great information, but since he has 3.73, he thinks its going to be a good setup.....Oh well, we tried to tell him!
 
Back
Top