speedo gear nightmare....what gear should I have?

killer5.0 · May 3, 2010

bought one already...21tooth from cjponyparts (should be red)...and i think they sent me the wrong one..its white 23tooth..speedo is still off by about 10mph...plus the bolt broke off in the housing so now i have to have the crossmember dropped to lower the rear so i can get a drill in there to drill it out and re-tap it...PB blastered it and let it soak to...still wouldn't budge here is what the car has for mods and i will be changing tires in a few weeks i will post the new sizes will it work for both tire sizes?

BBK headers, h-pipe to borla dumps (b4 rear axle)
BBK 70mm Throttle Body
BBK 70mm MAF
BBK CAI (fendermount)
3:73 gears
F303 cam
GT40 Upper and lower intake manifold
BBK FP regulator (at 38lbs at idle)
19lb injectors
200a alternator

245/45/17 currently
275/40/17 and 255/40/17 new tires
thanks

Beasty306GT · May 3, 2010

Speedometer Gear Application Guide
Mustang Speedometer Gear Application Guide
Ring & Pinion Speedo Gear
1983-89 Mustang Manual 5-Speed
3.08 18 Tooth
3.27 19 Tooth
3.55 20 Tooth
3.73 21 Tooth
4.10 23 Tooth
1990-93 Mustang Manual 5-Speed
3.08 20 Tooth
3.27 21 Tooth
3.55 23 Tooth
1984-89 Mustang Automatic AOD
3.27 19 Tooth
3.55 20 Tooth
3.73 21 Tooth
4.10 23 Tooth
1990-93 Mustang Automatic AOD
2.73 19 Tooth
3.08 20 Tooth
3.27 21 Tooth
3.55 23 Tooth
1996-98 Mustang Cobra Manual 5-Speed
3.27 19 Tooth
3.55 20 Tooth
3.73 21 Tooth
4.10 Speed Cal
1994-98 Mustang Manual 5-Speed
Except 1996-98 Cobra
3.08 20 Tooth
3.27 21 Tooth
3.55 23 Tooth
1994-98 Mustang Automatic AOD
2.73 19 Tooth
3.08 20 Tooth
3.27 21 Tooth
3.55 23 Tooth

killer5.0 · May 3, 2010

thanks but i dont see my application on the chart...1993 5.0 5spd manual. i see 50resto offers a kit with the speedo gear and a drive gear for $25...they say its the best setup for the t5 with 3:73's. anyone know if i need a tailhousing gasket for that since it would have to be removed?

ReefBlueHatch · May 3, 2010

I don't wanna rob the the thread, but I have a question...
I just ordered 3.73s and is the the 21 tooth correct for me?

killer5.0 · May 3, 2010

called 50resto...they said to change the drive gear is a hassle and the 21 tooth is the closest ill be able to get without it and that it will bring me to about 7mph off...he said any bigger gear it will start to strip teeth off...anybody have any other ideas? thanks

Mustang5L5 · May 3, 2010

That's because there isn't a correct application for the 1993. Best you can do is the white 23 tooth and that will be off some.

Ifnyou truly want an accurate speedo, you ned to replace the drive gear with a yellow 7 tooth drive gear and then run a red 21 tooth speedo gear.

But 90-93 have a black 8 tooth driven gear, so the white 23 tooth is the one to get.

ReefBlueHatch · May 3, 2010

Crap! I better call LRS in the morning and change the speedo gear from red to white before they send out my order.

killer5.0 · May 3, 2010

have the 23 tooth in currently...just ordered a 21 tooth b/c thats what 50resto said was the highest i could run without risk of stripping teeth?

Mustang5L5 · May 3, 2010

That is true. The 23 tooth tends to strip as the teeth are thin.

Is your trans original? If not, look inside at the speedo drive gear and check if it's yellow or black

Yellow -21 tooth
Black -23 tooth

But 23 tend to strip

killer5.0 · May 4, 2010

it is the original trans (so far as i can tell) and it had a black speedo gear in it...but i only counted 20 teeth on it?

LRSjmac · May 4, 2010

If the trans is original to the car it will have a greenish/yellow 8 tooth drive gear & it sounds like this is what you have if you are still 10mph off with a white 23 tooth driven gear.

83-89 T5 has a yellow 7 tooth internal drive gear
90-95 T5 has a greenish/yellow 8 tooth internal drive gear
FRPP M-7003-Z T5 has a yellow 7 tooth internal drive gear

The black 6 tooth internal drive gear was originally used in the 4 speed tranny, but works great to exactly correct for 4.10s when used with a pink 19 tooth driven gear.

Without changing the internal drive gear on a 90-93 T5, the 23 tooth driven gear is the closest you'll get for 3.73s, but you'll be 10mph off.

While the 23 tooth gear does have a higher failure rate when used with an 8-tooth drive gear, most of the time a worn speedo cable is to blame.

killer5.0 - If you want your speedo correct, the only way is to swap out your internal drive gear to a yellow 7 tooth unit & use a red 21 tooth driven gear.

killer5.0 · May 4, 2010

i just ordered a red 21 tooth..i wanted to do the drive gear but you have to remove the tailhousing of the tranny if im not mistaken and its pretty in depth...i was told bits and pieces of the internal parts come out with the tailpiece making it a pain...is that correct?

LRSjmac · May 4, 2010

killer5.0 said:
i just ordered a red 21 tooth..i wanted to do the drive gear but you have to remove the tailhousing of the tranny if im not mistaken and its pretty in depth...i was told bits and pieces of the internal parts come out with the tailpiece making it a pain...is that correct?

Using a red 21 tooth driven gear with your stock 8 tooth drive gear will put you even further off than 10mph, closer to 15-20mph off.

Removing the tailhousing of the trans isn't fun, but it's not that hard either. It can be done in the car, but is easier if you pull the tranny. With the broken speed sensor retaining bolt in the tailhousing, you may be doing this to repair that anyway.

Here is a link to the Tremec repair manual for the T5.

http://www.ttcautomotive.com/English/onlineorder/pdf/LD05-0510-0199_173.pdf

Go to page 16 (3-4 on the manuals pg #s) & follow those directions referencing that diagram. If you have mild mechanical ability & hand tools, you can perform this job!

cjrpony · May 4, 2010

LRSjmac said:
Removing the tailhousing of the trans isn't fun, but it's not that hard either. It can be done in the car, but is easier if you pull the tranny. With the broken speed sensor retaining bolt in the tailhousing, you may be doing this to repair that anyway.

+1, I have done this and I didn't think it was that bad. I did it with the trans in the car and had no problems. The shifter was a bit tricky because there is a pin that needs to be removed and put back in (if I recall)
but every thing else is straight forward.

killer5.0 · May 4, 2010

LRSjmac said:
Using a red 21 tooth driven gear with your stock 8 tooth drive gear will put you even further off than 10mph, closer to 15-20mph off.

Removing the tailhousing of the trans isn't fun, but it's not that hard either. It can be done in the car, but is easier if you pull the tranny. With the broken speed sensor retaining bolt in the tailhousing, you may be doing this to repair that anyway.

Here is a link to the Tremec repair manual for the T5.

http://www.ttcautomotive.com/English/onlineorder/pdf/LD05-0510-0199_173.pdf

Go to page 16 (3-4 on the manuals pg #s) & follow those directions referencing that diagram. If you have mild mechanical ability & hand tools, you can perform this job!

thanks i appreciate the help and the link

LRSjmac · May 4, 2010

killer5.0 said:
thanks i appreciate the help and the link

No problem man! If you have any other questions, hit me up.

koala33 · Nov 9, 2012

I have an 89 5.0 manual. Just changed from stock gears to 3.73. I was told that replacing only the speedometer gear (21 tooth) will fix the speedometer 100% without changing the drive gear in the transmission. Is this correct?

LRSjmac · Nov 9, 2012

koala33 said:
I have an 89 5.0 manual. Just changed from stock gears to 3.73. I was told that replacing only the speedometer gear (21 tooth) will fix the speedometer 100% without changing the drive gear in the transmission. Is this correct?

If you have the stock trans & stock rolling diameter rear tires, then yes, 21 tooth will get you correct

koala33 · Nov 9, 2012

LRSjmac said:
If you have the stock trans & stock rolling diameter rear tires, then yes, 21 tooth will get you correct

Perfect, that's a relief. I was told yes and also no so just trying to confirm.. after driving for 10 minutes so far I'm impressed with the change..

from6to8 · Feb 21, 2023

LRSjmac said:
Using a red 21 tooth driven gear with your stock 8 tooth drive gear will put you even further off than 10mph, closer to 15-20mph off.

Removing the tailhousing of the trans isn't fun, but it's not that hard either. It can be done in the car, but is easier if you pull the tranny. With the broken speed sensor retaining bolt in the tailhousing, you may be doing this to repair that anyway.

Here is a link to the Tremec repair manual for the T5.

http://www.ttcautomotive.com/English/onlineorder/pdf/LD05-0510-0199_173.pdf

Go to page 16 (3-4 on the manuals pg #s) & follow those directions referencing that diagram. If you have mild mechanical ability & hand tools, you can perform this job!

sorry to rehash this old thread but needed an answer. I have a 94 Cobra with the stock manual trans and put 3:73's in and running a 315 30 18. With the stock speedo gear black 20 tooth it was 20 mph off and with a red 21 its about the same so will a 23 put it only about 10 off? I can live with 10 off honestly and dont feel like messing with the trans to change the drive gear.

speedo gear nightmare....what gear should I have?

killer5.0

Beasty306GT

Active Member

killer5.0

ReefBlueHatch

Active Member

killer5.0

Mustang5L5

That is…until I whipped out my Bissell

ReefBlueHatch

Active Member

killer5.0

Mustang5L5

That is…until I whipped out my Bissell

killer5.0

LRSjmac

killer5.0

LRSjmac

cjrpony

Member

killer5.0

LRSjmac

koala33

Member

LRSjmac

koala33

Member

from6to8

There's suction so I used that end O_O

Similar threads

speedo gear nightmare....what gear should I have?

Active Member

Active Member

That is…until I whipped out my Bissell

Active Member

That is…until I whipped out my Bissell

Member

Member

Member

There's suction so I used that end O_O

Similar threads

Privacy & Transparency

Privacy & Transparency