Speedo Gear Woes....

fooey · 08-17-2003, 01:10 PM

Okay, 98 GT, 4.6, Auto, rear has obviously been changed, to what, do not know, but at 60, shows as round 82ish...

Anyone car to take a shot at figuring what rear gear was put in and what speedo gear I need to correct the speedo reading?

fooey · 08-17-2003, 05:01 PM

door sticker shows axle HZ

RaceRat · 08-17-2003, 05:53 PM

Quote:

Originally posted by fooey
but at 60, shows as round 82ish...

takes a big gear jump to throw the speedo off that much at that speed! Is there any chance your overall tire diameter is smaller than stock too?
I have no idea what your ratio was stock, but a 2.73 to 4.10's may account for that.

Nighthawk · 08-17-2003, 07:32 PM

post a tire size, speed at a certain RPM in a certain gear

fooey · 08-17-2003, 09:04 PM

well, rear tires are 285-40-17's and the way I drove back since the speedo was off was by the whine of the engine that I was guessing was around 2500 and how fast the stripes were going by..

, but wife finally caught up to me and around 2500 with speedo reading about 82ish, she said we were doing 60-61ish.

ken97gt · 08-23-2003, 11:15 PM

Jack the back end of your mustang up and rotate the hub and note how many revolutions the driveshaft does in relation to one revolution of the hub. BTW rear axle code HZ is a 3.08:1 limited slip which is kinda weird because I thought that our cars came with a base or 2.73 or an upgrade of 3.27 (what I have)

. Anyhow if someone upgraded the rear from 3.08 to 4.10 and didn't correct the speedo gear then you could have a significant variation but I'm not sure about that much of a disparity. Ken

Nighthawk · 08-24-2003, 03:32 AM

4.10's and an auto should be cruising around 2500 at 60

and 3.08's were also an option as were 3.27's in 96-98 years

fooey · 08-26-2003, 10:46 PM

thanks for the replies.
I broke down and cracked open the punkin' tonight and stamped right there on the pinion gear is 4.10....

So...

It had a 19 tooth speedo gear, yesterday I purchased a
J316-7393 (23 tooth) speedo gear from Mopar of all places (sent there by the ford shop), installed, and testing on a side by side drive with an 98 Expedition (which is prolly off a bit since I put larger tires on it also), it seems to be off about 6-8 mph.

So, if someone can finger out the specifics, I am tired of messing with this and am about to break down and by a speedcal.

HZ oem rear = 3.08
now has 4.10
oem tires = ?
285-40-17's on rear

have a 19 and 23 tooth speedo gear
19 tooth has speedo showing around 20-22 mph fast
23 tooth has speedo showing around 6-8 mph fast.

Can anyone tell me if the speeds are closer or farther apart by my above numbers, since the vehicle I was testing with has slightly larger tires than oem...???

Thanks

Nighthawk · 08-27-2003, 12:44 AM

285/40-17 aren't really bigger than stock...not enough to throw off the speedo to where you could notice. it would be like 1 mph off at 60 mph

SVTCobraLTD · 09-18-2003, 08:29 PM

If you need a speedo gear let me know the size or what gears you have and ill get the correct one.

SVT

08-17-2003, 01:10 PM	#1
fooey Registered User Join Date: Jul 2003 Posts: 112 Trader Rating: (0)	Speedo Gear Woes.... Okay, 98 GT, 4.6, Auto, rear has obviously been changed, to what, do not know, but at 60, shows as round 82ish... Anyone car to take a shot at figuring what rear gear was put in and what speedo gear I need to correct the speedo reading?

08-17-2003, 07:32 PM	#4
Nighthawk technology > displacement Join Date: Jun 2003 Location: San Antonio Posts: 4,659 Trader Rating: (6)	post a tire size, speed at a certain RPM in a certain gear __________________ My Garage

08-24-2003, 03:32 AM	#7
Nighthawk technology > displacement Join Date: Jun 2003 Location: San Antonio Posts: 4,659 Trader Rating: (6)	4.10's and an auto should be cruising around 2500 at 60 and 3.08's were also an option as were 3.27's in 96-98 years __________________ My Garage

08-27-2003, 12:44 AM	#9
Nighthawk technology > displacement Join Date: Jun 2003 Location: San Antonio Posts: 4,659 Trader Rating: (6)	285/40-17 aren't really bigger than stock...not enough to throw off the speedo to where you could notice. it would be like 1 mph off at 60 mph __________________ My Garage

09-18-2003, 08:29 PM	#10
SVTCobraLTD Registered User Join Date: Sep 2003 Location: Easton, PA Posts: 38 Trader Rating: (0)	If you need a speedo gear let me know the size or what gears you have and ill get the correct one. SVT __________________ *1993 Ford Mustang Cobra SVT #4622* Engine mods: 393, .040 TRW pistons, Twisted Wedge Heads, 11.5:1, Scat stroker crank, Trick Flow stage 3 cam, Crane retro-fit lifters, Trick Flow R series intake, 1.7 Trick Flow RR's, Trick Flow valve covers, 3g 200 amp alternator, Mac longtube headers, Mac 3" prochamber, Mac TrueFit 3" catback, MSD 6AL box, BBK 75mm throttle body, C&L 76mm kit, EGR Delete Kit, Dual Walbro fuel pumps hooked to Aeromotive fuel lines, FMS 30# injectors, Ramchargers Dual Fan. Suspension Mods: D&D tubular K member, FMS 1/2" lowering springs, Koni yellow shocks and struts, KYB qauds, BBK rear upper control arms, Lakewood liftbars, STQ front and rear sway bars, BBK subframes, BBK caster/camber plates, 17x9 chrome Cobra R's with 245/45 BFG's. Drivetrain Mods: Richmond 3.55 gears, Cobra world class T5 tranny, Mac rear cover, FMS alum driveshaft, Hurst short shifter. Exterior/Interior Mods: Teal exterior, Cobra ground effects(stock), GT Stalker front ground effect, Stormin Norman 2.5" hood, 5 % tint, GTS window shades, GTS solar wing, GTS headlight and taillight covers, Gray leather interior, white faced A/C gauges, Autometer fuel pressure and oil pressure Phantom gauges on pillar, Autometer 5" Phantom Tach, Autometer Gauge Cage with Phantom Water Temp, not to mention the sterio! 420.6 rwhp/470.8 rwtq My Car RIP Brian M Bender Feb 27, 82 - Aug 11, 99 Two companies to NEVER deal with: - Indy Mustang - Cincinnati Composites aka Cobra Auto Design

08-17-2003, 05:01 PM	#2
fooey Registered User Join Date: Jul 2003 Posts: 112 Trader Rating: (0)	door sticker shows axle HZ

08-17-2003, 09:04 PM	#5
fooey Registered User Join Date: Jul 2003 Posts: 112 Trader Rating: (0)	well, rear tires are 285-40-17's and the way I drove back since the speedo was off was by the whine of the engine that I was guessing was around 2500 and how fast the stripes were going by.. , but wife finally caught up to me and around 2500 with speedo reading about 82ish, she said we were doing 60-61ish.

08-23-2003, 11:15 PM	#6
ken97gt Registered User Join Date: Aug 2003 Location: Corpus soon to be SA Posts: 99 Trader Rating: (0)	Jack the back end of your mustang up and rotate the hub and note how many revolutions the driveshaft does in relation to one revolution of the hub. BTW rear axle code HZ is a 3.08:1 limited slip which is kinda weird because I thought that our cars came with a base or 2.73 or an upgrade of 3.27 (what I have) . Anyhow if someone upgraded the rear from 3.08 to 4.10 and didn't correct the speedo gear then you could have a significant variation but I'm not sure about that much of a disparity. Ken

08-26-2003, 10:46 PM	#8
fooey Registered User Join Date: Jul 2003 Posts: 112 Trader Rating: (0)	thanks for the replies. I broke down and cracked open the punkin' tonight and stamped right there on the pinion gear is 4.10.... So... It had a 19 tooth speedo gear, yesterday I purchased a J316-7393 (23 tooth) speedo gear from Mopar of all places (sent there by the ford shop), installed, and testing on a side by side drive with an 98 Expedition (which is prolly off a bit since I put larger tires on it also), it seems to be off about 6-8 mph. So, if someone can finger out the specifics, I am tired of messing with this and am about to break down and by a speedcal. HZ oem rear = 3.08 now has 4.10 oem tires = ? 285-40-17's on rear have a 19 and 23 tooth speedo gear 19 tooth has speedo showing around 20-22 mph fast 23 tooth has speedo showing around 6-8 mph fast. Can anyone tell me if the speeds are closer or farther apart by my above numbers, since the vehicle I was testing with has slightly larger tires than oem...??? Thanks

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