Diff Gear Changeover

Mustang Australia
« previous next »
Pages: [1] 2   Go Down

Author Topic: Diff Gear Changeover  (Read 11788 times)

Offline Azz67

  • Thoroughbred
  • **
  • Posts: 174
  • Location: Brisbane
Azz67
Diff Gear Changeover
« on: July 15, 2015, 08:33:58 pm »
Hi all,
Looking for some advice regarding a change out of rear end gears. 3.9 to 3.5.
How long should it take to change out (by a mechanic)?
And usual cost of parts?

Thanking you in advance.
Logged

Offline shaunp

  • GT 500
  • *********
  • Posts: 8496
  • Location: Brisbane
shaunp
Re: Diff Gear Changeover
« Reply #1 on: July 15, 2015, 08:45:26 pm »
Quote from: Chuck Steak on July 15, 2015, 08:33:58 pm
Hi all,
Looking for some advice regarding a change out of rear end gears. 3.9 to 3.5.
How long should it take to change out (by a mechanic)?
And usual cost of parts?

Thanking you in advance.

Are you changing the center or rebuilding the center with new gears to very different things. To swap a complete center about an 1-1/2 hours, to remove and rebuild much more and most mechaninics  dont know how to rebuild a diff. A rebuilt centre with a LSD fitted new parts will cost about $1500 + refitting.
Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #2 on: July 15, 2015, 08:53:21 pm »
That's a bit of a job . It's not only a R&R but changing the gears . On average with someone that knows what they are doing 3/4 hr to take out same for refitting . Then doing the center ,changing the crown wheel and pinion and setting up ,time wise I don't really know maybe 1 hr . So maybe a 3 hr job plus parts ,oil etc . Is it a 8 inch or 9 inch diff ? . Have you worked out the revs on engine for what you want before you change it all . 3.9 is low for hwy cruising that's for sure .
Logged

Offline mert

  • Supercharged
  • *****
  • Posts: 2038
  • Location: Brisbane
mert
Re: Diff Gear Changeover
« Reply #3 on: July 15, 2015, 09:03:05 pm »
I'd guess those times assume the diff is out of the car.  If you are looking for drive in, drive out add a couple hours...
Logged
8R01S, 8R03S, 8R01C-Cal Special, 8F01X - EXP500 Repli-bute

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #4 on: July 15, 2015, 09:11:49 pm »
No diff in the car,center out and back in 1.5 hr ,changing gears in center not sure guess 1 hr ,plus filling up with oil etc total 3 hrs .
Logged

Offline Azz67

  • Thoroughbred
  • **
  • Posts: 174
  • Location: Brisbane
Azz67
Re: Diff Gear Changeover
« Reply #5 on: July 15, 2015, 09:19:19 pm »
Its a gear swap out. 8 inch with true trac.
Logged

Offline shaunp

  • GT 500
  • *********
  • Posts: 8496
  • Location: Brisbane
shaunp
Re: Diff Gear Changeover
« Reply #6 on: July 15, 2015, 10:00:52 pm »
Quote from: Chuck Steak on July 15, 2015, 09:19:19 pm
Its a gear swap out. 8 inch with true trac.

Ok doubt a mechanic  will do it, most have no idea how to set up a diff, only swap them out. You need an dial indicator torque wrench to set up the pinion preload, not many people have them, diff shops aside, and me off course. Gears are about $170 US, true track $480, bearing rebuild kit about $100, + labour. Aussie diffs at the Gold coast do them for about $1500, + fitting I think.
Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #7 on: July 15, 2015, 10:07:19 pm »
$1500 plus fitting would be about right  .
Logged

Offline barnett468

  • Cobra
  • *********
  • Posts: 7174
barnett468
Re: Diff Gear Changeover
« Reply #8 on: July 16, 2015, 11:53:09 am »
.
not all gears and bearings are created equal . . some gears whine and some bearings fail prematurely.

i would only buy us gear gears and timken bearings.

Logged

Offline J.hatzivalsamis

  • Worked
  • ***
  • Posts: 208
  • I'm new here
  • Location: Darwin
  • Name: jimmy hatziv
J.hatzivalsamis
Re: Diff Gear Changeover
« Reply #9 on: July 16, 2015, 03:40:23 pm »
Hey Aaron just had mine done in Darwin all new crown wheel 3.5 strange gears LSD centre new and set up $1850.00 give us a call if you wish to discuss.
Logged

Offline GEOFF289

  • Blue Printed
  • ****
  • Posts: 1643
  • Location: Melbourne
GEOFF289
Re: Diff Gear Changeover
« Reply #10 on: July 17, 2015, 08:12:44 am »
Aaron, you are sure you've got a 3.90 in it now, aren't you?

Because when you were trying to get it registered said in this post http://www.mustang.org.au/forum/index.php/topic,25183.msg250958.html#msg250958 that it had a 3.50 trutrac

Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #11 on: July 17, 2015, 08:56:23 am »
If you are unsure about the ratio there are a couple of ways to check if needed .
Logged

Offline GEOFF289

  • Blue Printed
  • ****
  • Posts: 1643
  • Location: Melbourne
GEOFF289
Re: Diff Gear Changeover
« Reply #12 on: July 17, 2015, 08:59:17 am »
I've separately given him a link to how to figure this out.
Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #13 on: July 17, 2015, 09:05:34 am »
Ok all good   :thumb:
Logged

Offline Azz67

  • Thoroughbred
  • **
  • Posts: 174
  • Location: Brisbane
Azz67
Re: Diff Gear Changeover
« Reply #14 on: July 17, 2015, 09:12:27 am »
Thanks Geoff and Glenn.
Will get the ratio hopefully verified today mechanic says.
Is the wheel rotation test fairly accurate i.e can you tell the difference between 3.9 and 3.5.?
Half a revolution versus nearly a full one you'd think so.?




Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #15 on: July 17, 2015, 09:25:33 am »
Yes that will work .  Does it have a 4 speed auto now? ,what size wheels and tyres are on the car  ? And does it have a tachometer ? Is the speedo correct ?  :grin:  :thud: .
Logged

Offline Azz67

  • Thoroughbred
  • **
  • Posts: 174
  • Location: Brisbane
Azz67
Re: Diff Gear Changeover
« Reply #16 on: July 17, 2015, 09:34:21 am »
4spd auto -check.
225/45/17s
no tacho
speedo is outta whack.

Logged

Offline GEOFF289

  • Blue Printed
  • ****
  • Posts: 1643
  • Location: Melbourne
GEOFF289
Re: Diff Gear Changeover
« Reply #17 on: July 17, 2015, 10:54:08 am »
Quote from: Chuck Steak on July 17, 2015, 09:12:27 am

Is the wheel rotation test fairly accurate i.e can you tell the difference between 3.9 and 3.5.?
Half a revolution versus nearly a full one you'd think so.?

If it is a Trutrac you do it with both wheels up and turn the wheel one rotation. A 3.90 gear should see the driveshaft and pinion rotate all but 4 times and a 3.50 3 1/2 times. Fairly easy to see the difference.

If an open diff you just lift one wheel and turn it two rotations.
Logged

Offline StephenSLR

  • Top Streeter
  • ******
  • Posts: 3449
    • www.lycanthia.com
  • Location: Sydney
  • Car: 1965 Fastback
StephenSLR
Re: Diff Gear Changeover
« Reply #18 on: July 17, 2015, 02:22:41 pm »
Quote from: GLENN 70 on July 15, 2015, 08:53:21 pm
3.9 is low for hwy cruising that's for sure.

True but with the trend of fitting bigger wheels these days .....

s
Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #19 on: July 17, 2015, 03:33:30 pm »
A taller tyre will bring the revs down . Even with a 3.9 ratio  the revs won't be too bad at 100 kph because of the overdrive gear box . At a guess around 2400 rpm with your tyres on it now .
« Last Edit: July 17, 2015, 05:45:50 pm by GLENN 70 »
Logged

Offline barnett468

  • Cobra
  • *********
  • Posts: 7174
barnett468
Re: Diff Gear Changeover
« Reply #20 on: July 17, 2015, 04:30:42 pm »
.

put the air valve on the tire straight down

put a mark or piece of tape on the driveshaft do you have something to go by.

count the driveshaft turns until the tire valve is exactly at the bottom again.

heres a free rpm calculator

http://www.wallaceracing.com/gear-speed.php
« Last Edit: July 17, 2015, 04:33:15 pm by barnett468 »
Logged

Offline GEOFF289

  • Blue Printed
  • ****
  • Posts: 1643
  • Location: Melbourne
GEOFF289
Re: Diff Gear Changeover
« Reply #21 on: July 17, 2015, 05:02:03 pm »
Logged

Offline peter9231

  • Member-Society of Automotive Engineers Australasia
  • Worked
  • ***
  • Posts: 647
  • Location: Melbourne
  • Name: Peter
  • Car: 66 convertible
peter9231
Re: Diff Gear Changeover
« Reply #22 on: July 17, 2015, 05:04:07 pm »
Quote from: GEOFF289 on July 17, 2015, 05:02:03 pm
I have also put him on this calculator

http://www.allfordmustangs.com/Detailed/608.shtml

Good job,
Much better calculator.
Logged
"If you are not prepared to be part of the solution you forfeit your right to criticise"

Offline boofhead

  • Blue Printed
  • ****
  • Posts: 1077
boofhead
Re: Diff Gear Changeover
« Reply #23 on: July 18, 2015, 08:18:47 am »
If it is an 8 inch diff would not the (closest) ratios discussed be
3.55:1  and 3.80:1  .  The numbers used above are normally available 9 inch ratios. I guess rounding it a little is ok.
Logged

Offline GLENN 70

  • GT 500
  • *********
  • Posts: 8620
  • Location: Gold Coast .
GLENN 70
Re: Diff Gear Changeover
« Reply #24 on: July 18, 2015, 09:16:29 am »
If we are talking ford ratio gears ford made 3.5 not 3.55  Untill 1972 and newer .Talking 9 inch  its 4.11 not 4.0 , 3.89 not 3.9 , etc .  Ford 8 inch was a 3.50 and 3.80  and a 3.91 ratio from 1969 on  etc etc . They did make some weird ratios ,like 2.83 ,3,08 ,3.07 , etc,etc .  Anyway a lot of ratios in these old mustangs have been changed for decades  :grin: .  That's why by just turning the wheel once and counting the tail shaft turns is only a guide .  Taking the center out and counting the crown wheel and then the pinion then dividing the too gives you the correct ratio .
Logged
Pages: [1] 2   Go Up
« previous next »