• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

purpose of using gear compound when correct backlash is set?

  • Thread starter Thread starter PeteyAce
  • Start date Start date Sep 10, 2005

PeteyAce

Member
Jul 2, 2004
346
0
17
Sep 10, 2005
#1
  • Sep 10, 2005
  • #1
i dont understand, if the pinion depth and the backlash are within specs then what the hell is the point of seeing how the gears mesh?
 

GRGT1994

New Member
Sep 22, 2004
1,034
0
0
Sep 10, 2005
#2
  • Sep 10, 2005
  • #2
Even with those spec's within tolerance, the mesh pattern can still be off (too deep/shallow, too far to heel or tow). But you're probably right for street driven cars, shouldn't matter much.
 

vristang

15 Year Member
Mar 31, 2005
4,933
101
124
Seattle
Sep 10, 2005
#3
  • Sep 10, 2005
  • #3
GRGT1994 said:
Even with those spec's within tolerance, the mesh pattern can still be off (too deep/shallow, too far to heel or tow). But you're probably right for street driven cars, shouldn't matter much.
Click to expand...


Just verification of mesh pattern
 

RacEoHolic330

I like to dress like a pretty girl
15 Year Member
Mar 4, 2003
4,014
1,698
203
Allentown, PA
Sep 10, 2005
#4
  • Sep 10, 2005
  • #4
When I swapped out my stock diff for an Eaton posi. I just put everything back in the way it came out. I didn't use the compound to check the gear mesh. Probably not the right way to do things, but 2k miles later and I don't have any problems or gear whine.
 

7-UP BILL

Founding Member
Jan 4, 2001
885
19
49
My other car is a Firetruck
Sep 10, 2005
#5
  • Sep 10, 2005
  • #5
RacEoHolic330 said:
When I swapped out my stock diff for an Eaton posi. I just put everything back in the way it came out. I didn't use the compound to check the gear mesh. Probably not the right way to do things, but 2k miles later and I don't have any problems or gear whine.
Click to expand...



If you use the same gears and NOT change the pinion, you can just reinstall everything. Pinion depth was not altered.
 

RacEoHolic330

I like to dress like a pretty girl
15 Year Member
Mar 4, 2003
4,014
1,698
203
Allentown, PA
Sep 10, 2005
#6
  • Sep 10, 2005
  • #6
7-UP BILL said:
If you use the same gears and NOT change the pinion, you can just reinstall everything. Pinion depth was not altered.
Click to expand...

Yeah.. exactly. It seemed logical to think that nothing should change.
 

vristang

15 Year Member
Mar 31, 2005
4,933
101
124
Seattle
Sep 10, 2005
#7
  • Sep 10, 2005
  • #7
RacEoHolic330 said:
When I swapped out my stock diff for an Eaton posi. I just put everything back in the way it came out. I didn't use the compound to check the gear mesh. Probably not the right way to do things, but 2k miles later and I don't have any problems or gear whine.
Click to expand...

A well manufacutered dif will allow this. Keep production tolerances in mind though.
I will use a theoretical dimension of 4.000" with a tolerance of +/- .005" to make my point. This means the dimension can be anywhere from 3.995" to 4.005" and still pass QA inspection.
Now consider that this part has been in use for several years and is to be replaced. If the old part was 3.995" and the new part is 4.005", then there is a .010" difference between parts. Factor in the build up of production tolerances for each component in multiple part assemblies, and you can get into trouble pretty quick.

The error indroduced with production tolerances is (I think) the main reason for checking the mesh after any change. Plus there is always the off chance of some component being out of tolerance.

Feel free to disagree if you like, I would like to hear your opinions.
jason
 

txstang84

15 Year Member
May 21, 2005
1,639
42
69
Tuscola, tx
Sep 11, 2005
#8
  • Sep 11, 2005
  • #8
vristang said:
A well manufacutered dif will allow this. Keep production tolerances in mind though.
I will use a theoretical dimension of 4.000" with a tolerance of +/- .005" to make my point. This means the dimension can be anywhere from 3.995" to 4.005" and still pass QA inspection.
Now consider that this part has been in use for several years and is to be replaced. If the old part was 3.995" and the new part is 4.005", then there is a .010" difference between parts. Factor in the build up of production tolerances for each component in multiple part assemblies, and you can get into trouble pretty quick.

The error indroduced with production tolerances is (I think) the main reason for checking the mesh after any change. Plus there is always the off chance of some component being out of tolerance.

Feel free to disagree if you like, I would like to hear your opinions.
jason
Click to expand...

very well said...0.010" can wreak havoc in such a situation...if you've got the marking compound, go ahead and use it-the pattern should be a nice long wide CENTERED oval shape...this indicates your backlash is where it needs to be, pinion depth is correct and mesh pattern is dead on where it should be

for everyone else that has had good luck not altering any measurements and just swapping gears or gears and carrier-more power to ya-I'm glad it worked out well for you...just keep in mind some of us are not so "lucky"...I myself have been plagued with rear axle demons since I broke my original rear 10 yrs ago...and the bitch about that is that I sent it to a reputable (at least I believed) shop to have the work done, and then come to find out the a$$wipe that installed my gears set the backlash to double what it was supposed to be, and on top of that didn't put any limited slip additive...I caught that quickly-but not until it had already done damage to my brand spaking new Auburn unit...damn the luck...

sorry to gripe fellas, I know it's wayyyy :OT: but just had to let others know that sometimes it doesn't always work out the way it should for gear swaps...
 

vristang

15 Year Member
Mar 31, 2005
4,933
101
124
Seattle
Sep 11, 2005
#9
  • Sep 11, 2005
  • #9
txstang84 said:
very well said...0.010" can wreak havoc in such a situation...if you've got the marking compound, go ahead and use it-the pattern should be a nice long wide CENTERED oval shape...this indicates your backlash is where it needs to be, pinion depth is correct and mesh pattern is dead on where it should be

for everyone else that has had good luck not altering any measurements and just swapping gears or gears and carrier-more power to ya-I'm glad it worked out well for you...just keep in mind some of us are not so "lucky"...I myself have been plagued with rear axle demons since I broke my original rear 10 yrs ago...and the bitch about that is that I sent it to a reputable (at least I believed) shop to have the work done, and then come to find out the a$$wipe that installed my gears set the backlash to double what it was supposed to be, and on top of that didn't put any limited slip additive...I caught that quickly-but not until it had already done damage to my brand spaking new Auburn unit...damn the luck...

sorry to gripe fellas, I know it's wayyyy :OT: but just had to let others know that sometimes it doesn't always work out the way it should for gear swaps...
Click to expand...

I don't think there is any need to apologize. When others hear about all the things that some of us have had go wrong, they know what to watch out for later. It sucks that you ended up with damage to your new auburn unit (I love mine by the way), but everyone who reads this thread will think to ask their mechanic if they added friction modifier to the rear fluid. That is what this site is all about.
 

fiveohwblow

Official Member
15 Year Member
Jul 21, 2005
2,169
145
155
Sep 11, 2005
#10
  • Sep 11, 2005
  • #10
vristang said:
I don't think there is any need to apologize. When others hear about all the things that some of us have had go wrong, they know what to watch out for later. It sucks that you ended up with damage to your new auburn unit (I love mine by the way), but everyone who reads this thread will think to ask their mechanic if they added friction modifier to the rear fluid. That is what this site is all about.
Click to expand...
Makes me real glad that friction modifier was added when my gear swap was done about 1 week ago....
 

PeteyAce

Member
Jul 2, 2004
346
0
17
Sep 11, 2005
#11
  • Sep 11, 2005
  • #11
thanks again, as always you guys come through with the info. lol now how do i get in this damn s spring?
 

rd

Founding Member
Jan 12, 2000
3,316
63
109
Ocean Springs MS
Sep 11, 2005
#12
  • Sep 11, 2005
  • #12
I do both, set it up with gages, etc, and then check the pattern. The pattern check is easy, I use white lithium grease. It verifies that what you did is ok.

Done it without the gage check, and had good luck also, with all SVO parts.

My gage is a ground flat angle across the rear carrier bearing housing, and a dial caliper, so I do the extra check.

Both my 4.10 in my 7.5 and my 4.56 in my 8.8 seem to run quietly.
 
You must log in or register to reply here.

Similar threads

3
Eight inches is enough for me...
  • 351MooseStang
  • Nov 27, 2025
  • 1974 - 1978 Mustang II Talk & Tech
Replies
5
Views
544
1974 - 1978 Mustang II Talk & Tech Mar 2, 2026
Bullitt347
T
Drivetrain Can’t identify correct speedometer gear
  • townethug
  • Jul 12, 2025
  • Fox 5.0 Mustang Tech
Replies
6
Views
235
Fox 5.0 Mustang Tech Jul 21, 2025
FastDriver
S
Engine Stalls when downshifting/coasting
  • Scott_S
  • Nov 5, 2025
  • Fox 5.0 Mustang Tech
Replies
11
Views
680
Fox 5.0 Mustang Tech Nov 6, 2025
Mustang5L5
Fox Xtremely high fuel consumption
  • PonyGTrider
  • Apr 11, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 9 10 11
Replies
213
Views
3K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- May 9, 2026
PonyGTrider
C
Drivetrain 8.8” gear install
  • Chaz7795
  • May 2, 2023
  • Fox 5.0 Mustang Tech
Replies
14
Views
3K
Fox 5.0 Mustang Tech May 16, 2023
General karthief
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?