1st differential install - what went wrong? Long and some dumb questions.

SteveK · 05-06-2003, 12:14 PM

I have been rad racing for years. And some friends of mine convinced me to go. So I said " what the hell"

I never gave it much thought. I do realize that it takes some science to do it right. In roadracing, you don;t want to modify the car too much so you stay in the lowest class you can fit into. So my engine is stock with the exception of some suspension stuff.
Anyway, with that excuse, I ran 14.8 @ 93 MPH.
I was happy with it. It is a stock 98 GT with 3.73, no muffler and pullies.(199 RWHP)

Steve

Mike Souslin · 05-07-2003, 12:20 AM

Well I don't know why my first post linked another topic but I'll try again!!!First of all, please excuse my ignorance - this was our first try!

I am helping my buddy with his car. We have the suspension completely finished and started working on the rear end of his 91 coupe. We are installing an Auburn Pro, Moser 31 spline axles and 3.73 gears.

Everything went pretty well, we thought. We got the backlash on the ring gear right per the gauge and the pattern on the ring gear was close (we thought). When we went for the test drive this is what we noticed. At first the car sounded really bad - almost like a bearing or something - It sounded much better by the end of his street so we figured eveything was just getting lubed up. It drove very smooth but there is a lot of gear whine, more so on deceleration. We brought it back in the garage and started the trouble shooting.

We are assuming that the pinion depth is not correct. Unfortunately getting the bearing pulled off and pressed on is an issue for us since we will have to go to a shop with a press each time we try a different shim. I've read on the net that some people heat the pinion bearing with a propane torch and then they can slide it off of the pinion - is this OK to do???? Secondly, we are not really sure how much to tighten the pinion nut. What we did was set the emergency brake to keep it from turning and then tighten the pinion nut just until there is not front to back play. Is this correct? How do you guy's keep it from turning???
Next - the bearing caps that hold the differential in, what direction do the arrows on the cap point? Towards the differential or towards the wheels? (I was not there when they were removed)

After the test drive we jacked the car up and when you rotate one wheel that is some play before it "catches" and you can hear a "thunk" when slightly rotating the tire forward and backwards. Does this indicate that the backlash is not correct? It is pretty noisy just rolling the wheel too?!?

This time we are going to make SURE that the pattern on the ring gear is correct before taking her out!

Thanks for any imput you can provide - I figure that this is the only way we will learn how to do it!

Jeff Chambers · 05-07-2003, 06:55 AM

You could have any number of problems based on your description of the events. First off, with installing new gears AND diff you're probably wayyyyy off with bearing preloads.

For the pinion, you want to torque the pinion nut until you have about 18 in-lbs (note in-lbs, not ft-lbs) running torque on the bearings. The norm is 10-15 in-lbs for a used bearing, 20-25 in-lbs for a new bearing but right around 18 in-lbs is pretty safe for either. Too little preload and the pinion will move under both accel and decel. Too much preload and you'll burn the bearings up real quick.

For the carrier bearings, you want to slide the carrier in an begin adding shimming until you get to the point that the last shim installed has pretty heavy drag going in. This is the zero preload position. From there, take both shim packs out, measure them with a micrometer and add .006" shimming to each pack. This adds the proper preload to the carrier bearings. Arrows on the caps face outward.

To hold the pinion, you can build a pinion tool like I have, or you can try one of the following. 1) Install two bolts in the companion flange and use them to wedge a pry bar to counter the torquing force or 2) insert a hardened drift through one of the bolt holes so that it can be wedged under one of the stiffening webs on the carrier housing.

Don't check your pattern unless all bearing preloads are established; you'll get a false reading otherwise. Also make sure that you're setting your indicator perpendicular to the gear when checking backlash. I set street/strip backlash to 0.008-0.012".

Good gear setup is a game measured in thousandths of an inch. Patience and attention to detail are absolute keys.

05-06-2003, 12:14 PM	#1
SteveK Registered Member Join Date: Apr 2001 Location: Round Lake, IL, USA Posts: 51	My first time at the 1/4 mile track I have been rad racing for years. And some friends of mine convinced me to go. So I said " what the hell" I never gave it much thought. I do realize that it takes some science to do it right. In roadracing, you don;t want to modify the car too much so you stay in the lowest class you can fit into. So my engine is stock with the exception of some suspension stuff. Anyway, with that excuse, I ran 14.8 @ 93 MPH. I was happy with it. It is a stock 98 GT with 3.73, no muffler and pullies.(199 RWHP) Steve __________________ Steve K. 98 GT w/ 3.73 Your car is fast, are you?

05-07-2003, 12:20 AM	#2
Mike Souslin Registered Member Join Date: Sep 1999 Location: Grove City Ohio Posts: 226	1st differential install - what went wrong? Long and some dumb questions. Well I don't know why my first post linked another topic but I'll try again!!!First of all, please excuse my ignorance - this was our first try! I am helping my buddy with his car. We have the suspension completely finished and started working on the rear end of his 91 coupe. We are installing an Auburn Pro, Moser 31 spline axles and 3.73 gears. Everything went pretty well, we thought. We got the backlash on the ring gear right per the gauge and the pattern on the ring gear was close (we thought). When we went for the test drive this is what we noticed. At first the car sounded really bad - almost like a bearing or something - It sounded much better by the end of his street so we figured eveything was just getting lubed up. It drove very smooth but there is a lot of gear whine, more so on deceleration. We brought it back in the garage and started the trouble shooting. We are assuming that the pinion depth is not correct. Unfortunately getting the bearing pulled off and pressed on is an issue for us since we will have to go to a shop with a press each time we try a different shim. I've read on the net that some people heat the pinion bearing with a propane torch and then they can slide it off of the pinion - is this OK to do???? Secondly, we are not really sure how much to tighten the pinion nut. What we did was set the emergency brake to keep it from turning and then tighten the pinion nut just until there is not front to back play. Is this correct? How do you guy's keep it from turning??? Next - the bearing caps that hold the differential in, what direction do the arrows on the cap point? Towards the differential or towards the wheels? (I was not there when they were removed) After the test drive we jacked the car up and when you rotate one wheel that is some play before it "catches" and you can hear a "thunk" when slightly rotating the tire forward and backwards. Does this indicate that the backlash is not correct? It is pretty noisy just rolling the wheel too?!? This time we are going to make SURE that the pattern on the ring gear is correct before taking her out! Thanks for any imput you can provide - I figure that this is the only way we will learn how to do it! __________________ 91 Coupe with fresh rebuild. Running Stage 2 Avenger heads (51cc chambers), Stage 2 cam (.549, .566)1.72 Crane Gold Race rockers, Port matched GT-40 upper & lower, 75mm Bullet MAF, 65mm Accufab TB, MSD 6AL, Long Tubes through off road and 2 chamber flowbastards. Stock T-5, 3.73 gears, Center Line Convo-Pros with skinnies up front. My baby is now bottle fed!!! Best time on the motor was 12.92 at 109.57. UPDATE - Getting Ready to install: Tremec 3550, Blowproof Bellhousing, Strange Shocks/Struts, Moroso Springs, Upper/Lower control Arms, 31 spline axles and new differential. After this..... 347 heart transplant and Rollcage.

05-07-2003, 06:55 AM	#3
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	You could have any number of problems based on your description of the events. First off, with installing new gears AND diff you're probably wayyyyy off with bearing preloads. For the pinion, you want to torque the pinion nut until you have about 18 in-lbs (note in-lbs, not ft-lbs) running torque on the bearings. The norm is 10-15 in-lbs for a used bearing, 20-25 in-lbs for a new bearing but right around 18 in-lbs is pretty safe for either. Too little preload and the pinion will move under both accel and decel. Too much preload and you'll burn the bearings up real quick. For the carrier bearings, you want to slide the carrier in an begin adding shimming until you get to the point that the last shim installed has pretty heavy drag going in. This is the zero preload position. From there, take both shim packs out, measure them with a micrometer and add .006" shimming to each pack. This adds the proper preload to the carrier bearings. Arrows on the caps face outward. To hold the pinion, you can build a pinion tool like I have, or you can try one of the following. 1) Install two bolts in the companion flange and use them to wedge a pry bar to counter the torquing force or 2) insert a hardened drift through one of the bolt holes so that it can be wedged under one of the stiffening webs on the carrier housing. Don't check your pattern unless all bearing preloads are established; you'll get a false reading otherwise. Also make sure that you're setting your indicator perpendicular to the gear when checking backlash. I set street/strip backlash to 0.008-0.012". Good gear setup is a game measured in thousandths of an inch. Patience and attention to detail are absolute keys. __________________ Jeff Chambers 1990 Mustang GT 10.032 Seconds / 137.5 MPH 14-time Street Warrior World Record Setter CRT Performance 2001 Tropic Green Mustang GT - 12.181 / 113.2 MPH 2002 Ford F-250 Crew Cab 7.3l Power Stroke - 17.41@77.2 "There's nothing boring about a small block automatic shifting gears at 9400 rpm!"