[Fot] Differential Pre-load

Thu Jan 30 02:46:48 MST 2020

Peter, I agree but the same can be said about the differential bearings : the differential can get very hot too! I would rather stay with the explanation of Glen. B.t.w. : as the pinion is stretching, probably the preload will not cause friction loss at all when the differential is UNDER LOAD (accelerator pedal to the floor). Whatever the reason , you all have made it clear that the preload is necessary. 
Marcel 

Van: "Peter Vucinic" <pvucinic at netspace.net.au> 
Aan: "van mulders marcel" <van.mulders.marcel at telenet.be>, "barry rosenberg" <britcars at bellsouth.net> 
Cc: "fot" <fot at autox.team.net> 
Verzonden: Donderdag 30 januari 2020 10:22:13 
Onderwerp: RE: [Fot] Differential Pre-load 

You need clearance/end float in wheel hubs with tapered roller bearings to accommodate thermal expansion from heat generation in the braking system. 

"You can Make a Small Fortune From Motor Racing. As long as You Started With A Lage Fortune!" 

Kind Regards 

Peter Vucinic 

TR4 - TR7 V8 - Spitfire MkII 

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From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of van.mulders.marcel--- via Fot 
Sent: Thursday, 30 January 2020 8:12 PM 
To: barry rosenberg 
Cc: fot 
Subject: Re: [Fot] Differential Pre-load 

Barry, if that is true about the rollers/races, how do you explain the prescripion about the front wheel bearings : you need to back off the stub axle nut to get some play for the bearings? 

Marcel 

Van: "fot" <fot at autox.team.net> 
Aan: "fubog1" <fubog1 at aol.com>, "Bob Kramer" <rkramer56 at gmail.com> 
Cc: "fot" <fot at autox.team.net> 
Verzonden: Woensdag 29 januari 2020 19:02:55 
Onderwerp: Re: [Fot] Differential Pre-load 

Preload is more for the life of the bearings than the gears. You preload a bearing to take up manufacturing tolerances and account for the anticipated (by the manufacturer of the bearings) wear during their life time. There does need to be some 'squeeze" between the bearing races and the rollers or the rollers will not roll in lubrication. If any of you have ever rebuilt the rear outer suspension on old XKEs, the tapers roller bearing in the outer wishbone pivots wear out because the wishbone only moves up and down a few degrees. The tapered roller bearings never fully rotate and cause the rollers and race to pit. Roller bearing must roll 360 degrees around to survive. Preload makes them do that. 

Barry 

On Wednesday, January 29, 2020, 09:41:34 AM EST, Bob Kramer via Fot <fot at autox.team.net> wrote: 

I think the main reason a specified amount of preload is required is that it sets it up so that the bearings roll under mild tension. To tight and the components slide over each other. Too loose and they cock in place. Without rolling, bearings will soon fail the same way a lifter that doesn't spin fails. 

Bob Kramer 

On Wed, Jan 29, 2020 at 8:15 AM fubog1 via Fot < [ mailto:fot at autox.team.net | fot at autox.team.net ] > wrote: 

BQ_BEGIN

Does someone know why that preload is necessary? 

Yes it's basically because things want to move around a lot & the pinion wants to stretch.with torque on/off loads. 

Over time as the bearings wear, the preload will be lost, and any further wear will cause the gears to be out of mesh and the pattern will be lost and then they'll wear. 

Glen 

-----Original Message----- 
From: van.mulders.marcel--- via Fot < [ mailto:fot at autox.team.net | fot at autox.team.net ] > 
To: Bill Tobin < [ mailto:william.tobin31 at verizon.net | william.tobin31 at verizon.net ] > 
Cc: fot < [ mailto:fot at autox.team.net | fot at autox.team.net ] > 
Sent: Wed, Jan 29, 2020 8:14 am 
Subject: Re: [Fot] Differential Pre-load 

Does someone know why that preload is necessary? When I check a differential before using it and I notice there is almost no preload at all, I tend to be lazy, assuming no preload means less friction loss. 

Marcel. 

Van: "fot" < [ mailto:fot at autox.team.net | fot at autox.team.net ] > 
Aan: "fot" < [ mailto:fot at autox.team.net | fot at autox.team.net ] > 
Verzonden: Woensdag 29 januari 2020 04:06:57 
Onderwerp: Re: [Fot] Differential Pre-load 

Hi Scott I think that's the torque required to turn the pinion. Put a socket to fit the pinion nut on a?? inch pound torque wrench; measure how much torque it takes to turn the pinion. Get it turning and read the torque wrench while turning it. 12 to 15 inch pounds sounds ok. With shims either add or remove shims to get the correct preload. Thicker to lessen and thinner to increase I think. 

With a collapsible spacer it's easier. Keep?? tightening the nut and measuring the preload until it's right. Small increments. If you over tighten you take it apart and start over with a new spacer. (Ask me how I know this!) 

Also a "clicker" torque wrench isn't the ticket for this. Use an older beam type. 

Hope this helps. 

Cheers Bill 

On 1/28/2020 4:34 PM, Scott Janzen via Fot wrote: 

BQ_BEGIN

I???m rebuilding my differential. ??The manual says the pinion bearings should be assembled with spacers to yield a?? 

12-16 lb/inch pre-load, using a bar affixed to the input flange and a sliding weight. ??Of course there is a churchhill tool for that! 

Either I???m not grasping the concept, or 12 lbs per inch doesn???t seem right. ??I???m guessing this is supposed to be 12 inch-pounds, 

which I think means a one pound weight at the end of a 12??? lever. ??All testing is performed with the seal removed. 

Even if I am correct, I???ve got it set up with about a 1/2 lb pre-load right now, and that feels pretty stiff already. 

Anyone have any experience with this? ??This is a GT6 diff, but I???m guessing the instructions don???t vary much. 

Thanks, 

Scott 

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