Differential Preload

[Drfatz 0]

I have been trying to set the preload on my differential but I can't find a tool to set the castellated nut! Any ideas? I have already gone down the wood and plastic hammer route and I just can't tighten it enough.

Suggestions wanted

-Graham

[Jonathan 13]

I bought another castalated nut and just used that in reverse with 2 bolts drilled and tapped into it.

Worked an absolute treat and cost a fraction of the cost of making one / buying the correct tool, plus you get some spare seals in it as well - bargain.

Are you installing new thrust bearings or keeping the old ones, there is a different pre-loading tequnique.

[Drfatz 0]

I had not thought of that. In fact I have another nut on the burnt gearbox I have! Sounds like a plan to me :-P

From my understanding to set the preload I have to put the box together without the shafts in it and torque it down. Then wrap a sting around the diff and tighten the nut down until 11 lbs of force is required to pull the string in steady state motion. Is this correct? I am using the existing bearings.

I bought another castalated nut and just used that in reverse with 2 bolts drilled and tapped into it.

Worked an absolute treat and cost a fraction of the cost of making one / buying the correct tool, plus you get some spare seals in it as well - bargain.

Are you installing new thrust bearings or keeping the old ones, there is a different pre-loading tequnique.

Edited January 19, 2007 by Drfatz

[Jonathan 13]

Ah, did you not mark the nut/casing where the original castle nut position was ?

The proceedure for spinning the diff with a pull weight is for re-fitting with NEW bearings so you don't tighten them too much they seize or run hot and too slack that they play. With run in bearings you will probably struggle achieving this depending on the wear.

When I did mine the plonkers who worked on it before took the nut off and just put it back any old how which mean the diff wobbled in the casing and was as slack as Alice - therefore I did not have a reference. With the advice of Mr UN1 (Derek Bell) the diff was loaded until the play was removed from the bearings and then nipped by 1/12th turn until they felt good (impossible to describe but it's tight not to free roll and loose enough to spin nicely).

I only mention it because I had to find this out the hard way, Derek Bell was about the only one not to give me the silent treatment on questions (perhaps they didn't know themselves ?).

Rest is piece of cake apart from the FINE threaded bolts at the rear of the casing - ENSURE they are clean threads or you might strip them as I did when reaching the torque, sadly they are fine threads and if a bit of poo gets in there it doesn't take much to bugger it all up - this happened to mine, I just hope the repair is upto scratch and the gearbox doesn't explode 1st time out !

[Drfatz 0]

The guys that put my gearbox together did not set the preload at all they just put the box back together and let it be thus I am basically starting with used bearings and no reference for the nut. So in my case should I just tighten it up until the dif feels like there is no play and then back it off 1/12 such that it "feels good"?

Ah, did you not mark the nut/casing where the original castle nut position was ?

The proceedure for spinning the diff with a pull weight is for re-fitting with NEW bearings so you don't tighten them too much they seize or run hot and too slack that they play. With run in bearings you will probably struggle achieving this depending on the wear.

When I did mine the plonkers who worked on it before took the nut off and just put it back any old how which mean the diff wobbled in the casing and was as slack as Alice - therefore I did not have a reference. With the advice of Mr UN1 (Derek Bell) the diff was loaded until the play was removed from the bearings and then nipped by 1/12th turn until they felt good (impossible to describe but it's tight not to free roll and loose enough to spin nicely).

I only mention it because I had to find this out the hard way, Derek Bell was about the only one not to give me the silent treatment on questions (perhaps they didn't know themselves ?).

Rest is piece of cake apart from the FINE threaded bolts at the rear of the casing - ENSURE they are clean threads or you might strip them as I did when reaching the torque, sadly they are fine threads and if a bit of poo gets in there it doesn't take much to bugger it all up - this happened to mine, I just hope the repair is upto scratch and the gearbox doesn't explode 1st time out !

[Jonathan 13]

Yep you were left in a similar position to me

Derek has rebuild upteen UN1's and also makes the upgraded shafts for it and that was his advice which I consider valuable.

I basically hand tightened it and then turned it about 1/8th turn each time until I could grab each of the output shafts and feel no play in the bearings with vigorous shaking, then I cranked it very slightly 'tighter' by a small fraction before marking it off.

The feel I thought was about right is when the differential initially is stiff but once it gets going it rotates freely but with no run out it, it stops dead when you stop pulling - Mine was smooth running but firm in that it had absolutly no play in it atall.

Remember when you part the gearbox again to back that nut off 1 complete turn or you can put false torque on the case bolts as they tighten up against the differential bearings and not the case havles ! Re-tighten the loading bearing when you've assembeld the whole lot and give it a rotation test.

Problem is unless you renew your bearings you're playing with a little bit of fire because setting this wrong can wear the crownwheel and pinion like what happened to mine, but I believe if you follow that somewhat then you've done the best you can.

I'd also be inclined to change the gearbox oil twice as regular for the 1st few periods and observe any fouling in the oil.

[Drfatz 0]

Well I certainly appreciate the advice! This whole project is like playing with fire, if any one thing breaks the whole project is blown to hell....but that

Edited January 19, 2007 by Drfatz

[sanj 12]

Well I certainly appreciate the advice! This whole project is like playing with fire, if any one thing breaks the whole project is blown to hell....but that

[Jonathan 13]

Personally I would never pre-load a used bearing with new bearing values, not just for the bearing's sake but the gear set as well.

The old bearings are going to be worn and by cranking that nut in too much to achieve NEW pre-load settings on a used bearing will result in pushing the crownwheel out and away from the pinion so they wont mesh propperly.

On my gearbox the nut bottomed out before the defined pre-load was reached which is what confused me, however, as Derek pointed out it's easy to skip over the small print in the manual/bible :

If the original differential bearings and crownwheel and pinion are refitted, tighten the nut to the reference mark and ensure the differential rotates freely without any bearing free play.

If new bearings and/or crownwheel and pinion are fitted, screw in the nut until the differential is slightly

stiff to rotate. Then check the preload as follows: blah blah blah

All Derek suggested is the same as the top paragraph. I done it by feel and it's certinaly not impossible

If you wanna go 100% then get new bearings and use the draw pull method, up to you.

[Drfatz 0]

I'm with you Jon, I did it by feel and if the gearbox blows up the first time out...well then at least it will build some character!

Personally I would never pre-load a used bearing with new bearing values, not just for the bearing's sake but the gear set as well.

The old bearings are going to be worn and by cranking that nut in too much to achieve NEW pre-load settings on a used bearing will result in pushing the crownwheel out and away from the pinion so they wont mesh propperly.

On my gearbox the nut bottomed out before the defined pre-load was reached which is what confused me, however, as Derek pointed out it's easy to skip over the small print in the manual/bible :

If the original differential bearings and crownwheel and pinion are refitted, tighten the nut to the reference mark and ensure the differential rotates freely without any bearing free play.

If new bearings and/or crownwheel and pinion are fitted, screw in the nut until the differential is slightly

stiff to rotate. Then check the preload as follows: blah blah blah

All Derek suggested is the same as the top paragraph. I done it by feel and it's certinaly not impossible

If you wanna go 100% then get new bearings and use the draw pull method, up to you.

[sanj 12]

I'm with you Jon, I did it by feel and if the gearbox blows up the first time out...well then at least it will build some character!

Having done the preload adjustment (with new bearings), I will guarantee you nobody without years of experience rebuilding these boxes is going to know what the correct "feel" is. The bearings are not that expensive, so it seems rather foolish to put it back together without replacing them. IMHO.

[Jonathan 13]

I'm with you Jon, I did it by feel and if the gearbox blows up the first time out...well then at least it will build some character!

It wont blow up, the gearboxes are a lot more durable than people give them credit for with the 4cy application. Mine was in a state before I stripped it down, upon inspection the only fault that was found was obvious wear on the pinion gear where the diff had not been pre-loaded at all and it was free to rattle around which is why it dropped 3/4 of it's oil past the seals !

The idea is to tighten the thrust bearing nut so they are not too slack in that play can cause expensive wear to the crownwheel and pinion (they are a matched pair and costs a bomb to replace, unless like me you buy one at a Lotus sale for 1/8th the cost ).

Conversly if they are too tight the friction is too high and the bearing temperature heats up significantly - this not only wears the bearings to a point where they wont be in tollerance, but also significantly raises the oil temperature inside the gearbox reducing it's lubrucation properties !

It mattered little to me as my crownwheel / pinion were already worn due to the mal-adjustment so adjusting it correctly will just lead to it re-wearing - since I intend to punish it on the track anways the thing is going to get better maintenance than most of the other road cars out there !

Am I right in thinking that you have the gearbox in 1 piece on the car atm or it's all apart ?

[Drfatz 0]

It

[sanj 12]

It

[Jonathan 13]

Dunno where you got 120-150 from, it not in my manual

The correct setting is 30-40nm or 8-9lb/ft.

Bearings, in the UK...about

[Drfatz 0]

Well I just ordered a set at $38 per and I knew there was something wrong with my manual because it definitely says 120-150 lbf (I believe it was 150 but may have been 140). I will just install new bearings so that there is no question about it.

Dunno where you got 120-150 from, it not in my manual

The correct setting is 30-40nm or 8-9lb/ft.

Bearings, in the UK...about

[Jonathan 13]

Incidently mark off a point on the nut/casing where you think the diff feels good now.

When you fit your new bearings and get teh correct pull weight, see how close you got when you wind it down.

It wont be spot on but it should be pretty close if the bearings are the same spec and tollerance.

Hope it all goes smoothly for you, it's a fun job - remember to clean them bolt holes out !

[Drfatz 0]

It is to bad I am here in the US and most all of you LEF guys are over the pond for when she is all finished she is going to be a masterpiece!

Incidently mark off a point on the nut/casing where you think the diff feels good now.

When you fit your new bearings and get teh correct pull weight, see how close you got when you wind it down.

It wont be spot on but it should be pretty close if the bearings are the same spec and tollerance.

Hope it all goes smoothly for you, it's a fun job - remember to clean them bolt holes out !

[sanj 12]

Well I just ordered a set at $38 per and I knew there was something wrong with my manual because it definitely says 120-150 lbf (I believe it was 150 but may have been 140). I will just install new bearings so that there is no question about it.

The '88-'92 service manual had an incorrect conversion from Newtons to lbf, resulting in the erroneous figure of 120-150 lbf. Late manuals corrected this conversion error, and also lowered the preload spec, resulting in a corrected value of 8-9 lbf.

[Drfatz 0]

I guess I still don't understand why they are listing a torque value. When you measure the pull strength using the fish scale you are measuring the load as applied to the differential outer housing. Yes this is a torque with respect to the center rotation shaft, but that means I have to go and measure the radius between the central diff shaft and the outer casing and convert that to the proper amount of force needed to pull the diff as read on the scale. Why didn't Lotus just say 8-9 lbs of pull force? Instead of lbf? Or did they mean it as a load and not a torque, i.e. if my scale reads 8 lbs as I pull on the diff then I am okay?

The '88-'92 service manual had an incorrect conversion from Newtons to lbf, resulting in the erroneous figure of 120-150 lbf. Late manuals corrected this conversion error, and also lowered the preload spec, resulting in a corrected value of 8-9 lbf.

[Jonathan 13]

Initially it's all got to do with my mate Mr Newton (Issac to his mates)

When he invented gravity

Yes the measurement is a form of torque but given that the radius of the diff body is say....3" (or 0.25 feet)

0.25' radius x 8 lbs = 2ft/lbs ?

Do you know a torque wrench that can do that hehe

The only accurate way to do it is to use a spring balance really.

They must mean lbs instead of lbf as the other reading of 30-40 newtons is approx 3.3 - 4.4kg of load (at earths gravity to be picky - 10 newtons roughly equals about 1.1kg of force). There are approx 2.2 lbs in a kilo so you can work it out from there.

You put the scale on and pull, you take the measurement when the diff is rotating at a constant speed.

[sanj 12]

Or did they mean it as a load and not a torque, i.e. if my scale reads 8 lbs as I pull on the diff then I am okay?

This is correct, the use of lbf in the manual is incorrect IMO.

[Drfatz 0]

I figured it ment lbs and not lbf because lbf is not even a correct notation!

Initially it's all got to do with my mate Mr Newton (Issac to his mates)

When he invented gravity

Yes the measurement is a form of torque but given that the radius of the diff body is say....3" (or 0.25 feet)

0.25' radius x 8 lbs = 2ft/lbs ?

Do you know a torque wrench that can do that hehe

The only accurate way to do it is to use a spring balance really.

They must mean lbs instead of lbf as the other reading of 30-40 newtons is approx 3.3 - 4.4kg of load (at earths gravity to be picky - 10 newtons roughly equals about 1.1kg of force). There are approx 2.2 lbs in a kilo so you can work it out from there.

You put the scale on and pull, you take the measurement when the diff is rotating at a constant speed.