Radius arms. which side is up - IRS First Time Rebuild

(Matt Furness) #102

Yes!!! Nice. This should be in the Haynes XJS manual instead of the fuzzy illustrations in chapter 8…you have to take it to bits to understand how it works…which is a valid approach but can lead to frustration and completely eliminates the critical stage of beersies and staring at the manual…which CAN be unkindly misinterpreted by the wife as “time wasting”…!!!

(Matt Furness) #103

Yep…it is actually “clearance” between the tightly sandwiched hub/spacer/driveshaft and the bearing arrangement. I am fairly sure it is to cope with thermal expansion because if you do a quick and dirty calculation on the difference in expansion between the aluminium housing holding the bearings and the steel inner parts tightly sandwiched together…and assume a temperature increase of about 40 degC then you get about 0.002". Within ballpark …so a likely reason.
If it is thermal expansion then if you make it too little clearance the expansion increases the bearing contact pressures which increases the temperature which increases the contact pressure …and so on.
I don’t like the detail. My brand new bearings and spacer are set with 0.002" end float …and are a bit “loose” when cold…which I don’t like.
I must check this when it is warmed up after a moderate drive …hopefully it is “less loose”…!!!

(tony) #104

the puzzle (for me ) doesnt end there…the diff output shaft bearings have the same arrangement as the hubs, and set up with endplay also, but the housing is iron or steel afaic, and when I inquired I was advised by a pro here on this list that those bearings should be set up with pre-load

I have a diff pumpkin from a MKX which I checked to see if it was powr-lok (it wasnt), however, the output shaft is seized, and upon examination, this has taken place due to too much pre-load on the bearing

I was advised by that pro, that tapered roller bearings not setup with pre-load are liable to fail

in the end I followed the FSM and set the endfloat to spec

(Matt Furness) #105

I haven’t touched my diff…but according to the XJS manual …" when finally assembled there must be a compression (nip) of 0.003" on the oil seal and ball bearing…so deduct this from …etc etc"
So some preload specified…possibly the different expansion is the answer…

(tony) #106

Yes you are correct, I double-checked the manual, and it is a pre-load on the output shafts, and endfloat on the hubs, so the different expansion of aluminium vs steel makes for a logical explanation for that confusion, so thanks for that!

(Frank Andersen) #107

With tapered rollers; the aim is to give enough room for effective lubrication, grease, between rollers and tracks, Tony - without excessive play, and relating to nut torque…

Three illustrating examples. On front wheel bearings the nut is gradually tightened until rotation resistance is felt, ‘preload’ then then backed of to get intended bearing play. Nut torque is not specified…

The diff drive pinion bearing: A collapsible spacer is used - to be crushed gradually with increasing torque while measuring force required to turn the pinion. When the turning force reaches the spec value, ‘preload’, the bearing play is correct. The torque is not specified, though ‘ballpark’ figures are given. Theoretically; spacers could be used, but it would involve trial and error to get the preload right - impractical in this context…

The rear hub: Here a spacer is used to fix inner race position at the required clearance; the spacer abutting the hub - and the nut torque is specified. Torque is there only to hold the assembly together, but plays no part in bearing play…

In all cases, preload could be used - and is in a way on the front wheel bearings. On the rear hub, it could be used with hub carrier on the bench; the drawback is that two bearings are involved in measuring - which sort of complicates preload specs? And, as play can be checked and adjusted on-car; preload is then impractical due to driveshaft/diff interference…

So when ‘play’ tolerances is given; use that - and if ‘preload’ data are given use that. It’s means to the same end…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Mark Lee (Pay Pal Patron)) #108

Sorry for the delay, Damn work got in the way.

I’ve read the dummy bearing post several times; but I’m not sure if I understand; actually I know I don’t understand how that’s supposed to work? You’re still pressing stuff on and off multiple times right? Or do the dummy bearings have a bigger inside diameter so the dummies can slide on and off the shaft in order to set the preload,. Is this when its worth purchasing the bearing installation tool - This one?

The reason why I’m laboring over this issue is because I don’t have the proper pressing tools; I got the hub out of the carrier by using wood blocks, square tubing, pipe fittings for pressing & a ratchet strap to hold everything in place. To say it was a kluge would be an understatement. Orchestrating this kluge was like putting pantyhose on a drunk chick.

That being said, I don’t want to run the risk of damaging the already damaged hub; or damaging a replacement hub.

Sorry, I"m over thinking this process… I’ll stop here.

(Mark Lee (Pay Pal Patron)) #109

I sincerely appreciate the conversation over the preload. It’s given me alot more insight of what going on.

Thank you!

(Mark Lee (Pay Pal Patron)) #110

I was on XKS.com website, and they’ve got the bearing kits as well as fulcrum kits too. So does SNGBarratt.com In my personal opinion I prefer dealing with the later.

(tony) #111

I will explain it in more detail.

get the old (or a brand new bearing) do one of 2 things.

using a air die grinder or drill fitted with a small sanding drum, hone out either the ID or OD of the bearing.

do this very carefully, until such time as it is possible to push the bearing onto a shaft, (or into a housing if OD is honed)

this means instead of a interference press fit, it will be a tight slip fit, and can be installed & removed with hand tools, not a press…it cannot be at all loose

check google/youtube about this, there will be heaps!

an alternative is specail tools with dummy bearing blocks made of aluminium

its fairly difficult to remove some press fit bearings that are close to the hub, pinion head etc, even with a knife edge bearing separator, as sometimes you cannot get under the inner race, but the seperator grips the cage, and ruins the new tight bearing. This is a very unhappy situation if things are not right first time

you cannot use a damaged or worn bearing as a dummy bearing, it must be in excellent condition to start with, or it will not be accurate. One should measure the compressed thickness of old vs new bearing first and it should be within .001"

Once you have made a “kit” it is good for multiple re-use

here is one showing an ID to go over a shaft, as I mentioned, if can also be done to the outer race OD, if that is being pressed into a housing…note, imo, his bearing is too “wobbly” after honing, they should be as tight as possible

(tony) #112

that is why it is a really good idea to check the hub endfloat before dismantle

if it tests in spec, that means when it is put back together with new bearings, and the original factory master shim, it should be perfect 1st time

if the bearings or master shim are damaged, endfloat will not be correct when measured before you take it apart

I dont understand why the FSM doesnt say to do this first

on my 420G rebuild, as the hub area passed all tests in spec, was low mileage, and well lubricated, I did not feel it needed to replace the lower fulcrum or hub bearings.

I did pull the half-shafts, and replace all other parts

(Foggyoo) #113

Should there be movement at the tread of the tyre?
If so, how much?

(tony) #114


there should be no lateral movement at the lower link ?

according to the FSM there should me max ~.003" (cold) endplay at the hub bearings, which is part of the upper link

so maybe a very little.

havent ever put a dial gauge on the tyre to check exactly how much for that purpose

If I can feel a tyre moving laterally, thats a cause for investigation

(Foggyoo) #115

The xjs is safety checked every 6 months, and has been OK’d every time so far after checking the rear wheel movement.

(Mark Lee (Pay Pal Patron)) #116

The illustrations are so much better in the old manuals. I’ve got the XJ Series I - III and the Series I is my goto manual; unless what I’m doing is spacific to a certain Series.

I love the 420 such a wonderful complement of Style Grace and Pace.

(Robin O'Connor) #117

There will be a small amount of movement at the extremes of the tyre but not a great amount. If the testing station report play in the 12 - 6 o’clock ask them to identify if it is wheel bearings or play in the U/js on the half shaft.

(Frank Andersen) #118

Look at the ‘dummy’ pictured, Mark…

The big diameter acts on the bearing inner track - pushing it in. The smallest diameter fits inside the hub - where the driveshaft later comes in. The in-between step abuts the hub; it is actually a ‘dummy spacer’ (0,150" thick) restricting how much the inner bearing track can be moved as it is pressed in, by a press or whatever Which creates an initial play…

…which you measure. Then you remove the dummy, compute the required thickness for the proper spacer to give the correct play of 0.001 - 0,003". (Bewilderingly; 0.003 - 0.006 is also quoted - but the former is likely the right one). It’s actually the same procedure as adjusting valve lash with shims - if that rings a bell…:slight_smile:

Example; you measure 0.025" with the dummy, which is 0.150" thick. You want 0.002" - which is 0.023" smaller than the dummy. Or 0,150 - 0,023 = 0,127". Which is the spacer letter ‘G’…

You can of course omit the dummy and just fit a provisional spacer - just make sure it is of excessive thickness. Otherwise you have to struggle to retract the inner track from the hub…:slight_smile:

The important thing is to ensure that the inner track is pushed in square - whether you use a press or force it in by other means…

xj6 85 Sov Europe (UK/NZ)

(Frank Andersen) #119

Like checking the front wheel bearing play, Foggyoo - though a bit of slop up front is less important.

With proper bearing play there will inevitably be movement - ‘no’ movement is not really ‘good’, it implies too little bearing play…

xj6 85 Sov Europe (UK/NZ)

(Frank Andersen) #120

As an afterthought, Robin - rear hub/hub carrier temp can be easily measured with an infrared thermometer after a run. With inboard brakes; brake heat is likely negligible - as probably is tyre heat. So heat generated would be from the bearings - and not normally a hill of beans, unless something is wrong…?

xj6 85 Sov Europe (UK/NZ)

(Robin O'Connor) #121

True, next time I take the S11 out I’ll see if I can remember to check the temp of the rear hubs.