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MG TD TF 1500 - Front Wheel Bearings
|Has anyone changed the front wheel bearings on a TD from the original ball bearings to a tapered roller type? It would seem that the tapered style would handle the side loads of steering better than a ball bearing. |
If you have changed, what bearing and cup numbers were used? Any other problems or concerns?
|John - You have e-mail.|
|Instead of tapered roller bearings, why not fit angular contact bearings, which are ball bearings designed to take a much higher side load. If you type in "angular contact bearings" on google, you are sure to find a site that shows you how they are made; they were also the normal bearings fitted to wheels for much of the sixties, seventies and eighties. They are a direct replacement for the original bearings, thus no machining, and must be fitted back to back without the central spacer. Thus the main nut must be done up until the bearings just feel slight resistance. I fitted a set to my TD about fifteen years ago, and have yet to take up any wear.|
For the TD/TF/YB the bearing codes are 7304 and 7306 per wheel.
For the Y/TA/TB/TC fit 7304 and 7305 per wheel.
Are you certain that you can delete the spacer? I allways thought the smaller bearing races must be tightened up solid, against a spacer, otherwise they can rock on the shaft. The spacer's length must be adjusted with shims so that when the nut is tightened hard there is the correct end float on the bearing. This is detailed in the MG B workshop manual.
|I have installed a set of angular contact bearings in a customers TA. I used the spacer, but machined it down to a preload of about .005"-,010"|
The design of angular contact bearings, which are ball bearings, is such that the balls run slightly up the side of their housings, which are in fact one-sided. Thus they must be fitted in pairs, back to back, with the securing nut tightened until the bearings just have rolling resistance. The central spacer must not be fitted as it would prevent the securing nut being tightened correctly - this requirement is given by all the manufacturers of such bearings. Wear will occur after many thousands of miles, when the securing nut can be retightened, thus no need to replace the bearings.
These bearings are NOT the same as ordinary ball bearings, as they are designed to take a considerable side load. They do in fact do a similar job to tapered roller bearings, but these are normally used for front wheel drive wheel bearings, where there are considerably higher loads involved. Angular contact bearing are of a simpler design, and can normally be fitted, as in our case, as a direct replacement for ordinary ball bearings without any machining.
|I will try to get one of our MI MGT members to comment on these bearing issues.|
Tom Burke was for many years a bearing engineer and has knowledge far in excess of the multitude.
He has recently restored his TD and all of the bearing have been replaced with modern races.
We are talking safety here so it would be great if a bearing expert can comment. I still maitain that any bearing that takes a thrust / axial load must have a spacer so that the smaller races can be tightened up solid. If not the small races can move on the stub axle - ok only a couple of thou but still enough to cause metal fatigue in the shaft. Can you also ask Tom about the so called sealed bearings. I always thought the neoprene seal in these was to keep dirt out. I have spent a considerable time converting my pre war MG from felt to modern lip seals only to be told that simply replacing the old bearings with sealed ones will keep both grease and oil from leaking out. I can see it may work with the former but not the latter.
|It will certainly be interesting to get an expert opinion. When I first switched to tapered roller bearing on our TD, I left the pacer out since modern cars don't use a spacer between the inner races on their installation. I ran the TD for several years that way and never sao any indication that there was any kind of a problem. Later, I was convinced by other people who I considered more knowlegable than I, that the spacer was needed to tension the stub axle and that without it, the axle could develop a crack and eventually break. Since then I have dutifully run with the spacer in place. Other than meaning that I have to fuss with shims a bit to get the castelations of the nuts to line up with the cotter pin hole, this has not been a problem. I, for one, would be interested to hear what a real expert has to say on the subject. Cheers - Dave|
|Spridget (frt) and 1100/1300 & Mini (rear)use angular contact ball bearings, spacers on the fronts but not on the rears. Note that front wheel application involves significant side thrust loads, hence bending loads on the spindle; rears do not.|
Earlier (TD etc)cars use standard Conrad bearings, with spacers. These have very limited thrust capabilities, and are a poor choice for any application where increased thrust loads are used, as in racing or sticky tires.
mga twin cam & MGB use tapered rollers with spacers.
Most American cars use tapered rollers, without spacers.
Earlier American (e.g. Chevrolet) frequently used fully separable angular contact balls, without spacers.
Standard ball bearings, called Conrad bearings, have limited thrust capability, and great radial capability.
Angular contact ball bearings trade some radial for more thrust, usually this means the bearing can be smaller and lighter in auto apps.
The typical British angular contact bearing can have the races separated, but they are such that the races normally stay together unless worn.
The common early American type angular contact balls have easily separable races, giving greater still thrust vs radial capabilities.
Any ball bearing is much easier to manufacture than a tapered roller unit, and they were the first angular contact "anti-friction" or rolling element bearings - which is why they show up mostly in older designs.
Tapered rollers are also angular contact rolling element bearings. They have much greater load capacity in both thrust and radial directions for a given OD and width; the ratio is variable by changing the contact angle. They are much harder to manufacture, more critical in mounting, and give a much stiffer bearing/shaft assembly. They were a development of the Timken company, now effectively dead in the the US, though the name lives on. Note that all "Timken" bearings are tapered rollers, thus there are no "Timken" numbers for other types, something frequently requested on these boards.
The advantage of the shimmed adjustment is that it stiffens/strengthens the spindle, and once set, allows relatively troublefree assembly by people incompetent or too rushed to figure the adjustments out.
The no spacer/no shim system for either angular contact balls or tapered rollers is adjusted entirely by the nut position, and is subject to gross error or abuse at each dissassembly. It does not give the stiffness in the spindle assembly that the spacer provides.
Any angular contact bearing, with either shimmed or screwed adjustment, can be set with end play, zero play, or preload - which one depends on the application and expansion characteristics of the parts. Most common on wheel applications is minimum measurable end float - .002
The argument against the use of spacers locking the races in place is that it is desirable from a longterm wear standpoint to have the inner race SLOWLY rotate on the spindle, so that the mainly unidirectional load is not always on the same (bottom) area of the inner race. This is not nearly as important on the relatively lightly loaded auto hubs as it is on heavy duty parts like steel mill rolls, etc.
Personally, I regard the spaced tapered rollers as the best all around setup for wheel bearings. The overall stiffness of the assembly is especially important on heavily loaded disc brake spindles, where spindle or bearing flex knocks the pads back, giving poor brakes in the heat of battle.
|The engineers at M.G. were experts, and they were on a budget. If they put a spacer in the hub, then there was a good reason for it.|
|Gordon A. Clark|
|T series MG's were designed to use deep groove ball bearings on the front wheels. I believe they are 6304 and 6306.|
I was in the bearing business for 30 years, and I can tell you that the quality of today's bearings,versus 50 year old bearings, metalurgy, roundness, load ratings, speed limits, have improved drasticly.
The combined Dyn. load ratings (in today's bearings) of a combination of the 6304 and 6306 bearings on a front wheel is now 45 kilo newtons, or 9900 pounds, a deep groove ball bearing will accept at least 1/3 of this in thrust, whics is prox. 3300 lbs. (per wheel) What more do we need ?
I would not recommend the use of sealed bearings, because they are limited to the amount of lubricant which is injected into the bearing cavity before the seals are installed. this small quantity of lubricant looses its lubricity after a while and is not replennished.
The malor causes of bearing failure are improper installation and lubrication.
Back to the original:
DONT BUY ANTIQUE BEARINGS FROM A VINTAGE CAR PARTS DISTRIBUTOR.
Buy new bearings from a bearing distributor FAG,SKF, NTN,what ever (not chinese)
Inspect the bearing inner ring surface on the axle shaft, and the outer ring surface in the wheel hub. If there are any signs of metal distress :scaling, rust, scratches, flaking, then these parts need to be changed, or metilized and machined to the original tolerences.
Unlike most other mechanical applications wheel bearings are a slide fit on the inner ring, and intreferance fit on the outer ring (hub), which means the outer ring of the bearing is bigger than the hole it fits into. (Im sure you all knew this)
Once your shaft and hub fits are right, (any reputable machine shop can do this for you) You can install the bearings.
I suggest you pack the bearing cavity full of grease (make sure you use wheel bearing grease which is more fibrous than other greases and prevents it from washing out too quickly) then seal the bearing in a ziplock bag and put it in your freezer fo a half hour or so. this will shrink the bearing enough that it can be tapped into the hub.
Bearing rings are made of high carbon steel, and will crack easily, so dont hit it with a hammer, or a hard steel punch, instead get a piece of 1/4inch mild steel bar from your local hardware store and use this to drive the outer ring into the hub, by tapping your new tool with a hammer gently around the outer ring till it is driven home
Add an extra gob of grease inside the hub (close to the bearing) and in the hex. nut cap and your bearing will be happy, and live for ever !
I drove a TD for many years and now am the prowd owner of a 49 TC which I restored a few years ago, and spend much time fussing over, but I never worry about my wheel bearings.
Happy MG ing.
|Gordon A. Clark|
|This didn't actually come from me. I asked Bob Paquin to offer his comments on the angular thrust bearings, since he was in the biz for 30 years.|
|Gordon A. Clark|
|All well and good, but beware of using catalog bearing ratings for this application. The one sided loading at a considerable radius from the bearing causes much higher loads than you might think. The radius at the bearing race is on the order of one inch, while the load is applied to one side (bottom) at about 12 inches. That divides the rated thrust load by a factor of 12, giving around 300 lbs, and that does not include impact loading, which is unpredictable and way evil. Impact loads are virtually all on a few balls (draw a diagram, contact within the bearing is normally at the bottom of the inner race and the top of the outer, for angular contact bearings, or the top and bottom of both for Conrad bearings), and drive them into the races, causing early failure. In a hard turn, the entire car weight is effectively on the outside front wheel, to which you can add the unknown impact loading from a pothole, or the loads from braking or power on conditions. Spindle deflection is a known issue with many cars in hard use - and spindles do not deflect to the known degree with only "design" loads! OTH, catalog ratings are generally for many more hours than any car could dream of, so you may never experience a failure.|
|I like the tapered roller set up as it is robust and pretty foolproof. If I remember correctly it was a straight changeover operation. I discarded the spacer.|
|List of suitable Frt. wheel bearings for the TD|
Inner: R&M 23MJ30
NTN 6306LLUC3 sealed
Timken LM67048 / LM67010
Outer R&M 9MJ20
Timken LM11949?LM 11910
This is from a list of bearings given to me by Tom Burke (TD) who worked for many years on the Auto OEM supplier business.
This thread was discussed between 30/05/2007 and 19/06/2007
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