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MG TD TF 1500 Pinion Bearing BBS discussion at MG-Cars.net
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MG TD TF 1500 - Pinion Bearing
| Hi I am going to change the P and CW on my 1950 TD for an MGA 10/43. I have read all the archives and information I can find to prepare for the job, however some of the write ups seem to indicate that the outer races of the pinion bearing need to be frozen in dry ice for ease of fitting. I have tried to source dry ice to no avail is it possible to fit the bearing by just freezing in a domestic freezer, I will be making up a threaded rod puller to ease the fitting. Would be obliged for any experiences. thanks Barry |
| B Bridgens |
| Barry, We were able to source dry ice for our project at a place that sells bulk propane and industrial gases for welding to the public. I can't see how it would hurt to try cooling it among the frozen peas and carrots. If it works, great. If not, the dry ice search is on. Enjoy the process. Safety? Fast? Scott Ashworth - '54 TF |
| S. R. Ashworth |
| Hello Barry. You do not need to freeze the bearing. I use a threaded puller to pull both inner and outer races into the housing at the same time. I've done almost 100 conversions. Butch |
| R Taras |
| Hi Guys Thanks for the help, usually I put bearings in the freezer as a matter of course when fitting just to help a little. Yes Butch I was going to make up a puller, I started diving in this afternoon taking the whole thing apart. I'll order the bits tonight and see how I get on. thanks again for the help Barry |
| B Bridgens |
| Barry, do take a few photographs of the critical stages ;-) Best Regards Mike |
| Mike Fritsch |
| Barry, Where in France are you? I am in Antibes, if you are nearby I could help you with this conversion. Also I have all the parts ready to do mine. John 52 TD |
| J Scragg |
| Hi Mike I'll take some photos and post here. John I live near le Mans. I have to admit that reading the theory left me a little apprehensive, however now that I have started and with both MGA and TD exploded axle diagrams it all seems quite logical. I hope that is the case. Barry |
| B Bridgens |
| Hello Barry. Take car in setting the distance from the center of ring gear axis to the head of the pinion and the pre-load on the pinion bearings. The back lash between the teeth is the next thing to set carefully. The final thing is measure the thickness of the gasket between the housing halves. Set the gap the thickness of the gasket. I talked to Carl(who wrote the book) as I had a rear end come back with galled carrier bearings and discovered when doing the calculation for the bearing crush that he did not take into consideration the gasket crush. If you have questions don't hesiate to e-mail me. Butch |
| R Taras |
| Hi Butch Thanks for the advice, I'll be in touch if I have problems. Barry |
| B Bridgens |
| John, Barry, letīs keep in touch. I am just in the process of sourcing parts for my conversion. Iīm in contact with Declan Burns whoīs also close to starting. Unfortunately, we are all quite far from each other, Le Mans to Antibes is nearly as far as from me in the Frankfurt area. Best Regards Mike |
| Mike Fritsch |
| As for the cooling: blowing at the parts with a co2 fire extinguisher should also freeze them quickly (or any other compressed gas, preferably non combustibles) Rgds Mike |
| Mike Fritsch |
| Hi Mike, John I have never had problems fitting bearings by just putting them in the freezer so I gues this time will be no different, Butch seems to think it is not an issue. I have ordered the parts from Moss, fortunately they sell the special inner pinion bearing so I did not have a sourcing problem. I am replacing all the other bearings in the axle at the same time, seems sensible. The only problem I have at the moment is getting the pinion thrust washer surface ground to 2.38mm (0.094inch) which seems to be the general size requirement. I have also been told that the best size is the same as the original thrust washer taken from the TD axle. Either way I cannot find a local shop who will take it on. While the axle is out I am taking the opportunity to refurbish the springs and shock bushes, I have Girling shock absorbers, I am going to use the Nylatron pads from John James for the springs. I have a 4 ton press so hopefully I won't have problems with the shock arm and link bushes. more soon Barry |
| B Bridgens |
| Barry, I'm a little late to this thread, sorry. like Butch I have done about 70 of these conversions. I've exported one to Germany and one to New Zealand as well as more than a few to Canada. That aside pay close attention to everything Butch said. As to the replacement of the cones for the pinion bearings without building tooling the bolt method works well without freezing the cones. I use a little light oil on the case and cone surfaces. I've not tried it but I think you might be able to use the old bearings at each end of the bolt. Maybe upside down. I am concerned about using the arbitrary .094" spacer on the pinion shaft bearing. This is the "Atlanta Club" method and they have also done quite a few. I've tracked all of mine and they have been between .087" and the .094" Given Carl's belief that to be correct it needs to be within .001" I don't see how You can have it correct with that arbitrary number without risking improper mesh and wear to the gears. Dave |
| Dave Clark Arizona |
| Hi Dave Thanks for the input. The .087-.094 measurement you mention is that the measurement of the original TD pinion thrust washer. I feel that is the best way to go, measure the original thrust washer and machine the new one to that dimension, then use the inter bearing spacer reduced or plus shims to get the preload on the pinion bearings. Is this how you and Butch would do it? thanks Barry |
| B Bridgens |
| The machining of the thrust spacer is also the one point that really puzzles me. It starts with "how do you fix the thing",since itīs only a .1inch washer.... And when you look at "normal" adjustment procedures for other diffs, you would swap shims between the pinion head vs. between the 2 bearings to shift the pinion back and forth with constant preload. Now for the preload, the thin shims to do that are available, for the pinion thrust spacer, they donīt seem to be. And trying several ones at a cost of 30-40$ per unit is not really an option. Also, what do you do if you grind too much off ?? If we found a source that could make those at a reasonable price, I guess there would be some interest, or not ? I could imagine a base spacer of .085 and then a few thin ones to step it up to .95 should do the trick (e.g. .04, .03,.02,.01), if Daveīs range is representative, which I would believe is the case. Any ideas ?? Rgds, Mike |
| Mike Fritsch |
| Hi Mike The piece is held on a magnetic base for grinding. If you grind too much off a new one is not that expensive about Ģ6 from Moss, which would then have to be ground down again. The pinion thrust washer is I believe not a preload adjustment but a positional item to put the pinion in the right place. Preload is from the shims behind the bearing spacer. I don't really see how it is critical as the mesh of the pinion into the crown wheel can take quite a bit of positional movement any differences being taken out by backlash adjustment. I might be totally wrong here I am sure Butch and Dave will be along to put me right. Barry |
| B Bridgens |
| Barry, you are right anout the cost, I only looked at the smallest one, which is more expensive. Still, if you add the cost of the work, each one will probably cost 30, so there should better not be too many attempts... As for the exact positioning, Dave mentioned Carlīs .001 figure above, but you may be right and it is more tolerant if the backlash is adjusted properly. If the Atlanta chapter conversions all turned out ok in the long term, then that may prove the case for tolerance. Most of our cars are probably not driven that much, though, so it may be too early to tell ? To my understanding, the preload is still the sum of the thrust washer (which holds one end of the inner bearing) and the preload shims between the bearings (which hold the other end of the inner bearing). So if you change the thrust washer thickness to move the pinion back or forth, you need to modify the shims between the bearings to achieve the same amount of preload. I get the point about the magnetic base. Neat idea, but probably requires some specialised equipment. John, how were you planning to machine your washers ? Best Regards Mike |
| Mike Fritsch |
| Hi Guys. The pinion head spacer from the donor gear set can be used. It is ground on a surface grinder with a magnetic chuck to the distance needed. You can do a math calculation between the tow pinion heads to get a starting figure. I generally put in a .093 spacer and check with the factory tooling and use that as the starting point with the + or - on the new pinion head to grind the pinion head spacer. The pre-load on the pinion bearings is independent of the head spacer. Here again the spacer dimensioned by setting up with dummy spacer and shims then grinding on a surface grinder the spacer that came with the gear set to length. NOTE both the pinion head spacer and the pinion bearing spacer HAVE to be ground with parallel surfaces! The location of the pinion to the ring gear is such that you want the pinion meshing with the ring gear in the inner 3/4 of the tooth because as the rpm go up the mesh will move towards the outer edge of the gear under load. When you first start to take you differential apart open it and put bluing on the gears to see where they are meshing. Butch |
| R Taras |
| Mike, I have already done the work on the thicknes of the pinion head washer, did it by hand, initially on an oil stone then to finish on wet and dry paper and a piece of plate glass. I have the thicknes to 0.94" + or - 0.00025" (quarter of a thou) I am blindly following the virgin process. Dave Clark's commnt on this thickness being an arbitrary value is valid, as it does not consider the machining tolerences of the supports. The best way to to this job is with the original measuring jigs and fixtures. Anything else is a workaround. The preload shims easily available. I have point worth mentioning, which nobody has yet considered, it is the reference of the front bearing, this is the one nearest to the propshaft flange. The original number is "15100 S" (the S suffix is important) these are being replaced with a 15100 (NO S suffix) The only difference between these two parts is the the former has a much smaller redius on the internal diameter. However its price about 10 times the other. The only reason I can think of for using the S bearing is that there is a greater surface for the flange to press against, thereby reducing the pressure between the mating parts. Can anybody enlighten me on this? John |
| J Scragg |
| Hi John Well done on reducing the thrust washer thickness, do you have any fingerprints left? I don't know which front bearing will arrive with my order yet but I hope it is not smaller. I have removed the outer rings in the casing, the inner one wasn't too bad but trying to get a decent blow on the drift with a hammer on the outer one was pig, I have the grazed knuckles to prove it. To reduce the thickness of the pinion washer I have been trying to figure out a way of doing on my lathe but no luck yet. Other than the washer I am ready to go when the parts arrive. Barry |
| B Bridgens |
| John, why am I not surprised - being a semiconductor specialist, youīre the perfect guy for micrometer tolerances ;-). But good to know it can be done that way. Butch, good point to actually check the blueprint of the existing gear. That should indeed help to position the new one. I take it you donīt use any adjustment shims on the preload spacer except for the trials, but then make sure you gradually grind the final spacer to the right length? On the 15100S - I had the same question, Declan had the 1500S in his list as well. But I had the same issue you had when looking at the prices. Given that (if Iīm not mistaken) the bearing is the same that Moss and others supply for the MGA, I would trust the lower price, meaning the non-S version. The Atlanta chapter also lists the non-S. Since the torqe to the flange is transmitted via the splines, I donīt think the smaller area makes much of a difference (?) Best Regards Mike |
| Mike Fritsch |
| No worries guys,The 15100 (non S) will work fine. Dave |
| Dave Clark Arizona |
| Barry, It can indeed be done on a lathe. I tried making one yesterday just to see on my home built and it worked. The washer is held in with rare earth magnets. You need a very high quality chuck and take it very slowly-only a whiff at a time. The finish I got is actually really good but will do the final grinding of course on a glass plate. It actually turned out just as good as the one we made at my mate's place using a grinder for optical lenses. Regards Declan  |
| D Burns |
| Hi Declan Looks good,I would think you need a very sharp tool to cut the hardened steel. I compiled various methods in my mind, but by the time I had costed each one out for magnets etc. I went to a precision engineering company in le Mans who are surface grinding my washer for 30 which in the scale of things I think is very reasonable.I hope to pick it up on Friday and get on with the job. Barry  |
| B Bridgens |
| The washer thickness can be reduced by Aussie Bush ingenuity and very careful use of a flat bed belt sander. To hold the washer hammer a series of brads located around the internal diameter of the washer into a piece of flat wood. As the thickness of the washer reduces the length of the brads protruding from the wood reduce at the same rate,continual monitoring of the thickness reduction process needs to be monitored by taking micrometer readings at 12,3,6 and 9 0'clock around the washer. Graeme |
| G Evans |
| Yes Barry-you need a really sharp tool. I only used 2 5mm 52 grade magnets. It's just enough to hold it for fine cutting. The photo shows the holder with the washer removed. The finish is good even without grinding down. Regards Declan  |
| D Burns |
This thread was discussed between 20/11/2014 and 03/12/2014
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