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MG TD TF 1500 Gearbox Tip BBS discussion at MG-Cars.info
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MG TD TF 1500 - Gearbox Tip
| I've had a really good tip from someone who has had a great deal of experience with T Type boxes on resolving a common problem with the TD/TF gearbox, that being when difficulty is experienced engaging 3rd gear, or if jumping out of 3rd gear is a problem. The fault can be traced back to the centre mainshaft bearing washer, Moss P/N 324.480. Over time this washer gets hammered flat & ends up being way thinner than it should be, thus preventing total engagement when selecting third. The washer is cheap enough at just $2.79 but can make a huge difference to the operation of the box. If considering reconditioning your gearbox, add this really inexpensive component to the list of essential items to replace. Cheers Peter TD 5801 |
| P Hehir |
| Peter - The inner diameter of the aluminum washer from Moss is larger than the original. It fits loosely on the mainshaft so that it may contact only a portion of the circlip. The original fits tightly to the shaft. The Moss washer is flat instead of curved like the original. Don't know if either of these makes a difference. I elected to reuse an original washer in my TF gearbox that I am installing in the car today. And yes, it was mashed pretty flat between the bearing and the distance tube. Moss #324-480, WASHER, center mainshaft bearing, illustration #60. Lonnie TF7211 |
| LM Cook |
| Thanks Lonnie. Be nice if the after market stuff was the same as the original but I know I'm dreamin'. The fact that it isn't curved may well be a problem as the effective thickness of the washer is key to positive engagement. Let me know if you have any difficulty in finding 3rd once the box is back together. As you probably saw on the other thread mine was missing the split pin, spring, ball arrangement at the base of the lever. Increasing the tension on the ball did make a difference when engaging 2nd but 3rd is still a problem. I don't want to strip the box again, use the washer from my favourite supplier & find that I still have a problem. I'll ask the guru here what he thinks. I wonder if the gap you were inquiring about earlier could be down to this washer? Cheers Peter TD 5801 |
| P Hehir |
| Peter - The washer won't affect the gap between the circlip and first-second sliding hub. The washer goes on the other side of the circlip. I hope to finish installing carpet and hook up everything today. Then take a test drive before heading to Ocala (150 miles) for GoF South tomorrow morning. I'll let you know how it performs. Lonnie TF7211 |
| LM Cook |
| I found the same problem with third gear and the washer. On my gearbox it was actually missing and I could measure approx. 1.5mm play on the shaft. Barrie Jones spotted it immediately when I consulted him at the time-spot on. The Moss/Abingdon washer is not aluminium and needs to be dressed with a file for a tight fit. This reduced the play to 0.05mm. Regards Declan 
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| Declan Burns |
| Lonnie, Look me up at GOF South...I'll do the same! Gene |
| Gene Gillam |
| Gene - Will do. I'll be able to lower off the jack stands this afternoon. Cross my fingers ... hope the freshly rebuilt gearbox and other gremlins don't rear their ugly heads. Lonnie TF7211 |
| LM Cook |
| Peter: Does your expert have a similar explanation on why the car might jump out of first gear occasionally? Checked everything multiple times and replaced gears etc. and it still happens about 10% of the time. Since you never know you always keep your hand on the shifter with force to hold it forward. |
| Christopher Couper |
| Declan the aluminium description had me wondering but as the part came from you know who I figured anything was possible. Thanks for posting the pic. I can't see if it is slightly dished though. Is that the case? Lonnie does it engage 3rd easily when you're in the driveway with the engine off? I shall consult with the oracle Chris. One thing he did mention though was that driving with a hand on the gear stick actually causes wear, which of course is not what you describe doing. If an overly thin washer can cause jumping in third I'd guess the relevant washer thinned by wear could also produce the same symptoms in first. I will inquire & I'll report back. Cheers Peter TD 5801 |
| P Hehir |
| Just for everyone's info, Lonnie and his TF made the trip to Ocala. Nice putting a face to a name! Gene |
| Gene Gillam |
| Chris I Googled your question & a BBS reply from George Butz in early 2014 suggests a possible remedy. "This is a very common problem. My car did the same with new cluster and first gear for years under hard acceleration. Make sure that the detent ball/spring under the rear of the top cover is engaged and centered in the notch in the 1/2 shift rail when in first. If not, something in the mainshaft is mis-shimmed or out of position. If it is, then the "fix" is to add an extra detent ball/spring. Search archives, details in there somewhere. There is a slotted screw in the rear tranny housing, I think on the right side and adjacent to the row of detent balls and springs. Remove the screw, shift into first, use a thin punch and make a dimple in the 1/2 shifter rail. Then remove the rail (don't let the detent ball bearings fall out into the bottom of the tranny!), and file/grind a detent notch into the side of the rail (match the contour of the top ones). Reassemble , put ball bearing into the hole, and fit a detent spring (you will have to shorten it a bit) and adjust, put the screw back in. This give first an extra detent in first only, and cures the popping out. I think John Twist does this on all of the TD trannys he rebuilds. George" Yet to talk to the knowledgeable one here but when I do I'll be back in touch. Cheers Peter TD 5801 |
| P Hehir |
| I think there were issues with the mainshaft flange nut being loose that caused popping out of 3rd. Maybe the washer squishing causes the nut to loosen? BTW, ate dinner last night with Gene and Lonnie, what a great evening of cars and camaraderie! George |
| George Butz |
| I picked up the steel washer mentioned above from Sportsparts this morning & have run my digital vernier over it. The washer I purchased is 0.040" thick, isn't dished, it's totally flat. The other two dimensions are as follows; O.D. 1.501" I.D. 1.118" I'm going to see if I can find a local replacement that is cheaper than either the Sportsparts item & the even more expensive washer from Heritage MG Spare Parts in Sydney. As it's just a washer it should only cost a few cents, not $6 plus! Also wonder if it's available in stainless & if so whether it would then be more durable? Cheers Peter TD 5801 |
| P Hehir |
| Precision Shims in Melbourne can make them for about $4 each in stainless to the exact dimensions above. Metric equivalent is 38.1 x 28.4 x 1. (40 thou is actually 1.016 mm but being 0.016 mm thinner shouldn't make that much difference). Lead time is about 5 working days. I've ordered 3. Cheers Peter TD 5801 |
| P Hehir |
| The bearing shield at the top of the photo is Moss #324-480. The original shield is below it. Both are aluminum. The Moss shield is approx 1.1735" inside diameter. The original is approx 1.120" I.D. Barrie Jones' gearbox video shows the bearing shield fitting tightly against the mainshaft. Both are the same O.D. The Moss shield is thicker than the original. I did not measure. A previous shield that I bought from Moss had the same instructions as the one that is in Declan's pack ... "This may require some smoothing/filiing to properly fit." It has an Abingdon Spares part number on the package. I don't know what a proper fit is. The Moss shield is flat. The original is dished. Barrie Jones says that the convex side goes against the bearing. You can see the impression of the split ring on the original shield. The other side is mushroomed at the motion shaft where it was pressed into the chamfer of the bearing. The distince tube inside the rear case presses the bearing into the shield and against the split ring. I read somewhere that the torque of the rear flange pressing the tube is 65 ft-lbs. The larger I.D. of the Moss shield will not contact the split ring uniformly. Lonnie TF7211 
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| LM Cook |
| Lonnie the washer that I purchased from Sportsparts is the washer identified as Moss 324-480 illustration number 60, described as washer centre mainshaft bearing. This is as I described, a flat hardened steel washer, as are apparently all washers/shims used in automotive gearboxes because of the need to withstand the forces exerted. Aluminium washers or shims simply couldn't take the pressures involved & would be reduced in thickness quite rapidly. The TC box did have a dished washer but this was never fitted to the TD/TF. I have again measured this washer & the dimensions are as stated. See pic below. It is just possible that Sportsparts have provided the incorrectly dimensioned hardened steel washer & I will only know whether this is so when it is fitted to a gearbox that is currently being assembled. I'll pass it on to the guy who is reassembling that gearbox & report back. Cheers Peter TD 5801 
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| P Hehir |
| Chris, according to a gentleman who has restored "dozens of TD/TF gearboxes" apparently there are many causes of TD/TF boxes jumping out of 1st, almost all due to wear in the selectors, forks, springs, hubs etc. There is one notable exception. About 25 or so years ago a number of cluster & 1st gears were made for & sold by a company in England by the name of Toolman Motors. What is not generally known is that 1st gear is not parallel cut as everyone states, but actually has a 1 degree offset! This helps ensure that the gears stay engaged. When the manufacturer who provided a batch of the cluster & first gears to Toolman Motors machined these gears, the drawings they worked from neglected to include the offset. The result was a sudden jumping out of 1st under acceleration. This was only discovered some considerable time after these gears were in service. Cheers Peter TD 5801 |
| P Hehir |
| Interesting. My cluster gear was replaced after a long search in the mid-70s. Don't know if it was a finally unearthed factory gear or a repro at that time. Selector rail, balls and springs were replaced with NOS stuff I found on ebay some years back, and it still jumped out, hence the modification. George |
| George Butz |
| Peter - I suspect you mean Toulmin Motors. Tom Lange MGT Repair |
| t lange |
| I guess so Tom. I got the info over the phone & orthography was never my strong suit. I still have indents across the knuckles from the ruler wielding nuns! Cheers Peter TD 5801 |
| P Hehir |
The guard washer that was in my latest TD parts transmission on disassembly was worn badly where the circlip ate into it. It measured .031" thick and was steel. I ordered one from Abingdon Spares and got the one in the photo. It is steel and measures .060" thick, 1.500" od, and 1.1735" id. It is a loose fit on the shaft and would not evenly distribute the load on the circlip. Since the thickness of these washers from various suppliers seems to differ so much, I don't know what thickness is correct to purchase in advance from another source. Obviously, the thicker the better since the washer carries the load against the circlip when the tail shaft nut is torqued. I guess, I will have to wait and dry assemble the main shaft parts to see what the gap becomes between the bearing and circlip, and then find a washer that provides adequate clearance. I was looking in the McMASTER-CARR on line catalog and it shows various thickness steel shim washers in a size that I believe will fit tightly on the shaft and work even though the od is a little larger. 
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| Richard Cameron |
One more comment--- With seriously worn original guard washers observed, and replacements of incorrect dimensions. One can only imagine how many transmissions are in service with faulty parts producing shift problems. Thanks Peter for the "Heads Up" resulting in discovery of this issue. |
| Richard Cameron |
| The stainless washers that I can get made in Melbourne are either 0.86 mm (0.0335") or 1.15 mm ((0.0453"). It seems the thicker this washer is the less likely the synchros are to engage completely, if I understood what the guru here said correctly. He did say that the box was a precise piece of engineering, that tolerances were small & that a few thou could make a huge difference. I'd love to know exactly what this washer/shim size was when the boxes were assembled originally. Is it possible that they differed in thickness even then, due to slight manufacturing variations in the cumulative arrangement of the gears? Perhaps this was one place where any variation could be negated? Just thinking out loud is all. Cheers Peter TD 5801 |
| P Hehir |
| My guess is that the thickness of the bearing shield determines the position of the mainshaft and therefore the sliding hubs and dogs under the shift forks. All detent balls should be fully seated in each gear. A too-thick or too-thin bearing shield could move the mainshaft enough to prevent one or more balls from completely seating. Result could be noise and rapid wear of the forks and dogs, or even jumping out of gear(?) Pretty hard to determine the thickness that is needed in a 60-year old gearbox. Probably need to assemble it with new parts, measure the free play of the forks in the dogs; then disassemble and insert a shield of the required thickness. Don't know many people willing to do so. My freshly rebuilt gearbox makes a "ZZZZZZZZ" sound in the shift lever. I assume that it is caused by the forks rubbing against the dogs. Possibly a result of the mainshaft positioned too far aft because of the worn/thin bearing shield. It shifts fine and stays in gear under hard acceleration. Lonnie TF7211 |
| LM Cook |
Agree with Lonnie's input above. However, some have said the original washer in question is concave/convex. I suspect this isn't the case and the original was flat. The washers seen that are dished is because they have been distorted by applying so much torque on the tail shaft nut. The washer presses against the low profile circlip and the chamfered edge of the adjacent bearing which bends the inner edge of the washer. I don't know who came up with the 65FtLb torque of the tail shaft nut, but it seems way too much to me. I don't see how anyone could expect that low profile circlip to handle that kind of pressure. the nut certainly needs to be rather tight and be cotter pinned, but What is the right torque? |
| Richard Cameron |
| Peter, I have never seen any documentation on how to align the box, but I can give you my observations. I have determined 4 reference points, with the box in neutral, how each part should be placed compared to these points. Reference points are: 1/ Position of the centre indent of the 3rd/4th selector shaft should align with its ball and spring. 2/ The 3rd/4th sliding dog locates on its sliding hub by 6 spring loaded balls. 3/ The 3rd/4th sliding hub has one spring loaded ball in its bore, this locates in an indent in the mainshaft (mod on later gearboxes). 4/ The 3rd/4th selector fork should sit into its sliding dog without pushing the sliding dog out of its rest (Ref 3/ and 4/) position. All of these give the required postion of the mainshaft and is adjusted by shimming between the circlip and the centre mainshaft bearing guard. Adding thickness moves the mainshaft forward, removing moves it rearwards. The bearing guard is the washer which you mention in your initial comment. Now the problem is how to determine the correct shim thickness. Firstly I made a fixture which held the springs of the 3 selector rod balls compressed, this replaces the top cover. Then I assembled the complete mainshaft and primary shaft and placed it in the box,added, spacers bearings rear flange and nut. everything but the the layshaft assembly and rear casting.. Then fitted the 3rd/4th selector rod and fork with its balls and spring and used the homemade fixture to locate the shaft, (My reference point 1/). I then fitted a dial indicator, with a magnetic base, to the front of the box and the plunger on the 3rd/4th selector rod front end. Now this is where I needed a "feel factor" I checked the position of the 3rd/4th striking dog compared to te sliding rod, if required moved them into their correct location and read the dial gauge. this reading is then the thickness of the shim which either needs to be added or removed, depending on the direction mainshaft moved. This may seem an overkill, but I prefer to spend time up front, than pull the box out of the car. John |
| J Scragg |
| John - Thanks for your tip. Eliminating the input shaft and laygear from the test fit simplifies the process. I'll use your method to adjust the mainshaft bearing shield when I rebuild my spare gearbox. Lonnie TF7211 |
| LM Cook |
| I agree that the original was flat Richard & no doubt the cause of the dishing is as you suspect. Your method makes sense John. The fixture you mention I've used when examining the operation of my gearbox with the cover off. It was made from the end of a cover from an old gearbox that had seen better days. Just needs to be big enough to cover & compress the balls in the end of the box. I especially like the removal of the layshaft & the use of the dial gauge. Clever. Cheers Peter TD 5801 |
| P Hehir |
While cleaning the old bearings to determine their suitability for reuse, I discovered a new (to me) fact I hadn't noticed before. The original main shaft bearing R&M LJ1-1/8G that is adjacent to the guard washer has a sharp 90 degree inner edge on the front side. It isn't chamfered like some bearings. My bet is that replacement bearings have chamfered edges (thus the bent washers). I ordered new bearings, so I will see what I get soon. 
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| Richard Cameron |
This thread was discussed between 20/04/2016 and 30/04/2016
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