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MG TD TF 1500 TD gearbox rebuild BBS discussion at MG-Cars.net
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MG TD TF 1500 - TD gearbox rebuild
| I rebuilt my late TD gearbox as part of my restoration. I replaced the layshaft (not the laygear), 1st gear and sliding hub, and all bearings, bushings, shims, and seals. It is still jumping out of 1st gear under load. The small gear on the laygear was deemed worn but serviceable by a mechanic but now I have doubts. Another suggested that the new 1st gear may not mesh as well with the worn laygear as the worn one did. Finally, the new sliding hub (the inner part of the 1st gear on the splined shaft) is slightly shorter on the shaft than the old one, allowing it to slide nearly 1/8" back and forth on the splined shaft. The old one had some movement but not as much. Is this part of the reason for jumping out of 1st gear? What is the factory spec length for this inner hub? Any ideas will be welcome. |
| B Roseberry |
| Did you replaced the " spigot bushing on the flywheel ? A worn bushing could be the source of the problems you discribed . |
| Gerard Hengeveld |
| Gerald, How does a worn pilot (or spigot) bushing effect the trans in such a way to cause it to pop out of first gear? Alex |
| Alex Waugh |
| Was it jumping out of 1st before you did the rebuild? If so, it is hard to see that the little extra movement in the new sliding hub could be the cause this problem. Since there must be some lateral force on the gears to make them slide out of mesh I suspect that the small gear on the cluster has teeth that are tapered along their length. Unfortunately it is impossible to have a look at the cluster unless the gearbox it totally dismantled. Cheers, Hugh |
| H.D. Pite |
| Alex, Hugh gave you almost the answer or better possebilety's severe play on the gears ( first motion shaft )COULD be the culprit . But as Hugh stated you have to take the gearbox apart to investigate. Gerard |
| Gerard Hengeveld |
| B, are you sure the gear mechanism is fully engaging the gears? i.e. all the slop in the remote shifter, shifting rails and forks is taken up? is there significant shift lever movement when it pops out of first? regards, tom |
| tm peterson |
| The remote shifter was rebushed and seems smooth. The selector forks seem pretty snug in the striking dogs. The 1-2selector rod does seem to want to move into neutral but only when the top detent ball is not under pressure. When under pressure from the spring, it seems reasonably fixed. The bushing at the back of the crankshaft was replaced during the earlier rebuild. The TD has only several hundred miles since then. So far, the only obvious things to me seem to be the fore/aft movement of the inner 1-2 slider on the third motion shaft splines or wear on the small gear of the laygear. I did find that the nut on the flange which connects to the driveshaft was a little loose, allowing some minor fore/aft movement of the flange at the back of the gearbox. Again, thanks for your ideas. |
| B Roseberry |
| The shift lever does move toward neutral when it jumps out of gear. |
| B Roseberry |
| 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 |
| George Butz |
Is the shifter fork worn? Ed |
| ECS Stanfield |
| George, I'll look for that slotted screw tomorrow when I get back on it. I believe I understand the concept but it will be clearer when I'm actually looking at it. I do think the existing top detent is correctly located under the spring & ball. Ed, when I wiggle the selector shafts fore & aft, there isn't any noticeable play in the forks. I think the forks fit the striking dogs within tolerances. Thanks again for the suggestions. Bill |
| B Roseberry |
| I second the diagnostic from Hugh? That there is wear on the first gear cog on the layshaft cluster. If the teeth are worn to a taper then you will get a component of the force pushing the first gear forward. The only thing preventing the assembly from sliding apart is the detent ball and spring, if the teath are worn then the ball and spring are not strong enough to keep the gears from separating. If the teeth are pefectly parallel then the separating force will be near zero, in that case the detent ball and spring is capable of holding the two gears together. John |
| J Scragg |
| Thanks for all the great suggestions. I'll be tearing into it again tomorrow and be back here when I have the laygear out. Bill |
| B Roseberry |
| Note my comment: mine would come out of gear with a brand new cluster and first gear, so that had absolutely to do with wear on the teeth! Really search the archives for this, as it has been thrashed around before in detail (which I don't remember). Adding the extra detent and spring may take an hour, not a bad idea to try that first IMHO. George |
| George Butz |
| George, I pulled the 1-2selector rod and added the described 1st gear detent. I had spare ball for the application but I need to get a spring. Looks right and makes sense. Guess I'll find out if it solves the problem when things go back together. Back on this site when I know. Thanks all. Bill |
| B Roseberry |
| Back again after getting everything out of the gearbox. The first motion shaft and bearing came out cleanly by tapping on the back of the third motion shaft. Laygear had been lowered to the bottom of the box to clear. I was at a loss to get the third motion shaft and it's bearing out. It was tight in the case and snug on the shaft. I Finally figured that what worked for the first motion shaft should work in reverse so I gently tapped on the front of the third motion shaft w/ a brass punch and lead hammer and the bearing gradually came out of the back of the case. It was still stuck on the shaft so I offset it from it's hole in the back of the case and tapped on the rear of the shaft until it popped loose. I supported the front of the shaft while doing this and there was no contact with the laygear. It seemed a lot easier than trying to pry it out with all the gears in the way. Attached is a picture of the laygear. These are the worst teeth, most are similar to the lower 2. Is it salvageable or am I screwed? Bill  |
| B Roseberry |
| Do not hesitate to give John Twist a call. He answers questions during their lunch break. He does transmission rebuild workshops and would most likelygive you exactly what you need to figure this out. |
| Bruce Cunha |
| john has a gearbox rebuild seminar coming up in the next few weeks i believe. regards, tom |
| tm peterson |
| I've worked on a lot of TD/TF gearboxes, as an amateur. The odd thing is that the TC box was sought after by dirt track racers for V8's, while later boxes are lucky to stand up to ordinary use. My idea, for what it's worth, is that the long rear shaft is the problem - it flails around. So, I'd recommend close attention to all the bearings that keep the two - piece shaft in line. David. |
| D A Provan |
| I've been offline for a while but I want to thank everyone for the great info and advice on my gearbox rebuild. Here's an update: After discovering the laygear was pretty worn on the 1st gear, I pulled and tore down the gearbox in my parts car TD. I put together one good gearbox from the best parts of both. I also added the extra 1st gear selector rod detent and ball for more positive action. While it was out, I inverted the engine and redid the front seal w/ the Volvo unit and new cork seal at the rear. After reassembly and getting engine and gearbox back in the car, I added a PCV system from the tappet cover road tube to the intake manifold balance tube w/ a pinto PCV valve. The gearbox now seems to work well and my pie plate oil puddle is now down to dime size or less. Thanks again for all the great suggestions. Bill |
| B Roseberry |
| Bill, I was thinking of you the other day. Thanks for the update and glad to hear you're back running again. Alex |
| Alex Waugh |
| Bill, Glad to hear that the PCV valve helped-it really does work as I have mentioned on here several times. Regards Declan  |
| Declan Burns |
| Declan, you picture fascinates me. I use three oil catch pans on the garage floor (big plastic storage bin tops) and although the quantity of oil loss is very small, it is always present when I bring the cart in from a run. Am I correct in understanding that the tube shown in your pic going dwn from the flame trap is connected to the road tube in the tappet cover and that the pcv valve vents into the back of one of the air filters? Also, is the cork in the valve cover vent tube holeless (i.e., no vent at all)? Thanks. Jud |
| J K Chapin |
| Bill, hope to see it in person this Saturday. Ed |
| efh Haskell |
| Jud, That is correct. The photo below shows it clearer. There is also a black rubber seal at the take off point on the tappet cover. The Pinto valve has two inlets one going to each side of the inlet manifold. The rubber bung has no hole and the oil filler has a similar but larger bung. Every source of infiltration air is sealed off as far as possible. The engine develops a vacuum at tick over which decreases with increasing revs. Air is drawn in through the leaky bits and where air is drawn in oil can't come out. It's that simple and it works. From a torrent to a trickle and a very cheap solution to an age old problem. It does upset the idle a bit. Regards Declan  |
| Declan Burns |
| Very interesting on the PVC stuff. I sure would like to see more pictures of the side cover hose/ fitting attachment, and know if the road tube is actually closed off. |
| Richard Cameron |
| Richard, There is no road tube. The side cover vent is plumbed directly to the flame trap. That engine side cover in the photo is actually from a Wolseley which I bought from Peter Edney in the UK. My car had an aftermarket Aluminium side cover which was not suitable for this mod but the standard TD cover can be used.It needs to be completely sealed. Regards Declan |
| Declan Burns |
| Not to hi-jack this tranny thread, but a few people asked about the PCV system. Here are a couple of pictures. |
| B Roseberry |
| Oops. No luck uploading my pictures. I'll try later. |
| B Roseberry |
I shrunk my files. Here's the PCV attachment to the tappet cover using a Pinto PCV valve.
 |
| B Roseberry |
Here's where I tapped into the balance tube of the intake manifold. It was suggested to go from the valve cover to the intake manifold, but I was trying to make the plumbing less conspicuous. It also allowed me to keep the stock air cleaner configuration.
 |
| B Roseberry |
| The copper tube in the previous picture has nothing to do w/ the PCV system. It's part of an AMPCO top oiler. |
| B Roseberry |
| I guess I'm the hijack culprit for bing so interested in Declan's PCV setup but now the deed is done and I don't know how to move all the PCV messages into a new thread so I'll just press on and make matters worse with apologies to the group. After looking at the PCV set up I was looking at the intake manifold on my TD and notice there is what appears to be about an 1/8" bung conveniently located on the top of the balance tube (see pic attached). I don't know if this is original or something a PO added but I'm wondering if it wouldn't be a good place to terminate a PCV setup similar to the ones shown by Declan and R. Roseberry? Also, instead of tapping into the road vent tube, could one just clamp a hose to the end of the tube and use that as the starting point for a PCV system? Thanks. Jud  |
| J K Chapin |
| Jud, I'm also to blame on the highjacking of this thread. It would be a good starting point but I would tap both sides of the manifold the next time you have it off just to be sure you have the right balance. Just connect the road tube to the flame trap with a Piece of hose as a starting point and ensure that it is sealed. How do we go about having the PCV discussion copied to a sepatate thread? Regards Declan |
| Declan Burns |
| I copied all the PCV stuff and put it in a new thread called something like "PCV for TDs." Jud |
| J K Chapin |
| Reactivated thread. Chris I found this thread (where the post from George came from) as I was keen to see if Bill ever solved his jumping out of 1st problem. It certainly seems as though he has, suggesting that the extra indent that George argues for is well worth doing & that the cause is not wear on the cluster & first gear but excessive fore aft movement. Cheers Peter TD 5801 |
| P Hehir |
This thread was discussed between 16/02/2014 and 24/04/2016
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