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MG MGB Technical Intermittent transmission judder BBS discussion at MG-Cars.info
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MG MGB Technical - Intermittent transmission judder
| Hi, Appologies in advance for the lengthy post! I've had my '66 GT (3 sync + overdrive) for 9 years now; since I bought it, it's always had a problem with intermittent transmission judder. Most of the time it's completely smooth. However, sometimes it will start to judder very badly when moving off from a standstill in any gear (well, 1st, 2nd and reverse anyway). The judder is only whilst engaging the clutch - there's no roughness to the engine, and once the clutch is fully engaged it's business as usual. Changing gear whilst moving is also normal and there's no roughness or pushback from the clutch pedal - hence I don't think it's clutch judder. I don't think it's ever done it from cold, but normally it's after a run and everything's nice and hot. Other times it won't do it at all! Over the years I've tried various things and taken it to various garages and specialists. Of course, it never judders for them...! I have changed the engine and gearbox mounts (except the very rearmost gearbox one - the garage gave up trying and said it looked in good condition anyway). One garage suggested it might be hot oil leaking into the bell housing, but it uses very little oil and there are no drips from the housing. We've even tried slipping the clutch in a high gear to try to burn off any contamination on the clutch but nothing has worked. I've learned to live with it, but it does rather spoil the driving experience and is quite embarresing in stop-start traffic! Today, however, I noticed what might be a new clue. We moved house recently and the new driveway is gravel rather than tarmac or paving. I've noticed that when juddering, it will VERY easily spin a wheel on the gravel (today it was the left wheel whilst reversing but I don't know if that's always the case). By "very easily", I mean it's almost impossible to move the car without digging a hole in the gravel first! I wondered if this might be a sypmtom or clue? I guess it might be because of the "snatchy" nature of the power transfer to the wheels and a function of the diff (as it's not limited slip)? I wondered if it might be a rear brake sticking, but I can still roll the car by hand and the rear brakes have been rebuilt during my ownership with no change to the juddering issue. I think the only other thing to mention is the rear axle has some slack in it (resulting in the normal "clunk" when taking up drive) but I don't think it's too bad and I don't see how that could contribute to an intermittend problem like this. The specialists who have driven it also didn't comment on it. I gather it's also not the "correct" axle for the car - I can never remember if it's a banjo or Salisbury, but it's the one it shouldn't be for a '66 GT! Again, don't think that would make a difference but mention it for completeness. Any ideas would be very much appreciated! Cheers, Tim |
| T Jenner |
| Tim, I've owned my '67 B since '72 and I'd bet money that you have a contaminated clutch disc or perhaps a broken spring in your pressure plate. It seems to me that a clutch replacement is at hand. The earlier diff that you are running, the same as I have, makes no difference as far as your problem is concerned. RAY |
| RAY |
| Tim I would bet with Ray on this one, a little oil on the disc can cause an on and off judder without a major slipping problem. When you take it apart,[and you will take it apart] let us know what you find. Ric |
| RIC LLOYD |
| Tim, I think I'm going to have to go with RAY and Ric on this one. Sounds like it is in the clutch to me. I can only think of one other thing I’ve had that is a similar experience, which seemed like the clutch or driveline, but was not. I have a tendency to come off the clutch from a stand still at very low RPM. I thought I had a snatching clutch or wind up in the drive line, but it turned out to be the need for new points or cap or rotor or wires (not sure which since I did them all at the same time). At the low RPM the engine was trying to die, and when it caught up, it felt like snatching. Since you have had the problem for 9 years, this is not likely to be your problem. Charley |
| C R Huff |
| I had a Celica that would very occasionally clutch judder on take-off, I just pushed the pedal back in a bit and tried again. I had a new clutch in my roadster and that juddered far more frequently than the old clutch, usually manouvering at slow speed, I found using higher revs than I otherwise would avoids it. Others have said using higher revs *causes* it. Whatever, that was umpteen years and 40k miles ago, it still does it, I still avoid it, and I have no intention of digging into it until the clutch needs replacement again anyway. OTOH I had a Mini with a leaking crankshaft oil seal which had contaminated the clutch, and that was also either in or out i.e. would spin a wheel on loose surfaces. That took the CV joints, so I had clutch, oil seal and joints replaced as a package. If it *is* an oil seal you should have oil dripping out of the hole in the bottom of the bell-housing, which should have a loose split-pin floating around in it to keep it clear to reveal just such a leak. |
| Paul Hunt |
| Thanks for the feedback, all. I was hoping there'd be a magic fix which wouldn't involve changing the clutch! :) I'll have another look to see if there's any oil dripping from the bell housing, must admit I've never noticed a split pin under there. If it turns out to be contamination, which seal is it which would cause it and how much of a job is it to fix? Cheers, Tim |
| T Jenner |
| Tim, A leak out the hole where the cotter pin should be can be either the rear main seal for the engine, or the front input seal for the transmission. Either way, the engine has to come out to fix it, at which point you might as well replace both along with the clutch. Alternatively, just keep trying to drive around it as Paul mentioned, and make sure everything has enough oil. Charley |
| C R Huff |
| Well I did some ringing around to see what sort of money I'll be looking at. I would normally tackle it myself, but I'm pushed for space in the garage and want the car driveable for what's left of summer! Quotes range from £550 (ouch!) to a slightly more palateable £300-ish to supply and fit a Borg & Beck 3 part kit (plus extra if there's a leaking oil seal to fix, etc). However, one garage mentioned the frightening possibility that it could be an overdrive problem. I'd not thought of that before - has anyone else come across it? I don't think it is the OD as the juddering stops as soon as the clutch is fully engaged - I can't imagine how an OD fault could behave the way it does? Cheers, Tim |
| T Jenner |
| Tim, I have a 66 BGT which had the same faults as yours. I did what Paul did/is doing, waited until the engine needed to come out for a rebuild, then changed the clutch plate (worn), thrust bearing (worn out), but retained the pressure plate which was still in good condition. I did partially remove the glazing on the flywheel and pressure plate. It is now working the way it should and with no indication of a judder. Stop kidding yourself looking elsewhere for a quick fix, it is the clutch. :( Richard. |
| RH Davidson |
| I would vote for clutch, maybe thrust bearing? The choices are to do it now, or leave it until it's a lot easier to diagnose, and just relax and enjoy the car in the meantime. The main reason for posting is that the GT was only ever fitted with the Salisbury axle. |
| Stan Best |
| Tim, If your immediate concern is having it running for the rest of the summer, I suspect it is already fixed. Check the engine and trans oil now, and lay it up for repairs when the weather gets nasty. Maybe by then you will have the room to do it yourself. Charley |
| C R Huff |
| I don't think space is going to get any better unless the garage grows or the car shrinks! Is the "thrust bearing" another term for the release bearing (i.e. the carbon one which comes as part of a 3-piece clutch kit)? I'm almost resigned to having to get it done - is there anything else sensible to do whilst the engine's out? For example, if there's no sign of a leaking oil seal is it worth changing regardless? Thanks, Tim |
| T Jenner |
| Tim, Over here a clutch release bearing and a throw out bearing are the same thing, but a thrust bearing is in the engine (as part of the main bearing set) to keep the crankshaft from floating fore and aft. Tough call on an old oil seal that isn't leaking. I would probably change it anyway thinking that it may be getting hard even if it hasn't started leaking. Charley |
| C R Huff |
| Highly unlikely to be an OD problem if it only occurs when moving off from a standstill i.e. when slipping the clutch. If there is oil dripping it could be from either the crankshaft oilseal, the gearbox first-motion shaft oil-seal, or the gasket for the carrier for that oil seal. However only the crankshaft oil seal is likely to contaminate the clutch. The problem with "while I'm in there" is that it can lead to changing all three of those oil seals and gasket plus the pilot bearing, and there is nothing to say that you won't be replacing a good item with a faulty and start a leak where there wasn't one before. OTOH the disturbance caused by splitting and reassembling the engine and gearbox could cause an old seal that isn't leaking already to start to leak if it isn't replaced! A friend and I recently changed his clutch and decided to leave everything else as it was, and I think we have got away with it. However we did a 3-piece replacement i.e. friction plate, cover plate and release bearing, I think leaving the old cover plate in there when you have it apart for the purposes of changing the clutch is false economy. |
| Paul Hunt |
| It certainly looks like your clutch disc and pressure plate needs to be replaced but check that there is no play in the universal joonts and that the rear axle U-bolts are tight |
| Iain MacKintosh |
| Well I had a quick look under the car last night and found a couple of interesting things. First off, there IS a loose split pin under the bell-housing - I'd just not noticed it before! Next, there IS quite a lot of oil all over the underside of the engine and gearbox; however, I think it's old oil covered in road grime. It's impossible to see where it's coming from but there are no drips from the split pin that I could see. If I get a chance at the weekend I'll try to clean it all off and go for a drive to see if anything appears. The last thing I noticed is the clutch arm is missing the rubber boot to seal the hole in the bell housing. The arm itself is covered in what looks like an oily greasy mess! I don't know if it's oil, road grime, or what and I can't tell if it's coming from inside or being coated from the outside. How critical is the boot - is it possible that oil from under the engine along with road grime and muck is getting onto the clutch through the hole and causing the judder? How easy is it to fit a new boot - can I just unbolt the slave cylinder, slide the boot over the clutch arm and bolt the cylinder back on? I did get a picture but couldn't upload it last night for some reason. I'll try again tonight. Cheers, Tim |
| T Jenner |
| I actually meant to type release bearing but had thought abut oil on the clutch and thrust washer must have been an engineering Freudian slip. I imagine you could get contamination of the clutch if the boot was missing, so a new one well worth trying although I'm not sure you can get it over the fork, a bit of washing up liquid may save you here. Your idea of a clean up and then a test drive is the place to start though. |
| Stan Best |
| OK, managed to upload a picture of the clutch arm now - ugly, isn't it?! You can see an aweful lot of "gunk" on the arm - any ideas what it is or where it's coming from? I've ordered a gaiter so will try to fit at the weekend, along with cleaning everything and checking the rear suspension U-bolts for tightness. Cheers, Tim 
|
| T Jenner |
| Tim, When you check the U-bolts, don't confuse tight U-bolts with nuts rusted solid to the U-bolts. Charley |
| C R Huff |
| Thanks; should I check the U-bolts with the car jacked up or on the ground? Cheers, Tim |
| T Jenner |
| Page 34 of the new Moss download catalog discusses resolution to the problem as you describe. Pulling the engine to replace the clutch will give you a chance to clean everything up and look for any oil leaks. Save the new gaiter until then. I'm betting that the problem is the flywheel-to-clutch disk surface. Wayne |
| Wayne Pearson |
| Looking at that picture i would say that there will certainly be contamination on the clutch plate. It doesn't really matter if it has come from the inside to the outside or vice versa, the clutch will need changed. Pulling the engine is not that difficult and will take you a day and save you about £200. Up to you whether you pay someone or not! You could do with working out where all that gunk has come from. I'd clean it off and see where it starts to appear from. If it is from somewhere else then fix that leak. Unless you find evidence of an oil leak from the crankshaft seal or gearbox front cover then I would leave them alone. More chance of introducing a leak! Cheers Iain 67 BGT |
| I D Cameron |
| Thanks, guys. Was hoping a good clean up and fitting the gaiter might put off the clutch for a while given the intermittent nature of the problem but it sounds like that would be optomistic! I'll still do the clean up and depending on the weather at the weekend maybe do the gaiter. I'll also try to book it in for a new clutch! Would like to have a go myself (have helped remove the engine and fit a clutch to a Morris Minor before but there's a bit more space to work in there!) but I fear lack of time and space in my own garage would turn it into a rather longer exercise than I would like! Wayne - can you point me to where in the Moss catalog you're talking about? Page 34 seems to just talk about changing clutch fluid to synthetic? Cheers, Tim |
| T Jenner |
| Tim, For checking the U-bolts, it doesn't matter if the car has weight on it or not. I don't think your are going to fit under it and be able to see anything if it is not elevated. Ramps would be nice. I have done it by driving one side of the car up on a curb. I don't think cleaning anything you can reach while the car is assembled is going to fix anything. But, cleaning it up before you disassemble it may be the only way to know where the leaks are coming from so that you can fix them while it is out. Like Iain said, you can do it in a day (if you are well organized, have the parts on hand, and have someone who can resurface the flywheel while you wait). Charley |
| C R Huff |
| That looks like external dirt and oil to me. As the arm aperture is below the centre-line of the clutch I can't see much getting up inside to contaminate the friction plate. If some at least is from a leaking crank seal, hence dripping off the split-pin, then the usual evidence of that is oil spots on the ground where you park. Of course maybe where you regularly park looks like the Torrey Canyon has passed by at some point, but if you put a clean board underneath overnight then before you move it look to see what and fresh drops line up with. Of course it could also be leaking from the gearbox seal or seal plate gasket, as the gearbox should contain engine oil you won't be able to tell the difference, so you will have to lay in all three. |
| Paul Hunt |
| The catalog is located at: http://www.mossmotors.com/SiteGraphics/CatalogPDFs/MGB-0808.pdf The page 34 that I referred (looking at the numbers at the bottom of the page) is actually 97 of the pdf document. Page 1 of the catalog (after you get past all the sale and special item stuff) is 64 of the document. Wayne |
| Wayne Pearson |
| A lot of that looks like road dirt to me, although my car is quite clean in that area. Personally I would fit the new boot, be careful not to let the piston out of the slave cylinder, then clean it with a degreaser and see how it goes. The clutch may improve to the point where you can run it for close to its expected service life. |
| Stan Best |
| What's the best way of fitting the gaiter with minimal disassembly? I was thinking of undoing the two bolts holding the slave to the gearbox casing, moving it to one side leaving the pushrod attached to the clutch arm, then undoing the split pin and removing the pushrod from the arm. From the manual it sounds like the pushrod just pulls out from the clutch slave - is that right? Presumably, then, you just push it back in when you reassemble? Do you need to remove the boot from the slave cylinder or take any special steps to stop the piston coming out? I'm also assuming you can't get the gaiter on the clutch arm by just undoing the split pin and pulling the pushrod off - you have to move the slave cylinder out of the way to get enough clearance? Cheers, Tim |
| T Jenner |
| The piston should be retained within the cylinder, the push-rod simply pulls out of the boot on the slave, the bell-housing gaiter slotted on, and and the push-rod pushed back in again. When you buy a new slave cylinder it comes ready assembled, the existing push-rod is just pushed through the boot. BT, DT, recently. |
| Paul Hunt |
| Well, I tried to clean up and fit the gaiter this afternoon and failed miserably! I can't get the car high enough with my (cheap) axle stands to get far enough under gearbox to work. :( However, I did manage to get a better look at what's what and it does appear to be oil from inside leaking out rather than road dirt getting in. The split pin in the bottom of the bell housing was surrounded by muck so I cleared as much as I could and will keep an eye out. Interestingly, I also checked the gearbox oil (something I used to do regularly but confess I worked out it's been about 7 years since I last did!) and it was just below the minimum mark (I used to make sure it was at Max). There were also clean oil drips on the gearbox drain plug - I don't think it's leaking from there, so I guess it runs down to there as a low point? Regardless, I'll book the car in - hopefully a clutch and a couple of oil seals will sort it! Thanks for all the advice, I'll report back on what the garage finds! Tim |
| T Jenner |
| Tim, My 66BGT has similar symptoms so I'd be interested to know how you get on. I'd also be interested in knowing which garage you use - I am in Surrey too. Where abouts in Surrey are you? cheers Richard |
| Richard |
| Richard, I live in Woking. I'm probably going to book it in with MotoBuild in Egham - never used them before but they're close and quoted a good price. Unfortunately it's going to be another 3 weeks until I get a chance to take it down there (as they'll need it for a couple of days due to some other minor work I want them to do) but I'll report back on what they find. Cheers, Tim |
| T Jenner |
This thread was discussed between 16/08/2008 and 26/08/2008
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