tonycharente Posted January 7, 2018 Report Share Posted January 7, 2018 (edited) Hello All, My totally standard 1966 TR4A IRS has developed a bad clonking noise under load, and I am hoping for help with diagnosing the problem, please. After much searching I've not found a previous post with quite the same symptoms as I have. The car makes an awful noise only when it is going along and I think it is coming from the rear of the car. It is a loud “clonk clonk clonk” noise. I checked the oil level of the rear axle which is fine - very dirty (there is no drain plug on IRS diff) but up to level. When going forwards, it only makes the noise when under load. It does not make the noise at a standstill, nor when you lift your foot off, nor in neutral (or clutch in) coasting. I do not think the noise changes in turns compared to straight ahead, but it changes frequency depending on the speed of the car, turning into a steady growl at speed. There is no vibration, nor, I think, significant play in any of the U.J.’s. When going backwards it’s the same noise but only when decelerating. Otherwise driving in reverse there is no noise. With one rear wheel jacked up it is possible to get the same sort of “clonk clonk clonk” noise by spinning the wheel, but only by spinning the wheel backwards. Spinning the wheel forwards there is no noise. I worked out that when spinning one wheel backwards (as above) you get 13 clonks for 7 turns of the wheel. As the car has a 3.71 diff this means that the clonk is made once per revolution of the prop shaft - I therefore think I can definitely rule out the drive shaft U.J.’s. I am fearing that I have a broken tooth on the pinion in the diff, but if it’s that I can’t understand why the noise is direction of movement related. All thoughts and suggestions very welcome, thank you. Tony Edited January 7, 2018 by tonycharente Quote Link to post Share on other sites
RogerH Posted January 7, 2018 Report Share Posted January 7, 2018 Hi Tony, I think I'm in agreement with your diagnosis. With the car jacked and you spin the other wheel will it clonk as if going forwards.? You can remove the diff back plate and see inside - I think somebody did that recently. Roger Quote Link to post Share on other sites
tonycharente Posted January 7, 2018 Author Report Share Posted January 7, 2018 (edited) Hi Tony, I think I'm in agreement with your diagnosis. With the car jacked and you spin the other wheel will it clonk as if going forwards.? You can remove the diff back plate and see inside - I think somebody did that recently. Roger Thanks for your rapid reply Roger. I will definitely try what you suggest tomorrow, but what should I conclude from the result please? Not easy to remove the diff back plate on the IRS. I think my next step after doing what you suggest will be to disconnect the prop from the diff and then try the wheel spinning test again. If I get exactly the same noise I'll have eliminated the possibility that the noise is coming from the prop or even the gearbox. (Sources of noise can be very deceptive...) If I do get exactly the same noise with the prop disconnected, I'll see whether I can manage to remove the diff back plate with the rear axle in situ. Any tips for that, please? Many thanks Tony Edited January 7, 2018 by tonycharente Quote Link to post Share on other sites
RogerH Posted January 7, 2018 Report Share Posted January 7, 2018 Hi Tony, I've never done this so it would be useful if somebody came on and gave a good answer. Looking at the Moos WebCat https://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/clutch-transmission-drivetrain/axles-differentials/irs-rear-axle-differential-tr4a.html The backplate has the diff rear attachment attached to it. So jack up the diff. Unbolt the diff rear attachment. Remove the rear plate. It may be possible to see inside the diff and not any missing teeth. Look in the bottom of the diff for any debris. I had a problem once under power all was good. Decelerate and there was a loud banging noise. The front pinion into the diff had come loose. 'Power on' kept the pinion hard forward - no noise. Decelerate and the pinion was driven backwards causing it to hit the planet gear. Roger Quote Link to post Share on other sites
tonycharente Posted January 7, 2018 Author Report Share Posted January 7, 2018 OK, Roger, thank you - I will see how I get on and I promise to report back! Quote Link to post Share on other sites
tonycharente Posted January 8, 2018 Author Report Share Posted January 8, 2018 It’s been mild here today and so I spent the afternoon in the garage, (mostly under the car). Here is my "report". I started by jacking up the other wheel and doing the spin test - exactly same result as with the first wheel - “clonk clonk clonk” noise when spinning the wheel, but only by spinning the wheel backwards. I then disconnected the prop shaft from the axle and did the spin test again - same result, thus eliminating the prop shaft and/or gearbox as potential sources of the noise. I then removed the two silencers to gain access to the rear of the axle with a view to removing the rear plate to enable inspection of the inside of the axle without removing it from the car, as suggested by Roger. However this looked to be particularly difficult to achieve as both the top nuts holding on the rear axle mounting bracket and the top nuts holding on the rear cover itself looked particularly hard to get to. I am afraid, Roger, that I therefore decided it would be easier to drop the axle than to attempt to remove the rear plate with it in situ. So I carried on, removing the exhaust Y piece, undoing the drive shafts and finally balancing the axle on a trolley jack, undoing its mountings and lowering it precariously down. By which time it was getting cold and dark, so I’ve stopped there for the night. Having gone to all this effort I think I will probably buy a rebuilt axle with the 3.45 ratio, as I think this will make the car more useable in today’s world, especially as distances are often considerable in France. Thank you again, Roger, and sorry to have let you down. Tony Quote Link to post Share on other sites
Alec Pringle Posted January 8, 2018 Report Share Posted January 8, 2018 Hi Tony, please see PM Cheers, Alec Quote Link to post Share on other sites
tonycharente Posted January 9, 2018 Author Report Share Posted January 9, 2018 UPDATE Today I removed the rear cover. Everything looked perfect EXCEPT for the pinion, which looked to be missing a tooth... In fact it was not missing a tooth, as I had feared - it was missing two teeth! I found the broken off bits in the oil, each measuring around 40mm long. No wonder it was making the clonking noise... It doesn't really matter, but I wonder what could have made them break? So now I have to decide what to do. Various of the usual UK sources show exchange units, with or without brand new CW&P's. One of them told me that they don't do them with new CW&P's and instead use good original CW&P's because repro ones are of poor quality. Any thoughts on that anyone please? Just a quick extra comment about Roger's earlier suggestion of trying to inspect the state of the diff with the IRS axle still in situ. I think that aside from the difficulty of accessing the higher nuts, it may not be possible to remove the diff rear attachment (mounting) without at least lowering the front attachment, since the rear attachment is fixed to the rear cover with studs, not bolts. I think it may be impossible to slide the rear attachment rearwards off the studs as the mounting pins would be in the way. I think you'd have to lower the rear mounting to clear the mounting pins, and to do that you'd have to lower the front mounting too, and to do that you'd also have to remove the exhaust Y piece, so then you're only the UJ nuts away from dropping the axle out... I took a photo of the two bits of broken off teeth to show you all, but I can't figure out how to attach a photo - can it be done? Thanks to all, Tony Quote Link to post Share on other sites
RogerH Posted January 9, 2018 Report Share Posted January 9, 2018 (edited) Hi Tony, posting pics Click on 'more reply options; This will give a new bigger screen Click on choose file this is where the pics are stored on your computer Double click your pic The file name will now be at the bottom left corner of the screen C;lick 'attach this File. position cursor where you want the pic Click on add file. The pics need to be about 100Kb. If they are too big they will not load. If too small thety are difficult to view. Regarding rebuilding the diff. There is a decent garage/workshop in Leatherhead Surrey England Hardy Engineering I think Kevo had his diff rebuilt here before Christmas. They have done my GB's and OD's They are good at what they do. Can be quick if you ask them nicely. Not overly expensive They use quality parts. Your pinion would be 50 years old - the teeth don't last forever - excited driving will kill them. Roger Edited January 9, 2018 by RogerH Quote Link to post Share on other sites
ianc Posted January 9, 2018 Report Share Posted January 9, 2018 I'm afraid that loss of teeth happens - I have had it occur 3 times in 23 years, and although the engine is uprated by about 30%, I don't do racing starts. The advice from Pete Cox when this happened to my TR4 two years ago was to fit a new 3.7 CWP set from Moss, which he did for me. Pete told me that Moss had sold about 600 sets of these, with only one proving a problem. On the Moss site, they are £220 + VAT for 3.7 and 3.45. If you mix CW and P from different places, I think you would be very lucky if the combination worked well. And there's always the question as to whether second-hand items might have been weakened by prior use. Ian Cornish Quote Link to post Share on other sites
tonycharente Posted January 9, 2018 Author Report Share Posted January 9, 2018 (edited) Thanks Roger, Don't know how small this photo will come out, but here goes ! Edited January 9, 2018 by tonycharente Quote Link to post Share on other sites
Kevo_6 Posted January 9, 2018 Report Share Posted January 9, 2018 Hi Roger is quite right, I lost a couple of teeth off both the crown and pinion last year on the way back from France. Fortunately I made home under my own steam. I did use Hardey Engineering in Leatherhead and they did a really good job, I highly recommend them. Quote Link to post Share on other sites
NickKerfoot Posted January 10, 2018 Report Share Posted January 10, 2018 I had MOSS put 3.45 into my TR4 about 12 years ago. Drives nicely and still goes well. Price hasn't changed much either! Regards Nick Quote Link to post Share on other sites
tonycharente Posted March 7, 2018 Author Report Share Posted March 7, 2018 UPDATE A very happy ending... Thanks to the enormous help and advice from Alec Pringle and the expertise of Peter Cox I now have my original axle back in the car fitted with a 3.45 diff. The axle is now very quiet with no clunks. Hooray ! Just to report on driving my TR4A with overdrive now with a 3.45 diff fitted... I started by comparing the speedo readings at various speeds with the GPS speed, and they are now pretty well spot on - which means the original set up was exaggerating by 7% !!! (3.70 / 3.4545) This is on 165/80 x15 tyres. I believe original radials would have been 165X80, which in turn I believe technically corresponds to 165/82X15, so this would only have explained a tiny part of the exaggeration I'm observing. Then assuming (???) the rev-counter is true, the car is now doing 3000 rpm at a genuine 70 mph, (overdrive top), which is great. This makes the car totally at ease on dual carriage ways. And as regards acceleration, it may be a little slower in the first couple of gears, beyond that it's just a question of using the (seven...) gears. And absolutely no problem pulling overdrive top even from 40 mph. ...for me it's a wonderful improvement ! My VERY BIG thanks to Alec and Peter Tony Quote Link to post Share on other sites
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