GT6M Posted May 5, 2017 Report Share Posted May 5, 2017 (edited) Heres one I aint ever come across befoerin OD and at below 2000 RPMs, foot oft pedal on cruise doonand rev counter should read 2000 at 52 MPHbutt, its started to drop to 1200-1300 rpms as soon as throttle is off{ rev counter is mechanical drov oft distributor, so its no electikery related,as can happen wid electric types }put throttle back on, revs come back up, and it drives wid oot slippingabove 2000,like 2200+, it dont doo itcleaned oot all plugs int OD sump, clean as owt,fresh oil, PSI reading 650 in 4th at 40 mph, or 2000 rpmsIm thinking Uni dirctional clutch, butt, may be wrong, wont be fust timeLooked every where ont tinterweb for similar symptom, but nowt there.Any ideas befoer I pull the thingyM Edited May 5, 2017 by GT6M Quote Link to post Share on other sites
RogerH Posted May 5, 2017 Report Share Posted May 5, 2017 Hi Marcus, in an old TRAction (about 5-8 years ago or so) Dr.Hugo did a very good article on the OD operation. I'm sure one of the cycles is a coasting cycle. If this is the case then perhaps the OD stopped the road speed keeping the engine revs up and it went to tick over. When you put your foot down again it came out of coast mode and it all worked as per normally. However I have been known to be wrong. Roger Quote Link to post Share on other sites
Guest ntc Posted May 5, 2017 Report Share Posted May 5, 2017 Do you feel it drop? the rev counter could be running dry easy fix. Quote Link to post Share on other sites
BrianC Posted May 6, 2017 Report Share Posted May 6, 2017 I read, or was told, many years ago to avoid using o/d below 2000 rpm. It's easy to remember that when engaging o/d but sometimes one can forget to disengage when the revs drop very low in traffic. Quote Link to post Share on other sites
GT6M Posted May 6, 2017 Author Report Share Posted May 6, 2017 Its deffo no the rev counter, as if it was, it,llbe dooing same in 4th,or other gears does it in 2 / 3 OD too Best way t, describe it is put,n it int neutral OR like an older auto box, when revs drop wen yer foots oft pedal most weird M Quote Link to post Share on other sites
boxofbits Posted May 6, 2017 Report Share Posted May 6, 2017 Hi Marcus Out of interest have you checked the oil level in the gearbox/overdrive by any chance? Kevin Quote Link to post Share on other sites
Graham Harris Posted May 6, 2017 Report Share Posted May 6, 2017 I have read that the main function of the uni directional clutch is to keep the engine connected to the drive train to stop it going into neutral as you have described, looks like box out? Graham Quote Link to post Share on other sites
Lebro Posted May 6, 2017 Report Share Posted May 6, 2017 It is to prevent the output of the O/D from rotating any slower than the input. (in forward motion only !) it fills the gap in drive when you move from non O/D to O/D & vica versa, and in the event of a failure of the clutches, or hydraulics you will still get home. So to me it sounds like the Non O/D clutch was slipping as you backed off, but on re-accelerating the one way clutch did it's job. Bob. Quote Link to post Share on other sites
Graham Harris Posted May 6, 2017 Report Share Posted May 6, 2017 You could be right Bob but you would think if the engine clutch was dodgy it would be more likely to slip under throttle rather than decelerating? Graham Quote Link to post Share on other sites
Lebro Posted May 6, 2017 Report Share Posted May 6, 2017 (edited) Graham. Not talking about the engine clutch, talking about the internal clutches in the overdrive - one for direct 1:1 drive, & one for overdrive. If the direct drive one slips, then under acceleration you would not notice, because the unidirectional "clutch" (actually rollers in a special housing) locks up, & preserves the drive. On decelerating, it no longer does tis, & is free to rotate, so there is nothing to stop the engine revs dropping. It may be an adjustment problem, if the "non overdrive" condition still allows a small amount of pressure on the pistons then the 1:1 clutch could be slightly lifting. Bob. Edited May 6, 2017 by Lebro Quote Link to post Share on other sites
GT6M Posted May 6, 2017 Author Report Share Posted May 6, 2017 Been oot the day, 140 mile roond tripit starts when its well an truly hotand, after some fart,n aboot, in gears in OD, 2,3,4that its presure related,as in OD 2, its happening right up at 4K revs, butt, flor it, its ok3rd is aboot 3000 and 4th is 2000 ishSo, this I can fathom,what I cant fathom, is why the revs drop to nearly idleeven in 2 0d, revs dropped to 1800-2000, in 4 th they go to 1200 ishthis I just cant fathom,Will doo a PSI test when box is really hot, after a runas it dont doo it wen coldand I did test wen it wer cold Its got plenty of oil init, If its the OD clutch, then ive had this befoer engine will rev, an forward momentum is no much butt its this dropping to nearly idle speed ont rev counter wen rev counter should be saying 2000 Butt, put foot doon slightly wen its at 100 rps { should be 2000ish ]then there is slight jerkiness as can be seen on rev counter fliking up/doon 500rpms, put foot right doon, and it dont doo it, it just jumps back to 2000 ish RPMs most weird Butt, the Cumbria Mobsters can see it happening the morrow on oor run oot t,ApplebyM Quote Link to post Share on other sites
ianc Posted May 7, 2017 Report Share Posted May 7, 2017 I recollect this happening with my TR4 in the early 1970s. I could be travelling at 70 mph in overdrive top, take foot off accelerator and revs would drop to near tickover, but as soon as I put foot on throttle, normal service was resumed. The condition occurred a number of times over a week or fortnight, then resolved itself. In your position, I would be inclined to wait a while as gearbox removal and replacement is a pig of a job! Keep fingers firmly crossed. Ian Cornish Quote Link to post Share on other sites
GT6M Posted May 7, 2017 Author Report Share Posted May 7, 2017 I recollect this happening with my TR4 in the early 1970s. I could be travelling at 70 mph in overdrive top, take foot off accelerator and revs would drop to near tickover, but as soon as I put foot on throttle, normal service was resumed. Says Ian Ello Ian, At least it aint me imaginationee going wild then this is a fact, its happening Butt, according to the OD Guru,s { frims 2 of em } it cannot happen its impossible for an OD t,doo this they say And it seems as though its no just a J type, as yours wud be an A type, so,same syptoms that are not supposed to exist are there in both,!!! had a good run oot t,day, it starts after 25-30 miles, and only below 2000 rpms just changed the O rings, and re cleaned oot the 3 plugs int bottom, and bunged in new oil olde oil was still nice an clean, only been in a month, so nee blackness aboot it, which would indicate wearing away clutch bits nee difference, started its antics just coming back into the toon 26 mile round trip so the morrow, I,ll tek the solonoid off, check the O rings on end of that I still cant say its pressure related or not as no done a hot test yet, but will doo that the morrow, see if the PSI drops wen its good an hot M Quote Link to post Share on other sites
GT6M Posted May 7, 2017 Author Report Share Posted May 7, 2017 Steev Jackson has just bunged this up on TE, He,s generally on the ball, an done some digg,n Markus - I think I've found the answer......I remember reading something about the importance of the helix angles on the sungear, planet gears & annulus, so I looked it up in my GKN Laycock J-type service manual. Under 'working principles' I found the following in a paragraph describing how the overdrive transmits drive in the direct gears:-"Since the sunwheel is splined to the the clutch member the whole gear train is locked, permitting over-run and reverse torque to be transmitted. Additional load is imparted to the clutch member, during over-run and in reverse, by the sunwheel which, due to the helix angle of its gear teeth, thrusts rearward and has for its reaction member the cone clutch."My understanding of this is that when the overdrive is not engaged, the four springs hold the sliding cone member against the cone surface on the annulus. When the engine is driving the wheels in forward gears, the unidirectional clutch locks, and that is the means by which torque is transmitted from the engine to the rear wheels. On the overrun or in reverse, the unidirectional clutch frees up, and the torque is transmitted by the friction between the cone clutch sliding member and the mating surface on the annulus. Pressure between the two is maintained by the four springs, aided by the pressure generated from the helix angle of gear teeth on the sunwheel & planet gears. So far, so good.The manual then describes operation with overdrive engaged, the engine driving the rear wheels, and includes the following:-"Movement of the cone clutch in a forward direction is effected by means of hydraulic pressure which acts upon two pistons when a valve is opened, by operating the driver controlled selector switch. This hydraulic pressure overcomes the springs which load the clutch member on to the annulus and causes the clutch to engage the brake ring with sufficient load to hold the sunwheel at rest. Additional load is again imparted to the clutch in a forward direction due to the helix angle of the gear teeth."So when the overdrive is engaged, the effect of the helix angle of the gear teeth is the opposite from that achieved in direct drive. The manual conveniently doesn't describe what happens on the overrun, but I reckon it's something like this - the cone clutch lining is pressed against the brake lining by the hydraulic pressure on the two pistons, which overcomes the spring pressure exerted in the opposite direction. The effect of the helix on the gear teeth in the overrun condition with overdrive engaged is to apply a rearward force to the sliding cone clutch - assisting the return springs and opposing the pressure from the two pistons pushing the sliding member forward.I reckon that if the hydraulic pressure is insufficient to overcome the return springs to get the cone clutch to hold against the brake ring, and the car is in an overrun condition with overdrive selected, the additional force generated by the helix gear teeth may be sufficient to cause the cone clutch to slip. In a more extreme case, the pressure from the helix gear teeth may be able to pull the cone clutch and brake ring apart, putting the car into coast mode. As soon as the accelerator is touched, the engine begins to drive the rear wheels, the thrust effect from the helix gears is reversed, and the cone clutch instantly moves back into contact with the brake ring - normal service is resumed.IMHO this is what is happening with your OD - for some reason the hydraulic pressure at the pistons is insufficient to press the cone clutch hard enough against the brake ring to stop it rotating on the overrun , and it's worse when the oil thins out as it gets hot. It may be that the outer lining on the cone clutch is worn, or there is a partial hydraulic blockage somewhere, but it sounds like a strip down job if cleaning out the hydraulics does't fix it .Edited 1 time(s). Last edit at 2017-05-07 04:54 AM by grumpicus. this in reply t, Steev Jacksons reply on TE site That sounds like it Steeve, as been think,n back a long long time,and an OD equiped car can slip in reverse gearthis is basicly similar t, what you described aboveButt, mine aint slipping in reverseas had t, reverse up quite a steep bit this morningand it did,nt slip at allbutt then, I did,nt have a car on a trailer as I had wid the PI saloonwen this was slipping in reverse So,maybe its near t,be sorted !! Ohh, for them no in the no, TE is quite a hive of info and there a TR section too for every thing TR,ish meb,e of some intrest t,some http://www.triumphexp.com/phorum/read.php?8,1455119,1455464 M Quote Link to post Share on other sites
Graham Harris Posted May 8, 2017 Report Share Posted May 8, 2017 As Bob said it could be simple adjustment of the operating leaver/valve, it may just need to go a fracker more to keep up the pressure on the operating pistons. Worth a try before any serious dismantling . Graham Quote Link to post Share on other sites
GT6M Posted May 8, 2017 Author Report Share Posted May 8, 2017 the OD was already 100 PSI over its normal TR pressure as a extra shim was added just got t,get the solonoid off, and check the 2 O rings ont end as thee,s blok off the pistons t,sump if ones leaking a wee bit, then its dump,n pressured oil into sump so at low revs, I wont ev enough t,hold the cones in against the pull oft gear teeth which are being drov frae the rear end, and no the GB end M Quote Link to post Share on other sites
GT6M Posted May 20, 2017 Author Report Share Posted May 20, 2017 Update, efta trying diff things, easiest first, non workedso had t, bite the bullet an pull the trans cover, that is a feat in its sell,And me 2 piece one, the solonoid nut is well back frae the H frame,so the lot ed t,come ootOnt end oft solonoid, there 2 O rings, was think,n that they gon offan letting oil escape at low pump speeds, which is = t, engine revs/gear speeds /ratiosO rings one ends looked OK,not got scuffs or crumbling,butt, they wer flattened ont edges quite alottan slack in their grooves, and measuresd 62 thou thicknessand slid oot the OD wid v v little resistancebunged on some new O rings, 80 thou thick, and a good fit into ODhoped it would cure me problemoOot for a test drive, should ev took me ear plugs, cos driving a GT wid the tunnel off is v v noisey, and v v drafty toogot over 20 miles,it wer okgot to 30 miles, OKgot to 40 miles, and OD was really hot, so oil was as thin as it wer gonna get.and,Its working great, no dropping doon t, idle on run doon,nee dropping oot at v v low revs,teks 2,nd od at 1000 rpms nee bother at allSo, if any you lot suffer the same, check yer O rings, bung some new,ns onand a nice tight fit into OD .M Quote Link to post Share on other sites
RogerH Posted May 20, 2017 Report Share Posted May 20, 2017 Hi Marcus, you are quite amazing. Roger Quote Link to post Share on other sites
ianc Posted May 20, 2017 Report Share Posted May 20, 2017 I was fortunate when this happened with my A type overdrive in the early 1970s in that, after a week or so of this freewheeling on the over-run, the overdrive went back to normal operation. I thought the condition might have been caused by some small particle of dirt in the hydraulic circuit, but never bothered to do anything about it, and it has never recurred. I hope all will now behave properly in your TR, Marcus. Ian Cornish Quote Link to post Share on other sites
TR NIALL Posted May 20, 2017 Report Share Posted May 20, 2017 Well Dome Marcus your persistence seems to have Paid Off,Hopefully. Quote Link to post Share on other sites
GT6M Posted May 20, 2017 Author Report Share Posted May 20, 2017 (edited) Thanks Ladds, but for woe ooh no no,s what or where the O rings are, they ont end of,t solonoid And, for good mesure, Ive just replaced the inner seals too, the ones on the inner valve rod And for those woe ev had this symptom, then going by the Guru,s that fix ODs, this cannot happen, !!! butt, we no different M Edited May 20, 2017 by GT6M Quote Link to post Share on other sites
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