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Heres one I aint ever come across befoer
in OD and at below 2000 RPMs, foot oft pedal on cruise doon

and rev counter should read 2000 at 52 MPH
butt, 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 slipping
above 2000,like 2200+, it dont doo it

cleaned oot all plugs int OD sump, clean as owt,
fresh oil, PSI reading 650 in 4th at 40 mph, or 2000 rpms

Im thinking Uni dirctional clutch, butt, may be wrong, wont be fust time

Looked every where ont tinterweb for similar symptom, but nowt there.

Any ideas befoer I pull the thingy

M

Edited by GT6M
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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

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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.

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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

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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.

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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 by Lebro
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Been oot the day, 140 mile roond trip
it starts when its well an truly hot

and, after some fart,n aboot, in gears in OD, 2,3,4
that its presure related,
as in OD 2, its happening right up at 4K revs, butt, flor it, its ok
3rd is aboot 3000 and 4th is 2000 ish

So, this I can fathom,
what I cant fathom, is why the revs drop to nearly idle
even in 2 0d, revs dropped to 1800-2000, in 4 th they go to 1200 ish

this I just cant fathom,

Will doo a PSI test when box is really hot, after a run
as it dont doo it wen cold
and 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,Appleby

M

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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

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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

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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 gear
this is basicly similar t, what you described above

Butt, mine aint slipping in reverse
as had t, reverse up quite a steep bit this morning
and it did,nt slip at all
butt then, I did,nt have a car on a trailer as I had wid the PI saloon
wen 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

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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

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  • 2 weeks later...

Update, efta trying diff things, easiest first, non worked
so 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 oot

Ont end oft solonoid, there 2 O rings, was think,n that they gon off
an letting oil escape at low pump speeds, which is = t, engine revs/gear speeds /ratios

O rings one ends looked OK,not got scuffs or crumbling,
butt, they wer flattened ont edges quite alott

an slack in their grooves, and measuresd 62 thou thickness
and slid oot the OD wid v v little resistance

bunged on some new O rings, 80 thou thick, and a good fit into OD
hoped it would cure me problemo

Oot 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 too

got over 20 miles,it wer ok
got to 30 miles, OK
got 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 all

So, if any you lot suffer the same, check yer O rings, bung some new,ns on
and a nice tight fit into OD .

M

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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

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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 :D

 

M

post-12368-0-37039300-1495316442_thumb.jpg

Edited by GT6M
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