Ol Boys Posted April 8, 2018 Report Share Posted April 8, 2018 hi there, i have a 1965 TR4A with o/d, if i put the o/d in when in 3rd all fine and dandy but if i back off the pedal it will disengage the o/d but doesn't in 2nd or 4th just 3rd, any suggestions, its not a bother to be honest as only really use it in top, regards, ol boys, Bucks Quote Link to post Share on other sites
RogerH Posted April 8, 2018 Report Share Posted April 8, 2018 Hi OB, have a look at the rubber gaiter around the gear stick. As you back off the throttle the GB may rock side to side and the gaiter may knock the gear stick enough to disengage the inhibit switch. 2nd and 4th are not normally affected by the gaiter. Roger Quote Link to post Share on other sites
Ol Boys Posted April 8, 2018 Author Report Share Posted April 8, 2018 wow, that sounds my sort of fix Roger, i am out in it Wednesday so will keep you posted, thankyou very much, Quote Link to post Share on other sites
TR4A1965 Posted April 8, 2018 Report Share Posted April 8, 2018 Just in case it is the overdrive:-) I have just been through this drill and the reason it would not disengage was a blocked valve:-( It was a mission to sort out as the whole interior of the TR had to be stripped out to get to the top of the overdrive. Once in there it was easy. http://tr4a.weebly.com/living-with-the-triumph-tr4a---2018.html Best. Paul Quote Link to post Share on other sites
ctc77965o Posted April 8, 2018 Report Share Posted April 8, 2018 What about if you hold it in third as you back off, does it disengage then?? if not then that proves the inhibitor switch theory...there's nothing wrong with the OD, its the GB selector floating about Quote Link to post Share on other sites
Motorsport Mickey Posted April 9, 2018 Report Share Posted April 9, 2018 Make sure you have the engine "torque reaction arm" fitted to the front of the engine and adjusted to minimise engine twist. Without it the engine tends to roam around the engine compartment especially when the power is released (hence torque reaction name). Being connected to the gearbox the "lurch" at the front of the engine is transmitted backwards and twists the gearbox on the rear gearbox rubber mount reducing the mounts life and bringing the gearbox into contact with the cover as per Rogers #2 post. Doesn't help the handling either, having a 200kg lump (engine and gearbox) deciding to realign itself within the engine bay when you have the car set up at the limit on a fast corner, that's why in the race car we developed a strengthened front engine plate with solid steel engine mounts* so the engine didn't move anywhere (no... the gearbox mount is left rubber to allow for chassis and drivetrain flexes and movement). Mick Richards *Made in steel as per the round "Bobbin" style and painted Matt black so they still looked like rubber and maintained the advantage of better handling from other competitors (you're getting all the good stuff now). Quote Link to post Share on other sites
RogerH Posted April 9, 2018 Report Share Posted April 9, 2018 (edited) Hi Mick, interesting about the Torque Reaction Arm. Not seen that before and according to the Moss WebCat is for the TR4 - not mentioned for the 4A https://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/engine/engines-components/external-engine-components-tr2-4a.html Item #58 Will have to investigate further. Roger Edited April 9, 2018 by RogerH Quote Link to post Share on other sites
stuart Posted April 9, 2018 Report Share Posted April 9, 2018 Hi Mick, interesting about the Torque Reaction Arm. Not seen that before and according to the Moss WebCat is for the TR4 - not mentioned for the 4A https://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/engine/engines-components/external-engine-components-tr2-4a.html Item #58 Will have to investigate further. Roger When I had my engine rebuilt last year we had the uprated Landrover engine mounts fitted and as they are slightly higher the reaction arm wouldnt fit as it was beyond its adjustment range. Though with the new mounts that engine is rock solid (It originally had the earlier round mounts fitted as the 4a ones weren't available then but they were genuine Leyland mounts and hadnt degraded at all) Out on our club run on Sunday one of our members 4a refused to start and in the process of elimination as to the problem when whirring it over I was very surprised to see the amount of movement of the engine, turns out it had repro round mounts fitted that were hardly holding it in place! Stuart. Quote Link to post Share on other sites
LGFromage Posted April 9, 2018 Report Share Posted April 9, 2018 The overdrive slips out of gear on the overrun because the pump pressure is too low with the most likely cause being dirt in the operating valve and ball. Re-seating of the ball may be necessary. The reason it slips out of gear is due to helical cut gears in the overdrive. When the engine apples torque (drive) the helical gears want to move in an axial direction. In the overrun (engine braking) a retarding torque is applied to the gearbox output and the helical gears want to move in the other direction. The direction of the helix is selected for the drive mode in order to help the gears remain engaged. On the overrun the opposite is true and there is a tendency to disengage thereby releasing the cone clutch if there is in sufficient pump pressure to stop this happening. Gearboxes can also suffer from the same problem if tolerances get too large and it is not unusual for a TR gearbox to jump out of third on the overrun. As for the torque reaction arm it is there for the overrun condition just in case the RHS engine mount de-laminates. If this happens the engine will raise up on that side causing the throttle to be open with exciting results. It seems strange that it is specified for the TR4 and not 4A though it is probably more appropriate for track cars. Tim Quote Link to post Share on other sites
RobG Posted April 9, 2018 Report Share Posted April 9, 2018 (edited) Roger Item #58 Torque Reaction Arm this explains it for me. I got my engine as a mix of parts TR4 and TR4A engine and this bit was left over in the box, I never worked out where it went. My end result is a TR4A engine in a TR4 but I guess I can still fit this part, I will attach and see where it bolts up to. Will also look in my box of frogs for the Buffer #59, guess that locates on the chassis ? Thanks for the full description and diagram. RobG Edited April 9, 2018 by RobG Quote Link to post Share on other sites
MRG1965 Posted April 9, 2018 Report Share Posted April 9, 2018 The overdrive slips out of gear on the overrun because the pump pressure is too low with the most likely cause being dirt in the operating valve and ball. Re-seating of the ball may be necessary. The reason it slips out of gear is due to helical cut gears in the overdrive. When the engine apples torque (drive) the helical gears want to move in an axial direction. In the overrun (engine braking) a retarding torque is applied to the gearbox output and the helical gears want to move in the other direction. The direction of the helix is selected for the drive mode in order to help the gears remain engaged. On the overrun the opposite is true and there is a tendency to disengage thereby releasing the cone clutch if there is in sufficient pump pressure to stop this happening. Gearboxes can also suffer from the same problem if tolerances get too large and it is not unusual for a TR gearbox to jump out of third on the overrun. As for the torque reaction arm it is there for the overrun condition just in case the RHS engine mount de-laminates. If this happens the engine will raise up on that side causing the throttle to be open with exciting results. It seems strange that it is specified for the TR4 and not 4A though it is probably more appropriate for track cars. Tim Hi Tim, you mention the gearbox jumps out of 3rd on over run. Are you able to confirm what the issue might be as my 4 occasionally does this on over run, the O/D and other gears are okay. Does not look like gaiter as I've checked this out before and jumps out with a loud click. I fitted the landrover engine mounts the other year, but had the problem before that, had assumed something to do with end float between input and main shaft. Although it does not jump out of 4th. Mark Quote Link to post Share on other sites
iain Posted April 10, 2018 Report Share Posted April 10, 2018 (edited) Just in case it is the overdrive:-) I have just been through this drill and the reason it would not disengage was a blocked valve:-( It was a mission to sort out as the whole interior of the TR had to be stripped out to get to the top of the overdrive. Once in there it was easy. http://tr4a.weebly.com/living-with-the-triumph-tr4a---2018.html Best. Paul Hi Paul this is the solution used by the Works Competitions department on the TR3A's to save all of that hassle in a side-screen car and it would probably save a fair bit in a windy-window job, Two carefully positioned holes allowing access to the valve. For reference here is the inspection plate on the other side. Iain Edited April 10, 2018 by iain Quote Link to post Share on other sites
LGFromage Posted April 10, 2018 Report Share Posted April 10, 2018 Hi Tim, you mention the gearbox jumps out of 3rd on over run. Are you able to confirm what the issue might be as my 4 occasionally does this on over run, the O/D and other gears are okay. Does not look like gaiter as I've checked this out before and jumps out with a loud click. I fitted the landrover engine mounts the other year, but had the problem before that, had assumed something to do with end float between input and main shaft. Although it does not jump out of 4th. Mark Hi Mark, Even when new the radial clearance between gears and shafts in a TR gearbox were a bit generous and with time they don't improve. This means that they can wobble about a bit on their respective shafts and on the overrun, particularly for 3rd gear, they can wind themselves out of engagement with in the synchro hub. The way to reduce/prevent this is to tighten up on the axial tolerances. I do not know if it is a feature of the TR6 3/4 gear synchro hub but for the GT6 Triumph introduced a modification to the hub to encourage the gear to remain engaged. If The TR6 hub has this feature it would further help to fix the problem. Regrettably it means a gearbox out to sort it so it might be reasonable to do nothing for a while. Tim Quote Link to post Share on other sites
TR4A1965 Posted April 11, 2018 Report Share Posted April 11, 2018 (edited) Hi Paul this is the solution used by the Works Competitions department on the TR3A's to save all of that hassle in a side-screen car and it would probably save a fair bit in a windy-window job, Two carefully positioned holes allowing access to the valve. IMG_2173.JPG IMG_2181.JPG For reference here is the inspection plate on the other side. P2017754.jpg Iain Iain, that is so damn sensible. They should have done that for the TR4 and 4A I have the Revington gearbox cover and it is sensibly in 2 halves. The issue is the split between the two halves is where the Overdrive Valve is? So putting an access there would be a bit of a mission for sealing purposes. I do like the access on your TR3 to the solenoid. Another great time saving bit of design, Again this is a whole cover out job on the TR4A. I have attached a picture of the valve and the diagram from the Laycock overdrive manual. You can also see how small that hole is that causes all of the trouble - a pin width that's all. Best Paul Edited April 11, 2018 by TR4A1965 Quote Link to post Share on other sites
iain Posted April 11, 2018 Report Share Posted April 11, 2018 Hi Paul I think a few of us on here have enjoyed the same struggle! At least with my car most overdrive issues can be dealt with without the tunnel having to be removed. The only one not possible is to align the actuation lever with the drill, but that doesn’t work due to wear. Iain Quote Link to post Share on other sites
MRG1965 Posted April 11, 2018 Report Share Posted April 11, 2018 Hi Mark, Even when new the radial clearance between gears and shafts in a TR gearbox were a bit generous and with time they don't improve. This means that they can wobble about a bit on their respective shafts and on the overrun, particularly for 3rd gear, they can wind themselves out of engagement with in the synchro hub. The way to reduce/prevent this is to tighten up on the axial tolerances. I do not know if it is a feature of the TR6 3/4 gear synchro hub but for the GT6 Triumph introduced a modification to the hub to encourage the gear to remain engaged. If The TR6 hub has this feature it would further help to fix the problem. Regrettably it means a gearbox out to sort it so it might be reasonable to do nothing for a while. Tim Cheers Tim, one for the winter, as the O/D has a small pressure leak from the solonoid side plate. Mark Quote Link to post Share on other sites
ianc Posted April 13, 2018 Report Share Posted April 13, 2018 Although I fitted Triumph's Torque Reaction Arm (see Mick's post #6, above), I devised an even better method of restraining the engine of my TR4, and this I described in TR Action 130, and it appears in pages G15-G19 of the Technicalities CD. My scheme would not work on a sidescreen car as, with the narrower track, the suspension uprights are closer together and the angles would be all wrong. Ian Cornish Quote Link to post Share on other sites
Ol Boys Posted April 14, 2018 Author Report Share Posted April 14, 2018 thanks chaps, there are a few things to go through, an inspection hatch is the first task as the speedometer angle drive needs replacing and its a little tinker to get to so two birds with one stone and all that, will update as soon as we get in there Quote Link to post Share on other sites
Hamish Posted April 14, 2018 Report Share Posted April 14, 2018 Torque relation arm spotted on eBay Coincidence ?? Triumph TR4 Torque Reaction Arm .Part no. 133471 https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F222922153974 Quote Link to post Share on other sites
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