MichaelH Posted December 9, 2020 Report Share Posted December 9, 2020 Hi Everybody Got a problems with my overdrive: I have had it apart and back together with a pressure valve showing 400 lbs pressure - filled it up with standard EP80/90 oil (which I recently checked is full at the gearbox side plug) When I drive along and use the O/D as a fifth gear I change up into 4th overdrive and it cluncks into drive and the rev counter goes down as it should , it will then stay in overdrive up to the legal limit and...:- but if I am in a hurry and I run the engine up to 3-4K revs and switch the O/D on - nothing happens until i stop accelerating then it will usually engage. I would appreciate opinions - like does running EP 80/90 make any difference? I have used it without this problem for years. Would adjusting the switch (actuated by the solenoid) help? Thanks in advance for your advice Regards MichaelH Quote Link to post Share on other sites
Nigel Triumph Posted December 10, 2020 Report Share Posted December 10, 2020 Different O/D unit, but the D type on my GT6 behaves the same way. Backing off the accelerator helps get it to engage, though I feel that shouldn't be necessary. Looking forward to others input here. Nigel Quote Link to post Share on other sites
Lebro Posted December 10, 2020 Report Share Posted December 10, 2020 EP 80W90 is probably not the ideal oil to use, a gearbox oil like Penrite GB40 etc would be better, also just a thought at higher revs the oil is more likely to be foaming, which would reduce the pressure available. Finally, is the oil level correct ? Bob. Quote Link to post Share on other sites
RogerH Posted December 10, 2020 Report Share Posted December 10, 2020 Hi MIchael, you may need to do a bit of chop and change investigation. If it was purely acceleration doing the dirty deed then it may be a dodgy wire connection connecting to the GB - but it is not. EP80/90 GL4 oil was recommended by ST (I'm sure in an attempt to reduce oil leaks - didn;t work). I'm with Bob in using a 40 grade gear box oil (it's designed for the job) Make sure your EP80/90 IS GL4 Thicker oils may hold air bubbles and these could be generated by the higher revs - why not change to something like Penrite GB40 and see what happens. It may also be the OD selector position. Even with the rigging arm in the correct place it may not be opening the valve enough to allow as much oil in as the pump desires - and so it's output fails. All stabs in the dark but it's a start. Roger Quote Link to post Share on other sites
ianc Posted December 10, 2020 Report Share Posted December 10, 2020 (edited) I think Roger may have put his finger on it. When accelerating harder, the gear selector shaft can be pushed slightly more one way or the other, and this might be sufficient to release the contact in the selector switch on the top of the gearbox. Or, selector switch may have become loose - that could create this sort of problem. Make sure that the two switches have not become loose, and check the operation of each as described in the Workshop Manual. If working correctly, overdrive should engage rapidly under full acceleration in any gear. In fact, to avoid jarring the transmission, always engage overdrive with right foot hard down, and open throttle slightly when disengaging. Ian Cornish Edited December 10, 2020 by ianc Quote Link to post Share on other sites
Nigel Triumph Posted December 10, 2020 Report Share Posted December 10, 2020 I'm going to Overdrive Spares in Rugby on Monday, to get a J-Type tested and probably rebuilt. I will ask what causes reluctance for the O/D to engage at high revs. Nigel Quote Link to post Share on other sites
MichaelH Posted December 10, 2020 Author Report Share Posted December 10, 2020 (edited) Thank you: got a little list to try Its the tedium of taking the seats and H piece out and getting to the box that really puts me off starting but I know that it won't happen until I do! The garage being cold doesn't help! Just seen Nigel's comment: I have always gone to Overdrive Repairs Services in Shefffield where I have to say they have been very helpful especially as I rebuild Overdrives myself. They happily do significant bits for me, friendly and give me advice derived from their wealth of experience. The sensible thing would be to ring them Michael Edited December 10, 2020 by MichaelH Quote Link to post Share on other sites
MichaelH Posted December 10, 2020 Author Report Share Posted December 10, 2020 Spoke to James at ORS who said it sounds like the clutch is slipping so check the pressure when running and engaged and if the pressure is 400lbs then it is clutch slip and needs a new cone With the combined advice from the forum and ORS I know what I need to do It is a great service! and we are very fortunate to have it Happy Christmas to all our Readers Michael Quote Link to post Share on other sites
stillp Posted December 10, 2020 Report Share Posted December 10, 2020 31 minutes ago, MichaelH said: Spoke to James at ORS who said it sounds like the clutch is slipping That seems to be ORS' standard diagnosis! Pete Quote Link to post Share on other sites
Nigel Triumph Posted December 10, 2020 Report Share Posted December 10, 2020 2 hours ago, MichaelH said: Thank you: got a little list to try Its the tedium of taking the seats and H piece out and getting to the box that really puts me off starting but I know that it won't happen until I do! The garage being cold doesn't help! Just seen Nigel's comment: I have always gone to Overdrive Repairs Services in Shefffield where I have to say they have been very helpful especially as I rebuild Overdrives myself. They happily do significant bits for me, friendly and give me advice derived from their wealth of experience. The sensible thing would be to ring them Michael I'm using Overdrive Spares in Rugby as they also have a strong reputation and they're only half an hour from home. I will still ask them the question about reluctant O/D engagement, though it seems we have an answer from ORS. Nigel Quote Link to post Share on other sites
ctc77965o Posted December 10, 2020 Report Share Posted December 10, 2020 If the gear lever is moving about as you come off the power then you might have a simple electrical interlock problem. otherwise, given oil pressure is good....it looks like a clutch issue...but if you drive like that with the clutch slipping in my experience it burns the oil pretty quick...you can smell it. One last thing- any chance your EP oil has a limited slip additive?? that will surely mess up the clutch. Quote Link to post Share on other sites
Andy Moltu Posted December 10, 2020 Report Share Posted December 10, 2020 Not sure that an electical gremlin on the O/D circuit should be affected by the revs. On or off throttle might affect a dicky connection if the wires were swinging possibly but it sounds more mechanical/hydraulic. If the pressures are OK and the filters clear then it would point to the clutch. I've always been impressed by the work done by ORS in Rugby and don't charge the earth. Quote Link to post Share on other sites
stillp Posted December 10, 2020 Report Share Posted December 10, 2020 Nice to see positive remarks about Overdrive Spares - I have my MOTs done next door to them. I must speak to them about rebuilding mine, which works fine when cold but is very sluggish when hot. Pete Quote Link to post Share on other sites
Hamish Posted December 10, 2020 Report Share Posted December 10, 2020 You can always cross reference the issue via a chat with Pete cox https://petecoxsportscars.co.uk who ever you use nice to have a few opinions. Quote Link to post Share on other sites
Richardtr3a Posted December 10, 2020 Report Share Posted December 10, 2020 The overdrive is one of my best repairs. Alan at Cox and Buckles took out the gearbox on a Monday morning. I drove it up to Sheffield on Monday pm and gave it to ORS Collected it on Tuesday pm and delivered it back to C&B Took the bus back to Alan on Wednesday afternoon and collected the TR. It has never caused me any problem since. The adjustment of the overdrive unit is best done on a workshop jig. The Sheffield company repaired my o/d and it is faultless for over seven years. Use the Penrite GB40 oil. Good luck Richard & B Quote Link to post Share on other sites
MichaelH Posted December 11, 2020 Author Report Share Posted December 11, 2020 (edited) Ha Ha now the joke: a few months ago I took the o/d box out of the car cos it was not working and took the o/d apart and rebuilt it with bits and help from ORS and tested on my rig which showed 400lb pressure on my dial. While I was recently bad mouthing my o/d box in the car I thought to check: the repaired one is still on the garage floor smiling at me. So all my claims about the box relate to the other box. I have decided that I will have to live with the present set up until I need to sort it out I should be so lucky to have a second box/o/d to put back in the car while I sorted the other out. Michael Edited December 11, 2020 by MichaelH Quote Link to post Share on other sites
Nobbysr Posted January 3, 2021 Report Share Posted January 3, 2021 On 12/10/2020 at 9:12 AM, RogerH said: Hi MIchael, you may need to do a bit of chop and change investigation. If it was purely acceleration doing the dirty deed then it may be a dodgy wire connection connecting to the GB - but it is not. EP80/90 GL4 oil was recommended by ST (I'm sure in an attempt to reduce oil leaks - didn;t work). I'm with Bob in using a 40 grade gear box oil (it's designed for the job) Make sure your EP80/90 IS GL4 Thicker oils may hold air bubbles and these could be generated by the higher revs - why not change to something like Penrite GB40 and see what happens. It may also be the OD selector position. Even with the rigging arm in the correct place it may not be opening the valve enough to allow as much oil in as the pump desires - and so it's output fails. All stabs in the dark but it's a start. Roger If you work on the basis that an ISO 100 industrial gear oil is the same viscosity as SAE30 engine oil and an 85W gear oil. An 80w/90 oil will be less viscous at lower temperature than an EP90 at the higher temp they should be nearly the same thickness but base oil quality, viscosity improver and other additives are also a significant factor.. Quite often where oils are concerned you get what you pay for and if you are adding treatments you have the wrong oil. Engine oils and Gear oils should have an anti-foam additive and published air release time, you can do the shake test with a new and a used oil in two glass jars and shake for a minute and time the release Engine oils were often used in gearbox application due to concerns over the active Sulphur (EP addative) caused yellow metal pitting which i haven't seen for many years . Gear oils can be a mine field in so much that that they can be an API GL4 but also have friction modifiers and anti wear additives that cause o/d clutch slip at the moment i use a Shell 75w/90 gear oil in my 3A and the O/D and gear box run smoothly I would pull the O/D replace the springs and check the clutch friction material after checking the solenoid .. If you do make sure the internal all line up before refitting, i use a long thin slotted screwdriver, In theory if the oil pressure is there the O/D should engage unless you have slippage Also please be aware that ZDDP Zinc is not the only anti-wear additive .A number of Locomotive engines use Zinc free oil and have done for many year but even the add packs for these oils have updated technology Rgds Steve Quote Link to post Share on other sites
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