MGB GT Episode 49 Overdrive Part 2

Checking power to solenoid and cleaning up the various parts of the overdrive to try and get it working
#MGB

[@remydubois6437]

Thank you for the great video! The overdrive on my 1971 GT isn't engaging so I'm trying to get as much info before I take the plunge and try to sort it out!

[@HenrysGarage]

Glad you like it Remy, unfortunately I never actually sorted the issue with my overdrive. I concluded I needed to take the unit out and I wasn't ready for that at the time. I will get back to it one day

[@user-kg3sc7rb1h]

looks like you have fitted the overdrive sump and filter the opposite way round than when you took it off. It should be as you took it off.

[@HenrysGarage]

Hi, it is some years ago since I made this mistake and I moved onto to other things. The overdrive still doesn’t work and you’re the first person to mention this so thanks. I’ll have to take a look when I finish the TR7

[@MGB-learning]

Great video!

[@HenrysGarage]

Glad you enjoyed it

[@stevo6900]

Haven't had a lot of experience with the LH type but the D type problems used to be blown fuse gearbox switch on top of gearbox or the solenoid it's self I have read some MGBs were fitted with a micro switch late 1976-feb 1977 they were dropped due to reliability issues

[@HenrysGarage]

Thanks Steve - mine is later than '77 so I hope that's not the issue - Carsten has pointed out I missed a step in the video (which wasn't just failure to video) so I'm having another go today

[@stevo6900]

Good luck it's usually electrical they can be expensive reconditioned did you top up the box with 20/50 engine oil

[@HenrysGarage]

@@stevo6900 yes - I think so. I completely drained and filled through main gears filler

[@garethgoodchild2643]

Hi Henry. Well as Carsten says you are narrowing down the list of potential problems. Hopefully the pump is the culprit and you can rectify it. Couple of things to consider. When you test the impedance on the circuit, I’d also check that the switch works while turning it off and on. You can leave your tester connected to the pin and listen for the beep as you turn the shifter switch on and off. Second, did you measure the little ball when you had the relief valve apart? It’s possible that the ball has been switched with the ball from the pump. When you get the pump apart, measure the ball and you will know that they are in the correct assembly. After reassembly, you can check to see if the pump is moving up and down before closing everything up. Watch Twist again. He doesn’t do it because the car is on a hoist and in gear but you can turn the drive shaft to check movement of the pump. Third, I didn’t notice you using any grease on the filter gasket. If you don’t use any it will leak. Good luck. If you still don’t have any joy, I suggest as before that you contact Dick Moritz or John Twist. You have the benefit of having him watch your videos so he should be able to help you out. Both are very happy to give free advice. Good luck. You are nearly there!

[@HenrysGarage]

Thanks Gareth - I'm in the middle of trying to remove the pump at the moment. It is very very very well locked in. So much so I've broken one set of pliers trying to twist it out - I'm currently attempting to fashion a tool for it

[@garethgoodchild2643]

Let’s hope it’s not “fubarred” as Twist would say!

[@garethgoodchild2643]

John Twist mentioned a special tool for the pump but never showed it in his video. He also mentions that quite often theses are seized up. Maybe a stronger set of pliers is needed?

[@garethgoodchild2643]

Once you get the pliers in place you could clamp on a pair of vice grips to hold them in place and give you some torque to twist it out.

[@HenrysGarage]

@@garethgoodchild2643 For now I've decided to take a break. I'm only driving local roads and 50 feels fast on those - it is also about when I want to click in overdrive so I'm going to come back to this

[@danielwoodard680]

Again, this was very helpful. Please tell us which rebuild/maintenance kit did you use?

[@HenrysGarage]

I think I bought it from MGHive - I cannot remember the exact kit but I'm pretty sure it had the filter, a gasket and 3 o-rings

[@AdrianBellVoiceovers]

Good video! I’m currently dealing with my 67 MGBGT, with overdrive not engaging! 😢 We have changed the oil in the gearbox (we put in 20W50), and I was hoping that would fix the problem. It didn’t Q/ I know where the drain plug is on the gearbox, but is there also a drain plug on the overdrive unit? We only removed the drain plug on the gearbox… did we make a small mistake here and is old fluid still in the overdrive unit? What we did find, is that the overdrive switch on the overdrive unit (under the car) is faulty. We found current on one side of the switch but not the other. I’m hoping this is the cause for my overdrive not engaging. Appreciate any tips and advice.

[@HenrysGarage]

Hi Adrian, I'm glad you found the video useful. No, there is no drain plug for the overdrive unit. The current difference sounds like it is your problem. The advice I was given when approaching this was start as close to the battery as you can and work towards the overdrive unit. Wherever you find the power drop is your problem. But please be aware I haven't fixed my overdrive because I had a new project turn up before I managed it - I believe I need to change the solenoid to fix my issue

[@rampakeshbharat1938]

Excellent video, who supplied the gasket set and o rings for the servicing the O/D unit? Thanks

[@HenrysGarage]

Hi Rampakesh, I honestly don't remember where I bought the kit, but probably either Midland Sports and Classics or MGHive

[@cairnsmore23]

Have you checked the inhibitor switch(s) can’t remember if it’s one or two - this /these prevents the overdrive being engaged in 1st, 2nd and reverse?

[@HenrysGarage]

Thanks Cairnsmore. Where do I find the inhibitor switch?

[@stevo6900]

On top of the gearbox Henry above the solenoid

[@carstenmoore5760]

Hi Henry, Got to admire your determination. At least every item you tick off the list of suspects is narrowing the search. Did you removed the oil pump when you took the large cover plate off? That is the item JT removes with his needle nose pliers half way through 105 overdrive episode 2. As John says, it's not uncommon for the pump to jam which results in no oil pressure. (especially if you car has stood unused for a number of years) The pump is very simple, it is only a plunger which has an end mounted roller bearing which rides on an eccentric cam mounted on the input shaft. I would certainly take a look at this before going to the expense of a pressure test. The gearbox drain plug is doing its job collecting the mettalic contamination in the oil. The larger items are probably a result of the grating gears when your clutch wasn't disengaging properly. I still reckon it's a good idea to do a continuity test on the solenoid coil just to tick that off the list. With the damage inside the solenoid pocket obviously someone has had ago at this before. Keep it up, the guilty party has to reveal itself soon! 😉

[@HenrysGarage]

Thanks Carsten - and OMG! how did I miss that as well. I watched those videos 4 times before I started the job. I'll do it again today. Could you advise me on how do I test continuity on the coil please - just to try and avoid having to do it a 4th time

[@carstenmoore5760]

@@HenrysGarage Simplest way to do the continuity test on the solenoid to to reinstall your needle through the cable and test the resistance between that and the overdrive casing. Just make sure the overdrive switch is in the off position so your not getting erroneous readings from the rest of the circuit. Ideally you would disconnect the bullet connector to test, but I appreciate the difficulty with this. I'm not entirely sure what the standard resistance reading should be, but maybe someone viewing this would be able to advise. Of course, if you get an open circuit that would prove the windings have broken down or been damaged. Hope this helps.

[@HenrysGarage]

@@carstenmoore5760 Brilliant - thank you

[@carstenmoore5760]

@@HenrysGarage Just had a dig around in my shed and found my old overdrive coil. Multimeter resistance across it measured 12.8 ohms. This was removed from a working solenoid and I have the same transmission as you, so yours should be around the same value. Wayne has a fair point that you could still have resistance in the supply circuit, so that may be worth exploring if the oil pump service doesn't cure the problem. BTW Some time ago I did ask a local MG specialist (sadly no longer trading) why the MGB gearbox requires engine oil. The answer I got was that the higher viscosity gearbox [EP] oils generally contain friction reducing additives. The overdrive unit contains a 'cone' clutch which relies on friction linings. Coating friction linings with anti friction chemicals [not a good idea!] will result in loss of grip which leads to increased heat, wear and ultimate failure. I believe the higher viscosity oils are suitable for standard, manual NON-overdrive gearboxes, but this is only what I was told at the time, so don't treat it as gospel. Seems to make sense though, which is why you can't put standard gear oil in some LSD axles....a bit of useless info for you.

[@HenrysGarage]

@@carstenmoore5760 I cannot quite remember but I think my resistance across the coil is 30ish ohms, but more importantly, I cannot budge the oil pump. I broke a set of pliers trying to get it started and tried fashioning a tool but failed. I'm going to take a step back and come back to this now I know more. I love the trivia and it helps me understand.

[@donthuis]

What a waste of effort that the O rings that were accessed were not renewed straightaway. Or were they renewed off camera out of our sight? The filtergasket indeed became more prone to leakage than before, let alone mimick the non-leaking OEM. New ones do not solve this. A very thin layer of sealant at the cover side and under the heads of these special screws is one solution for reducing leaks on the condition care is taken against it entering this pickup tube (tube is best temporarily removed anyway if the pump is taken out for inspection) Statistics by some say of the 50 problematic OD's, 49 can quickly be revived, often just by correcting the electrics. This one seems to exhibit the single case of non-electric failures unfortunately. BTW I would have added a least one thin shim to the valve assembly for raising the pressure

[@HenrysGarage]

Thanks for the information

[@waynebrannan4778]

I'm not sure 11.2v is ok. 12v system should have 12v. Anything above 0.5v would indicate some resistance. Plus us the oil you used in the gearbox correct?

[@HenrysGarage]

Thanks Wayne - It is the correct oil (I find it bizarre that MGB uses engine oil in gearbox) and I did manage 11.75v at the end with a good connection. You're right there is some resistance but I would have thought that would be enough to engage the solenoid

[@waynebrannan4778]

@@HenrysGarage i have a 72 gt, gearbox oil is 75w90... but I will double check that... normally with electrical diagnosis, we use battery voltage as a reference and hopefully power supply is within 0.5v at any consumer. Im enjoying your videos so keep going.

[@HenrysGarage]

@@waynebrannan4778 Thanks Wayne - I'm glad you're enjoying as I learn - I really appreciate all the help and encouragement many people offer