Odd transmission issue?
 

After a bit of advice...

Driving my car home from work this evening (car is a 1970 133 with M41 transmission with overdrive).

In second gear at say 10-15 mph. Accelerate as normal, the trans then kinds of 'jumps' for maybe a second and re-engages. Almost like I'd changed gear... it only does this is 2nd gear at lowish speeds. The gearstick doesn't seem to move when this happens. It's almost like the rear wheels are spinning and not transmitting drive correctly. There is no noticeable clunks or bangs coming from under the car.

Thoughts?

Gearbox oil level is OK, and the clutch seems to be fine with no slipping etc.

My initial suspect was the universal joints in the drive shaft - didn't get back till gone 7 so it's too dark to start poking around. If the rain holds off I'll have a look under the car this weekend, but just wanted to know if there's anything else to check.

Any advice would be appreciated as always.

Mike

Is it possible that you have selected reverse when the OD is still engaged. I know the inhibiter should stop that but dirt can also jam the valve in the OD and cause it to stay on. It might leak down slowly for a while and be OK if you don't go into reverse for a while after switching it off but at some point will catch you out. I don't know what actually breaks in the OD or box.
Coincidently Rob Henchoz mentions this in his latest video on YouTube, referencing a competition PV that has OD and the owner has messed up the box.
https://www.youtube.com/watch?v=_SAOUVwOTyo

I suppose it's possible the OD/reverse situation has happened at some point in the past, BUT I'm very paranoid about this happening and I always make sure the OD is off before reversing.

I'm so paranoid about it... I even disconnect the wires on the stalk switch on the rare occasions my car goes into a garage so there is no way someone who is not familiar with my car can accidentally mess things up.

Yes l was inclined towards Overdrive prob's when l read your symptoms, O.R.S (Overdrive Repair Services) in Sheffield are very good and could give some hint towards the right diagnosis.
They have a stand at many Classic Car Shows, the phone no is 0114 248 2632, good luck.

Hope you don't mind me asking, but you're sure this is the transmission and not the engine misfiring?

Sounds to me like the symptoms of when your points gap need looking at.

Good, erm, point! I'll check and gap the points this weekend (not done much work on my Amazon recently as my girlfriend's V70 has needed a new radiator. And headlights. And wheel bearings. And delta link bushes. And lower wishbones. And... lots of other stuff!).

I'll report back on points gap and UJ condition after the weekend.

That said, the old heap sprang to life instantly this morning and didn't do anything 'funny'. There's a steep long bridge on the way to work so I left him in second gear all the way up and eased off and on the power... no weird symptoms.

Been really busy at work, so forgot to update this post...

Got my Amazon in the air last Sunday: there is no play on the UJs that I can detect (fun job: lying on cold wet tarmac at the side of the road under a wet car. With a hangover). Adjusted the handbrake whilst I was under there as well.

The timing is spot on, the points are fine with the gap at 18 thou of an inch.

The only slightly dodgy thing I came across was the wire from coil>condenser. Terminal at the coil end was loose and a bit corroded - I crimped a couple of terminals onto a new bit of wire, so it has now been replaced.

The good news is that I've not had a re-occurrence of the original problem! I'll keep a close eye on things, and if it happens again I'll book into a local classic-friendly garage and let them have a look at it.

It is probably the OD clutch slipping a bit , how does it engage under load , do you get a positive jerk or is it lazy? An oil change might help .


second gear has a lot of torque , you might be able to reproduce it in 1st too if you try a bit harder .

OD comes on on nice and smoothly (I always dip the clutch when engaging OD in 4th gear above 45 mph ish).

Changed the gearbox oil about 18 months ago for Castrol 20/50. Didn't do the OD filter though (as I din't know about it!) so I'll have a look at this at some point.

i was trying to find out if the OD clutch slipped when you are in 4th with a little load on the engine and you engage OD .. if the clutch is ok it will give a jolt if it tends to slip the engagement will be smooth .
The main problem i had with these when i was working on them was the rubber O rings around the operating pistons leaking causing a delay and slow engagement at low road speed due to low oil pressure .. an easy fix .

There is no need at all to press the clutch when engaging and disengaging OD, in fact it almost defeats the object of such an easy to use device ..., there is nothing easier than a flick on the stalk with one finger to engage it , having to move your foot and press the clutch pedal is an effort :-)
What you need to do to get a smooth change is when going into OD ease your foot off the throttle a small amount , and when going out of OD give slightly more throttle , with practice you make a change which is un-noticable to any passenger or yourself :-)