Gearbox thump and lurch.

[Amphiscian]

Rather than hijack mr rosher's current thread "rough gears" here's another, similar gearbox question. Car is an '85 W123 230ce and a year or so ago the headgasket was done. Subsequently the gearbox failed to change up without backing right off the throttle, when it would change up, and then on to the same with next gear. Fine, that was sorted, adjustment of a little sliding adjuster on the cable to the 'box. Now just a little reluctant to change down, need fair amount of welly to push it down a gear, otherwise it just hangs on to a higher gear.

But the main problem at the moment (bu$$er, just had a call to say the chainsaw has been knackered. Brand new, well, three months. What do these people have in place of thought.) main problem at the moment is when the engine is hot, putting gearbox into "d" results in a thump and the car lurches, much to alarm of passing pedestrians. If one had granny in the car it would probably result in a small stain on the seat the first few times. And it makes manoevering into those tight parking spots (also subject of current thread) a bit of an unsatisfactorily lurchy business.

It's not the tickover speed, steady at about 600 rpm in drive, 700+ in neutral. I suppose it could be engine/gearbox mounts/drive train flexdiscs/diff (please God no, not the diff) but I would have thought it should slide/slur into gear in a refined manner, not this bang-lurch that seems to be happening. Can't be good for the drivetrain. Gearbox, by the way, got new fluid and filter and otherwise gear changes are absolutely fine; gently slipping from gear to gear. And only done 70,000 miles.

Any comments gratefully received. Would like to sort this out before taking the car abroad.

Now I'll go and sort out the imbecile who shrapnelled my chainsaw...

 

[television]

I am sure that your car has a vacuam line, this is consistant with having the head gaskit done and some one forgets the pipe.


Malcolm

 

[eric242340]

I am sure that your car has a vacuam line, this is consistant with having the head gaskit done and some one forgets the pipe.


Malcolm

Its worth checking, but if the vacuum pipe was off then the engine would have an air leak and be shaking, and your transmission would not shift gear properly. The other thing to check is the propshaft rubber joints as they tend to crak-up just around the bolts. Failing this its definately a transmission problem and possibly B1 or K2. And if this is the case it would be a transmission rebuild. But im sure its not the diff.

 

[television]

Its worth checking, but if the vacuum pipe was off then the engine would have an air leak and be shaking, and your transmission would not shift gear properly. The other thing to check is the propshaft rubber joints as they tend to crak-up just around the bolts. Failing this its definately a transmission problem and possibly B1 or K2. And if this is the case it would be a transmission rebuild. But im sure its not the diff.

On cars where the pipe has been off,the engine does not shake, the pipe off causes lumpy jerky changes,and this is what this car is doing. this has been the case on most cars that have had a head gaskit change, you said so yourself on the last gearbox thread.

Malcolm

 

[eric242340]

On cars where the pipe has been off,the engine does not shake, the pipe off causes lumpy jerky changes,and this is what this car is doing. this has been the case on most cars that have had a head gaskit change, you said so yourself on the last gearbox thread.

Malcolm

Agreed Malcolm but on the the other thread I hadent thought about the air leak side of it and yes it would make a shakey engine at idle, sorry about that but on the other thread I really had not thought about the effect on the engine. My brain was on the transmission.

 

[television]

Agreed Malcolm but on the the other thread I hadent thought about the air leak side of it and yes it would make a shakey engine at idle, sorry about that but on the other thread I really had not thought about the effect on the engine. My brain was on the transmission.

the reservoir tanks are quite large, and many cars do not notice that it is off, this sytem is not just one pipe that sucks at Idle.

Malcolm

 

[eric242340]

the reservoir tanks are quite large, and many cars do not notice that it is off, this sytem is not just one pipe that sucks at Idle.

Malcolm

What reservoir tanks?

 

[television]

Maybe I should not be answering threads today, got up and thought OK must get a Valentines card, funny all of the shops are clossed, lots of cars going down to the sea, bought the card and posted it, ah its almost 1pm time for the news, what do I get, "eastenders" look at the clocks, we had a power cut yesterday, no battery clocks are OK, funny its not dark enough for 7.30pm, put the Text on, and problem solved, its Sunday :grin:

malcolm

 

[eric242340]

Maybe I should not be answering threads today, got up and thought OK must get a Valentines card, funny all of the shops are clossed, lots of cars going down to the sea, bought the card and posted it, ah its almost 1pm time for the news, what do I get, "eastenders" look at the clocks, we had a power cut yesterday, no battery clocks are OK, funny its not dark enough for 7.30pm, put the Text on, and problem solved, its Sunday :grin:

malcolm

You think its bad, sunday I had to work all day, interesting problem, maybe Malcolm you may have some thoughts on this. Had a BMW 735Li with N38 engine and when revs raised to 1K, rev counter fluctuates up and down, I know its not a Benz but the systems are quite similar. Almost all the relevant parts have been changed by other garages, now they bring it to me? help? its a real headache, ouch -the test equipment finds nothing wrong. Oh well Ill try again in the morning.

 

[Hibbo]

The vacuum line senses throttle depression and thus engine load. If the pipe is disconnected somewhere between the manifold and gearbox, the box thinks you are on full-throttle all the time and so slams the gears in.

 

[Amphiscian]

Thanks for those. Doubt that there's a vacuum problem, car holds a vacuum for days when not used and anyway the gearchanges, when they happen, are fine, smooth, not sudden. Just a matter of fine-tuning when they happen, I think ... Certainly no engine shake on tickover. Had that on another MB when a mechanic cracked the vacuum pipe to the brake servo; engine shook like a, like a, well, like a Shaker. Very shakey ... (Enough shaking. Ed.)

No, it's simply the initial move into "d" or "r" from "p" or "n" that causes the thump. Thereafter no problem. Could be consistent with play in the drivetrain, could be something else I thought of but which, in a Malcolm Moment, I have now forgotten. Must be distracted by the chainsaw massacre. Isn't there some sort of adjustment on the side of the box for something? Seem to remember reading something about that somewhere.

Eric in China, what happens to your setup over CNY? Every car in the land will be doing gargantuan mileages but presumably all your guys will be part of the movement? Or do you pay large bribes to some to stay on duty? Normally everyone's gone gone gone for a couple of weeks ...

 

[Hibbo]

All I can think of (ie clutching at straws (or should that be torque convertering at straws? )) is the box is overfilled with ATF. The gear should flare in gently with the torque converter slipping nicely.

Are the slight-throttle gearchanges perfect?

 

[Amphiscian]

Wow, that was quick! And at this time of night ...? (It's 11.15am where I am, so just about awake.)

Yes, part-throttle changes absolutely fine. And ATF level also fine. Drive take-up, once it's in gear, smooth, changes are smooth

Just thought that if there's a vacuum pipe from the manifold to the gearbox it may be irrelevent that the rest of the vacuum system is tight. But then you'd think there would be a vacuum tube dragging along on the ground, "in the mud and the blood and the beer". Unfortunately the car's not with me at the moment so can't go and look, but it has been up on a lift since this started happening -for MOT and again for new waterpump- and I think I would have noticed hanging pipes. Tend to have a good look around when it's up in the air.

 

[Amphiscian]

What exactly -and in layman's English- happens when you put the gearshift lever into "d"? Engine links to torque converter which starts spinning, pumping fuid through the gearbox which starts all the cogs in motion but if brakes on there is a relief valve that allows fluid to pump around without forcing the box to transfer motion to drivetrain??? That sort of thing? Maybe there's an adjustment to how the torque converter links up with the gearbox internals?

Or/and, if there is play in the drivetrain that play would be taken up quite briskly, giving a lurch? So, soft engine/gearbox mountings+worn/cracking rubber joints+wear in all the bits and pieces in the diff (Oh God no, not the diff) and driveshafts etc could combine to give a fair amount of play.

Still, got to somewhere near the bottom of the chainsaw story. My wife loaned it to someone ... But I love the woman, she can do no wrong!

 

[eric242340]

Eric in China, what happens to your setup over CNY? Every car in the land will be doing gargantuan mileages but presumably all your guys will be part of the movement? Or do you pay large bribes to some to stay on duty? Normally everyone's gone gone gone for a couple of weeks ...[/QUOTE]
For the last four years ive worked over chinese new year, double pay. But this year the Boss said no double pay, so my wife (God bless her cotton socks) said OK ive booked the flight and were going to north china for hols, at which point the boss promptly fainted. He knows if I dont work then no-one else will lol. Anyway come the 16th im off to freeze my nuts off:-x what a holiday and with 30 million chinese travelling its going to be fun aint it:evil:

 

[eric242340]

gearbox thump

What you have described so far, points to the brake band B1 (thats inside the front of the transmission) just behind the trans oil pump. And if thats the case, the box will have to come out for repairs. On the other hand it could be the valve body, which can be replaced without removing the trany, however if it is the valve body very expensive part and second hand ones are no use. Ive tried second hand a million times and they dont work.

 

[Hibbo]

What exactly -and in layman's English- happens when you put the gearshift lever into "d"? Engine links to torque converter which starts spinning, pumping fuid through the gearbox which starts all the cogs in motion but if brakes on there is a relief valve that allows fluid to pump around without forcing the box to transfer motion to drivetrain??? That sort of thing? Maybe there's an adjustment to how the torque converter links up with the gearbox internals?

I don't know much (anything) about the internal workings of an autobox
(I think the actual gears (cogs) are always meshed - clutches and brake bands control where the drive is applied and taken from, and brakes hold certain bit still depending on ratio required - Magic!), but I think you are way off with your description of what happens when you select 'D' for P or N.

The TC is always 'linked' to the engine (it's bolted to the driveplate) and is always 'linked' to the gearbox. In N (or P) the engine spins the TC which spins the input end of the gearbox. When you select a gear, the gear engages (using internally generated hydraulic pressure) regardless of whether you are on the brakes or not. (It is a common misconception that if you are in gear and stationary the box is not transmitting drive (like your 'relief valve' thinking)) The gear is engaged and the TC is now slipping as the input side of the box is locked to the (stationary) wheels.

It could be cause by play in the drive train, as all the 'flare' when the gear goes in is 'used up' taking the lash out of the drivetrain. Thus when the wheels start to move the gear is fully engaged.

You should be able to feel any drivetrain backlash by coming off the throttle when honking along.

Also, jack up a driven wheel and turn it by hand (with the car in P). Doing this whilst looking underneath you should be able to see where the play is.

 

[television]

I think it would be best if you Google how automatic gear boxes work you are way off on this. I am 72 comming up and dont have that much time left


http://en.wikipedia.org/wiki/Automatic_transmission


malcolm

 

[Hibbo]

Was that aimed at me Malcolm?

I know how to sort the vacuum, anything further than that is a bridge to far for me!

This is a good site too http://auto.howstuffworks.com/automatic-transmission.htm

 

[television]

Was that aimed at me Malcolm?

I know how to sort the vacuum, anything further than that is a bridge to far for me!

This is a good site too http://auto.howstuffworks.com/automatic-transmission.htm

No young man,it was not aimed at you , just a pile of threads with so many wrong answers today, it gets hard work. Your link is also very good, but a little more in detail than the one I put up.

malcolm