Bad trans governor = no shift? - PeachParts Mercedes-Benz Forum

New2MB · #1 06-12-2012, 12:39 PM

I read that the governor in the transmission builds pressure with centrifugal force in a gradual proportion as the speed of the tranny increases.

Now I would think that would mean that if the governor was not building enough pressure at say 3000rpm in order to shift from 1st to 2nd then it would also not have enough pressure at 3000rpm to shift from 2nd to 3rd.

Is that correct?

If the governor is failing will the transmission shift at all?

Stretch · #2 06-12-2012, 01:47 PM

If we're talking 722.1 / 2 / 3 / 4 and possibly 722.5 (I'm not 100% sure about that one but I've been told loads of 722.3 parts are in it) then the governor is on the output shaft.

So the governor "runs with the back tyres".

The governor is the brain that effectively "tells" the rest of the transmission when to shift but it works independently of the engine speed. However, the transmission won't shift if there isn't enough pressure produced at the engine end by the front pump.

Does that help?

As far as I can tell with these transmissions there isn't a kind of built in redundancy - after all it isn't a critical aircraft type system. So low working pressure (can't adjust it => means knackered front pump) might stop a transmission from shifting and a faulty governor could also stop a transmission from shifting. But you'll be pleased to hear that many other things can also stop a transmission from shifting!

New2MB · #3 06-12-2012, 02:45 PM

Do you know if it would take more pressure to go from 2 to 3 than from 1 to 2?

I suppose I just need to figure out a way to test the pressure.

Zulfiqar · #4 06-12-2012, 02:45 PM

if the governor is not spinning (broken heli gear) or if the petals are stuck (sludge) then it wont open up its control ports which direct oil pressure and it wont shift, you will get 1st and reverse gear though.

I believe the MB722.xxx trans have a very easy to remove governor plate. Cant say about the guvner, - Army??? whats your take can it be removed easily with trans in place.

Air&Road · #5 06-12-2012, 03:15 PM

Although a bad governor or servo can indeed cause a late shift, this is more commonly caused by the modulator, or even more often a vacuum leak leading to the modulator.

New2MB · #6 06-12-2012, 03:41 PM

Quote:

Originally Posted by Zulfiqar

if the governor is not spinning (broken heli gear) or if the petals are stuck (sludge) then it wont open up its control ports which direct oil pressure and it wont shift, you will get 1st and reverse gear though.

I believe the MB722.xxx trans have a very easy to remove governor plate. Cant say about the guvner, - Army??? whats your take can it be removed easily with trans in place.

Alright, well that helps me narrow it down.

Must be the last thing I worked on. Hence my tagline.

How do you screw up a front pump!?!?

The damn thing has all of three parts to it.

Zulfiqar · #7 06-12-2012, 04:03 PM

For starters, When I witnessed a toyota automatic trans being worked on, the mechanic told me NEVER EVER TOUCH THE GEARS - His take on it was that the gears wear like a chain/sprocket and if you by accident misalign them - the fires of hell will rise onto the earth.

In this same trans I actually saw a governor slightly sticking with sludge.

to answer the question of shift pressure, the pressure of the governor rises with vehicle speed, it is about 1/2 to 3/4 ratio to vehicle speed in mph, 30 mph 15-20 psi governor pressure.

Stretch · #8 06-12-2012, 04:16 PM

The 722.3 transmission does have a governor that can be removed from the outside of the transmission - however I think you should

1) Listen to Larry - see post 5
2) Read this thread Help - stuck on road 722.3 no 3rd/4th gear it doesn't seem to be as easy you might think.

There's lots of stuff to do before you end up with the last option => pulling the governor out.

I'm sorry to do this to you as it is a lot of reading but here's the best place to start

DIY W123 Transmission Diagnose and Adjustment 722.xx OM 616-7 - Benzworld.org - Mercedes-Benz Discussion Forum

New2MB · #9 06-12-2012, 04:49 PM

Thanks Army, I've eliminated the kickdown, Bowden cable, and vacuum as potential cause. I've read a good bit of the Benzworld post.

All I can figure to do is measure the pressure, everything else is just guessing.

Zulfiqar · #10 06-12-2012, 05:59 PM

I beleive your best investment right now would be a low cost pressure gauge set to test the transmission pressures.

Stretch · #11 06-13-2012, 03:27 AM

Indeed measurement is everything.

I agree with the low cost gauge option - but with a twist. This twist makes stuff a bit more complicated but I think it is worthwhile as it gives you a sense of security and confidence in the "low cost" measurements you'll be making.

I think it is sensible to get hold of some T connectors (local hydraulic shop for example?) and ideally three gauges. You'll need the 3 gauges so that you can measure

a) working pressure
b) modulating pressure
c) governor pressure

It will probably be useful / more meaningful to be able to do this simultaneously...

However before you start driving about with hoses hanging out of windows and gauges flopping about inside the car hook all of the gauges up to one source of pressure so that you can compare the readings on each of them. This is sometimes referred to as a comparison calibration - in this way you can get a better idea of how your cheap gauges are behaving. I can't afford to buy precision calibrated by NASA grade equipment but I can afford to get an extra gauge to reduce the odds of having something that is wildly inaccurate.

Have you got a copy of the ATSG manual?

Stretch · #12 06-13-2012, 03:30 AM

Oh yes and if you get this one sorted out you'll have to change your user name as New2MB won't be appropriate anymore!

New2MB · #13 06-13-2012, 08:46 AM

No, I don't have a copy of the ATSG manual.

I'm looking at a 0 - 200psi gauge (Google: G25-BD200-4LB)
And a 0 - 600psi gauge (G25-BD2600-4LB)

Grand total $24.25 with shipping from Automation Direct.

I have to admit I have a bad feeling about all this, I think I should just get another transmission.

When I first got the car the transmission fluid looked something like that gray anti-sieze grease, somehow it shifted fine.

Then when I re-installed the trans I didn't quite get the TC drive ears lined up and broke the front pump.

Then I replaced the front pump and now it won't shift out of 2nd.

Now I'm going to hook up these pressure gauges and probably find that I screwed up the front pump install and then what?

Pull the transmission, fix the pump, reinstall, pray it works.

I think I'd rather try my luck with a used trans, it's not like the one I have is any sort of gem.

Feel free to talk me out of it but my gut is telling me to quit messing around with this thing.

Zulfiqar · #14 06-13-2012, 09:30 AM

the gears I mention on my above post were the gears in the front pump

Stretch · #15 06-13-2012, 01:09 PM

Quote:

Originally Posted by New2MB

No, I don't have a copy of the ATSG manual.

I'm looking at a 0 - 200psi gauge (Google: G25-BD200-4LB)
And a 0 - 600psi gauge (G25-BD2600-4LB)

Grand total $24.25 with shipping from Automation Direct.

I have to admit I have a bad feeling about all this, I think I should just get another transmission.

When I first got the car the transmission fluid looked something like that gray anti-sieze grease, somehow it shifted fine.

Then when I re-installed the trans I didn't quite get the TC drive ears lined up and broke the front pump.

Then I replaced the front pump and now it won't shift out of 2nd.

Now I'm going to hook up these pressure gauges and probably find that I screwed up the front pump install and then what?

Pull the transmission, fix the pump, reinstall, pray it works.

I think I'd rather try my luck with a used trans, it's not like the one I have is any sort of gem.

Feel free to talk me out of it but my gut is telling me to quit messing around with this thing.

I've sent you a PM - so look out for that!

As for buying a few pressure gauges - I'm of the opinion that there's no such thing as too many tools. You never know when they'll come in handy. Also you might find that you'll get a similar problem with a replacement transmission - in my experience it is almost always "better the devil you know".

It doesn't sound to me like your transmission is dead just yet. But like you say measurement is the only way to check for sure.

For my 722.1 transmission I think I got a gauge that goes to 20 bar for the working pressure (that's about 290 PSI) and then two smaller gauges that go to 5 bar for the modulating and governor pressures (that's about 75 PSI)

I can't find the specified pressures for the 722.3/4 transmissions in the ATSG manual however - I have another source - I'll see what I can do for you!