trans problems revisited (nothing there after second gear.. not "slipping") - PeachParts Mercedes-Benz Forum

12MPGHWY · #1 02-28-2008, 06:01 PM

Ok, so It turns out I wasn't correct or specific on my trans problems.

Went and played with it, now its fresh in my mind,

here it is:

I have 1st and 2nd gear, that don't slip in the classic sense of slipping.

As I accelerate from a stop, first, feels good, shifts to second, second feels good, depending on throttle position somewhere between 20-35, it goes to shift into third, thats when it happens.

No third gear, at this point I might as well be in nuetral. If I'm going slow enough when it happens more throttle will cause it to shift back into 2nd. If not, like I said car's in neutral (for all purposes), not slipping in 3rd, its like there is nothing there.

What I have done so far:

change fluid and filter, fluid was old but not burnt, some metal flakes, not abnormal amounts for an old car. B2 valve looked good (not broken, not worn, maybe it was replaced).

Play with the bowden cable, first I confirmed that its not broken, then I adjusted it so as to make the problem easier to diagnose, by increasing the tension some, I get later shifts, which helps to know what gear its in.

So next, I tried disconnections the vacuum to the vacuum modulator. Drove like this, makes for hard 1-2 shifts but no change going into 3rd.

Tried adjusting the T handle, in both directions, not the proper method of adjustment, just trying to see if I can make a change in its behavior at this point. No real change.

So what else can I look at?

Any thoughts?

Oh, and the trans isn't making any noises.

pawoSD · #2 02-28-2008, 06:05 PM

Will it go into 4th either? If you get going fast enough in 2nd...perhaps 25-35mph (hold it back with the shifter in L/2) or hold it back with the kickdown.....then let off and coast for a couple seconds, it should fall into 4th....if not, then 4th is probably gone too. In which case....its likely rebuild time.

12MPGHWY · #3 02-28-2008, 06:11 PM

No I haven't seen it go into fourth, what is the minimum speed for fourth regardless of throttle position?

There is a hill near my house, that will probably get it into fourth, and if I put the bowden cable all the way in I may be able to keep it there.

I'm thinking maybe the valve body is clogged, with debris, I may as a last ditched effort take it out, take all the removable components out of it and have it hot tanked.

pawoSD · #4 02-28-2008, 06:31 PM

If I let off the throttle on any of our cars while coasting above about 22mph or above they will all drop into 4th.

12MPGHWY · #5 02-28-2008, 06:36 PM

Mine certainly doesn't do that, the fastest it will go is about 35-38, after which its reaching 4500 rpm in second which I'm not willing to exceed.

Quote:

Originally Posted by pawoSD

If I let off the throttle on any of our cars while coasting above about 22mph or above they will all drop into 4th.

pawoSD · #6 02-28-2008, 06:42 PM

Its probably a valve body problem or dead clutch packs on the 3rd/4th gears. In which case it probably needs to be torn down. Is it a high miles tranny?

You mentioned metal flecks in the pan when you took it off.....its been my experience that you should never actually see any metal particles in the pan on these trannys....they are very precise and metal particles means something bad is happening or happened.

12MPGHWY · #7 02-28-2008, 07:04 PM

car has 200000 miles or so. It just looked like clutch flakes, more metal dust than flakes really.

Correct me if I'm wrong, but the valve body comes out pretty easy right?

I think I will try cleaning/inspecting the valve body first, and pull the trans and possibly either rebuild it myself or find a used one.

I have fully rebuilt an auto transmissions before. Its a lot of little parts, but not as bad as people make it out to be.

Ive never had clutches be so worn on a trans that the car wouldn't engage at all. Usually what happens is the classic "slipping" in gear. Ive seen this happen for a long time, even to the point where the car isn't even close to drivable, but it will still shift into the gear, just when any load is put on the trans it slips.

Quote:

Originally Posted by pawoSD

Its probably a valve body problem or dead clutch packs on the 3rd/4th gears. In which case it probably needs to be torn down. Is it a high miles tranny?

You mentioned metal flecks in the pan when you took it off.....its been my experience that you should never actually see any metal particles in the pan on these trannys....they are very precise and metal particles means something bad is happening or happened.

pawoSD · #8 02-28-2008, 07:09 PM

I have personally not removed a valve body on a tranny before...perhaps someone else will chime in. If you're confident in rebuilding I'd say go for it! Could save a ton of money in the process.

12MPGHWY · #9 02-28-2008, 07:23 PM

Searching and reviewing about 100 threads found this one:

http://www.peachparts.com/shopforum/showthread.php?t=201899&highlight=valve+body+removal

Wish I would have seen this before I did the fuid/filter job.

Oh well, I will try this before pulling the trans.

nscarr · #10 02-29-2008, 07:04 PM

Quote:

Originally Posted by 12MPGHWY

Tried adjusting the T handle, in both directions, not the proper method of adjustment, just trying to see if I can make a change in its behavior at this point. No real change.

What kind of car/trans?

Messing with my modulator T didn't do anything on mine when it was bad--also had bad shifting, including (at one point) high rev shift to second and no shift to third...

nscarr · #11 02-29-2008, 07:06 PM

Oh, and pulling the valve body wasn't a problem in my 722.118 transmission. I took the thing apart, cleaned every spring and bearing, stuck it back in, *then* found out it was the vacuum modulator...

12MPGHWY · #12 03-01-2008, 10:41 PM

mine is a 772.3 trans, in an 81 SD