Transmission issue: No forward drive gears in 78 300CD - PeachParts Mercedes-Benz Forum

gavin_leslie · #1 11-13-2007, 05:53 PM

(posted on benzworld.org as well)

Hopefully someone can point me in the right direction with this. Ive been searching and gathering info on what this could be but the more I look the more I get confused.

This is my Girlfriends car first of all. It is one of the greater achievements of german automotive endeavors...the 1978 300CD. Transmission is the 722.118 four speed, four bolt.

In the past there have been minor slippage between 2-3 (mainly uphill) and some hard kickdowns (again, mainly on hills). Nothing I would consider too too awful. Up to last week the car was running fine then within the span of 3 days the GF reports that the transmission started slipping while in drive on flat stretches of roads. Now the slipping is constant to the point where the car seemingly has no forward gears.

The car will move forward, but its almost as if the gears do not engage. As if the forward motion is just through the shear forces in fluid of the torque converter. Pressing the accellerator doesnt yeild a shift or any faster forward momentum. The car will slowly build speed, but it might as well be accelerating off of idle. Reverse is perfectly fine, engages immediately and accelerates like, well....like its in reverse.

Ive searched around an found lots of references to mysterious things like the B2, B1 valves, K1 spring, etc etc. Most of this though seems to be for the newer 722.2-3 transmissions. I did pull the B2 valve in the transmission but nothing seemed damaged(no broken spring as seems to be the case with the 6-bolt transmissions).

Vacuum is also a culprit mentioned. This car however, has no vacuum box on top of the engine. The transmission also does not have a vacuum modulator on the passenger side of the transmission as shown on this page 722.118 Transmission Adjustments

There is only a large bolt where the modulator should be. As a matter of fact I cant find a vacuum line anywhere on the transmission. Is this normal?

Ive also found a couple pages on the transmission itself like so.. 4 Bolt Pan Not too helpful though as there isnt a glossary of parts.

This has been the best reference that I have found so far about the troubles of the 722.118 transmission, a post here from a couple years back..complete with pictures of what I should be looking at (although theres the vacuum modulator thats not on this transmission) 722.118 transmission B2 servo/piston - ShopForum

One thing that I have to redo is completely remove the B2 piston and look at the piston bore as this other fellow had. I neglected to do this the first time when I looked at it. I dont have compressed air at my disposal, whats a good way of getting that piston ring past the groove for the C-clip?

I also removed the valve body and noticed a couple things. A lot of wear marks on some of the tabs of the valve body housing.

wider shot

far side

I am not sure if these are normal happenings or ....something else

Also, what is this (very)worn metal tab and why is it pressed into the band here?

I notice in the link above the pictures show the same metal tab but it isnt worn or contacting the band..normal or....?

Anyway, I have been chasing my tail on this and if someone has an idea as to what direction I should go in it would be greatly appreciated.

Gavin

junqueyardjim · #2 11-13-2007, 06:49 PM

You're looking at a 30 year old transmission and of course you give us no clue to mileage or any evidence of repair or replacement. You have a difficult problem to solve. I would suggest you look at a replacement transmission here.
http://www.mercedesnewparts.com/start.wws?cookieID=24L0UKU7F24L0UPC2N&clientid=mercedesnewparts

gavin_leslie · #3 11-13-2007, 07:40 PM

Mileage is ~340,000miles.

The engine has been replaced at some time during its life but i cant see any indications that the transmission has as well so it may be the original unit.

Understood about the age of the car. I am a "whats the worst case scenario?" guy, so if this is whats needs to be done(replacement) then thats what has to be done. However, I ask because I am not that familliar with this particular transmission and if there is something obvious(or not) that I am missing.... well, I ask.

I will check your link.

Gavin

junqueyardjim · #4 11-14-2007, 10:17 AM

That is I mean, experienced on that transmission. A few of the guys have been able to keep them working after the B2 valve went out, but there are no helps out there on trannys. So you are out there in no mans land. If there was knowledgeable help around, the guys would respond. I would say you have two ways to go. See if someone here on forum, or your favorite junkyard has one that they feel has some life in it. Remember, it is always, "a pig in a poke" and you never will know what you have until it is installed all the way. But there are used ones around to buy. Myself, I would buy a rebuilt if the car warrants it. If the car is history, tell the girl friend that it is time for new wheels. Let me ask, what do you think of the car as a whole. Does it look like it has been really cared for over all 340,000 miles. Are suspension, engine, body and interior really good for that many miles? Only you can determine that, but I think members would be interested to know the general condition.

rs899 · #5 11-14-2007, 12:51 PM

If you have had some slippage for several years and you suspect the mileage on the tranny is 340K, I would think that much, if not most of the friction material on the clutches and bands is gone. I think you will be pulling it apart. The 722.1xx are not noted for B2 piston problem, although anything is possible.

gavin_leslie · #6 11-14-2007, 02:23 PM

Doesnt seem like there is much information/experience with the pre 80s transmission unfortunately.

Ive had an auto transmission die on me before, an A602 out of a 3.3l Dodge caravan. That transmission was hurt when I got the van and I nursed it back into functionality for another 2 years before it finally died. That was a slow and gradual failure. This by comparison was a quick failure. My gut instinct is "something broke" instead of "something wore out". But what that something is I have no clue, and with (seemingly) light info on the older transmissions I am very blind to what that could be.

junqueyardjim.... The car was in an accident in 2000 as indicated by the service records. Car was repaired fully under insurance to the tune of $6000. The engine was fully rebuilt in 1995 to the tune of $5500. The body is straight and the alignment holds well. The paint is a little faded and there is a bit of an "oops" around the fuel filler where the biodiesel kinda ate away at the paint a little. The engine runs strong with very little startup smoke.

I have so far....replaced the dash with a non cracked item, replaced all the other interior surfaces, newer front seats (that are a bit ass worn, but not ripped too shreds) mind you..these are coupe specific items. 1yr old Bilstien HDs, new rear calipers, new engine mounts/dampers, adjusted valve lash, diesel purge, rebuilt injectors, replaced broken swaybar linkages, the usual repeated fluid changes. Oh yes, I replaced the tri-star hood ornament as the original had broken off(This is the greatest achievement Ive done according to the GF). The only things that dont work are the A/C and the climate control system(stupid ACC servo and wtf vacuum system?).......oh yeah, and the transmission.

Honestly, I like the car. A lot. I would be more than willing to put more sweat equity into it. However, assuming $3000 minimum for a rebuilt transmission and installation..thats a fair amount for (as you mentioned) a 30yr old car with 30yr old parts. Ive seen listings for newer cars for the same outlay of money. We will have review our options on this.

rs899...the slippage has always been on cold days and cold startups getting out of the driveway and never at any time. This however may be a moot point though if theres nothing that can be done with the transmission

Gavin

junqueyardjim · #7 11-14-2007, 04:51 PM

I may have, but don't recall using the $3000.00 figure. I think you should get it done for $2000.00 using a $600.00 figure to R&R the transmission. Of course then the core has to pass their inspection to get the money back from that. And $600.00 might not cover the R&R transmission, but it should cover a big part of it. Shipping might eat up a couple hundred also. Like the old saying, it all goes fast when you're having fun.

rs899 · #8 11-15-2007, 06:46 AM

Gavin-

You are right- there is precious little info to be had on the 722.1xx. I have only gone so far as to replace a front pump and TC on a unit that only had 125K miles. Why not consider rebuilding your unit yourself? You probably can do it yourself for less than $500. JIE.com has all the parts and can probably help you through the hard bits. I like your style- a writeup of a 722.1xx would be a valuable tools for users here.

Rick

gavin_leslie · #9 11-15-2007, 05:49 PM

This is an ....interesting option.

I have not really given much thought to rebuilding the transmission myself as the possibility seemed remote/beyond my means. I lack some of the niceties that would help removing a transmission, a lift, air tools, tranny/engine lift....a factory service manual(although the user guide is very detailed in the mechanical pieces of the car).

Have others gone this route(rebuilding their own transmission)? Is this a realistic DIY project, especially in light of the limited tools and background on this transmission?

What tools are required for something like this? Is there a detailed schemetic available for the 722.118 transmission? The one on JIE is the one linked above and its a bit limited/poor quality in terms of detail.

I did call JIE and they suggested checking the band around the rearmost band as that tends to crack. I will look at the transmission again to see if this is the case and also to see what would be involved in a removal and perhaps rebuild.

Gavin

rs899 · #10 11-15-2007, 06:59 PM

Gavin-

Several guys have rebuilt 722.3xx trannys, but nobody here currently has rebuilt a four-bolt and there's no write-up. I myself have rebuilt a Ford C-4 and I am in the (slow) process of stripping 3 parts trannies to try to make one good 722.315 for our 300D. It's not rocket science and is very educational ( as in....hmmm ...no wonder these things break)

You really don't need any special tools. A tranny jack IMO won't do much good because you can't get the car high enough with the tranny on board.

There is an ATSG service manual for the 722.1xx tranny. Consider it if you have the time.

Another option may be to find a car with a 722.1xx tranny in a u-pullit that was obviously running when it was hit or hit something. If nothing else, you can get some practice removing the unit on a junker.

Rick

gavin_leslie · #11 11-29-2007, 06:56 PM

Well after thinking about this for a long(and doing a lot of reading and weighing of the options), the GF and I have decided to keep the old girl. However we will not be using the 722.118 automatic transmission.

After looking at the options(new auto trans, rebuild, replace car) I went with option #4.....4-speed manual that is.

before this idea came along I was really set on the idea of repairing the 722.1xx trans and doing some documentation of that, but this idea was much more realistic for me for a multitude of reasons. Yes, its a "punt", but a good one I think.

Have to figure out some wiring, but I think the car will be running by monday. I wonder if this makes it the first 300D coupe with a 4speed manual in the US?

Good lord what am I doing?

Gavin

t walgamuth · #12 11-29-2007, 07:30 PM

I have an 82 300cd that we converted last summer.

Tom W

gavin_leslie · #13 11-29-2007, 07:59 PM

Excellent!

This is where I can take advantage of your "extensive" knowledge

I have been going through the usual suspects http://www.peachparts.com/shopforum/showthread.php?p=1105195#post1105195 and nothing seems too out of the order but I did have some questions.

-There was a mention of different(?) pilot bearings. Was this an issue for your conversion?
-The shift linkages need to be shortened and threaded. I notice the threads are rolled(extruded) threads. Was this an issue with thread engagement as the existing threads are thicker than the actual shaft.
-whats the installation order of the shift rods? I, er....forgot to label what went where in my haste to remove the trans in the yards

(hey, it was 50% off, I was swept up in the tide of savings)
-where are these indexing marks I keep hearing about? I must be blind because I havent seen any on the flywheel or the driveshaft.(but does this really matter since they will be on a different car and be balanced(driveshaft) and not(5-cylinder engine/4cyl flywheel))
-I hear that the 5-cyl engine is inherently unbalanced because of the odd firing sequence. What is the real day to day reality of vibration from the engine/. Also, with regards to bearing life, has there been any indication that the additional vibrations from the engine have prematurely worn crankshaft/main bearings?
-Wiring. I assume that brake lights/reverse lights will be a plug in affair..what else?

The driveshaft is at the workshop to be shortened and balanced. Just a bit of measuring of the transmission lengths (6.125" difference) and "add" that to the length of the driveshaft (stock stubby was 13.375"). Total new stubby length will be 19.5".

Gavin

unkl300d · #14 11-29-2007, 08:46 PM

Gavin, my 79 300D tranny had some slippage about 8 yrs ago. I caught it in time to have it rebuilt by Peter Schmidt Trans. ($1800 installed)

The clutch plates were suspect.

Anyway, having a 4 speed manual sounds dandy.

a member, ridge, had done these up in the past and well documented as well as added turbos. see archives.

gavin_leslie · #15 11-29-2007, 09:33 PM

I will do a search on that as well. I also will keep the auto trans as well and fiddle with it at my leisure. I figure I (probably) cant make it any more broken-er and theres a chance I might learn a thing or two. Who knows, I might actually be able to fix the thing.

PS: The thanksgiving weekend was one of sales and sure enough the local pick-n-pulls were having a 50% off sale for the weekend. The transmission was $40. I lucked out and the clutch and pressure plate were brand new(no seriously..the painted lettering on the clutch disk face was still visible), the flywheel just surfaced. The 240D that donated the transmission had a broken camshaft(indicating that at the very least, it wasnt in the yards because of a broken transmission). With the pedal assembly, slave/master cylinder and driveshafts it was all a bit less than $150.

Maybe its a sign?

Gavin