Transmission: rebuild or repair?

[Strand]

Hi all,

My 84 300D is currently at a mechanic getting the 200k mile service it needs to get things where they should be.

One point of contention came out with regards to the transmission. The transmission currently shifts a little hard (which is most likely related to the vacuum pressure and modulator rather than a specific defect within the transmission itself).

However, it has also been displaying all of the symptoms of a failing B2 piston: slow to get into Drive from Park, slipping out of gear once any throttle is applied, and only slowly re-engaging once the engine is revved up. Subsequent shifts between 2nd and 4th gears appear fine, hard shifts and occasional flaring notwithstanding.

The mechanic working on the car is recommending a full transmission rebuild. I'd usually discount that suggestion entirely, but the car is 30 years old with 200k miles and an unknown transmission history.

Unlike many members here, I have nowhere to do any sort of heavy DIY work on the car, and the transmission just isn't something I can realistically work on in the street. At this point, I'm fairly certain that replacing the B2 piston would solve most of my immediate issues. However, the idea of going for the rebuild now as a piece of preventative maintenance doesn't seem unreasonable.

All and any thoughts, comments and/or suggestions are welcome.

Thanks!

[Zacharias]

You say the shop is recommending a full rebuild, by that do you mean they propose to have a rebuild done on yours or they want to sell you a rebuilt unit? I would not trust any shop to rebuild one of these transmissions.

First, it sounds like you need to get the B2 piston done immediately. (Voice of experience, my 300d is sitting dead outside due to that.)

Many shops, even those who claim to be specialists in older Mercedes, do not adequately understand the transmission controls. This situation was not helped by Mercedes consistently refusing to sell their transmission repair documentation here in North America.

The shop may take the point of view that if they just change the B2 for you, you may be back in 6 months with the trans blown and they will be blamed for not "properly" fixing it the first time. It's a valid point of view for them, as it does happen. (More or less the same reason many shops refuse to install a new voltage regulator on an alternator... they will only sell a rebuilt unit.)

No one here as driven your car, so it's hard to give advice. But based on your description the B2 is overdue and you haven't done the trans any favours by driving it that way (revving to get into gear). You should not be driving it with those symptoms.

So FWIW, I would say do the B2 and then make a serious effort to get your vacuum controls working properly (verify vacuum pump output, check vacuum control valve function and adjust as necessary, replace all vacuum connection rubber parts to ensure no leakage, check modulator cap is holding vacuum, and then if necessary adjust the modulator).

But one thing if you do want to go the full monty route, I would recommend you get a off-the-shelf reman transmission before you let any shop start rebuilding yours. There are known reliable suppliers of reman units... my brain is blank right now as to a name but there is a transmission guy in FLA who used to be a contributor to this forum who has all kinds available.

[SD Blue]

Sounds like a matter of $$'s and sense. (not mispelled)

A rebuilt transmission from Sun Valley Transmissions (a well-known rebuilder) is $1750. A B2 piston is ~$150 and would take someone with a lift, about 2 hours to replace.

It appears to me, the best option might be to ask for the B2 repair without a guarantee of no continuing problems.

[ROLLGUY]

Originally Posted by SD Blue

Sounds like a matter of $$'s and sense. (not mispelled)

A rebuilt transmission from Sun Valley Transmissions (a well-known rebuilder) is $1750. A B2 piston is ~$150 and would take someone with a lift, about 2 hours to replace.

It appears to me, the best option might be to ask for the B2 repair without a guarantee of no continuing problems.

X2 Agreed.

[cooljjay]

Why not start by replacing the bushings in the shifter and transmission levers? If they are bad the transmission can act very strange too...even a bad motor n trans mounts can effect shifting....I wouldn't go and toss a new transmission in it, until I did the simple things surrounding the transmission....as I told someone else...the shotgun repair approach doesn't apply to these cars...

[Strand]

Thanks for the feedback, all. Based on further thought as well as your comments, it seems like convincing the shop to do the B2 repair is the way to go--if not just as a stopgap measure to get the car back to New York, where the transmission can be examined by a shop that truly knows what they're working with.

Originally Posted by Zacharias

Many shops, even those who claim to be specialists in older Mercedes, do not adequately understand the transmission controls. This situation was not helped by Mercedes consistently refusing to sell their transmission repair documentation here in North America.

The shop may take the point of view that if they just change the B2 for you, you may be back in 6 months with the trans blown and they will be blamed for not "properly" fixing it the first time. It's a valid point of view for them, as it does happen. (More or less the same reason many shops refuse to install a new voltage regulator on an alternator... they will only sell a rebuilt unit.)

This is an important point--in spite of their assurances to the contrary, I don't feel like this shop is knowledgeable enough with these transmissions to be trusted with the rebuilding process. From what I've gathered, they seem reluctant to even take on the B2 piston, perhaps for these very reasons.

Originally Posted by SD Blue

A rebuilt transmission from Sun Valley Transmissions (a well-known rebuilder) is $1750. A B2 piston is ~$150 and would take someone with a lift, about 2 hours to replace.

I'm tempted to go for an off-the-shelf rebuilt unit from Sun Valley, but between r/t shipping and third-party installation costs, I'm leaning towards getting one of the reputable shops in the NYC Tri-State areas tackle the job.

[Strand]

Originally Posted by cooljjay

Why not start by replacing the bushings in the shifter and transmission levers? If they are bad the transmission can act very strange too...even a bad motor n trans mounts can effect shifting....I wouldn't go and toss a new transmission in it, until I did the simple things surrounding the transmission....as I told someone else...the shotgun repair approach doesn't apply to these cars...

These are all things that I'll be approaching on a piecemeal basis once the vehicle is back in reliably running condition. The mounts--both motor and transmission--do need to be replaced, but I doubt that they are primary cause of the current symptoms.

What's concerning at the moment is that this shop is clearly inexperienced when it comes to the more specific details of the vehicle. For example, hard shifting (as we all know) is *not* a good reason to replace a transmission.

[Jeremy5848]

I can't comment on the quality of Sun Valley's work. In general, though, generic rebuilds are cranked through as quickly and cheaply as possible. Having your transmission rebuilt by a shop that knows what it's doing is the best solution although not necessarily the least expensive.

[Zacharias]

Originally Posted by Strand

This is an important point--in spite of their assurances to the contrary, I don't feel like this shop is knowledgeable enough with these transmissions to be trusted with the rebuilding process. From what I've gathered, they seem reluctant to even take on the B2 piston, perhaps for these very reasons.

It would be unusual, these days, if the shop planned to do it themselves. Chances are "their" rebuild would actually be done by a transmission shop they deal with.

Chances are they are reluctant to take on the B2 because many shops are of a mindset that something a customer read on an Internet forum doesn't qualify as expert advice. Sitting on their stool, that is a fair comment.

Or they may sincerely believe the B2 will end up being a short-term bandaid.

[86-300sdl]

I opted to have the trans replaced with a reman from Sun Valley Trans at around 300,000 miles. That was around 100,000 miles ago and I remain glad I went that route. The trans works flawlessly and not a drip to be found.

The original problem was believed to be a B2 thing too, however at 27 years the original trans seals were starting to go. I replaced a couple i.e. secondary pump seal but could not get to the rest of the seals.

So even though I needed B2 work I also needed seal work due to age...in particular the front main pump seal. I even came a hair away from buying a rebuild kit....but then although I've rebuilt a few manual trans over the years I read more about these trans and opted out of the DIY program for this repair.

Ran me about $1500 installed at Sun Valley in North Los Angeles. Kind of a "fix and forget" repair. These people are great.

It was one of only two times I've had to use a shop in 15 years but it was worth every nickel.

[cooljjay]

You guys put a lot of trust into rebuilt transmissions.......

I remember at one point in life were we would listen to those who have more experience....now we just pull it out and fight whom's is bigger.....

I have one of the 1500$ transmission that the shop charged the poor ol original owner 2500$ bill for....

I had(lost in fire) the original receipts and I even had the dealer repair paper work...

The dealer charged this poor person to replace the shifter bushings...well the dealer replaced one...

Now after that the transmission of course had to be replaced because of bad shifting well....

The garage happy applied with one of these worth their weight in gold rebuilds we are all bragging about......

So the transmission was replaced with this heart of gold...in the late 2000's..I bought the car because of this transmission....well wouldn't you know the car was still not shifting right...

Well lots of hard work later....I noticed that the transmission was installed in the car as promised....but...

They figured the starter only need one bolt, the stuck on reverse light NSS was also fine, all the missing bushings were just fine and well who needs a firm transmission mount...the pile of goo the old one was..was just fine....

So after many many many many many many many hours of getting all the neglected maintenance done, missing bushings reinstalled and linkages adjusted against the FSM...I had a great shifting car...

Fast forward now till a year ago....and the yoke on the rear the transmission decided to come off...

Remember this is that 1500$ heart of gold transmission that was just bought from that lovely place we rave about...

I have only owned the car since 2012....

So bashing my head against the wall I decided to crawl underneath in the mentality I was going to have to rip the back of the transmission off....

Well after removing the carrier bearing and transmission cross-member the drive line fell off the transmission....

Well turns out this amazing transmission rebuilder NEVER ordered a new rear seal, a replacement nut and locking hardware....he had sliced the old nut to unlock in and simply reinstalled it...

Well if that isn't enough....now today I have a transmission that is still leaking and maybe oh just maybe 6 years old...

Why????????????????

Well this amazing company never found it necessary to order the parts the FSM states to also replace during a rebuild because they weren't included in the kit they ordered probably from Napa Auto....

Now I have to pull this transmission in the feature and replace all the seals for all the rods that come out of the transmission because the old yellowed 38 year old seals were reused....

Now that I stated my point on a transmission so highly valued by people with no experience dealing with a garage replaced transmission....I will stick mine back in my pants....

Peace out!!