danglerb

I think I would do my learning on a cheap used AT.

Make sure you have a large very clean area to work, and opening the valve body may not be wise.

Black Sea RD

I watched over the shoulder of a rebuilder as he rebuilt my 928 auto trans over a period of days to fully understand what it's all about.

It is not brain surgery but it is close until you do a few of them. You need a few special tools, a rebuild kit and a good manual.

If you want to learn then go for it.

If you want to save money only, it will not be worth it.

And there are more than a few areas where you can screw it up and not know about it until you drive it in your car.

Cheers,

fraggle

I'd do it myself just because I think I could. It's already hose so why not? Winter's here anyway. Take a lot of time and getRdone!

fbarnhill

Well, I have rebuilt several Mopar automatic transmissions so I would not be intimidated. I have also rebuilt several Muncie 4 speeds with all the little needle bearings between all the shafts. In my opinion the autos were a HELL of a lot easier than the Muncie or a motorcycle gearbox. It sounds like you are compfortable with tools and have some mechanical abilities so go for it. Get a digital camera and take pictures after every step. Yours doesn't sound like a valve body issue so don't mess with it any more than you have to. I am not sure if you can remove it intact or not but if you can, then just do so and put it aside in a very clean place. They usually have little metal ***** inside so don't even flip it over or move it around too much. There are others who can tell you about that way more than I can.

Where are you located anyway? It is not in your signature. Maybe there are some folks willing to help you. If you are near me, I would love to get together and help as much as I can. Remember this, if you screw it up, you can still buy a used one off of ebay or an individual that doesn't require a core.

Best of luck and Merry Christmas,

GregBBRD

We shipped out automatics from the 928 to several different vendors over the years. I bothered me that we did everything else "in house" and sent these out for repair, so it was inevitable that we would dig into these to find out what made them work.

They are not very difficult (for me). Everything is logical and fairly straight forward. There are really four things to think about.

Genuine Mercedes pieces are a bit tough to get. While Mercedes still has everything, inventory in this country can be an issue. I concluded that the only way to deal with this problem was to put everything in stock, which we did. BTW...I found it intersting that the genuine Mercedes pieces were hard to get...what do other people use when they rebuild them? There are aftermarket cluches, gaskets sets, etc., but why would anyone use this stuff? The Mercedes stuff lasted (in most of these transmissions for 20 years and over 150,000 miles) extremely well.

The second thing that was hard was information. The guys that rebuild these transmissions are not generally "fothcoming" with information. Seems that the "mystery" part of the transmission suits them just fine. While there is "generic" information about rebuilding these transmissions, specifics about parts supercessions is really hard to get. There are multiple supercessions that are not obvious. Changing one part will require changing another....and that information is unobtainium. While it might be buried somewhere in a Mercedes technical bulletin, or exist in a rebuilder's head, it is almost impossible to find, now.

The third thing that was hard was the valve bodies. I've yet to take a valve body apart that didn't have at least one broken spring/part. Sometimes there is so much stuff broken that I can't understand how the things every worked! Getting valve body stuff is tough.

The final thing that I found hard to obtain was a supply of the different thickness shims. circlips, clutch pieces, etc. There are many, many dimensions that are set-up by changing a part to a different thickness. It is totally impractical to have all these different thickness pieces on hand, if you are doing only one transmission...buying all the different size pieces costs more than sending the transmission out for rebuilding could ever cost. Of course, since I planned on doing many of these transmissions, I bought every size of every part that existed in multiples. What does this mean to the home guy? It means that you better be patient and have a damn good memory...because you are going to move forward one step and then be stuck, until you order the part in the thickness that you need. You then will move forward a step or two and be stuck again, for the same reason. By the time you get everything in the thicknesses that you require, a bunch of time will have passed by...and remembering how to put it back together, properly, is going to be tough.

Have fun and keep us updated!

blown 87

Lots of electrical stuff in this transmission.

I am a mechanic by trade, over 40 years of it, and I pay some one to build mine after I went down that road a couple of times.

one thing is certain, if the trans is done, you are not really going to loose much by taking it apart.

dr bob

You eliminate the option of having yours rebuilt if you start disassembling it yourself anf then change you mind. In my lmited experince, most folks get into it for a while, until something goes booing-clatter as it shoots off into a dark corner of the shop, and there gets mixed up with the pile of other parts that went booing-clatter on their way to that corner from some other project. The continue until they need a special tool to remove a framus valve, and decide that a deep socket, extension, and abrass hammer will do the job as well. Booing-clatter. Then the pump body need to come out, straight out, perfectly straight out. And you want to keep the pump planetary gears assembled as they were so you can take pictures to help get it back together correctly later. After all the housing bolts are out, you pull gently on the pump shaft. But the o-ring that seals the pump housing is old and tired, and the housing, o-ring and pump now seem to be as one. Thank heavens for those little roll-head bars you got in the kit from Harbor Freight! Jam one under each side, roll them up, and the pump starts out but then gets a little cocked in the casing. Pry a little harder. Booing-clatter! But it looks like you dinked the edge of the casing with the bars, and all the gears fell out. Those damned bars did it... Booing-clatter. Just tap it all back together as best you can, and send it to a rebuilder. Who tells you that you have done irreparable damage, that those critical parts that went booing-clatter are unobtanium, that the falling gearset jammed into the pump casing weren't quite correctly lined up when you retorqued the wrong bolts back into the housing.


Go ahead. Pick a nice piece of precision hydraulics as your first major 928 DIY project. Mark had 1 used one that fits your car, and two others are eyeing it. I might go buy it just because I know that you'll need it in a week or two. Too late to call Mark tonight, but maybe a web order will beat your Monday morning frantic call. Yeah, that's the ticket...!!!

pcar928fan

I'll be calling you for that trans soon Dr. Bob! Just hang on to it for me!

danglerb

My guess is that some amateur rebuilds work for the same reason the valve body with all broken parts worked, its a robust design, and if you don't know what one in good working condition is like, you won't notice any difference with a sort of working home rebuild.

It's easier to find/make more money than it is to find a way to fix a 928 cheaper.

blown 87

How well I know that point.

danglerb

I especially like the part when you bring your box of parts into a mechanic and expect a discount since its already disassembled.

EspritS4s

I've never tackled an automatic transmission myself, but I know that most mechanics outsource this work to specialists, which should tell you a lot. My father has been in the business since the seventies and has owned his own repair shop for 30+ years. He's rebuilt a few over the years, but he sends all transmission jobs out now or just buys a rebuilt. That was enough to convince me that I should treat automatic transmissions as black boxes.

blown 87

Many people actually think they should get a discount.

GregBBRD

The very first sport-o-matic for a 911 came disassembled, in boxes, and missing pieces.

It turned out to be easy.

The very first 4 valve 928 I did came disassembled. They got the passenger head off, with the engine in the car, but couldn't get the driver's head off.

It was fun.

I think I might need mental help.

danglerb

Meaning no disrespect, watching a professional do their work it very often looks easy. A lay person may not learn a thing because none of the critical steps are explained, or the possible variations each step can have.