Does my automatic transmission need to be rebuilt/replaced?
02-23-2015, 04:22 AM
#1
Racer
Thread Starter
Does my automatic transmission need to be rebuilt/replaced?
('83 4-speed)
This is a question for the experts. I've been having some problems with my tranny and I'm wondering whether it's worth attempting further exploration of possible causes/fixes or whether I should bite the bullet and hand the thing over to the professionals and prepare for bankruptcy.
About a month ago I posted how the transmission would randomly 'kickdown' to lower gears. I'd have to nearly redline it to change back to a higher gear. This would happen every few minutes or so.
The tranny was low on fluid due to a leak. Had lots of great advice on this forum including the suggestion of using Trans-x. I drained the pan, refilled with fresh fluid and a bottle of Trans-X. A couple of days later, it seemed as though the gearbox was fine again. Leak gone too. I had planned on removing and inspecting the governor and a few other things, but it seemed like I didn't need to.
A month or so later, problem has returned. Fluid level perfect, won't stay in a high gear. Is it worth me poking around or is there the overwhelming likelihood that the tranny is toast?
Any help very much appreciated.
This is a question for the experts. I've been having some problems with my tranny and I'm wondering whether it's worth attempting further exploration of possible causes/fixes or whether I should bite the bullet and hand the thing over to the professionals and prepare for bankruptcy.
About a month ago I posted how the transmission would randomly 'kickdown' to lower gears. I'd have to nearly redline it to change back to a higher gear. This would happen every few minutes or so.
The tranny was low on fluid due to a leak. Had lots of great advice on this forum including the suggestion of using Trans-x. I drained the pan, refilled with fresh fluid and a bottle of Trans-X. A couple of days later, it seemed as though the gearbox was fine again. Leak gone too. I had planned on removing and inspecting the governor and a few other things, but it seemed like I didn't need to.
A month or so later, problem has returned. Fluid level perfect, won't stay in a high gear. Is it worth me poking around or is there the overwhelming likelihood that the tranny is toast?
Any help very much appreciated.
02-23-2015, 06:09 PM
#2
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
I doubt it is toast. I had some episodes of my tranny dropping from 4th to 3rd while cruising. I inadvertently discovered that briefly shifting into neutral then back to drive after a few seconds would "fix" it initially for a few hours, then for several days. In fact, it hasn't done it now for months. I suspect the valve body needs cleaning and maybe a few seals renewed. No surprise at 278K miles. Sure it could be a problem with the governor or kickdown. I can't tell you, but I don't think it's "toast".
02-23-2015, 09:24 PM
#3
Rennlist
Basic Site Sponsor
Basic Site Sponsor
These transmissions are way beyond their "service life" in terms of years, much less mileage.
Automatic transmissions depend on internal O-rings and seals to hydraulically engage the different brake bands and clutch packs to allow them to function. These 0-rings and seals start life as soft pliable rubber. They are now all virtually hard plastic, from the heat and use.
Products like "Trans X" are designed to make the rubber seals and O-rings swell and regain their sealing ability. Generally, these products are short term solutions, if they work at all.
Automatic transmission "rebuilding" probably has the most smoke and mirrors, in the automotive world.....maybe more so, in the 928 world. There are, quite frankly, very few people qualified to rebuild one. However, there are lots of "Mercedes transmission experts" who will take them apart, throw in a gasket set and a new set of clutches for a "flat price".
"Flat price" rebuilding, without an itemized list of parts and where those parts come from, is akin to buying "snake oil" back in the 1850's.....not the best idea or value.....for the majority of the 928 world.
I'm working on a "primer" to put on my web-site to help people understand what needs to be done, what is involved, and how to assure that they are getting the best value for what their needs are.
Should be ready for "prime time" this week.
Automatic transmissions depend on internal O-rings and seals to hydraulically engage the different brake bands and clutch packs to allow them to function. These 0-rings and seals start life as soft pliable rubber. They are now all virtually hard plastic, from the heat and use.
Products like "Trans X" are designed to make the rubber seals and O-rings swell and regain their sealing ability. Generally, these products are short term solutions, if they work at all.
Automatic transmission "rebuilding" probably has the most smoke and mirrors, in the automotive world.....maybe more so, in the 928 world. There are, quite frankly, very few people qualified to rebuild one. However, there are lots of "Mercedes transmission experts" who will take them apart, throw in a gasket set and a new set of clutches for a "flat price".
"Flat price" rebuilding, without an itemized list of parts and where those parts come from, is akin to buying "snake oil" back in the 1850's.....not the best idea or value.....for the majority of the 928 world.
I'm working on a "primer" to put on my web-site to help people understand what needs to be done, what is involved, and how to assure that they are getting the best value for what their needs are.
Should be ready for "prime time" this week.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
02-24-2015, 02:55 AM
#4
Racer
Thread Starter
Thanks for the replies guys. Greg: I'll stay tuned to your website for that article. Sounds interesting.
It would be interesting to know how just how interchangeable the unit is between a suitable model Mercedes and a 928 (if that's not too dumb a thing to ponder). Were I to be looking for a low milage salvage transmission, I have a feeling one from a Mercedes would have a lower sticker price than one from a Porsche.
It would be interesting to know how just how interchangeable the unit is between a suitable model Mercedes and a 928 (if that's not too dumb a thing to ponder). Were I to be looking for a low milage salvage transmission, I have a feeling one from a Mercedes would have a lower sticker price than one from a Porsche.
02-24-2015, 05:11 AM
#5
Rennlist Member
Used porsche 928 trans are cheap on ebay as far as used transmissions go. You can pick up a good one for around $600 or less usually. You can even upgrade to an 89 trans if you wanted to.
The only thing in common with the merc unit is most of the internals. All the rest is 928 specific.
The only thing in common with the merc unit is most of the internals. All the rest is 928 specific.
02-24-2015, 05:47 AM
#6
Rennlist Member
@ The Forgotten One
Congratulations! This was your post #1000
Identification of MB parts in the 928 automatics is simple. Just look at PET and you will find part numbers that are shorter (not the Porsche usual 11 digits). Plus they don´t start with 928.
These are all MB parts and if you take these part number to your local MB dealr, he can get you the parts OEM and for a lot less.
I replaced reverse in my 722.3 Rogerbox and wrote an extensive post about it: https://rennlist.com/forums/928-foru...ement-diy.html
I went with a B3 clutch replacement and all accessible seals replacement only. I own my GTS since 2003 and I know the service history, that's why I did not rebuilt it completely.
Otherwise Greg is absolutely right! The amount of work involved to remove and reinstall does not justify a "fix only what's broken" approach. The amount of labor involved is high, regardless what you do. WYAIT is the key, unless you are a serious DIY'er with a lot of tools and you don't mind wrenching.
Congratulations! This was your post #1000
Identification of MB parts in the 928 automatics is simple. Just look at PET and you will find part numbers that are shorter (not the Porsche usual 11 digits). Plus they don´t start with 928.
These are all MB parts and if you take these part number to your local MB dealr, he can get you the parts OEM and for a lot less.
I replaced reverse in my 722.3 Rogerbox and wrote an extensive post about it: https://rennlist.com/forums/928-foru...ement-diy.html
I went with a B3 clutch replacement and all accessible seals replacement only. I own my GTS since 2003 and I know the service history, that's why I did not rebuilt it completely.
Otherwise Greg is absolutely right! The amount of work involved to remove and reinstall does not justify a "fix only what's broken" approach. The amount of labor involved is high, regardless what you do. WYAIT is the key, unless you are a serious DIY'er with a lot of tools and you don't mind wrenching.
02-24-2015, 05:25 PM
#7
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
If your problem were flaring or slipping I might be more inclined to say rebuild, addressing brake bands and clutches. You simply report some random downshifts, like I had. This points to the valve body which can be accessed and serviced or replaced with a rebuilt unit without removing the tranny. Although I'm sure these trannies have a finite lifespan, I opened mine up at 200K miles, due to a torque converter seal leak and I found brake bands and clutches in good shape. I did some minor part swapping (prmary pump and torque converter). I think your particular issue doesn't point to needing much more than a valve body swap or rebuild. I'm all for regular maintenance, but I've been burned several times by replacing parts that are not broken simply because of age or mileage. I think there should be some more indications that your tranny needs rebuilding or replacement than what you report.
Trending Topics
02-24-2015, 07:39 PM
#8
Rennlist
Basic Site Sponsor
Basic Site Sponsor
If your problem were flaring or slipping I might be more inclined to say rebuild, addressing brake bands and clutches. You simply report some random downshifts, like I had. This points to the valve body which can be accessed and serviced or replaced with a rebuilt unit without removing the tranny. Although I'm sure these trannies have a finite lifespan, I opened mine up at 200K miles, due to a torque converter seal leak and I found brake bands and clutches in good shape. I did some minor part swapping (prmary pump and torque converter). I think your particular issue doesn't point to needing much more than a valve body swap or rebuild. I'm all for regular maintenance, but I've been burned several times by replacing parts that are not broken simply because of age or mileage. I think there should be some more indications that your tranny needs rebuilding or replacement than what you report.
The ones I see with mileage like yours need pieces like drums, steel clutch parts, etc.
Once you start buying these "hard parts" the "economy" of driving one past 150,000 miles or so quickly disappears. A new B-1 drum, for your car, is now over $850 and a new B-2 drum is over $925.
For me, true economy isn't about how many miles one can drag out of something before it is trash....it's about how many miles one can get out of something and still economically rebuild it.
02-25-2015, 05:20 AM
#9
Rennlist Member
The great thing about rebuilding these things when they need O-rings and seals, brake bands, clutches, and updates is that you usually can "catch" them before the "hard parts" get torn up.
The ones I see with mileage like yours need pieces like drums, steel clutch parts, etc.
Once you start buying these "hard parts" the "economy" of driving one past 150,000 miles or so quickly disappears. A new B-1 drum, for your car, is now over $850 and a new B-2 drum is over $925.
For me, true economy isn't about how many miles one can drag out of something before it is trash....it's about how many miles one can get out of something and still economically rebuild it.
The ones I see with mileage like yours need pieces like drums, steel clutch parts, etc.
Once you start buying these "hard parts" the "economy" of driving one past 150,000 miles or so quickly disappears. A new B-1 drum, for your car, is now over $850 and a new B-2 drum is over $925.
For me, true economy isn't about how many miles one can drag out of something before it is trash....it's about how many miles one can get out of something and still economically rebuild it.
Well put- my perception of value is that the units should be economically refurbishable after covering 300k miles providing they have been well maintained in the interim [perhaps with a valve body refurb at 150k miles?]. If that is not the case then I would be worried. Fortunately most examples do not see the kind of mileage Bill has covered so perhaps it is an academic point.
What I can say for sure is that much as I would fancy a go at rebuilding a 928 engine or possibly a manual tranny [with appropriate technical guidance on hand] an auto trnasmission I consider another animal altogether and I rather suspect there are not too many places on the planet capable of such assuming there are not many masters like yourself around.
The one thing you can probably be sure of in an auto box is that if it is not put together correctly there are going to an awful lot of small metal bits in the casing within minutes of starting to drive the thing.
As a matter of interest- how many hours does it take to do a major rebuild on one of these things [assuming such info is not proprietary]?
Regards
Fred
02-25-2015, 04:12 PM
#10
Rennlist
Basic Site Sponsor
Basic Site Sponsor
Greg,
Well put- my perception of value is that the units should be economically refurbishable after covering 300k miles providing they have been well maintained in the interim [perhaps with a valve body refurb at 150k miles?]. If that is not the case then I would be worried. Fortunately most examples do not see the kind of mileage Bill has covered so perhaps it is an academic point.
What I can say for sure is that much as I would fancy a go at rebuilding a 928 engine or possibly a manual tranny [with appropriate technical guidance on hand] an auto trnasmission I consider another animal altogether and I rather suspect there are not too many places on the planet capable of such assuming there are not many masters like yourself around.
The one thing you can probably be sure of in an auto box is that if it is not put together correctly there are going to an awful lot of small metal bits in the casing within minutes of starting to drive the thing.
As a matter of interest- how many hours does it take to do a major rebuild on one of these things [assuming such info is not proprietary]?
Regards
Fred
Well put- my perception of value is that the units should be economically refurbishable after covering 300k miles providing they have been well maintained in the interim [perhaps with a valve body refurb at 150k miles?]. If that is not the case then I would be worried. Fortunately most examples do not see the kind of mileage Bill has covered so perhaps it is an academic point.
What I can say for sure is that much as I would fancy a go at rebuilding a 928 engine or possibly a manual tranny [with appropriate technical guidance on hand] an auto trnasmission I consider another animal altogether and I rather suspect there are not too many places on the planet capable of such assuming there are not many masters like yourself around.
The one thing you can probably be sure of in an auto box is that if it is not put together correctly there are going to an awful lot of small metal bits in the casing within minutes of starting to drive the thing.
As a matter of interest- how many hours does it take to do a major rebuild on one of these things [assuming such info is not proprietary]?
Regards
Fred
Most of these transmissions end up in the hands of "flat rate" Mercedes transmission rebuilders. They remove the entire differential section, as a unit , and set it to the side. Sometimes they will clean the outside, sometimes they bolt it back on filthy. I have no idea when they think the differential section is going to get looked at and re-sealed....most are seeping from the O-rings and seals getting hard, long before the transmissions need attention. They throw in a gasket set, a set of "offshore" clutches, grind off the hot spots on the steel clutch pieces, and throw them back together. No updates. No brake bands. No thrust bearings. Nothings but a basic transmission rebuild kit that they by for under $400.00. Toss in a "painted" convertor for under $200 and they are done. They charge $2500 for a non-itemized "rebuild", which gives them the highest profit margin possible. And the buyer gets the lowest quality end product possible.
This stuff should be reserved for the "used car lot" people....not for people that want to keep their cars.
I charge $1250 (12 hours) labor for a rebuild, plus parts. I rebuild and reseal the differential. (If it is a limited slip, I charge an additional $300 to service the limited skip, plus parts.)
I can't do one in 12 hours....can't get close. I'm not interested in how fast I can do one...never have been. Do it correctly the first time and be done with it.
Here's how it currently breaks down (approximately), for me:
2 hours----Disassemble with "gross" inspection during disassembly.
4 hours----Clean and do second "micro" inspection of pieces....make parts list while doing inspection.
4 hours----Sub-assemblies. Replace "hidden" 0-rings (machine clutch drums to accept new "hidden" O-rings). Rebuild clutch drums with new discs. Set up clearances in drums. "Rebuild" front pump assembly. Re-assemble planetary. Install new seals and 0-rings in case. Etc. Etc.
4 hours----Rebuild valve body. (Need to be left completely alone, without interruptions to be able to do one in this amount of time.) I ultrasonically clean every single tiny piece....not spray off the outside and blow it clean.
6 hours----Re-assemble and set-up clearances.
02-25-2015, 05:46 PM
#11
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Greg--
How much extra $$$$$$$$$ would it be if I helped?
How much extra $$$$$$$$$ would it be if I helped?
02-25-2015, 07:12 PM
#13
Drifting
Without knowing what the parts list and costs would come to....Greg's post above has convinced me to remove the transaxle, clean it real good, and ship it to him for a true rebuild. Tremendous peace of mind knowing GB rebuilt it. Fortunately, my car has a very minor leak (few drops at shutdown) between the torque converter and trans that has almost stopped with TransX added -- just buying a little extra saving time.
02-25-2015, 09:27 PM
#14
Racer
Thread Starter
Is there a way to determine whether the problems I'm having are valve body related?
It would certainly be the most convient major problem as I can handle removing that and sending it off (someplace) for rebuild rather than have the whole tranny excised and couriered (which I would have to have to pay to have done).
02-25-2015, 11:52 PM
#15
As I learned last summer.... You can do it the DIY way.... and again.... and again.... and again. If you want to be involved, remove the unit. Buy a big ice cooler from Walmart... insert the transmission in the cooler... and send it to California for Greg to inspect. Or You can do what I did, by the way did I tell you I'm really good at removing the 4 speed automatic transmission from a 928.