News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

TH425 Transmission- suggested maintenance with engine out

Started by toukow, July 08, 2019, 10:30:28 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

toukow

Hello: I am planning on pulling the engine on my 76 Eldorado with 75k miles in order to change the timing gear set, and clean out the oil pan. I am sure I will post on that separately. I have only owned the car two years, but believe the prior maintenance was minimal.

This car will probably never see another 5k miles under my ownership, but I want it to be reliable. I would like to replace whatever makes sense, while I have the opportunity. 

My question has to do with the transmission, of which I know pretty much nothing. Once I pull the engine, what items should I consider replacing/servicing on the transmission? Will I need to pull the transmission in order to do the suggested maintenance items, or can it remain in the car?

The only two items I would note on the operation of the transmission are 1. It is clunky shifting into reverse during high idle, and 2. The gear selection indicator on the steering column is somewhat off, which I infer is due to something external to the transmission itself.  Otherwise, it seems fine.

Your comments appreciated, Toukow


The Tassie Devil(le)

I think all transmissions clunk when shifting into reverse at high idle.    May not be the transmission the the backlash in the differential, which is attached directly to the transmission.

If you have any leak around the drive chain housing, I would be removing it and cleaning everything up, and when replacing it, use Loctite 5900 to seal the cover.   This stuff is impervious to Auto Trans Fluid, unlike normal RVT.

Basic servicing can be done with the trans in the car, and even replacing the shifter shaft "O" Ring.

Plus, whilst the engine and Trans are out, it is the best time to service the axles/CV Joints, and hub seals, as they are a simple "pull inwards" once the axle nut on the hub is removed.

But, a word of note.   Don't roll the car on the wheels with the axles out, or you risk popping the inner bearings.   I know from experience.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

bcroe

There are some minor tricks to pulling the engine, flex plate cover removal
and chaining up the final drive to keep it from falling down come to mind. 
A shop can pull the trans from the trans from below, but as a DIY I
pull the trans and final drive set from above after the engine is out. 
Others may pull the engine/trans/final drive package together, but that
is a lot of weight, and there is much chance of collateral damage to
surrounding components. 

There are a few more tricks to servicing the TH425 trans, most of
which I learned from TH400 work and the factory manual.  A few
more are on my PHOTOBUCKET site, 2 albums.  The problem with
a 43 year old low mileage trans is the rubber seals on the internal
rotating assembly, plenty of attention to these in the factory manual. 
I WOULD NOT replace any hard parts which should be like new, just
the $30 rubber seal kit.  Half my car failure these days are due to
replacement parts inferior to originals, including a couple rebuilt
torque converters in my near million miles since 1985. 

The rubber piston seals I remove from decades old transmissions
are sometimes splitting, sometimes so hard they break when bent,
your results will vary.  Once they let go clutches can slip, severe
damage will occur. 

Negotiating the above with a shop is not easy, and everything must
be written out or it will be instantly forgotten and not done.  That in
part is why I finally took over all my own trans work in 1985. 
good luck, Bruce Roe

Big Fins

Not to start a war here, but why pull the entire thing to do a job that can be done with the engine and trans in place? If nothing is wrong with the rest of the engine and the transmission, why do an additional 20 hours of work? 75K on a '76 car? Not unless it sat for the past 30 years. If used even sparingly the seals and all should be good.

Does it shift properly? Is your high/low idle set properly?  If you plan on flipping this car, your busting your butt for nothing if it's operating properly as it is. Do you think advertising that the timing chain has been replaced will get you an extra few G's. I doubt it.

Edit: Gear selector being off is most likely due to worn plastic bushings in the shift linkage. Another $10 fix.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

bcroe

My advice is not for those who want to FLIP cars, it is for those
who actually drive their cars as they were meant to be driven,
and want the car to perform as well (or better) and be as reliable
as new.  If you have had dozens of 4 decade old TH400/TH425s
apart you have some idea of what fails inside.  My own experience
is they vary from sort of OK, to levels of gradual failure, to
catastrophic and costly failure. 

Easy for me to say pull the trans, who can get a TH400 on the
bench in an easy hour, and do it myself.  Others will have to decide
what to do, cars are not a cheap hobby.  Bruce Roe

67_Eldo

I should take my car to Bruce's house! :-)

Not to hijack this thread, but I took my leaking THM425 -- along with its attached leaking 429 -- back to the transmission shop that rebuilt it in 2016-17 as part of my bazillion-dollar repair fiasco. The transmission is leaking from a few spots and the front and rear engine seals are leaking as well. The leaks are the main reason I took the car anywhere to begin with.

The transmission shop said it would honor its two-year warranty on repairs. I took the Eldorado in around the middle of May and they still haven't started working on it yet.

The familiar refrain is that "we need to fix peoples' daily drivers before we can work on the classics." That mentality is so irritating. Just set up an appointment, I'll bring the car, you fix it, and give it back to me. They don't need to judge how daily-driver-ish someone's car is. If I had it, I'd drive it.

Anyway, we'll see if the shop pulls the trans completely (which they should because the chain cover is one of the leaking spots) or if they just slap a new pan gasket on and call it good. And if they pull the trans, they should replace the rear-main seal (at the very least) too.

Rant over. I now return you to your regularly scheduled transmission chat.

TJ Hopland

#6
If you know of someone that can work on it and can afford it now I would just get it done and be done with it.   

   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

The Tassie Devil(le)

Quote from: 67_Eldo on July 09, 2019, 10:24:32 PM
I should take my car to Bruce's house! :-)   
Different Bruce, but you can bring it around any time you like to my place.   Have the unit out and back in in a day.   I have it down to a fine art since working on my mates' and my own.

Bruce. >:D

PS.   Doing the repairs might take a tad longer.
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

bcroe

Quote from: 67_EldoI should take my car to Bruce's house!

I took the Eldorado in around the middle of May and they still
haven't started working on it yet.

The familiar refrain is that "we need to fix peoples' daily drivers before we can work on the classics." That mentality is so irritating. Just set up an appointment, I'll bring the car, you fix it, and give it back to me. They don't need to judge how daily-driver-ish someone's car is. If I had it, I'd drive it. 

Lots of places use a very un business like process.  Last time that
happened (for paint) after a week, I took it to another (mass production
style) shop and got it done on time.  Another reason to do as much as
you can yourself, it might take a lot less time even for a slowpoke. 

This is the stuff recommended to me by an expert GMC guy,
to glue the chain cover on.  It has worked for me. 

I have accumulated the tools to make repairs as easy as possible
for me.  There is not the slightest doubt that the cost in money
and time has very quickly paid off, if I am willing to take on the
work.  However I wear a few other hats, have spent years putting
in new state of the art HVAC equipment and rewiring 2 buildings,
in conjunction with the hundred plus solar panels I put up, doing
ECUs and switch pitch controls, fixing my own cars, and all the
stuff that insists on breaking around here.  So I am not too able
to work on anyone else's car.   retired (?), Bruce Roe


67_Eldo

Thanks for the offers and advice! :-)

I did consider taking my car to a place where I know repairs will be done correctly (Hyde Park Auto here in KC), but I figured that I should take advantage of the "warranty" and that it wouldn't take but a few days to get my car back.

We'll see what happens.

toukow

Quote from: Big Fins on July 09, 2019, 06:16:58 PM
Not to start a war here, but why pull the entire thing to do a job that can be done with the engine and trans in place? If nothing is wrong with the rest of the engine and the transmission, why do an additional 20 hours of work? 75K on a '76 car? Not unless it sat for the past 30 years. If used even sparingly the seals and all should be good.

Does it shift properly? Is your high/low idle set properly?  If you plan on flipping this car, your busting your butt for nothing if it's operating properly as it is. Do you think advertising that the timing chain has been replaced will get you an extra few G's. I doubt it.

Edit: Gear selector being off is most likely due to worn plastic bushings in the shift linkage. Another $10 fix.

Flipping? Shows how naive I can be as I never thought of many members here flipping cars. With my great negotiating skills, the best thing I could have done after purchasing this car was SELL IT, and minimize the hit. I don't expect a cash return of a couple grand, but I hope there will be some minor return when selling to a knowledgeable buyer. Many things on this car seem labor intensive and parts cheap. I have a two post lift, air tools, etc. so hopefully such work would not be too difficult (HEY, I can dream!). I think your advice is reasonable though, and unless I find something wrong later on, will probably leave the transmission in the car. The transmission seems fine, and I'll check the fast idle speed per your point. Thanks.

BTW: The gear shift indicator postion was strange in that it is controlled by a 'thread' connected to the steering column which can be moved to adjust its position. Or I'm simply going about it all wrong.

I'm just one of those guys where photos like at the link with all the garbage in the oil sump, and the minimum engagement of the timing chain on the bottom gear bother me. So with the engine out, I'm trying to avoid the 'you know what you should have done when the engine was out was .......' like the Tassie Devil's point about the wheel hub seals, so that's why I'm asking.

http://forums.cadillaclasalleclub.org/index.php?topic=143947.msg353911#msg353911

Given I'm ignorant of the gaskets and such may be needed, I had found this item on Amazon labeled 'TH400 Transmission External Gasket and Seal Kit - 1965 and Up' which seemed what I would need EXCEPT there is no description of the exact gaskets included.

https://www.amazon.com/gp/product/B01H986ACW/ref=ox_sc_act_title_3?smid=A2QOROTAURQN0I&psc=1

Thanks to everyone for their input, D. Harrison

Big Fins

But you are showing a link for a rear wheel drive car. A THM 425 is a front wheel drive transmission. An 'External Gasket and Seal Kit' is just that. There are no internal seals for the unit. It is used for only the external gaskets and seals that you would be able to see without opening the unit.

Sorry that you misunderstood the word, 'flipping'. Maybe I missed something in you initial posts.

Quote from: toukow on July 08, 2019, 10:30:28 PM
Hello: I am planning on pulling the engine on my 76 Eldorado with 75k miles in order to change the timing gear set, and clean out the oil pan. I am sure I will post on that separately. I have only owned the car two years, but believe the prior maintenance was minimal.

This car will probably never see another 5k miles under my ownership, but I want it to be reliable. I would like to replace whatever makes sense, while I have the opportunity. 

My question has to do with the transmission, of which I know pretty much nothing. Once I pull the engine, what items should I consider replacing/servicing on the transmission? Will I need to pull the transmission in order to do the suggested maintenance items, or can it remain in the car?

The only two items I would note on the operation of the transmission are 1. It is clunky shifting into reverse during high idle, and 2. The gear selection indicator on the steering column is somewhat off, which I infer is due to something external to the transmission itself.  Otherwise, it seems fine.

Your comments appreciated, Toukow



I questioned pulling the engine when your posts reads that you want to 'off' the car. That reads flipping in my world. Not even wanting to put 5k on it says to me that you are buying it for a quick fix up and broom it out the door. Could I be wrong? Sure. Could you have worded it to read differently? Sure.

I'll bow out here on this thread.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

67_Eldo

Even though we know that the Eldorado's THM425 is operationally identical to the RWD THM400, I'd be reluctant to assume that a gasket set for a THM400 would fit a THM425. GM and Cadillac had a habit of messing around with tiny-but-crucial details.

I'd take a peek at a THM425 kit -- https://www.ebay.com/itm/TH425-TH-425-Transmission-Transaxle-Gasket-Set-PAPER-RUBBER-KIT-1966-1978/153457652775 -- and, even then, call them or email in advance to make *sure* that the kit will fit your car.

I've been the beneficiary of too many screwed-up parts orders to endure more "oops" moments. Here in 2019, the person taking the order probably won't know what a '76 Eldorado is. Many times, the parts books used by parts sellers are wrong too. For example, I've had parts people, via email and over the phone, *insist* that my '67 Eldorado has coil springs in the rear. (It doesn't.)

Leave nothing to chance. Good luck!

Scot Minesinger

It is very simple to replace the timing chain without pulling the engine.  Unfortunately the oil pan cannot be dropped unless the engine is pulled.  If you are planning on only driving another 5k miles in your ownership that may be an option for you.  This avoids having to remove the hood, which is a pain.  To remove the front cover, use a punch and drive those two 5/16" metal dowels out and catch them in your hand.  Then when reinstalling, just put cover in place and drive them back in.  I did this on a 1972 Eldorado with more mileage.

Understand that this was not your question.  Here you go:

If the transmission is out, I would replace all the internal soft parts and reseal it, provided of course it is operating correctly now.  Also, at this time I would clean up the engine bay, and there are so might as wells available now it is almost intimidating.  More of a late fall winter start of the season project.  You may also want to have the hood hinges rebuilt by the outfit in Vermont (maybe NH).  They rebuilt mine and they work very well.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

The Tassie Devil(le)

Quote from: 67_Eldo on July 17, 2019, 05:09:06 PM
I'd take a peek at a THM425 kit -- https://www.ebay.com/itm/TH425-TH-425-Transmission-Transaxle-Gasket-Set-PAPER-RUBBER-KIT-1966-1978/153457652775 -- . 
AH HA.   Finally, a kit with the rear drive chain cover gasket.

This is the first time I have seen one of these, even after searching the net for one when I had a cover leak.

Thanks for finding, and posting it.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

67_Eldo

Quote from: Scot Minesinger on July 17, 2019, 08:31:08 PM
> Unfortunately the oil pan cannot be dropped unless the engine is pulled.

The oil pan on my '67 Eldorado *can* be pulled without moving the engine or transmission. And it only cost me $3k to endure the guys who figured out how.

Here are the steps:

1. Acquire a set of "horseshoe" wrenches (or combinations of adapters) that would allow you to remove the bolts holding the FWD "pumpkin" in place.
2a. Take lots of pictures and measurements of the oil pan. You'll need them.
2b. With a beefy, well-aimed hammer, beat the heck out of the oil pan until you get enough clearance to access the aforementioned "pumpkiin" nuts/bolts.
3. Spend hours removing the bolts that hold the "pumpkin" in place because you'll be able to turn a wrench only about 1/16th of a turn at a time.
4. Drop the "pumpkin." As long as you've got it out, replace its various seals (although the "pumpkin" apparently *never* breaks. Thanks, Buick!)
5. Pull the axle shafts and front-suspension pieces that you'd normally have to pull anyway.
6. DROP THE PAN!
7. Repair the stuff that required dropping the pan. [In my case, this was the rear-main seal, the part they'd failed to replace when the transmission was completely out of the car. The new rear-main seal they installed using this procedure lasted for all of 3-4 months before it started leaking again. Not long thereafter, the new front engine oil seal started leaking again too.]
8a. Take measurements that will allow you to figure out how to reshape the oil pan in a way that will a) allow wrenches to get to the "pumpkin" fasteners back on, and b) hold oil. In my case, I (reportedly) lost about 1 pint of oil-pan capacity.
8b. Construct a new oil pan using new sheet metal + the original un-smashed sections.
9. Install the new/old oil pan.
10. Spend hours reinstalling the "pumpkin" fasteners, 1/16th of a turn at a time.
11. Put the rest of the original pieces back together.
12. Pay the man $$$$ for all the shop time this technique required.

You'll find none of that in the official shop manual. You're welcome.

toukow

Thanks you guys, you're a wealth of information.

Big Fins- I can see why you drew the conclusion I was going to flip the car per my comments. I should have added 'the car won't see 5k miles because it's a total garage queen and I live in the land of forever rain (PNW, at least this year!)'. I won't bore you with the work I've done, but I'm in too deep to walk now. As someone once said to me about stocks 'It's not a loss, until you sell'. I'll have to use that logic here.  :D

67_Eldo: Thanks for straightening me out on the parts. I had read that the two models of transmission were pretty much identical, so incorrectly inferred most of the gaskets would work. Thanks for the link, even if some of the items don't work or are not needed, hard to go wrong at that price.

Scot Minesinger: I had read comments about using the procedure you reference for timing set replacement, and leaving it in the car which is very appealing. I thought comments were made about having difficulty sealing it back up when using such an approach. I'll review. Of course, as you note, that leaves all the debris (inferred) in the oil sump.

Thanks everyone for the education as usual, Dean

bcroe

Quote from: The Tassie Devil(le)
AH HA.   Finally, a kit with the rear drive chain cover gasket.

This is the first time I have seen one of these, even after searching the net for one when I had a cover leak.   Thanks for finding, and posting it. Bruce.   

That does look like the SOFT kit for all TH425 internal seal refresh. 
Possibly a few other parts could benefit replacement while in there.

However, do not expect much from that cork chain cover gasket.
At least it will need to be glued to the chain cover, then hope it
stays in place when assembled.  The bottom of that cover has little
area to seal against, just where it needs it the most. 

Failing that try the GMC guys glue.  Bruce Roe

Big Fins

Quote from: toukow on July 18, 2019, 05:17:32 PM
Thanks you guys, you're a wealth of information.

Big Fins- I can see why you drew the conclusion I was going to flip the car per my comments. I should have added 'the car won't see 5k miles because it's a total garage queen and I live in the land of forever rain (PNW, at least this year!)'. I won't bore you with the work I've done, but I'm in too deep to walk now. As someone once said to me about stocks 'It's not a loss, until you sell'. I'll have to use that logic here.  :D


Okay! I just couldn't figure out why you wanted to bust your butt for nothing.

Boring? Never. I learn by other's posts, problems and solutions. When I put them to use in the real world and think that it was worth all of the educational value of the the Club. No matter the car or the year, I always take away something and if I can, use it to help someone else.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

The Tassie Devil(le)

Quote from: bcroe on July 18, 2019, 06:24:09 PM
However, do not expect much from that cork chain cover gasket.
At least it will need to be glued to the chain cover, then hope it
stays in place when assembled.  The bottom of that cover has little
area to seal against, just where it needs it the most.   
Failing that try the GMC guys glue.  Bruce Roe 
When I had the leak on a couple of these covers, I searched and found that Loctite 5900 was perfect for the task, as it does not degrade in Auto Transmission Fluid, and therefore perfect.

The Supplier told me that it is used extensively in the mining industry, and he could only supply the cartridge, which is rather expensive.   BUT, it worked.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe