Installing a later 4R70W transmission in a 98 Mark VIII ?

DANTB94

DANTB94

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Oct 14, 2023
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55
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St-Philippe QC
Vehicle Details
94 Thunderbird, 4.6 DOHC, TR3650, 3,73L ; 98 Mark VIII Collectors Edition #1087
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Hi everyone, after restoring and modifying my 94 T-Bird, I happened to see a 98 Lincoln Mark VIII Collectors Edition for sale, and couldn't resist buying it... However, it is looking a bit beat up and needs a general restoration. Very little rust except for the rocker panels, never been in an accident, original paint and windshield, and 136400 KM (84755 MILES). Everything runs well, but I know the transmission has been abused and is showing signs of wear. The fluid is dark brown, it slips slightly 1-2, and leaks from both ends.

I have done some research here and elsewhere on the internet, and I believe my best bet for fixing my problem would be to either rebuild my original transmission, or find a 1998-2004 transmission from a F-150, or a Grand Marquis. (These are the only models available in my area).

Since I am willing to take the transmission apart and do the work myself, what would be the best thing to do?

Or find a transmission newer than mine to use parts from to rebuild a better one?

Any advice would be greatly appreciated. Thanks in advance!
 
I had the one in my 98 rebuilt locally. Fortunately in my case it wasn't beat on and I made the call to rebuild it proactively at 208,000 miles (335,000 km). The shop said it was due - clutches were all but spent, but otherwise it was in decent shape for its age.

Since the 98 already has the mechanical diode it accounts for the bulk of the changes recommended to the 4R70W as of the time Jerry wrote his thesis. With the mechanical diode, if you drill the separator plate to Jerry's settings the only parts that I know of that it could benefit from would include the updated valve body and hardened gearset. Of those, on a stock application, I don't think either are terribly important.

The changes to the valve body in 99 are mainly load capacity springs and those are different for trucks than cars. If you were to get a truck trans for its parts, its valve body would be useless in your rebuild. Since that's the only other part that's any better for a 98, a truck trans would be a waste. I think there are some improved parts from other models/years of trans (e.g. IIRC 2003+ started using the 5.4 hardened internals for all applications) but I don't know enough to tell you what to look for.

IMO, rebuild your 98 as-is and J-mod it, or for the extra edge get a 99-02 from a car (or just grab its valve body) and rebuild it instead.
 
Thanks Terminator93 for your advice, it is always appreciated. So I will proceed according to your information and not use a truck transmission. I will disassemble my transmission probably during the winter and see the condition of the gears, bearings, clutches etc, to know what I need to change.

If I see that the magnet is full of metal debris, I will look for a 1999-2002 transmission for perfect compatibility, or if not, a 2003-2004 for reinforced gears.

According to the information in the 4R70W technical section, I have to keep the original Mark VIII torque converter. How can I tell if it is still good? I heard that it is possible to test it by driving the vehicle... The transmission leaks forward, but it may just be a seal.
 
1997ThunderbirdLXV6 said:
I can't answer your question, but where can I see more of your Thunderbird? How difficult was it to fit the Mark VIII mirrors? Any interior mods?
Click to expand...
I will eventually post some pictures and info in the Garage section. To mount gen 2 Mark VIII mirrors on a Cougar or T-Bird, just re-use your car's mirror mounting plates and modify them in order to have an adaptor plate, as thin as possible. Then drill holes on them to install on your door. Fill the gap between the monting plates with black sealer, and paint the mirrors before installing. Electrical connectors must be modified to make them work properly, as the Mark VIII system is completely different. At the same time, it is possible to connect your turn signals on them, as well as dome lights for convenience.
 
@DANTB94
I figured it wasn't a direct fit. Thanks for the explanation. I'm all about mixing & matching OEM parts for a subtle custom look. I actually considered the Octastar wheels, too, but ultimately decided against them. I'm using a Lincoln LS carved wood shift knob and Mark VIII headrests in my Thunderbird.
 
Any trans you buy will need a rebuild.This is the best way now, if they dont delete my link.

How to: - 4R70W Transmission Rebuild Diary

Foreward to this Diary: I have only been building transmissions now for about 4 years or so. I do not claim to be a pro, expert or genius about this topic. Yet, I have been wrenching for 30 years now and at one time did work for FORD. (Seems like another life). I have built engines, component...
www.explorerforum.com www.explorerforum.com
The one piece teflon seals on the direct shaft eliminated my direct clutch issues. Raybestos plates and kolene steels, in stock thickness and stackup works best for my driving style, and the "blue plate specials" are great in the direct. you need vss, so a 98 is plug and play thru 03, later require parts from an older one. a Superior shift improvement kit adds some sonnax partsc that wear. Check the acc bores and vb valves for wear, and jmod it.
I have 3 cars running that method, with over 300k mi between them.
 
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Thank you very much Grog6, much appreciated, I will take note of it.
 
I used one from a 2000 Mustang GT, + J-MOD and got 200k before damn radiator tank leaked and ruined what was a great running trans. I did have to re-pin the connector on my Tbird. I am not certain about the '98 Lincoln. I recall a friend telling me when I needed a trans to get one from a Lincoln. I wound up w/ the mustang one thanks to flea Bay and a flex plate and Torque Converter and I was GTG. All junkyard trans from the '98 - '03 range need to be rebuilt as all seals are dryed up by now. Thanksfully they ae reasonable to rebuild. I just had one done for my '94 F150 for $1800 out the door.
 
Strictly speaking one from a Lincoln would be fine, except the Town Car has a longer tail shaft and housing (to shorten the drive shaft) which means you either need a shortened/custom drive shaft for use with our chassis, or to re-use the stock trans tail shaft and extension housing during the rebuild.
 
I've replaced a shitload of these. a 98, a '00, and 3x 02's.
All from non police gran marquis.
I was going to buy a TC one and swap parts, because 725 miles was all the miles on it.
But, it was a rear impact when I saw the car, and the ds bein stuffed into just broke it in half; I did buy the engine tho, it's now in the red car.
My count is:
Lazarus 4, Red Cougar 3, Tbird 2.
All are now 02s.
I killed them all thru failing the direct. clutch.
All, I traced to a leaking Scarf-cut teflon seal on the direct shaft.
This causes the Direct clutch to burn. The stock tune's constant 3-4,4-3 'hunting' behavior doesn't help.
So, I finally used every Good trans east of nashville.!
Being an engineer,I bought a set of seal installers and a rebuild kit, read evwrything I could find.
I found the linked site above, and it supplied the missing piece:
The one piece teflon seal.
It needs its own install tool, but IT IS THE KEY TO A TRANS THAT DOESN'T FAIL!
I rebuilt 3, and all are still working.Laz got his last one at 300k mi, in '06, and it's still working @550k mi. when I broke the crank.
 
When I do a rebuild,I start with disassembly. Lay out all the parts on a strong table.
Clean all parts with Mineral Spirits. dip clean parts in fresh Mercon 5 ONLY!!

To successfully do this, you need several special things.

1. a bag of clean, Lint-free rags. A single thread from a red shop rag will fail a trans. btdt;cost $500 to rebuild it again. :)

2. a large clean pot,to dip parts in fluid.

3. A Large tub of trans assembly lube or vasolene. Note: If you walk out of walmart with a male friend, and a quart jar of vaolene, people will talk, lol.

4 set of seal installers, both for the 4r,and the teflon.

5 two rolls of 'super 33 electrical tape.
6. A "master rebuild kit", with Raybestos std.plates.
A set of 'Kolene steels", for the direct at least.
7. a superior 'shift kit.
8. a torrington bearing kit
9. A bushimg kit.

Tomorrow,


3
 
Thanks for all the advice! I'm starting to get excited about tearing this transmission apart to see if I can rebuild it with a 1999-2004 valve body, or if I should look for another 1999-2004 transmission to rebuild.
 
In both cases, I plan to:
- Do the J-Mod,
- Use a 1999-2004 valve body,
- Buy a "master rebuild kit", with Raybestos std.plates,
- BUY a set of 'Kolene steels",
- Buy all bushings, bearings, seals and gaskets, if they are not included in the rebuilt kit,
- Keep my original torque converter,
- If I rebuilt a 2003-2004 one, I will keep my 1998 extension case for VSS use.

I will consider buying a shift kit, but not sure for now. Rockauto should have all that stuff, otherwise I will search for other sites. If a specialized seller is better, I'm open to suggestions.
 
The J-mod "is" the shift kit for the 4R70W. Shift kits from TransGo and the like are fine on the AOD, but on the 4R70W it's a different animal. :)

I'm not sure which year/application it changed but I know as you get closer to the time of the 4R75W's introduction the number of pips for the input shaft speed sensor changed on the 70W.
 
on an 04, you will also need the tailshaft, as an 04 won't have the gear teeth to drive the vss.
That ended with 02. it'sthe last piece out, and the first to go in. Your original trans has a 7 tooth, and gives a wider range of speedo gear options.
an 04 is also missing the plate under the 3-4 acc, and is known to hammer dents into the seperator plate. Instead of drilling the plate you have, get the "super-tuff plate for an 04. It's very thick, and pre modified. Sonnax makes a protect plate, and I strongly recommend you add it. it requires drilling two holes in the right spot.

The superior kit I recommend adds different springs for the vb,and cures several annoying problems with the post 96 vb
 
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Grog6 said:
an 04 is also missing the plate under the 3-4 acc, and is known to hammer dents into the seperator plate. Instead of drilling the plate you have, get the "super-tuff plate for an 04. It's very thick, and pre modified. Sonnax makes a protect plate, and I strongly recommend you add it. it requires drilling two holes in the right spot.
Click to expand...
Oh, that's a good detail to know... Thanks!
 
When it's time to rebuild a 4R70W, is it possible to change the overdrive ratio for a lower one, just like I did for the TR3650 in my T-Bird ? I plan to install a 3:55 axle...
 
Ok. Thanks for clarifying.
 
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