Lost overdrive on my 1997 Mark VIII

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Florus

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Hello!

Today I lost the overdrive on my 1997 Mark VIII transmission. It shifts nice from 1 to 2 to 3 but when shifting into 4th gear in feels like it's going into neutral. The engine just revs up when you hit the gas.

When I press the 'O/D off' button it shifts perfect. What could this be?

Searched for some hours now, I found that the MLPS could cause this problem. How can I check it?

Thank you!

Florian
 
Roadboss said:
How old is the tranny fluid & filter?
Click to expand...

Made a complete flush with Mercon V about 1500 miles ago.

Today I removed the MLPS and cleaned the contacts with contacts spray. Overdrive is working now. But I think I need a new MLPS anyway because this is only a temporary fix. Also the indicator for 'P' doesn't light up and I can start the car without hit the brake so the shift interlock doesn't work either. Maybe this is related to the MLPS as well.
 
Florus said:
Made a complete flush with Mercon V about 1500 miles ago.

Today I removed the MLPS and cleaned the contacts with contacts spray. Overdrive is working now. But I think I need a new MLPS anyway because this is only a temporary fix. Also the indicator for 'P' doesn't light up and I can start the car without hit the brake so the shift interlock doesn't work either. Maybe this is related to the MLPS as well.
Click to expand...

You have to hold the brake to start the car during normal operation? That sounds annoying as hell.
 
Unfortunately to problem starts again, after about 18 miles of driving the overdrive jumps into neutral. I replaced the MLPS for sure, but it didn't cured the problem.

I been in a car shop today, and they did read out the error codes (there aren't any) the guy (specialized on US-cars; kind of difficult to find a mechanic for such cars in Germany) said that I need a new transmission. I can't believe that, the problem only occurs when the car is warm and driven for a period of about 18 miles. So I think it's an electric problem.

Any tipps what to look next?
 
Florus said:
I can start the car without hit the brake so the shift interlock doesn't work either.
Click to expand...

the Mark VIII does not have a brake starter interlock. you do not need to ave your foot on the brake.
you must be in park or neutral, but that's it.

the Mark VIII does have a brake shift interlock. you must press the brake to shift out of park.
 
Sapperfire said:
Solenoids
Click to expand...

Can I test them? I think a New Star tester is needed, correct? :-/

@chris2523
Oh good to know! Unfortunately my Park indicator doesn't work. They made a lot of **** when they 'updated' the car to meet German regulations (i.e. Amber tail turn signals), they just cut the wire from the brake on/off switch and wired the brake signal to the tail lamps. That's why my cruise control didn't disengage when I hit the brake - wired it back to US style, but I have a new solution for amber turn signals. :)
 
You say when you turn the OD off it shifts perfect..
With the OD off you're only going to hit 3rd on an AoD4
What does it do at the top of 3rd gear when you turn the OD On?
 
get it rebuilt, its cheaper then getting a new tranny....unless you can find one cheap here in the u.s. and have it shipped to you in Germany....check out car-parts.com
 
Sapperfire said:
You say when you turn the OD off it shifts perfect..
With the OD off you're only going to hit 3rd on an AoD4
What does it do at the top of 3rd gear when you turn the OD On?
Click to expand...

The car shifts pretty good (also in OD), the problem starts when the transmission is hot. The car just jumps into neutral, at least it feels like neutral. I can push the gas pedal and nothing happens, expect the engine revs up.

When the problem starts I click the OD off/on button and the transmission shifts into 3rd gear. When I press the button again the transmission shifts up in 4th gear and some seconds later it goes in neutral again. That's why I think it's not a mechanical problem, the OD works but only when the transmission isn't that hot. (Of course I have an external cooler installed)

@Modular97LSC
Rebuild a transmission is expensive as he'll here in Germany. For a rebuild you pay about 1800 Euro (around $2500). Of course I can buy a used transmission, but first I want to try to repair it because that might be cheaper than replace a whole transmission.

But I think replacing the 1997 tranny with a better 1998 tranny wouldn't be a bad idea at all.

Also the problem starts when we made a jmod on the tranny, before that there where no problems. But we double checked everything, and why does it only make this error when it is hot? Arrrghh... :-(
 
When you did the Jmod, was the pan magnet inspected for clutch material? If it was fuzzy looking, Jmod shouldn't have been done as this indicates a transmission that is not healthy enough.

What did the Trans Fluid look like upon doing the Jmod. If it was brown, transmission should not have even come apart.

I would suggest adding some transmission friction additive for the 4R70W transmission, if this helps correct the issue, start saving up for a '98 or newer transmission
 
Ok, now I lost 3rd - I did let it cool down for about 5 minutes restarted it and 3rd gear is back. I though when something is shot shouldn't it STAY shot? I am happy that it works again, but for how long? That really drives me crazy.

Looking for a used transmission now.
 
It really sounds to me like your clutches are all worn down. When you did the Jmod, this probably escalated the failure due to the new fluid washing out what friction material was still allowing the clutches to grab.

Seriously, try some Friction additive..

And while this method isn't an Experts favorite: I've seen that adding some (a few table spoons) of Saw Dust into the filler tube and then wash it down with just enough trans fluid to clean the tube out, Will help those clutches grab again. I would try this as a last resort if Friction Additive can't be found/ or doesn't seem to cure the issue. This won't be a Fix, but may buy you some time until you can locate another transmission.

Good Luck
 
Sapperfire said:
When you did the Jmod, was the pan magnet inspected for clutch material? If it was fuzzy looking, Jmod shouldn't have been done as this indicates a transmission that is not healthy enough.

What did the Trans Fluid look like upon doing the Jmod. If it was brown, transmission should not have even come apart.

I would suggest adding some transmission friction additive for the 4R70W transmission, if this helps correct the issue, start saving up for a '98 or newer transmission
Click to expand...

There was no magnet in the pan, also the fluid looked like new. It seems that they done the 1-2 accumulators which I was up to do myself. The pre-owner didn't know if something has been done on the tranny. Of course I added a magnet after I noticed it was missing.

Can you recommend any additive?

@slowmkviii

Of course not. ;-) I just enlarged the holes as shown in the specification. In another thread I wrote that hole 9 and 11 (or was it 10?) where already over specification, the holes where larger than supposed to be drilled to.
 
Sapperfire said:
It really sounds to me like your clutches are all worn down. When you did the Jmod, this probably escalated the failure due to the new fluid washing out what friction material was still allowing the clutches to grab.
Click to expand...

But why does this only happen when the transmission is warm?

Sapperfire said:
Seriously, try some Friction additive..

And while this method isn't an Experts favorite: I've seen that adding some (a few table spoons) of Saw Dust into the filler tube and then wash it down with just enough trans fluid to clean the tube out, Will help those clutches grab again. I would try this as a last resort if Friction Additive can't be found/ or doesn't seem to cure the issue. This won't be a Fix, but may buy you some time until you can locate another transmission.

Good Luck
Click to expand...

I'll try some friction additive, I hope I'll get it in a local car parts store.

I have heard of that (putting saw dust into tranny), but wouldn't it clog all the small holes in the tranny? Also won't the transmission filter 'clean' the oil from the saw dust?

I want to say thanks to all of you! I am really happy to get so much feedback and help!
 
Roadboss said:
Don't put saw dust into your tranny!!!!
Click to expand...

+1

Try a bottle of Lucas transmission fix.

When you did the jmod did you torque the valve body bolts to the proper torque? Valve bodies can do funny things if all the bolts aren't tightened up properly
 
Roadboss said:
Don't put saw dust into your tranny!!!!
Click to expand...

Ok. :)

@opalescent 96
Mh... no we did not use the proper torque for tighten the valve body up. Hmph... I'll drop the pan soon, maybe I can see anything. Of course I'll torque them at specs then.

@OchoMarko
Of course, checked it several times. It's perfect red and clean. And it smells like fresh Mercon V (it smells worser than any tranny fluid I know ;-))

Found a junk yard in the Netherlands, he has a rebuild 1997 4R70W for around 1,100 Euro (around 1,500 dollar) which seems to be a good price for a rebuild transmission.
 
Florus said:
Ok. :)

@opalescent 96
Mh... no we did not use the proper torque for tighten the valve body up. Hmph... I'll drop the pan soon, maybe I can see anything. Of course I'll torque them at specs then.

@OchoMarko
Of course, checked it several times. It's perfect red and clean. And it smells like fresh Mercon V (it smells worser than any tranny fluid I know ;-))

Found a junk yard in the Netherlands, he has a rebuild 1997 4R70W for around 1,100 Euro (around 1,500 dollar) which seems to be a good price for a rebuild transmission.
Click to expand...

I wouldn't spend that money on a rebuilt 97 .. Keep looking for a 98

And yeah, sorry bout the saw-dust advice, guess that was an old timey trick for back in the '60s lol
 
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