Transmission fluid change advice.

slowfiveo

Well-known member
Jun 26, 2014
107
0
39
Elizabethtown
Hi folks,

I'm preparing my 170k mile 99 Discovery 1 for a 4000+ mile road trip through Arizona and Colorado this summer. I've been going maintenance crazy replacing anything that seems tired or worn out. I've only owned it for a year and the history of the vehicle is vague at best so, I'm really being particular about every detail.

With that being said, I had planned to do a transmission fluid, diff fluid, and transfer case fluid change before the trip. Upon inspection of the transmission fluid I noticed it was looking dirty, more of a reddish brown than red. My natural mechanical instincts said to simply change it out. Fortunately, I learned early to do a search on every simple detail I change on this vehicle and have found procedures to sometime be quite different!

So....upon research and inspection I can say that the fluid does not have a foul or burnt(coffee pot) smell to it. I have a very large nose and would have noticed.
However, it is in need of replacement.

I must state, I am in no way changing this fluid in hopes of saving a dying transmission. My trans shifts smooth and delivers each time. This is unfortunately the first automatic I've owned and I didn't pay attention to change the fluid when I bought it.

Is there a link that I could be given that would give a step by step process?
Any advice on how to go about this?
I understand with the fluid being reddish brown and having a lack of history presents issues. I even ran a carfax in hopes of finding a recent service record but, didn't find much after 2006 except for brakes and oil changes .

Thanks!
 

MM3846

Well-known member
Feb 18, 2014
1,221
161
LI, NY
Do NOT change it all at once. Do multiple drain and refills over time. There is a drain plug and you fill it through the dipstick. Drain the ~4.5 qts, fill it and check level. Drive a few thousand miles, do it again. Rinse and repeat. I use Mag1 full synthetic ATF and it seems to be working well for me. Valvoline high mileage ATF is also really good juice.
 

slowfiveo

Well-known member
Jun 26, 2014
107
0
39
Elizabethtown
Do NOT change it all at once. Do multiple drain and refills over time. There is a drain plug and you fill it through the dipstick. Drain the ~4.5 qts, fill it and check level. Drive a few thousand miles, do it again. Rinse and repeat. I use Mag1 full synthetic ATF and it seems to be working well for me. Valvoline high mileage ATF is also really good juice.

So, should I change the filter with the first flush? Or do you change it each time to avoid clogging?
 

MM3846

Well-known member
Feb 18, 2014
1,221
161
LI, NY
I never touched the filter. Is it even a filter or is it just a screen? Someone else would know. I just pull the drain plug, no need to drop the pan.
 

slowfiveo

Well-known member
Jun 26, 2014
107
0
39
Elizabethtown
I never touched the filter. Is it even a filter or is it just a screen? Someone else would know. I just pull the drain plug, no need to drop the pan.

From what I understand there's a filter that needs to be changed as well. I could be very wrong. There is alot of mixed information across all of the forums I've searched. The filter and pan gasket kit is only $15 at the local O'Reilly auto parts.
 

luckyjoe

Well-known member
Oct 10, 2004
455
118
New Jersey USA
There is a filter in the ZF pan. It generally is a bear to get to - disconnect O2 sensors, drop Y-Pipe, unbolt & drop cross-member - now you can service the ZF filter. Did I mention exhaust manifold stud & nut drama? Wet these down regularly with your preferred penetrating lube, starting weeks before you plan the actual job! I also like to have as much elbow room underneath as possible, so I crib 4-8 inches under the tires.

One last thing - before going this far in it's a good time to consider replacing your trans cooler lines. These will spray ATF on your CAT's if they let go, and they don't last the life of the vehicle, hint-hint.
 

slowfiveo

Well-known member
Jun 26, 2014
107
0
39
Elizabethtown
There is a filter in the ZF pan. It generally is a bear to get to - disconnect O2 sensors, drop Y-Pipe, unbolt & drop cross-member - now you can service the ZF filter. Did I mention exhaust manifold stud & nut drama? Wet these down regularly with your preferred penetrating lube, starting weeks before you plan the actual job! I also like to have as much elbow room underneath as possible, so I crib 4-8 inches under the tires.

One last thing - before going this far in it's a good time to consider replacing your trans cooler lines. These will spray ATF on your CAT's if they let go, and they don't last the life of the vehicle, hint-hint.

Is it absolutely necessary to service the filter or will simply cycling out the old fluid be sufficient?
 

K-rover

Well-known member
Jan 15, 2010
2,163
62
Raleigh, NC
Not sure about a D1, but the fluid and filter change in my D2 was fairly painless.
Drain the existing fluid
drop the pan, (no removal of y pipe was needed, again on a D2)
replace screen/filter
replace pan
fill through fill port until it started overflowing
Then start the truck and run through all the gears while continuing to fill.

No issues before or after and its been about 2yrs now.
 

luckyjoe

Well-known member
Oct 10, 2004
455
118
New Jersey USA
Is it absolutely necessary to service the filter or will simply cycling out the old fluid be sufficient?

I've read mixed opinions on this - some say yes, some say no.

Since any particular drain-n-fill only drains a percentage of the ATF volume, multiple changes is a good idea as you get a higher percentage of the old fluid. If you do the filter and cooler lines you can get even more fluid out, but more importantly, you get all the particulate trapped by the filter. So, a drain-n-fill or two, prior to changing the filter (and lines) should set you up really well. I've always subscribed to this method.

I just did the filter on my '95LWB last Fall (D1 is exactly the same). In NO WAY could I drop the pan and do the filter without dropping the Y-pipe and x-member. Never even looked at a D2, so I can only speculate that it is entirely different...
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
I always say this about trans filters and nobody ever really listens to me. So let me start this statement with this. I have worked on cars professionally in high end car dealerships since 1981. I rode the Oldsmobile / GMC thing untill Olds fell off. In 99 I switched over to Rover. In those General Motors days I did a shit ton of trans repairs. I would do so many trans repairs that I got audited and 2 suites came and sat on stools in my stall to see how the fuck I did so many trans overhauls in a week. Now that I said that, let me say this. DONT REPLACE THE GOD DAMN FILTER!!!!!
I have seen one time that a filter caused a trans failure. That was because some ass hat left a rag in the space between the transfer case and the trans on a 2500 series GM pickup truck. So it wasn't the filter really. It was an ass hat. Think about this. If there is anything, anything , in that filter it's because something in that trans has come apart in a major fucking way. Trust me on this.
If this was my truck I would pull the drain plug and drain what's in the pan. Keep in mind that there is more fluid in the converter than in the pan. So your only getting almost half the fluid anyway. Drive it a week and do it again.the second time your going to get a mix of your new fluid and what was left behind in your converter . If you still don't like the fluid quality do it again.
 
One last thing - before going this far in it's a good time to consider replacing your trans cooler lines. These will spray ATF on your CAT's if they let go, and they don't last the life of the vehicle, hint-hint.


Bumping this thread. Any luck with making new lines or just take the hit and buy lines from the usual suspects?

I have the crimping tools to put new hose between the hard line sections. I am wondering if the known failures are in hard line fatigue or flex line leaks.
 

kennith

Well-known member
Apr 22, 2004
10,891
172
North Carolina
Don't back flush it unless you've been replacing the fluid regularly. A lot of mysterious ZF problems come back to that.

Just drain and refill. Do it twice if you have to, but don't back flush it under pressure.

Cheers,

Kennith
 

kennith

Well-known member
Apr 22, 2004
10,891
172
North Carolina
I always say this about trans filters and nobody ever really listens to me. So let me start this statement with this. I have worked on cars professionally in high end car dealerships since 1981. I rode the Oldsmobile / GMC thing untill Olds fell off. In 99 I switched over to Rover. In those General Motors days I did a shit ton of trans repairs. I would do so many trans repairs that I got audited and 2 suites came and sat on stools in my stall to see how the fuck I did so many trans overhauls in a week. Now that I said that, let me say this. DONT REPLACE THE GOD DAMN FILTER!!!!!
I have seen one time that a filter caused a trans failure. That was because some ass hat left a rag in the space between the transfer case and the trans on a 2500 series GM pickup truck. So it wasn't the filter really. It was an ass hat. Think about this. If there is anything, anything , in that filter it's because something in that trans has come apart in a major fucking way. Trust me on this.
If this was my truck I would pull the drain plug and drain what's in the pan. Keep in mind that there is more fluid in the converter than in the pan. So your only getting almost half the fluid anyway. Drive it a week and do it again.the second time your going to get a mix of your new fluid and what was left behind in your converter . If you still don't like the fluid quality do it again.

Yup. Drain it and then drain it again if you don't like the result.

Do as little as possible; but do remember to drain it with at least some amount of regularity.

Cheers,

Kennith
 

jprover2

Well-known member
Apr 8, 2017
146
10
Birmingham,Al
I've been raised in a transmission shop, my father has owned it for 38 yrs. We have people come in and ask your question all the time. Has this trans ever been serviced before? If not, you need to look at the fluid, "pull dip stick or drain plug" to get enough to put on the tip of your finger. If the fluid is dark in color, has a burnt smell "not talking about friction modifier smell in new fluids" but burnt!!! Do not touch. If said fluid is still reasonably red sure change it and filter. But if fluid is dark/burnt then there is a high chance you will create problems by changing it. Reason being the transmission fluid has a detergent ability to it when new. "Don't believe me let your hands get really greasy and use new trans fluid to clean." Over time the clutches in your trans lose friction material, these loose pieces smaller than grains of sand get built up in certain areas and are fine there until new fluid is introduced. That detergent ability of new fluid will break things loose and create a problem. I'm not trying to scare you, you may get away with it. But normally if your over 100k mi your asking for trouble by doing a drain and refill, and especially a flush. "The only way you truly get all the old fluid out is tearing trans down and replacing torque converter" Are there any sign of wear? Slips, converter shutter, flares? If not, a road trip would not be my first choice to try a fluid change. Just my two cents. Take it or leave it.