4R70W Forward Clutch disengaging at stop
#1
08-18-2018, 02:36 PM
Join Date: Aug 2018
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
4R70W Forward Clutch disengaging at stop
I've just finished a rookie rebuild of a 4r70w. Actually I've been through the trans multiple times now.
I'm having a couple problems.
1) after it's good and warmed up, occasionally when taking off from a stop, it will momentarily lose drive (go nuetral) then pop back into gear. Using pressure gauges today I confirmed this is the FORWARD clutch disengaging momentarily (pressure dropping to near zero, then re-engaging).
One TSB I found mentioned this:
Quote: The cause may be, a partially clogged Shift Solenoid No. 2, which will stroke the 3-4 shift valve far enough to exhaust some of the forward clutch oil.
Given that I put a new 1/2 solenoid set in it, does anyone have an alternative idea for what might cause it to "stroke the 3-4 shift valve far enough to exhaust some of the forward clutch oil." ?
Problem #2:
When it shifts into O/D, I hear a very faint but noticeable "scuffing" sound. After the last time I took it out, it seemed the new O/D band was grinding off/scuffing the reverse drum, though there was no noticeable slippage while driving.
I put in a new O/D servo for good measure, but that doesn't seem to have changed anything.
Since idle pressures look good per the gauges, I'm thinking something's wrong in the valve body. Only intentional change was the Sonnax line pressure valve and new solenoids.
Any ideas would be greatly appreciated!
Paul
I'm having a couple problems.
1) after it's good and warmed up, occasionally when taking off from a stop, it will momentarily lose drive (go nuetral) then pop back into gear. Using pressure gauges today I confirmed this is the FORWARD clutch disengaging momentarily (pressure dropping to near zero, then re-engaging).
One TSB I found mentioned this:
Quote: The cause may be, a partially clogged Shift Solenoid No. 2, which will stroke the 3-4 shift valve far enough to exhaust some of the forward clutch oil.
Given that I put a new 1/2 solenoid set in it, does anyone have an alternative idea for what might cause it to "stroke the 3-4 shift valve far enough to exhaust some of the forward clutch oil." ?
Problem #2:
When it shifts into O/D, I hear a very faint but noticeable "scuffing" sound. After the last time I took it out, it seemed the new O/D band was grinding off/scuffing the reverse drum, though there was no noticeable slippage while driving.
I put in a new O/D servo for good measure, but that doesn't seem to have changed anything.
Since idle pressures look good per the gauges, I'm thinking something's wrong in the valve body. Only intentional change was the Sonnax line pressure valve and new solenoids.
Any ideas would be greatly appreciated!
Paul
Last edited by proctoidpaul; 08-18-2018 at 02:46 PM.
#3
08-22-2018, 11:42 AM
no idea what the scuffing noise is on the OD band, unless the band is not seated correctly in the case.
on the shifting issue, the only time I have run into something like that is when the solenoid regulator valve is leaking or sticking. I bought the bore resizing tool, which works very well. resizing the bore and installing the Sonnax replacement valve usually resolves this issue.
https://www.sonnax.com/parts/2399-so...ator-valve-kit
on the shifting issue, the only time I have run into something like that is when the solenoid regulator valve is leaking or sticking. I bought the bore resizing tool, which works very well. resizing the bore and installing the Sonnax replacement valve usually resolves this issue.
https://www.sonnax.com/parts/2399-so...ator-valve-kit
#4
08-24-2018, 05:09 PM
Join Date: Aug 2018
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Sorry for the late reply...been traveling.
The trans is 2003.
Page 95 of https://shop.ukrtrans.biz/wp-content/uploads/catalogs/4R70W.pdf exactly describes what I'm seeing on this issue. It mentions the valve issue you describe. It also mentions a possible grounded wire or sticking or blocked solenoid 2 valve. Given that I don’t have any codes shown and it's intermittent only after warming up, I don’t think it’s the wiring issue.
Since the one thing that is different is the solenoid pack since before the rebuild, I think that's the most likely issue. I will probably rule that out first by just putting the old one back in. If that doesn’t fix it, then will have to pull the valve body.
I'll just have to keep digging on the O/D issue. Don’t have any leads on that yet.
Thanks!
Paul
The trans is 2003.
Page 95 of https://shop.ukrtrans.biz/wp-content/uploads/catalogs/4R70W.pdf exactly describes what I'm seeing on this issue. It mentions the valve issue you describe. It also mentions a possible grounded wire or sticking or blocked solenoid 2 valve. Given that I don’t have any codes shown and it's intermittent only after warming up, I don’t think it’s the wiring issue.
Since the one thing that is different is the solenoid pack since before the rebuild, I think that's the most likely issue. I will probably rule that out first by just putting the old one back in. If that doesn’t fix it, then will have to pull the valve body.
I'll just have to keep digging on the O/D issue. Don’t have any leads on that yet.
Thanks!
Paul
#5
09-05-2018, 08:28 AM
Join Date: Aug 2018
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Well, I'm glad to say things are working now. Thanks for all the input & suggestions.
Here's what I found.
As mentioned previously, with the use of pressure gauges, I had confirmed that I had good pressures in the transmission. The problem then pointed to the valve body and I was able to eliminate all the suggested fixes for this issue, including bad wiring.
Going through the valve body in great detail, only found two things.
1) The OD pressure boost valve (little valve in the cap) was a bit sticky. So I cleaned that up with very fine emery cloth until it moved freely.
2) I found two spots on the top of the body where it appeared that fluid had "bridged" across a couple of the pathways. Because I was also having some slipping of the O/D band, this was putting black residue into the fluid. This enabled me to see the gaps where I believe fluid was "leaking" across the paths. As the fluid got up to temperature, then I believe this is what was leaking into the 3/4 shift valve channel, causing the pressure venting. Although this was a different root cause than the TSB causes mentioned, it did make sense.
A third thing I found is that two of the many holes in the separator plate were smaller than the original. I had installed the after marker "super tough" plate. So after arguing with myself quite a bit, I drilled these two holes "back to spec" as compared with the original plate.
The last precaution, just to make sure I hadn't messed up some of the valve springs, I went to local "self serve" junk yard, pulled a matching valve body, and pulled/bagged each and every spring. Took 30 minutes or so, but for less than $5 I took home a full set of springs and compared those to what I had. I found no problems but this put a great deal of ease in my mind.
I got new gaskets for the valve body and paid very careful attention to torque values and patterns this time. I think that's where I went wrong previously, setting up the leaks.
Got about 100 miles on it now, over about a dozen trips. Working absolutely perfect and no more slippage of the O/D band either!
So lessons from a rookie:
Read, Read, Read. Then read some more!
There are a lot of contrary opinions out there on "modifications". Focus on fixing only what's known to be bad.
Watch your torques!
Paul
Here's what I found.
As mentioned previously, with the use of pressure gauges, I had confirmed that I had good pressures in the transmission. The problem then pointed to the valve body and I was able to eliminate all the suggested fixes for this issue, including bad wiring.
Going through the valve body in great detail, only found two things.
1) The OD pressure boost valve (little valve in the cap) was a bit sticky. So I cleaned that up with very fine emery cloth until it moved freely.
2) I found two spots on the top of the body where it appeared that fluid had "bridged" across a couple of the pathways. Because I was also having some slipping of the O/D band, this was putting black residue into the fluid. This enabled me to see the gaps where I believe fluid was "leaking" across the paths. As the fluid got up to temperature, then I believe this is what was leaking into the 3/4 shift valve channel, causing the pressure venting. Although this was a different root cause than the TSB causes mentioned, it did make sense.
A third thing I found is that two of the many holes in the separator plate were smaller than the original. I had installed the after marker "super tough" plate. So after arguing with myself quite a bit, I drilled these two holes "back to spec" as compared with the original plate.
The last precaution, just to make sure I hadn't messed up some of the valve springs, I went to local "self serve" junk yard, pulled a matching valve body, and pulled/bagged each and every spring. Took 30 minutes or so, but for less than $5 I took home a full set of springs and compared those to what I had. I found no problems but this put a great deal of ease in my mind.
I got new gaskets for the valve body and paid very careful attention to torque values and patterns this time. I think that's where I went wrong previously, setting up the leaks.
Got about 100 miles on it now, over about a dozen trips. Working absolutely perfect and no more slippage of the O/D band either!
So lessons from a rookie:
Read, Read, Read. Then read some more!
There are a lot of contrary opinions out there on "modifications". Focus on fixing only what's known to be bad.
Watch your torques!
Paul