700R4 Shift Problems
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Joined: Aug 2014
Posts: 71
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From: Albuquerque New Mexico
700R4 Shift Problems
Hey everybody.
My '89 started having an issue shifting recently. I had the tranny rebuilt about 2yrs ago, and had a B&M Shift kit installed at the same time. Up until now, it has had a nice neck jerking "chirp" when shifting to second under moderate to heave acceleration. Now, when it shifts into second, it has a "thump" and no neck jerking "chirp". I thought u-joints were the culperate. But, if I take off in Drive, instead of Overdrive, or shift it manually from 1st to 2nd, it will shift like it used to. Fluid is still nice and red, and not smelling like anything is heating up. Does anyone have any ideas as to what is going on? Could it be a valve sticking in the valve body? Maybe, an additive I can try?
Any help will greatly be appreciated!
Pat
My '89 started having an issue shifting recently. I had the tranny rebuilt about 2yrs ago, and had a B&M Shift kit installed at the same time. Up until now, it has had a nice neck jerking "chirp" when shifting to second under moderate to heave acceleration. Now, when it shifts into second, it has a "thump" and no neck jerking "chirp". I thought u-joints were the culperate. But, if I take off in Drive, instead of Overdrive, or shift it manually from 1st to 2nd, it will shift like it used to. Fluid is still nice and red, and not smelling like anything is heating up. Does anyone have any ideas as to what is going on? Could it be a valve sticking in the valve body? Maybe, an additive I can try?
Any help will greatly be appreciated!
Pat
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Years ago I was with a friend of mine talking with Art Carr (transmission expert). My friend's car went through two transmissions that were built by B&M (at their facility). Art said B&M set up the transmission to shift hard from 1st to 2nd because people like the chirp. He also said that tore up the transmission. He said it should be set up to shift firmly to keep from slipping the clutches and causing heat that would destroy them. My friend's trans lasted until he sold the car after Art rebuilt it. A cautionary tale, as they say...
I think something broke. The sun shells are well known for that. The only way to find out is to take it apart and see what it looks like inside.
I think something broke. The sun shells are well known for that. The only way to find out is to take it apart and see what it looks like inside.
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
If the sunshell broke, the OP would not have 2nd. - or 4th and reverse for that matter. He states that if he manually shifts from 1st to 2nd or selects D instead of OD, it shifts as before. It is more likely that something has changed in the valve body or the front sprag is leaving town, as the sprag is bypassed by the over-run clutches in D and manual 1-2 shift.
Thread Starter
Advanced
Joined: Aug 2014
Posts: 71
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From: Albuquerque New Mexico
Years ago I was with a friend of mine talking with Art Carr (transmission expert). My friend's car went through two transmissions that were built by B&M (at their facility). Art said B&M set up the transmission to shift hard from 1st to 2nd because people like the chirp. He also said that tore up the transmission. He said it should be set up to shift firmly to keep from slipping the clutches and causing heat that would destroy them. My friend's trans lasted until he sold the car after Art rebuilt it. A cautionary tale, as they say...
I think something broke. The sun shells are well known for that. The only way to find out is to take it apart and see what it looks like inside.
I think something broke. The sun shells are well known for that. The only way to find out is to take it apart and see what it looks like inside.
I appreciate you sharing the experience you had with your friend. I am a stubborn person who still will want the chirp unfortunately!
As for the sun shell, I am not a trans person, I take it, it is not accessable through the valve body correct? If I take it in, they will likely want to rebuild whole tranny?
Also, I left out, I am only running the stock hp in my vette.
Thanks
Pat
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Joined: Aug 2014
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From: Albuquerque New Mexico
So, being that I am not a trans person, how hard of a job is that? Can I purchase an aftermarket piston and plate?
Thanks
Pat
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Joined: Aug 2014
Posts: 71
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From: Albuquerque New Mexico
If the sunshell broke, the OP would not have 2nd. - or 4th and reverse for that matter. He states that if he manually shifts from 1st to 2nd or selects D instead of OD, it shifts as before. It is more likely that something has changed in the valve body or the front sprag is leaving town, as the sprag is bypassed by the over-run clutches in D and manual 1-2 shift.
Like I told the other guys, I am not a trans person, I am only running stock hp, and unfortunately, I still like the chirp. What is the front sprag, and is it accessable through the valve body?
Thanks
Pat
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
Sorry, but no. The front sprag is located inside the input drum and would require disassembly of the transmission. A sprag is like a one way bearing. It allows something(in this case, the front sun gear) to turn one direction, but not the other. It only comes into play in the freewheeling state when the trans is in 4th gear. As mentioned in another post, shift kits, while giving the "chirp", tend to tear up transmissions. When a 4l60 changes to 2nd gear, it does so by stopping the sunshell from turning. With a shift kit, this stopping is done violently, thus causing enhanced strain on the sprag. Eventually, the sprag will fail. I believe in your case, it is only slipping at this point when the shift takes place. By changing to D instead of OD, the overrun clutches are employed, bypassing the sprag and the "chirp" is restored. My thoughts anyway.
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Advanced
Joined: Oct 2014
Posts: 94
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From: Tampa
You can inspect it easily once the pan is down.
3 bolts (10mm) hold on the 1-2 accumulator housing.
Housing and piston and seal (if your inspection requires they be replaced) are available from GM.
The accumulator plate is long discontinued from GM, so (if needed) a Transgo plate can be used.
To change the plate, you must drop the valve body.
If you are comfortable doing tasks such as brake jobs and tune ups, the trans stuff I mentioned is easy to do with a shop manual.
Should your problem ultimately be internal, trans removal is needed, and difficulty ramps up very high for the average wrench once you start going inside.
Thread Starter
Advanced
Joined: Aug 2014
Posts: 71
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From: Albuquerque New Mexico
Sorry, but no. The front sprag is located inside the input drum and would require disassembly of the transmission. A sprag is like a one way bearing. It allows something(in this case, the front sun gear) to turn one direction, but not the other. It only comes into play in the freewheeling state when the trans is in 4th gear. As mentioned in another post, shift kits, while giving the "chirp", tend to tear up transmissions. When a 4l60 changes to 2nd gear, it does so by stopping the sunshell from turning. With a shift kit, this stopping is done violently, thus causing enhanced strain on the sprag. Eventually, the sprag will fail. I believe in your case, it is only slipping at this point when the shift takes place. By changing to D instead of OD, the overrun clutches are employed, bypassing the sprag and the "chirp" is restored. My thoughts anyway.
I appreciate your feedback on my trany problems. Today, she decided to do something that makes her undrivable. It started blowing out white smoke out the exhaust. Possible head or intake gasket? Anyway, I am gonna close this post for now and possibly open a new one on the dang white smoke thing!
Thank you again!
Pat
Thread Starter
Advanced
Joined: Aug 2014
Posts: 71
Likes: 0
From: Albuquerque New Mexico
Pat,
You can inspect it easily once the pan is down.
3 bolts (10mm) hold on the 1-2 accumulator housing.
Housing and piston and seal (if your inspection requires they be replaced) are available from GM.
The accumulator plate is long discontinued from GM, so (if needed) a Transgo plate can be used.
To change the plate, you must drop the valve body.
If you are comfortable doing tasks such as brake jobs and tune ups, the trans stuff I mentioned is easy to do with a shop manual.
Should your problem ultimately be internal, trans removal is needed, and difficulty ramps up very high for the average wrench once you start going inside.
You can inspect it easily once the pan is down.
3 bolts (10mm) hold on the 1-2 accumulator housing.
Housing and piston and seal (if your inspection requires they be replaced) are available from GM.
The accumulator plate is long discontinued from GM, so (if needed) a Transgo plate can be used.
To change the plate, you must drop the valve body.
If you are comfortable doing tasks such as brake jobs and tune ups, the trans stuff I mentioned is easy to do with a shop manual.
Should your problem ultimately be internal, trans removal is needed, and difficulty ramps up very high for the average wrench once you start going inside.
I appreciate your feedback on my trany problems. Today, she decided to do something that makes her undrivable. It started blowing out white smoke out the exhaust. Possible head or intake gasket? Anyway, I am gonna close this post for now and possibly open a new one on the dang white smoke thing!
Thank you again!
Pat