Run down of transmission pressures
10-23-2013, 07:05 PM
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Run down of transmission pressures
87 s4 4sp Auto...179k miles
I picked up a new liquid filled pressure gauge to test my transmission pressures. the old gauge was cheap and failed pretty quick and didn't trust the results.
I had my video camera on for all the tests I did the second time around so I could go back and see what was taking place...
Fluid level is good as is the Bowden cable.
The problem..
In a nut shell my car at times fails to shift from 2nd to 3rd..then from 3rd to 4th. If it does get into 4th it will occasionally slip out of 4th at hwy speeds into 3rd. During some cases I can rev the engine freely as if it were in neutral when this happens. The issues seems to get worse as the fluid gets warmer. All of this now is leading me to think my valve body needs cleaning/refurbishing/replaced.
During all the tests I did, the vacuum line was disconnected which makes the transmission shift firmer. It also seemed to help the shifting problem. The car would shift as normal but firmer and hold gears at speed....actually ran great!
Im going to start with a fluid filter change and see what that does...then I will pull the valve body if that doesn't work. If that fails to fix things, in goes the spare 4speed with LSD.
I bought a new liquid filled gauge and did all my tests again.. Operating...modulating and governor pressures as well as a stall test.
Operating pressure in Drive 4th gear appx 30-35mph vac line off...
190-200psi
2nd gear....245psi
3rd gear....195psi
Operating pressure during a stall test at appx 1400rpm, in drive, warm/hot fluid vac line off, brake applied
275-310 psi
The Modulating pressure in Drive, warm to hot fluid..4th gear at 35-40mph..vac line off is
85psi
Governor Pressure during a road test in Drive 4th gear, warm/hot fluid, vac line off
20mph...25psi
30mph...35si
40mph...40psi
50mph...40psi
60mph...43psi
70mph...45psi
80mph...47psi
90mph...50psi
95mph...50psi
I picked up a new liquid filled pressure gauge to test my transmission pressures. the old gauge was cheap and failed pretty quick and didn't trust the results.
I had my video camera on for all the tests I did the second time around so I could go back and see what was taking place...
Fluid level is good as is the Bowden cable.
The problem..
In a nut shell my car at times fails to shift from 2nd to 3rd..then from 3rd to 4th. If it does get into 4th it will occasionally slip out of 4th at hwy speeds into 3rd. During some cases I can rev the engine freely as if it were in neutral when this happens. The issues seems to get worse as the fluid gets warmer. All of this now is leading me to think my valve body needs cleaning/refurbishing/replaced.
During all the tests I did, the vacuum line was disconnected which makes the transmission shift firmer. It also seemed to help the shifting problem. The car would shift as normal but firmer and hold gears at speed....actually ran great!
Im going to start with a fluid filter change and see what that does...then I will pull the valve body if that doesn't work. If that fails to fix things, in goes the spare 4speed with LSD.
I bought a new liquid filled gauge and did all my tests again.. Operating...modulating and governor pressures as well as a stall test.
Operating pressure in Drive 4th gear appx 30-35mph vac line off...
190-200psi
2nd gear....245psi
3rd gear....195psi
Operating pressure during a stall test at appx 1400rpm, in drive, warm/hot fluid vac line off, brake applied
275-310 psi
The Modulating pressure in Drive, warm to hot fluid..4th gear at 35-40mph..vac line off is
85psi
Governor Pressure during a road test in Drive 4th gear, warm/hot fluid, vac line off
20mph...25psi
30mph...35si
40mph...40psi
50mph...40psi
60mph...43psi
70mph...45psi
80mph...47psi
90mph...50psi
95mph...50psi
10-23-2013, 08:16 PM
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Tony:
My tranny has done very similar things when a fluid change is overdue. Recently, it started to drop from 4th to 3rd sporadically for no reason, like yours. In the past it has failed at times to drop into first and has freewheeled between gears sometimes. I'm not going to analyze your pressures, but just recommend that you do a fluid/filter change before anything else and add a bottle of something like Trans-X. Most likely this is a valve body issue with sticky shift valves. Long ago when mine failed to drop into first I did a fluid change and that fixed it for a week or so. When it returned I dropped in a bottle of Trans-X and the problem disappeared for 30K miles. The tranny was fine for another 30K miles, which is the fluid change service interval. It's interesting that mine seems so sensitive to fluid age - I use Mobil 1 synthetic - but it sure is. The fluid is always clean cherry red - not burned or dirty. Since it responds so well to fluid change and/or Trans-X, I've not gone any further. My next step would be to examine the shift valves and springs in the valve body.
My tranny has done very similar things when a fluid change is overdue. Recently, it started to drop from 4th to 3rd sporadically for no reason, like yours. In the past it has failed at times to drop into first and has freewheeled between gears sometimes. I'm not going to analyze your pressures, but just recommend that you do a fluid/filter change before anything else and add a bottle of something like Trans-X. Most likely this is a valve body issue with sticky shift valves. Long ago when mine failed to drop into first I did a fluid change and that fixed it for a week or so. When it returned I dropped in a bottle of Trans-X and the problem disappeared for 30K miles. The tranny was fine for another 30K miles, which is the fluid change service interval. It's interesting that mine seems so sensitive to fluid age - I use Mobil 1 synthetic - but it sure is. The fluid is always clean cherry red - not burned or dirty. Since it responds so well to fluid change and/or Trans-X, I've not gone any further. My next step would be to examine the shift valves and springs in the valve body.
10-23-2013, 09:23 PM
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thnx for the input Bill.
yeah I plan on the fluid filter thing first. I just wanted to check pressures to see if there was anything glaringly wrong with the internals.Anyone see anything on the surface?
Ive been running Amsoil Synthetic(same as Darien has in his) now since my last change...that was probably close to 20-30k ago?..i would have to check. I have an additional external cooler in the circuit as it gets hot out here and Im putting out way more than stock power.
I do have a small drip leak from the front converter/ mainpump seal area but I don't think that is an issue in all this. The tranny will come out at some point to address this as well. I just hate that job.
yeah I plan on the fluid filter thing first. I just wanted to check pressures to see if there was anything glaringly wrong with the internals.Anyone see anything on the surface?
Ive been running Amsoil Synthetic(same as Darien has in his) now since my last change...that was probably close to 20-30k ago?..i would have to check. I have an additional external cooler in the circuit as it gets hot out here and Im putting out way more than stock power.
I do have a small drip leak from the front converter/ mainpump seal area but I don't think that is an issue in all this. The tranny will come out at some point to address this as well. I just hate that job.
10-23-2013, 09:52 PM
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These transmissions, although sturdy, do not have "magical" pieces inside of them. The clutches and bands wear, just like every other automatic transmission, on the planet.
I wouldn't spend too much time or effort on a transmission with over 150,000 miles on it.....pieces are worn out, internal seals are leaking, internal passages are partially blocked with clutch and band debris, and there are generally broken springs in the valve body.
I wouldn't spend too much time or effort on a transmission with over 150,000 miles on it.....pieces are worn out, internal seals are leaking, internal passages are partially blocked with clutch and band debris, and there are generally broken springs in the valve body.
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greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
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10-24-2013, 07:10 PM
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Of course, Greg's point is well taken - you should expect wear issues in high mileage trannies. You guys may remember I had my tranny mostly apart recently and the bands, clutch plates, and other parts I could see showed very little wear despite the high miles. My issues have always been shift related (other than a leak from an inadvertently ripped converter seal) and only appearing near the end of the recommended fluid/filter service interval. Surprisingly, there have never been slipping or other performance issues. The shifting issues (primarily failure to drop into 1st gear) always responded to fluid changes with a little help from the solvents in Trans-X (or a similar product). The sporadic drops into 3rd from 4th gear while just cruising along, the same as Tony reports, are something that never happened until a month ago. I checked the fluid level and added some Trans-X. No time to do a fluid/filter change at the moment, and it's just at 30K miles anyway. The odd 4-3 downshifts reappeared occasionally but stopped after a week. So, it's now been operating normally again for the last week. I plan to drain, drop the pan and look at the valves and springs. Tony, short of a rebuild, try a valve body inspection and service, since your symptoms sound valve body related. The shift command valves and springs are accessible without full disassembly of the valve body.
My layman's look at the pressures you measured is that they seem to agree with the WSM vol 3 section 38, page 110a.
I will add that George Suennen has a temp sensor on his auto tranny pan and I believe we have not seen over 160F with just the stock cooler despite the high horsepower pushing the car very hard.
My layman's look at the pressures you measured is that they seem to agree with the WSM vol 3 section 38, page 110a.
I will add that George Suennen has a temp sensor on his auto tranny pan and I believe we have not seen over 160F with just the stock cooler despite the high horsepower pushing the car very hard.
10-24-2013, 07:18 PM
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Of course, Greg's point is well taken - you should expect wear issues in high mileage trannies. You guys may remember I had my tranny mostly apart recently and the bands, clutch plates, and other parts I could see showed very little wear despite the high miles. My issues have always been shift related (other than a leak from an inadvertently ripped converter seal) and only appearing near the end of the recommended fluid/filter service interval. Surprisingly, there have never been slipping or other performance issues. The shifting issues (primarily failure to drop into 1st gear) always responded to fluid changes with a little help from the solvents in Trans-X (or a similar product). The sporadic drops into 3rd from 4th gear while just cruising along, the same as Tony reports, are something that never happened until a month ago. I checked the fluid level and added some Trans-X. No time to do a fluid/filter change at the moment, and it's just at 30K miles anyway. The odd 4-3 downshifts reappeared occasionally but stopped after a week. So, it's now been operating normally again for the last week. I plan to drain, drop the pan and look at the valves and springs. Tony, short of a rebuild, try a valve body inspection and service, since your symptoms sound valve body related. The shift command valves and springs are accessible without full disassembly of the valve body.
My layman's look at the pressures you measured is that they seem to agree with the WSM vol 3 section 38, page 110a.
I will add that George Suennen has a temp sensor on his auto tranny pan and I believe we have not seen over 160F with just the stock cooler despite the high horsepower pushing the car very hard.
My layman's look at the pressures you measured is that they seem to agree with the WSM vol 3 section 38, page 110a.
I will add that George Suennen has a temp sensor on his auto tranny pan and I believe we have not seen over 160F with just the stock cooler despite the high horsepower pushing the car very hard.
Where did George place his sender? I have a gauge all wired in and the wiring ran, just never had to drop the pan in order to install the bung etc. so i never bothered. I will PM him also.
10-24-2013, 08:00 PM
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Interestingly enough, I've found it very rare to not have broken springs in these valve bodies. I've got a huge box full of "donor" bodies that I take springs and plungers from.
There's one common spring that is broken on probably 40% of the valve bodies. I've completely "exhausted" the supply of this spring, in my "donor" box. I'm going to have to source these or have them wound. I've noticed that most of the "rebuilders" simply cut a spring down from another application and stuff it in.....I'm not convinced that a random spring, cut down to fit, is the correct solution to this problem. This spring is for the 1st to 2nd shift, so not likely your problem.
There's one common spring that is broken on probably 40% of the valve bodies. I've completely "exhausted" the supply of this spring, in my "donor" box. I'm going to have to source these or have them wound. I've noticed that most of the "rebuilders" simply cut a spring down from another application and stuff it in.....I'm not convinced that a random spring, cut down to fit, is the correct solution to this problem. This spring is for the 1st to 2nd shift, so not likely your problem.
10-24-2013, 08:37 PM
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Interestingly enough, I've found it very rare to not have broken springs in these valve bodies. I've got a huge box full of "donor" bodies that I take springs and plungers from.
There's one common spring that is broken on probably 40% of the valve bodies. I've completely "exhausted" the supply of this spring, in my "donor" box. I'm going to have to source these or have them wound. I've noticed that most of the "rebuilders" simply cut a spring down from another application and stuff it in.....I'm not convinced that a random spring, cut down to fit, is the correct solution to this problem. This spring is for the 1st to 2nd shift, so not likely your problem.
There's one common spring that is broken on probably 40% of the valve bodies. I've completely "exhausted" the supply of this spring, in my "donor" box. I'm going to have to source these or have them wound. I've noticed that most of the "rebuilders" simply cut a spring down from another application and stuff it in.....I'm not convinced that a random spring, cut down to fit, is the correct solution to this problem. This spring is for the 1st to 2nd shift, so not likely your problem.
Just got home and drained the fluid out of the pan and I'm prrrrrrrrrrrrrretty sure I found my problem
Lots of sludge...a few large chunks of friction material..either clutch or band, Im not sure. Either way its not conducive to a properly functioning transmission!
My filter is marked 3-6-06 157,000 miles.
I'm currently at 178,000.
Im uploading a video now.
Plan of attack now is a fluid /filter change (A DUH!!
) drop the valve body and clean it. Put it back together and see if that fixes my issues. If it does then i will then drop the transmission and put in my spare with 88k miles on it and "attack" this one with a rebuild attempt. Either way this transmission wont see much more time in my car. I basically want to see what was causing my issues before i swapped it out....i think pictures sum it up.What say the jury....
10-24-2013, 08:38 PM
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Thats the plan Bill. I dropped the pan today but have yet to look at it..time to pick up the rugrats from school..heading back down in a little bit though. Fluid looks fine at this point but i want to see the pan and the filter for any sediment etc.
Where did George place his sender? I have a gauge all wired in and the wiring ran, just never had to drop the pan in order to install the bung etc. so i never bothered. I will PM him also.
Where did George place his sender? I have a gauge all wired in and the wiring ran, just never had to drop the pan in order to install the bung etc. so i never bothered. I will PM him also.
George drilled a hole on the side of the pan, low down, so it should always be submerged. It was a pleasant surprise to find out how cool his tranny runs.
10-24-2013, 08:40 PM
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Uhoh! That looks bad.
Looks like Greg's suspicions are confirmed in your case. I hope I don't find something similar. I'm not expecting it since my tranny's innards looked nice when I opened it up last year.
That is so much crap that although cleaning the valve body may fix the shifts for a while (although I rather doubt it now), you know the bands are falling apart. It won't be long before it fails, perhaps dramatically.
Looks like Greg's suspicions are confirmed in your case. I hope I don't find something similar. I'm not expecting it since my tranny's innards looked nice when I opened it up last year.
That is so much crap that although cleaning the valve body may fix the shifts for a while (although I rather doubt it now), you know the bands are falling apart. It won't be long before it fails, perhaps dramatically.
10-24-2013, 08:55 PM
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Uhoh! That looks bad.
Looks like Greg's suspicions are confirmed in your case. I hope I don't find something similar. I'm not expecting it since my tranny's innards looked nice when I opened it up last year.
That is so much crap that although cleaning the valve body may fix the shifts for a while (although I rather doubt it now), you know the bands are falling apart. It won't be long before it fails, perhaps dramatically.
Looks like Greg's suspicions are confirmed in your case. I hope I don't find something similar. I'm not expecting it since my tranny's innards looked nice when I opened it up last year.
That is so much crap that although cleaning the valve body may fix the shifts for a while (although I rather doubt it now), you know the bands are falling apart. It won't be long before it fails, perhaps dramatically.
Trust me it wont be in the car too long after the "cleaning". At least i will know what the problem was and can go about a rebuild at my own pace. I have an 88k spare with LSD
to go in.Heres the video...pretty ugly...then again its rather pretty when it glistens in the evening sun. Looks like gold!!!!
10-24-2013, 09:25 PM
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Whoa...I don't remember seeing any crud when we reaplced the filter and fluid. Wonder how much of that has spread to other places? Be curious to see what's inside the filter casing.
Good thing you have the spare
Good thing you have the spare