| Slant Six Forum https://slantsix.org/forum/ |
|
| 904 Guru help needed. https://slantsix.org/forum/viewtopic.php?t=40512 |
Page 1 of 2 |
| Author: | Reed [ Sat Jun 05, 2010 2:39 pm ] |
| Post subject: | 904 Guru help needed. |
I just got done tearing down, inspecting, and re-installing the transmission in my brother's 1983 Dodge van with a 225/904T combo. Symptoms: Fine when cold. However, once it is hot, transmission shudders under light load only between 25-35 MPH, such as going up a grade with light throttle pressure. And when I say shudder, I mean the whole van gets shaking. Also, when cruising on the highway, the van won't kick down into passing gear when you floor it. Inspection: all clutch plates/friction discs present and in good condition. Oil pump in good condition and all clearances within factory specs. Bands look good and are adjusted as close as I could get them without a inch-pound torque wrench. Torque converter is a new low stall unit (but the transmission did the same thing with the remanufactured high-stall converter that was in the tranny when I bought it at the boneyard). Fluid is full and is ATF+4. Filter is new. Driveshaft is rebuilt and balanced. I installed a Transgo SK-1 shift kit and set everything to the firmest setting. Rear transmision mount is new. All bolts torqued properly. I have torn this transmission down twice and I can't figure out what is causing the shimmy/shudder. Could it be the front band adjustment? Could it be the kickdown/line pressure adjustment? Am I just cursed? Should I just rebuild either the 1979 or 1973 904s I have in the garage and try that? Any help greatly appreciated. |
|
| Author: | SlantSixDan [ Sat Jun 05, 2010 3:18 pm ] |
| Post subject: | |
No kickdown + shudder suggests too-short throttle pressure ("kickdown") linkage adjustment or related problem inside the trans. How's the 1-2 and 2-3 shift timing? |
|
| Author: | Reed [ Sat Jun 05, 2010 3:43 pm ] |
| Post subject: | |
Thanks Dan. 1-2 and 2-3 shift timing is just about spot on. I am in third by 15 MPH. I am waiting for the engine to cool and then I am going to start futzing with the kickdown. I am going to try setting it so that the kickdown is all the way towards the back of the car at WOT. If that doesn't make a difference or fix it, then I am getting ready to throw in the ATF+4 soaked towel(s). On the valve body, I adjusted the line pressure screw according to the TransGo shift kit instructions and put the tab on the end of the spring just flush to the body of the spring housing (it makes sense when you look at the part of the valve body I am talking about). Should I try putting it back to the Mopar spec of 1-15/16 inches out from the valve body? |
|
| Author: | Reed [ Sat Jun 05, 2010 4:27 pm ] |
| Post subject: | |
Okay- I adjust the kickdown linkage so that the arm on the transmission is all the way back when the carb is at WOT. This seemed to help, but the shudder is still there, albeit less severe. 1-2 shift occurs at approximately 14 MPH and 2-3 shift occurs approximately 20 MPH. That seems a tad late. Factory specs are 1-2 at 8-11 MPH and 2-3 at 11-14 MPH. Argh. I think I am going to say Uncle and take it to a shop on Monday. 
|
|
| Author: | turboram [ Sat Jun 05, 2010 4:56 pm ] |
| Post subject: | |
I never adjust the line pressure that light .I would adjust the plate 3-4 turns in from flush.also I don,t like atf+4 TOO many friction modifiers (read slipping) |
|
| Author: | SlantSixDan [ Sat Jun 05, 2010 5:25 pm ] |
| Post subject: | |
Quote: I don,t like atf+4 TOO many friction modifiers (read slipping)
That is a common misunderstanding. In fact, ATF+4 is a significantly better fluid in every way than Dexron (-II, -III, -IV) and vastly superior to ATF+ (+2, +3), and it does not cause, promote, or aggravate slippage.. It maintains the specified viscosity across a temperature range that's wider at both the hot and cold ends, its lubrication and antiwear properties are better, it's more resistant to oxidation, sludging and varnish formation, and it smells better. It might even taste better, I don't know. There's an extremely detailed Chrysler Engineering paper comparing every aspect of ATF+4 vs. ATF+3, ATF+2, ATF+, and Dexron-III/IV.All that said, the RWD Torqueflites really don't need anything more exotic than a good-quality Dexron. They work fine with Dexron. I do run ATF+4 in mine 'cause I like to use the best when it's practical. (And because someone's likely to bring it up if this fluid discussion takes hold, using Type-F is a poor idea; it's an archaic fluid with seriously inferior performance by just about every measure.) |
|
| Author: | bigslant6fan [ Sat Jun 05, 2010 7:22 pm ] |
| Post subject: | |
was it a 78-79 trans,or did you see any 78-79 date coded parts in there? The lock-up module was known to shudder,80-up module was better. And what, No inch-pound torque wrench? 
|
|
| Author: | Reed [ Sat Jun 05, 2010 9:31 pm ] |
| Post subject: | |
No, no inch-pound toorque wrench. Actually, I DO have one, but it is a "clicker" model and I never figured out how to work it, plus, it doesn't go to a low enough setting to use on the tranny. The transmission currently in the van now, and the one I am working on, is a 1984 904T. Lockup, wide ratio gears. I also have a 1979 904 lockup, and a 1973-ish 904 non-lockup.
|
|
| Author: | turboram [ Sun Jun 06, 2010 6:02 am ] |
| Post subject: | |
I agree with you Dan that the synthetic +4 is a better fluid. What I was talking about was that dex-3 has less friction modifiers and we use it in high horsepower diesel trucks when we build a trans because it promotes a shorter snappier shift. the down side is less fluid life.......................... reed I didn't realise you pulled the 904 you could always isolate the torque converter by unplugging the wire on trans,then if the converter is at fault you can diagnose the circuit .the torque converter switch valve can stick causing all kinds of headache |
|
| Author: | Reed [ Sun Jun 06, 2010 7:47 am ] |
| Post subject: | |
There is no wire on the trans that controls the torque converter. The only wires are for the neutral start switch. If I remember correctly, only the final year 1987 slant six transmissions got an electronically controlled lockup on the torque converter. All previous models, including the one I am working on, are hydraulically controlled. However, I do not believe it is the lockup that is the problem. I have pulled apart and inspected the lockup mechanism on the valve body and the torque converter is new. The transmission has had this shudder with three different torque converters. The transmission also has the stiffer spring in the lockup valve to prevent premature lockup. |
|
| Author: | Dave95693 [ Sun Jun 06, 2010 2:00 pm ] |
| Post subject: | |
Reed, I had a similar occurence in a 71 904 after installing a Transgo kit. I doubt this is your problem but maybe it will lead to something. After the install, I also got a severe shudder going from 2 to 3. When I took it apart the second time, it was obvious to me that some how one of the steele balls got wedged into one of the bolt holes. PLEASE don't ask me how I did that. Of course I ended up with one bolt extra duh! But upon reinstalling the valve body, with the ball in the correct position, all was well and I raced that car all season long with no problems. So check the ball locations and sizes and make sure they are where they are supposed to be. Also, in that kit, one of the balls is left out so if you took out the wrong one it may also be a cause. |
|
| Author: | Reed [ Sun Jun 06, 2010 3:26 pm ] |
| Post subject: | |
Hmmm. I took the valve body apart, reused ALL the balls, and verified (with a micrometer, no less) that the correct size ball went into the correct locations on the valve body. This was fairly easy since there are a bunch of small same-sized balls but only one big ball. As Angus would say, "I've got a big ball." Oh well. Tomorrow it is going in to someone who plays with this stuff for a living. My back is getting messed up from crawling around on cement and lifting this !(*@^@*^(&#% transmission up and down.... |
|
| Author: | bigslant6fan [ Sun Jun 06, 2010 3:27 pm ] |
| Post subject: | |
OK, time to do pressure checks like the service manual says.The trans-go shift kits are the best in my opinion and it should shift very firm.stock line pressure with wide open kick down linkage should be 80-90 PSI,with the shift kit it shoud be about 100-120 PSI.This will raise your shift points about 10%,so that seems fine.Maybe your front pump is worn,and not letting full pressure to the clutches,or, did you flush the trans cooler REAL GOOD so you know that isn't a problem. |
|
| Author: | Reed [ Sun Jun 06, 2010 3:45 pm ] |
| Post subject: | |
The shifts are great. It is just this dang shudder that is driving me nuts. 95% of the time the trans works beautifully. My only gripe is the shudder which seems to occur immediately before kickdown and the lack of highway kickdown. But, like I said, tomorrow, it becomes someone else's problem. Yay! |
|
| Author: | emsvitil [ Sun Jun 06, 2010 4:12 pm ] |
| Post subject: | |
I have to ask............. How are the U-joints?
|
|
| Page 1 of 2 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|