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| Favorite low/no buck valve body mods - PB 904 https://slantsix.org/forum/viewtopic.php?t=56619 |
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| Author: | Dart270 [ Tue Nov 25, 2014 1:41 pm ] |
| Post subject: | Favorite low/no buck valve body mods - PB 904 |
Dear Slanted Sages, Our LeMons race team (1987 BMW 325 with 225 Slant) is looking to modify our PB 904 (1964, IIRC) for harder shifts. Please share your valve body mods with me, if you would. I know about turning up the line pressure, but there should be some easy mods like pulling out check balls and drilling holes and replacing the accumulator spring with a $3 hardware store piece. I have done this on an A500 based on a High Perf Mopar mag article from the late 90s, but I haven't done this on an old 904. Thanks and all the best, Lou |
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| Author: | sixinthehead [ Wed Nov 26, 2014 5:46 am ] |
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When I was 16, I got a junkyard 65 904 for my 318 conversion. At the time, DC was selling a 'shift kit' which consisted of a pan gasket, filter, Allen wrench and a short piece of pipe. The instructions were to crank up the line pressure until the spring seat was at the edge of the bracket, and to replace the accumulator spring with the pipe so that the piston sat at the top of its bore. That was it. I beat the snot out of that tranny for over 120,000 miles and it still hit hard on both shifts. |
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| Author: | Dart270 [ Wed Nov 26, 2014 6:59 am ] |
| Post subject: | |
Thanks, Joe! That is the kind of info I'm after. Anyone else with favorite tricks? Lou |
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| Author: | bigslant6fan [ Thu Nov 27, 2014 6:56 pm ] |
| Post subject: | . |
I don't normaly recomend greatly increasing the line pressure on used high mileage transmissions,but I understand this is a low budgit "claimer" car. Torque-flite Patty sells a stiffer line pressure spring on EBAY for $16. When installed at the factory adjustment, it delivers about 140 PSI 
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| Author: | sixinthehead [ Fri Nov 28, 2014 6:08 am ] |
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Now that I think of it, that high line pressure actually helped keep my tranny alive. When I put that drivetrain together, I didn't have any kickdown linkage to fit it. My 16-year-old brain knew that the linkage controlled shift points but didn't know about it controlling pressure also. My solution was to wire the lever partway back and live with fixed shift points. I would manually downshift and hold it (Bcuda floor shifter)when I wanted to go faster, or if I was in town and wanted 3rd earlier a quick click into neutral and back to drive would provide the upshift. I finally added the linkage 100k miles later, not long before the switch back to slant/4spd power! I bet it wouldn't have lasted as long if I hadn't helped the pressure. I hadn't thought about that driving technique for a long time - thanks for the memories! |
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| Author: | wvenable [ Fri Nov 28, 2014 8:17 am ] |
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Don't know all the details but the accumulator spring can be left out so the piston floats. Rick Allison has done this for me a couple of times. If ya need more info I could drop by his shop. This was not PB trans however. |
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| Author: | Doctor Dodge [ Fri Nov 28, 2014 9:41 am ] |
| Post subject: | |
It is good to think about automatic transmission "hard shift" in different ways: Conventional wisdom tells us to increase the oil pressure / volume and that is where many "shift kits" focus. (also shift "timing" is important... you do not want a lot of shift "over-lap" or a huge "run-away" shift) Another place to look at closely is oil "displacement" & drain-back, away from the friction contact surface(s). A second gear "flex band" with large slots or many holes, helps get the oil out from the contact area, when it is applied. The same holds true with the clutch discs & steels. That is why you see the "waffle" pattern on forward clutches and why fewer clutch discs can produce a harder "hit". Also pay attention on how the oil gets out of the clutch drum itself. (a few small drilled holes in the OD)   So be sure to think about of getting the "cushion" of oil out from between the friction material... as well as getting a lot of oil in there, during the "apply". DD |
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| Author: | Dart270 [ Sun Nov 30, 2014 2:48 pm ] |
| Post subject: | |
Thanks again, everyone. We will take all of this into consideration on our tranny freshen up for the LeMons car... All the best, Lou |
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| Author: | olafla [ Sun Nov 30, 2014 9:18 pm ] |
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Isn't there a difference in behaviour from the choice of transmission oil too? The ATF type F used by Ford is supposed to firm up the shifts, but I don't know if it is suitable for this gearbox? Olaf |
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| Author: | Dart270 [ Mon Dec 01, 2014 4:23 am ] |
| Post subject: | |
Works OK, but has a worse heat tolerance, apparently, so we will stay with Dexron. Lou |
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| Author: | Charrlie_S [ Mon Dec 01, 2014 4:57 am ] |
| Post subject: | |
The type "F" has a higher coeffience (sp) of friction, therefore the clutches/bands grab slightly harder. The down side is, increased ware on bushings and trust washers. When Dexron first came out, the oil manfactures specified that you could use type "F" in place of Dexron, but not to use Dexron, in place of type "F". The Fords were smoking the clutches when Dexron was installed. Can you spell "lawsuit"? PS: The old B&M Trick shift fluid, was just type F with blue dye added. |
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| Author: | SpaceFrank [ Tue Dec 09, 2014 8:33 am ] |
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"I would like to subscribe to your newsletter..." We need to rebuild our original 904 as well, after 5 races. Most likely putting it off until after the holidays, though. |
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| Author: | Reed [ Tue Dec 09, 2014 9:29 am ] |
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The latest trans fluid recommendation I got from SlantSixDan was to use the latest generation Mercon fluid (VI I think?) because that has performance specifications equal and/or superior to thoserequired by Dexron. Plus it is cheaper than ATF+4. |
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