Powerglide Questions

[lake_harley]

I built the Powerglide for my FED using Carl Munroe's book "Powerglide Transmission Handbook" as a guide. When we did a few mild test passes with the car last week it seemed that it was more "sluggish", and took more throttle to move in Low than it did in 2nd (Drive) or Reverse (valve body converted to manual only, providing I did things right) The converter is a 10" Boss Hog unit that is considered 5000 stall but I was told by them that with the low HP of my car it would probably stall at about 4200 RPM. The PG doesn't have a trans brake....we're foot braking it. In general it just seemed it took less throttle in the pits to move in Drive or Reverse gears than it did in Low gear.

I have several thoughts on what might be causing the sluggishness, if it indeed does have an issue;

A) Perhaps nothing is wrong and it's quite normal? I've never had a light car like this with a high stall converter.

B) The Low band isn't holding? I can and will double check the band adjustment.

C) When I built the transmission I tried various steel and friction disc stacks to set clearance in the high gear clutch pack. After trying several combinations they all seemed to go from really loose to borderline tight. I finally assembled with the clearance borderline tight thinking that there might be a tiny bit of friction disc break-in wear on the new discs and that it might quickly  loosen up. I know the high and reverse clutch packs "slip" in low gear, so that might be adding too much drag if either clutch pack is tight?

D) I have read that Type F ATF provides a sharper shift than Dextron ATF. That sounded like a positive thing so I used Valvoline Type F fluid. Could it be that the Type F fluid is creating "stiction" in the clutch pack(s), especially with tight clearances? If that's a potential issue, are the fluid types compatible enough that I could drain and refill the transmission a couple times to dilute the amount of Type F fluid in the transmission?

Perhaps there could be other issues, or there might not be an issue at all, so I'm open to comments and suggestions.

Thanks, in advance!

Lynn

[JEFF/21C]

without being there it's hard to analyse, type f trans fluid is what you should use.clutch clearance should be on the loose side. band adjustment is very important every 6 runs.should feel 1st engage just as you would a street car

[masracingtd1167]

How tight is the clutch pack ? I would go no tighter than .060 for high gear or reverse !

[JEFF/21C]

no .060 should be good, the min is .010 x the number of face plates 

[tcoupekyle]

In my experience, it sounds like nothing is wrong. Convertor in both my cars starts moving as soon as I put it in gear. Both run FTI convertor both stall fine. One is 2600lbs 615hp 5400stalland the other is roughly 1000hp and 1600lbs with about 4000-4500 stall

[JEFF/21C]

 tcoupekyle IS RIGHT! You should feel the convertor i have used 9.5, 8 , and 7" convertors and you feel the engagement if it's too tight you can't get a proper idle

[lake_harley]

Well, my FED now has about 20-22 (1/8 Mi.) passes on it. We were at a nostalgia 2-day thing at Sikeston, MO on Friday and Saturday. Overall things went OK I suppose. I was very pleased that the car and even the "lollypop" trailer I built got a lot of compliments.

It was mid to upper 90 degrees and at one point when I called a nearby airport the density altitude was 2500+ Ft, even though the track is at about 450. I guess that might explain why the car seemed to get slower as the day(s) wore on.

On the last pass the time and speed were MUCH slower and when it came back to our pit the driver said it didn't shift when he popped the lever from L to D. We jacked up the car and ran it it 1st and hit Drive and it seemed to shift OK. Did it again and it didn't shift. Made a quick check of the shift cable adjustment and when the shifter is in Drive the lever on the transmission is solidly in the detent. Fluid level is OK and the fluid was only about 135 degrees and didn't smell burnt.

I haven't gotten around to checking anything else, but plan to check line pressure and drop the pan to see if there's anything in there that shouldn't be. A quick look in the Powerglide book by Munroe suggested that the sluggishness/dragginess we always have experienced in low might be a leaking low band servo, and if I read right that might also affect application of drive. Does that sound right or possible? I would be a happy camper if the problem didn't go any deeper than the servo!

I welcome any suggestions of what might be the problem. I'd rather not experience the joy of pulling the engine and transmission (again) to completely go through the transmission. I'd rather wait to freshen/rebuild it in a few months when there's no racing.

Thanks

Lynn   

[tcoupekyle]

I don’t have much insight but I’d check adjustment on the band.

[JEFF/21C]

I used TCI servo like I stated in another post checked band adjustment about every six runs other than that, I didn't have many problems

[lake_harley]

I pulled the low band servo today and found a tiny chunk of something that was attracted to a magnet....on the spring side of the servo piston. Didn't find the source of the small piece. The piston ring on the servo piston was in great shape and no scratches or other damage in the bore of the case. Pulled the valve body down, managing to knock over the drain pan and dumping about 2 quarts of ATF on the floor, and double checked all of the spool valves for smooth operation. All seemed good.

I had converted the valve body to manual operation using the installation instructions for a TransGo kit by using a 1/4" long piece of tubing under one of the valves....shift valve I believe. Double checked the length at exactly .250" to be sure it was right.

I don't have a trans brake (just foot brake the car) and instructions on installing a shift kit said to install the vacuum modulator but not to hook up a vacuum tube to the intake. Check. It is an adjustable vacuum modulator and wonder if it needs to be adjusted in some particular way to make the modulator spool valve operate correctly with a manual valve body? Thought is that improper adjustment might be screwing up the 1-2 shift. I have a 50/50 shot with my guess, but I'm thinking the adjustment should be screwed in to seat "snug" like an idle needle in a carburetor as a starting point thinking that would simulate a low vacuum, high load situation? My transmission is a later one with the separate pin and spring on the tip of the modulator spool. No mention of adjustment was seen in the instructions.

Any thoughts other than to leave racing transmission building to racing transmission builders?

Thanks

Lynn

[JEFF/21C]

I,ve run various powerglides with modulator vacuum disconnected  never had a problem, always sharper up shifts when using stock valve body I've broken stock band and incurred wear on the drum(not flat . you only learn by doing!

[lake_harley]

Thanks for the reply. I do not have a vacuum line going to the vacuum modulator and the connection point for a line is left open. My question is should the adjustable vacuum modulator adjusting screw be turned "in" to limit the travel of the modulator valve? If I understand correctly from the Powerglide book I have if the modulator valve moves toward the rear of the transmission it might actually lower the line pressure possibly having a negative or softening effect on clutch and band application. There are so many moving and inter-related parts in motion in a valve body my brain goes into overload trying to put it all together. I probably have a short attention span too, which doesn't help.

Lynn

[lake_harley]

After some thought and a couple conversations with people much smarter than I about transmissions (Carl Munroe's son in particular), the engine and transmission is coming out. Transmission will come apart mostly to re-do the drive clutch pack to get more clearance so it can "slip" more freely in low gear. The valve body will also be redone with a new TSR manual shift kit rather than the home-brew manual shift conversion I did.

Not transmission related, I also talked with someone (Cliff Ruggles) about a slight hesitation the car has had off the line. A couple things were suggested to get the Q-jet carburetor set up a bit different to get rid of the hesitation/bog. He also made some suggestions about starting line procedure that hopefully will get the car off the line better and improve our 60' times.

If this all improves the car as expected, I am hoping to cut about .1 to .2 seconds off our best-so-far ET. I guess we'll see in a week or two.

Lynn

[tcoupekyle]

Thanks keep us posted!!

[lake_harley]

My FED now has 26 - 1/8 Mi. passes on it. With the transmission not shifting to drive on pass #21 I pulled the engine/transmission and got into the tranny. I had always suspected I didn't leave enough clearance in the high clutch pack. To remedy the problem I replaced the 5 .098" friction discs with 4 new .098" discs and one .060" disc. That got my clearance up to about .086" and now the car isn't draggy in 1st gear. Big difference!

To cure the "no shift" issue I pulled the valve body apart and installed a TSR manual shift kit which also boosted the line pressure. Previously I had followed a manual shift conversion that I found online, but this TSR kit is so much more complete and it really seemed to wake up the transmission.

On to results...which in the end is all that counts. The first 21 passes the car had made were more or less Test-n-Tune runs not actual racing. Last night after 2 timed passes we ran a foot-brake bracket class for the 1st time at a different track than we had ever run. Our "home" track's timing system had taken a hard lightening strike and wasn't running. WE WON 3 ROUNDS!!! But, the night had dragged on so late we left after the 3rd win. The 4th round would have been a bye run for someone and 1 race, so we probably made someone happy (the driver who was handed the bye run) and someone mad (the driver we beat in the 3rd round). But, not wanting to sleep through church this morning we left and still didn't get home until 3 AM. In the 1st round we ran a 6.85 on a 6.85 dial! I couldn't believe my eyes when the ET lights lit up. The car ran another 6.85 again in the 3rd round. Those 6.85's were .21 faster than our previous best and our 60' times were .10 quicker than our previous best. I attribute the improvements to the properly clearanced high clutch pack no longer "dragging" in 1st gear and what seemed like a crisper shift to the driver.

I still have a smile on my face! I'm pretty sure my driver does too.

Lynn