Motorsports Village

PowerGlide Transmission Problem
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Author:  Ken0069 [ Thu Aug 01, 2013 8:38 am ]
Post subject:  PowerGlide Transmission Problem

I've been doing PowerGlides for a local guy now for longer than I can actually remember. About 4 or 5 years ago I put a 1:80 straight cut planetary in his tranny and at that time I changed over his high gear clutch pack to 8 disks instead of the usual 6.

Along with that mod I also left out half of the 24 high gear piston release springs as I'd done that with a couple of other transmissions including my own as a way to increase apply pressure to the high gear clutches without actually increasing line pressure. Those springs only purpose is to RELEASE the high gear piston when the transmission is put in either low gear or neutral so for a drag application, I didn't see where leaving 12 of them out could be that much of a problem.

Fast forward to a couple of weeks ago and I got a call from that local guy saying he was having problems with his tranny, mainly when he shifted it driving around the pits. So he pulled it out and brought it to me and we pulled it down. I noticed that the fluid was a little burnt but didn't think much of that since it had been together for that long. When we pulled the high gear drum apart we found the problem. Here is a picture that will explain it better than I could write it.


The reason these springs are bent over like this is because the piston turned inside the high gear drum? Never seen this before and I've had mine down since I did this mod to it and didn't see this problem with it?? Ennywho, I put it back up with all 24 piston return springs in and sent it out the door.

As usually is the case, this was on my mind constantly after that so I contacted Barry (Beretta) via Email telling him what happened and by that time it was my opinion that down shifting to low gear at any amount of speed "might" be the cause of this and if the driver was leaving the tranny in high gear in the shut down area then he'd be shifting back into low gear at the turn off and that may be where the problem originated. On mine I alway go to neutral at the stripe so that's never a problem for mine. So I called the guy and asked how he did in shut down and he does in fact leave it in drive until he gets to the return road then shifts into low gear as he makes that turn.

I know this mod was discussed on here a while back so I decided to post this so that if any of you reading this have done your high gear drum like this you might want to pay attention to how you drive after the stripe and AVOID DOWN SHIFTING AT SPEED!! NEVER DOWN SHIFT TO LOW GEAR UNLESS YOU'VE STOPPED FIRST!! That way nothing will be turning inside the tranny when it goes into low gear.

Author:  Ken0069 [ Mon Sep 02, 2013 2:56 pm ]
Post subject:  Re: PowerGlide Transmission Problem

Ya know, when problems like this come up that I can't get a concrete answer for I'm always revisiting it trying to understand why it happened. Same thing goes with this deal as I really can't explain it and have some new thoughts as to why this might have happened.

In order for that high gear piston to turn like that it would have had to have either a friction against it or a steel without the locking tabs. I didn't take it apart, the owner did so I got no way to know whether I assembled it correctly when I built it.

There is a thought that occurred to me that I may have machined the piston down far enough to allow the steels locking lugs to get UNDER that machined area in the drum periphery.

Ennywho, Barry and I have our thinking caps on with this one and I've put in a call to the owner to see if he still has the steels that came out of it. If he does, then I'll have him bring them to me so I can see if it looks like one of them has turned under that locking notch.

Author:  Ken0069 [ Wed Sep 04, 2013 4:26 pm ]
Post subject:  Re: PowerGlide Transmission Problem

Well, the transmission owner brought that clutch pack by the shop this afternoon and it's good news/bad news. Upon inspection of the steels I found the one that was against the hight gear piston so it was assembled correctly after all and that's good news. The bad news is I still don't know why this happened?? ](*,)

He's going to finish out the season with it like it is and then pull it down this winter so I can have a closer look at that drum assembly. Hopefully I'll be able to determine the cause of this problem at that time.

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