Can someone describe the overrun clutch in detail?

[Turbo Riviera]

Can anyone tell me what this thing does? Why is it in our transmissions?

Can it be eliminated?

Basically what I'm trying to accomplish is a lightweight, race-only trans, by eliminating overdrive, overrun and many other unnecessary parts from my transmission.

Question for Bruce specifically...

When you talk about strengthening the 2004R, you mentioned teflon bushings. Are you talking about replacing the brass bushings/bearings throughout the trans? Or just using teflon oil rings?

Is this for less parasitic loss, or strength?

As you can tell, I'm still giving lots of thought to building a lightweight, low rotating mass trans for the Stocker...

I'm getting closer to doing it, but I'm still a little unsure about a wholesale effort at deleting parts inside a very complex trans... I can build 'em but that doesn't mean I know how everything works! LOL

Thanks!

 

[transfixleo]

The Overrun clutches are there to keep the Input Roller clutch from back spinning when you let off the gas. It is what allows you to have engine braking but more importantly it keeps some of the shock off of the roller if you have it in D,2 or 1 when you get on and off the gas as it doesn't have to reapply since it will be held in the proper psoition.

 

[Maximumwarp]

Why not just use a turbo 400?

You can get anything for them, lower the frist gear, trans breaks, ect. ect....,?

Cheaper and more plentiful too.

Just an idea, HTH JS

 

[MeanBuicks]

Originally posted by Turbo Riviera
Basically what I'm trying to accomplish is a lightweight, race-only trans, by eliminating overdrive, overrun and many other unnecessary parts from my transmission.

Start with a Metric TH-200 three-speed transmission and you've already accomplised a couple of your goals. These are being used by an increasing number of class racers these days as they have proven to be quicker than a tricked-out, lightweight TH-350.

 

[WE4]

I agree....Talk with Scott McClay. He has perfected this... Just what you are looking for...,

Bruce
WE4
www.ptsnctb.com

 

[Turbo Riviera]

Sorry, I probably didn't explain why I wanted to do this very well...

I'm using a TH-325-4L trans (similar to a 2004R, but for front wheel drive) in a Riviera. That pretty much eliminates the metric 200 trans and 400 that have been suggested.

I could go with the TH-325 which is a 3 speed version of what I'm running now, but as per NHRA rules, if I run a "non-stock" transmission, then I can't run a lockup converter. I want to keep the lockup converter for that extra blast of ET if I need it during qualifying or for national record setting capability.

If I retain the stock trans, I can run the lockup and I can modify it in any way except a trans brake. This is why I'm thinking about eliminating 4th gear, and possibly the overrun clutches plus lightening up the rest of the trans.

Sorry, I should have been more specific.

Any ideas on this? Think of it as a 2004R and I'll adapt it to the 325-4L platform. They are VERY similar in design. Thanks!

 

[WE4]

To be honest in od the OR clutch is never on and as long as you never go to 4th ,wouldnt effect in the least. Just stack steels in 4th clutch with no frictions. This will accomplish what you want. There is very little drag. To eliminate the rest I could machine your parts with torrringtons and see what you pick up if any. I would be willing to try. let me know. the reason I need your parts to machine is all turn opposite way. Center support in lr is the same I think tho. Anyway I know I could pick up some. I beeen thinking bout this since you first posted. Lemme know.....

Bruce
We4
www.ptsnctb.com

 

[Turbo Riviera]

Bruce,

From what I recall, the center support is the same. I know that I use the same tool to pull it out that I use on the 2004R anyway. In fact, the forward and direct drums are almost identical as well... I know the forward drum is slightly longer in the 325-4L than the 2004R, but same design. I'd like to put torrington bearings in place of the stock thrusts for sure.

I was kind of hoping to actually machine off the 4th ring gear from the drive sprocket that attatches to the chain and input shaft. This would dramatically reduce the rotating mass right on the end of the crankshaft.

When you break down a 325-4L, it basically has the overdrive unit hanging off the end of the input shaft. If I could get rid of it, it would eliminate the ring gear, planet, sun, roller clutch, overrun housing, and all related 4th and overrun clutches and steels. Probably 10-15 pounds or so... Not to mention parasitic loss from the bearings, and friction plates.

I wonder if I could use an input shaft and drive sprocket from a TH-325 3 speed trans... Might be easier, might not. I'm not too familiar with the 3 speed trans. Hmm... Then I could maybe drill, tap and plug the 4th and overrrun passageways. I doubt it though, the 3 speeds probably didn't come with lockup converters so that's probably out.

Would this have any negative effects on decel at the track? Would it just basically freewheel on decel?

From the technical data that I have, the overrun clutch is applied in D3, D2, Low, but not D4 at all. Obviously 4th clutch is only on in 4th gear when needed. However, the OD roller clutch is holding in D4 2nd and 3rd, as well as reverse and neutral. So like you said, if I never put the selector into D4, 4th clutch would never be on anyway, but the OR clutch would be on in all forward gears with the selector in D3 (which is how I race it). If I took out the OD roller clutch would it affect reverse and neutral at all?

Meanwhile, everyone is thinking to themselves... "Why is this guy so retarded? Trying to make that front driver fast... DUH!" All I can say is it's all about what you're into. My thing is making stuff fast from stock parts in wierd bodied cars... What can I say? LOL

 

[GNVAIR]

Why not just use a regular 79-82 TH325 3speed? They are plentiful and maybe even more durable.

 

[WE4]

Well, I think I would have to look into it more.

As far as the front wheel drive idiot thing...............................
Well life would really SUCK if everybody had a 69 Red Camaro!!!!!!

I would be glad to assist you in your "unique" project.

I wish I had more time to look into this right now. If you got the time and gimme a chance I will look into a few things. Between workload (Buried) and constant pain in back now, it is getting harder to get stuff done as I'm sure you understand. However I can "roller" it for you. I was trying to rememeber if band and anchor was the same as 2004r? I have the fix to make that bulletproof. Plus I think the servo will work too but we have to modify the pin. As for C/S, if they are the same (which I believe them to be ) I got them all the time. I would need your ring gear (rear) and drum and Drum sator and forward drum. Given some time I know I can make this fly for you.


Bruce
We4
www.ptsnctb.com

 

[Turbo Riviera]

Thanks Bruce! I can sure appreciate the workload issue... I just moved into a new house, recently finished a complete paint job on my '87 GN, I have the engine and interior apart in my Riviera, start a new job on Thursday, etc. etc... It's never ending!

However, time is not really a factor here. I have a good working trans in the car now and I also have a spare. That is why I was trying to get some ideas about building it. It's probably going to be a winter project for me... So no rush. Take care of your needs right now. We'll keep swapping info on this though in the meantime.

My goals with this trans are more slanted toward making a fast, low drag trans. I have had ZERO durability problems with it so far. The trans I put together almost 4 years ago has over 500 runs on it and is still going strong. As always I'm looking to improve upon the factory durability, but I don't really need a 9 second capable trans. The fastest this car will EVER go is mid-high 12's and that's a ways off into the future right now. I am pretty happy with the shifting of the trans, the only thing that I would change is maybe a crisper 1-2. It has a slight delay between 1-2. 2-3 is really nice. I don't want a neck snapper on the 1-2 due to traction problems that might arise. Just crisp with no flare.

The servo cover is the same as the '84 GN 2004R, and I believe the apply pin is slightly different. I think it's longer from what I can remember. I do believe the anchor is the same, but I'll have to get my spare apart and check.

I'll see if I can't get it apart in the next few weeks and get a better idea of what I can and can't do. It's been 4 years since I've had a 325-4L apart, so my memory has faded a bit.

Thanks again!

 

[WE4]

Gimme call when you are ready. The more I think about it the more I am interested.


Bruce
WE4
www.ptsnctb.com

 

[Turbo Riviera]

Can do! Thanks for the help Bruce... Much appreciated!

 

[85 Riviera]

Hey Turbo Riviera hows it going. I rebuilt a 325-4L from a T type rivi and used the final drive as well (3.36) I have a few mods done to it but most are home made. I blocked off half the travel of the 1-2 accumulator with spacers on the oppisite side or the spring and I reversed the 3-4 accumulator spring and piston. I also use a 2400 stall. I use a mildly modified 307 with A5 heads the car pulls a mid to high 7 seconds 0-60 but soon it will be using a 350 olds thats now in the works. I was wondering if there is any tips you might have for me that I can do to this tranns to build it up some more without pulling it from the car again. I'm looking for a better 2-3 shift and even a slighly better 1-2 without killing the band. Thanx a bunch