Solid Transaxle Mounts...

1.2gees · 1.2gees's Garage

I was thinking yesterday about all the troubles I've had with the transaxle(s) on my 944...

Remembering how easy it was to move the tranny around when I was taking it off, I have to wonder how much it moves around in hard driving... When I need to shift at the exit of a slalom for example, or just shifting under hard braking/during or even after a turn, could the transaxle moving around be putting extra undue stress on anything, and making the shifter feel a lot worse?

If so, do you think solid mounts would help?

Just wondering the general opinion,
Thanks.
Ahmet

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It's all the driver...

kukunaokala · 02-28-2001, 06:02 PM

Good question. Try this mental exercise- the engine floats on rubber (oil?), the trans floats, the rear wheels can go up and down. You make any of these rigid, something's got to give, and it's most likely your frame.

I've got hairline cracks between the floor and wheel well. Oh well, I'm re-undercoating.

Aloha, Neal of spare wheel well infamy

eimkeith · 03-01-2001, 06:04 AM

Ahmet, I don't know where it would hurt anything, besides transmitting some vibration to the cabin.
With your transaxle issues, I would try it.
Any machine shop should be able to make you a solid mount...

awilson40 · 03-01-2001, 06:15 AM

Instead of a solid mount... how about removing your old mounts and replacing the rubber with a poly or rubber with a higher durometer reading. I'm sure it could be done, that would make the mounts stiffer without going full rigid.

1.2gees · 1.2gees's Garage

If polyurethane mounts would help, solid mounts should help much more, reducing the movement big time, right?

+they'd be cheaper to make, and possibly easier to work with as well.
Ahmet

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It's all the driver...

awilson40 · 03-01-2001, 12:06 PM

sure... I just thought the poly would give you a bit of vibration and torque dampening

hoff944 · 03-01-2001, 12:10 PM

I agree with kukunaokala. Something has to give. Look at it like this. Thats the same reason that you notice your aircraft wings flexing when you look out the window during your flight. It looks creepy, but if they didn't give, the would break a whole lot easier. Thats the way I see the problem.

lm6y · 03-01-2001, 02:11 PM

I agree with Hoff, Neal of spare wheel well fame

and Awilson. Keep in mind everything is aluminum, except for the steel bolts. If the drivetrain twists, which it will under torque, something will have to give. Most likely the threads on the trans case, or the mounting boss itself. The only thing connecting the engine, and trans, is a STEEL torque tube. The torque tube ain't gonna give before the aluminum parts will. The only way I see to do this, is to have solid engine mounts also.

1.2gees · 1.2gees's Garage

The torque tube can flex a small amount (in my opinion enough to let the engine move around as little as it does).

The "twisting" that will occur under engine torque is well, transferred to the cv joints-->the wheels. That's the way we want it, not trans moving around itself, as it does now.

The output shaft inside the torque tube wants to rotate the input shaft on the transaxle, while the transaxle mounts, the torque tube bell housing try to keep the transaxle FROM spinning! I don't see why anything would give because of this. It'll just solidify the transaxle's mounting, to the chasis. This in turn should make for a more responsive drivetrain, less moving around would have to translate into better shifting feel, as the shift rod actually goes through the transxle.

I can see more load being put onto the torque tube, and the casing under hard braking though, as the engine mounts allow the engine to move forward somewhere around 1/4th an inch, and the transaxle doesnt.

This is because the torque tube can handle some torsional stress/twisting, but not much fore/aft. Going to solid engine mounts should eliminate this altogether, as none of the components would move around any detectable amount. I'm not sure if I want to get into that, as that would most likely be a MUCH harder job to undertake, than tranny mounts alone.

What are your thoughts about this one? I'm guessing the general opinion is to leave everything alone?
Ahmet

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It's all the driver...

kukunaokala · 03-01-2001, 05:04 PM

Ask RealRacing?

Aloha, Neal

lm6y · 03-01-2001, 05:53 PM

Good points Ahmet. But my reason of thinking comes from a drag car a friend and I put together. We used solid transmission mounts, with normal engine mounts. The result was a broken trans tailshaft (where the trans mount
bolts to). This was on a high horsepower/torque engine, with fairly wide slicks. I know a 944 won't encounter the same stresses, but something had to give. A few of the "old" racers chipped in and told us that if we were going to run solid trans mounts, we had to use solid engine mounts.

To prove the point, I've seen a lot of advertisements for solid 911 engine mounts. I dont think it would be hard to make solid mounts for a 944. I bet there would be a lot of harsh vibrations though.

todd951 · 03-01-2001, 05:58 PM

Lindsey Racing sells both solid engine mounts and solid transmission mounts for the 944.

drew1 · 03-01-2001, 07:28 PM

Ahmet,
I know a couple of people that run solid rear mounts (trans) & stock mounts on the motor on a 914/4 with better shifting & no problems except loosening up every now & then. Have solid mounts on front & back of my 914, with nyloc nuts. Didn't have any problems except aggravation getting angled rear mounts off when dropping everything.
The 944 stock linkage feels a lot better to me than the 914 stock linkage & solid mounts definely help a 914.

Solid mounts seem to me to reduce body flex by transmitting some of this stress through the motor/trans. A bad example though would be Imy6 and chassis twist breaking a tail shaft.

I would get advice from Lindsey about solid rear & stock front since they make them both.

drew1

edit: don't know if I could really call my mounts solid, used different materials metal plastic clamped together.

[This message has been edited by drew1 (edited 03-03-2001).]

nigel · 03-03-2001, 03:10 PM

In my opinion the crossmember on the body, which the trans mounts bolt to, would crack around the edge of the nutplate, which is mounted inside the crossmember.
Probably OK on an out and out race car!! My race car has solid engine mounts, but just like big engined drag cars, it is mounted on a plate at either end of the block, not using the blocks original mounting holes. This is because I've heard of blocks breaking when solid mounts are used as rubber replacements.

Yes I know were talking about trannys here, but the theory is the same. As a guide to how much everything is moving, check your gearstick when braking hard or cornering, after all,its bolted (through the torque tube) directly to the tranny.
Does anyone know what Porsche did for mounts on the 944 turbo cup cars?

1.2gees · 1.2gees's Garage

drew1, you have to keep in mind, there's a LOT more chasis flex on a 914, in comparison to a 944. +On a 914, the mid engine design puts the chasis loads on either side of the transaxle (and engine). On the 944, the suspension mounting points are in front of the transaxle mounts. I'd VERY highly doubt if any chasis flex would occur between the two transaxle mounts! (on a 944).

The gearstick doesn't move too much on my 944, but it does noticably move under severe braking, not really noticable in pretty much any other condition. (Havent paid attention under cornering).

BTW, doesn't the 914 have cable actuated shifter? +the lincage has to go around the engine, which is a big pain, on the 944, the distance is kinda far, but not a huge deal. To improve the shifter feel, the best thing to do is get a lighter lincage, such as aluminum from a 968, or custom alloy. Shifter feel is not much of a concern to me right now, transaxle life is! I'm hoping better shifting, and less flexing of the lincage when in gear, etc. will help this.

nigel:

The turbo cup cars used factory turbo motor/transaxle mounts.

I don't think I'd cause anything to crack, if I got solid mounts in the front, as well as the rear. I'll be pulling the subfare out, and now that I think about it, shouldn't be too hard to fabricate some, maybe I'll try that.

PS: Drew, I'm still kinda looking for info on the trailing arm suspension roll centers, haven't been able to find anything, if I do, you'll know

Ahmet

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It's all the driver...

drew1 · 03-04-2001, 05:31 AM

Ahmet,
914s have a rod type linkage. The clutch is cable. The 70 - 72 with the tail shift trans have awful linkage, at least with a little wear.

There's not much more room beween 914 trans mounts & early 944. The strenghting against chassis flexing comes from solid mounts on motor & trans. Can't say I took any scientific measurements, just seemed to.

Thanks for looking for roll center info, but please don't neglect your school work or car, etc.

drew1

1.2gees · 1.2gees's Garage

drew, I'm not saying there's more/less room between the space for the 914 transaxle/944 transaxle.

However on the 914, the engine/transaxle are joined together. With this set up, they take up more space, at the given location (the middle of the car). Which is between the front, and rear suspension mounting/loading points. In short, the engine/transaxle assy. is bolted in the car where chasis flex takes place! +The hole in the chasis because of the engine/transaxle definately contribute the engine/transaxle getting more load, under flex.

I'm going to work on yet another english paper now, and as always thanks for the replies.
Ahmet

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It's all the driver...