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914World.com _ 914World Garage _ Does flat towing hurt

Posted by: Wild 6 Mar 6 2006, 07:19 PM

I had a mechanic tell me that flat towing hurts the transaxle. Specifically, the synchros and bearings. He told me that you need to stop every 100 miles or so and start the car to lubricate the transaxle parts. Is this true?

I have flat towed the car for 100's of miles at a time. Am I screwing up?

Posted by: Series9 Mar 6 2006, 07:24 PM

With a standard tranny, flat towing will never hurt as long as the shifter isn't loose enough to be bouncing against the shift parts while under way.

Posted by: iamchappy Mar 6 2006, 07:25 PM

I have flat towed my car from Washington to Minnesota still no problems with the transmission and that was 15 years ago.

Posted by: Series9 Mar 6 2006, 07:41 PM

Look, there's no oil pump in a standard tranny. It's all 'splash' lubrication.

If you're rolling down the road, 'splash' is happening. The tranny has no idea whether or not the engine is running.

Posted by: Aaron Cox Mar 6 2006, 07:43 PM

QUOTE (Series9 @ Mar 6 2006, 06:41 PM)
Look, there's no oil pump in a standard tranny. It's all 'splash' lubrication.

If you're rolling down the road, 'splash' is happening. The tranny has no idea whether or not the engine is running.

yep, im with joe,,,

the ring gear is turnin like crazy.... and then the pinion too... so as long as it is rolling it is getting lubed.....

(and make sure its outta gear)

Posted by: bryanc Mar 6 2006, 08:04 PM

Another opinion......

The input shaft is not turning though. This means that the bearings that the gears on that shaft are spinning, but not like they do when the power is coming from the input shaft. Furthurmore every other gear on each shaft is turning (i.e. 1,3,5 on the input and 2,4 on the pinion shaft or verse-vicea).

It's more or less like driving in 5th gear for several hundred miles without shifting, just a different shaft.

An additional difference is that the tranny never gets as warm as it does with the engine running. I don't know if this is good or bad???

Really I don't think it's a bad idea to flat-tow, it does cause wear on the transmission though, but much less stress than the engine does.

Posted by: Series9 Mar 6 2006, 08:09 PM

On a standard tranny, all the gears are constantly meshed. Additionally, the 'input' shaft is constantly turned by the drive axles while in tow. Lubrication fully occurs as it does in normal operation.

Your comment about the oil warming up is true, but inconsequential.

Posted by: Dan (Almaden Valley) Mar 6 2006, 08:09 PM

Direct from a 30+ year factory trained Porsche mechanic....flat towing does not hurt the tranny. As stated previously, splash lubrication during driving or towing.

I know personally many folks that have been flat towing 914s and 911s to and from AXs and Time Trials for many many years with no problems.
I am talking everything from fairly stock 2.0L 914s to 2.8L twin plugged and 3.4 twin plugged 915 gear boxed 911s. One of them is running 335 rubber on the rear.
Several of these cars have been towed this way for over 15 years.

That's it.

Posted by: gregrobbins Mar 6 2006, 08:11 PM

There have been threads about this before and the general consensus is that there is no problem. Andy, I just think Bryan wants to see you spend money on a trailer rather than more "go fast" parts.

Posted by: brp914 Mar 6 2006, 08:28 PM

I took trans rebuilding at a JC to kill time after work until traffic died down. We took apart cars that have cheapo gear boxes where gears are not mounted on needle bearings like on Porsche. Just gears mounted on shafts. Those types cannot be towed long distances without disaster. But whether the 1 - 3 synchros on a 914 are getting adequately lubed w/o the gears turning is debatable.

Posted by: Leo Imperial Mar 6 2006, 08:32 PM

3100 miles and no problem.
I'm also with Joe.

Posted by: bryanc Mar 6 2006, 08:37 PM

QUOTE (Series9 @ Mar 6 2006, 06:09 PM)
On a standard tranny, all the gears are constantly meshed. Additionally, the 'input' shaft is constantly turned by the drive axles while in tow. Lubrication fully occurs as it does in normal operation.

Your comment about the oil warming up is true, but inconsequential.

The input shaft to me is the shaft that attaches to the clutch. This does not turn when you are towing unless you are in gear. The pinion shaft does turn.

I do agree that the lubrication will work fairly normally, just cooler.

Posted by: Headrage Mar 6 2006, 08:39 PM

QUOTE (Wild 6 @ Mar 6 2006, 05:19 PM)
I have flat towed the car for 100's of miles at a time. Am I screwing up?

No...

Posted by: Wild 6 Mar 6 2006, 08:57 PM

Thanks for all the input. I have towed this car all over the Southwest and I plan to flat tow it to the PCA California Festival of Speed at the end of the month. I have a small fortune in this gearbox and didn't want to break it.

Posted by: ! Mar 6 2006, 09:11 PM

Tell yer wrench to lower his crack intake.....

Posted by: jimtab Mar 6 2006, 09:46 PM

QUOTE ("*" @ Mar 6 2006, 07:11 PM)
Tell yer wrench to lower his crack intake.....

nice one Z...

Posted by: Porcharu Mar 6 2006, 10:03 PM

The transmission is turning just like you are driving down the road, just less stress and strain. However the bearings and such will still wear - just like driving down the road. I would think a synthetic trans oil would be a good thing because the trans is spinning yet the load is tiny so the temp should be low.