Weird looking drive shaft and a wicked vibration

[Zgotrip]

Well I put the car up on stands to try and fix the leaky oil pan and find the source of a big time vibration that starts to come on about 5800 rpm and by 7000k feels like the wheels are coming off. The car will cruse at any speed no problem as long as the revs are down. The whole drive train looked pretty solid (except for the oil dripping off everything) and I couldn’t get any play out of the ujoints or mounts and the diff strap is failing but still holding its own at this point. But the drive shaft is this two piece slip together thing with a sticker from some truck driveline shop on it. I can feel play at the point where it slips together, rocking it and up and down, but not a lot at all. What gets me is after the last time I was under the car I figured the whole rear end and 5spd were from a early 79 just like the rear brakes, but then couldn’t you just use the drive shaft from the same car? Why this thing? So now im not to sure what I have, or what to replace it with. So do you guys think the drive shaft is the most likely cause of the vibration? how can I tell if a stock drive shaft will fit and what year to use?

[JMortensen]

That is a two piece driveshaft and you can't replace it with a one piece because there is no slip yoke on the tail end of the transmission, it has a flat flange that the driveshaft is bolted to. On two piece driveshafts it is possible to get them assembled "out of phase". If someone took the driveshaft apart and didn't put it back together in the right orientation, that will cause a nasty vibration.

 

This website shows driveshaft phasing: http://jniolon.clubfte.com/drivelinephasing/drivelinephasing.html

 

I've only seen that driveshaft on the steel synchro 5 speed transmissions. If that's what you have it might be worth some money to a racer, especially if it is the close ratio version. It could be something else entirely that I'm not aware of and not of any great value, but it's worth checking out.

[Zgotrip]

thats fairly interesting...thanks for the link. I was ready to toss that trans because the synchros feel pretty done, have to heel it just right to go from 3rd to 2nd without grinding. I have heard of those steel synchro transmissions how can i tell if this is what i have? Did they come in production cars or were they just a competition part? I will work on checking the phasing and see what that revels.

[JMortensen]

thats fairly interesting...thanks for the link. I was ready to toss that trans because the synchros feel pretty done, have to heel it just right to go from 3rd to 2nd without grinding. I have heard of those steel synchro transmissions how can i tell if this is what i have? Did they come in production cars or were they just a competition part? I will work on checking the phasing and see what that revels.

 

They came in production cars overseas. In the US I think they were dealer options on the older cars, but not many people seemed to want to buy it. They're pretty rare here. I think they also came in some roadsters. From what little I know, everything else was a competition part. You might be able to pull a fill or drain plug and shine a flashlight in there and try and spot the synchro rings. Years ago when I worked for a Porsche shop I did a direct comparison of the Nissan synchro and the Porsche 911 synchro from the older transmissions (called a 901 transmission maybe? It's been more than a decade). Anyway, the synchros are damn near identical, the gap in the ring was larger on the Porsche part. My boss who had worked on Porsches for 25 years was convinced that they would work and you can get the replacements pretty cheap if you don't buy Porsche brand parts. Not sure on availability for the Nissan stuff. Last I heard you had to buy the whole gear cluster with the synchro ring, which is ridiculously expensive.

 

If you don't want to fix it you could probably find a buyer and more than cover the cost of a good regular brass synchro style trans and driveshaft. If you want to fix it I'd take the part to a guy who knows Porsche transmissions and see if he can match it up for you.

[JMortensen]

P 108: http://books.google.com/books?id=j7wq62vJtXoC&pg=PA110&lpg=PA110&dq=porsche+911+synchro+ring+replacement&source=bl&ots=11RNffxG1n&sig=2JxwVhTp9ogOnz_xiNo47APPNqY&hl=en&ei=IqipS_PXEJGmsgPXwengBQ&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCAQ6AEwBw#v=onepage&q=&f=false

[getoffmyinternet]

Am I missing something? If a vibration occurs at a specific rpm range but not speed range, it is almost certainly caused by something upstream from the drive shaft...

[JMortensen]

Am I missing something? If a vibration occurs at a specific rpm range but not speed range, it is almost certainly caused by something upstream from the drive shaft...

No, that makes perfect sense. I just got hung up on the transmission itself and wasn't doing a very good job of analyzing the vibration.

[Zgotrip]

Am I missing something? If a vibration occurs at a specific rpm range but not speed range, it is almost certainly caused by something upstream from the drive shaft...

 

yea that's what always think to, its just that this vibration totally feels like its coming from the back of the car. there is no noticeable vibration in the shifter as i recall, and it wont occur if the car is in neutral and you just rev it hard. kinda at a loss for what to think at this point, i figured when i got under it it would be obvious. i may just go after the oil leak and get it back on the ground and see if i can narrow it down a little.

[JMortensen]

Might as well check the front crank bolt while you're at it.

[ozzzzz]

Remove the driveline and check to see if the u-joints move smoothly. Had an old Toyota that had a severe vibration in the upper rev range.Ran smooth below 4K rpm. The u-joints were really stiff. Replaced them and everthing was good afterwards.

[Zgotrip]

so i looked under the car today and noticed that the trans seems to be twisted to the right just a tad. its kinda hard to see because the car is on stands and not a lift...all the mounts LOOK good but i wounder if the drivetrain could be twisting under hard acceleration and causing the driveshaft to go out of phase and then back in when the revs come down? I dont know ...kinda shooting in the dark at this point.

[getoffmyinternet]

Sometimes a vibration seems to go away when there's no load on the engine. Plus an engine vibration could be transmitting through the drive shaft and it resonates at the back of the car (I suppose in some rare occasions a vibration could be caused by harmonics between the engine and the differential or something so it would seem like it's at certain rpm--two small vibrations are combining forces at a certain frequency). However, even then it's usually a range that you can power through, not one that just gets worse and worse the higher you go. Airplanes have a caution range because of harmonics between the engine and propeller for instance.

 

Torque does do some strange things in that area, but it seems like if it were the engine, if would vibrate at wot then once you were cruising it would go away, for everything else it would be a speed range issue. For instance, I remember in an r200 thread someone said he had severe vibration at like 40-50mph and after replacing everything one by one he figured out that it was the stub axles, which had a manufacturing defect that caused the bearings to become loose at that wheel speed but undetectable at rest.

 

It could still be the transmission, but I think it has to be on the input side. If it isn't mating with the engine nice and flush, I suppose the input shaft could be out of phase and cause an increasing vibration the faster it goes. If it was something else in the transmission, it would probably only happen in a certain gear or at a certain speed.