960: IRS Driveshaft Problems

[FlyingTog]

I have an M90 5 speed trans swapped 960 wagon and it needed the center support bearing replaced recently. I just did the job tonight. I bought a CSB from FCP and the automatic one they supplied me was in fact the same as the manual one that came on the driveshaft from England. Cool beans. Very happy with the interchangeability of these cars! I tapped the old CSB off along with the support (the real thing that was bad was just the rubber support) and I tapped the new one on along with the new support. I put the car all back together exactly the way it came apart (remember, I put this swap together myself back in May of last year. I know my way around this car) and I just took the car for a test drive. The driveshaft vibrates over 35mph. The driveshaft is a two piece design just like the solid axle 740s and 940s have, except the front half has a set screw in it to lock the splines in place. It also has a master spline so you can't put the two halves together backwards and mess up the balance. My problem is that I screwed up the set screw when I was tapping the old CSB off. I carefully put it back in the threads inside the driveshaft when I put the driveshaft back in, but I reassembled it wrong. I didn't hang the driveshaft first. The set screw missed the splines, went in front of them and went all the way into the driveshaft and fell out of the threads inside the driveshaft. I said "f*ck it! It doesn't need it" left the loose set screw in there and put the car the rest of the way back together.

My question is, do the IRS cars really need that set screw? I didn't do anything differently to the driveshaft (besides omitting the set screw) other than take it out of the car, put on a new CSB and mount and put it back together. Could it be a faulty new aftermarket CSB and mount from FCP? Could it just need to be broken in a little bit more? If all else fails I'll just take the car to a driveshaft shop and have a custom one made. It's not that expensive. I'd like to figure it out myself though and not have to spend an extra $300 that I wasn't planning on spending. Any ideas or thoughts? Thanks.


Pete.

Edit: P.S. could I get away with a single piece driveshaft since the car is IRS and technically shouldn't need the splines or the extra u-joint in the middle? The set screw seemingly eliminates the need for the splines anyway, and there are already u-joints at the trans and at the diff...

[FlyingTog]

Bump. I need help.

[Goatman]

Hello,


What you are really asking is ‘‘Why is my driveshaft vibrating above 35 MPH?’’ Since it wasn’t vibrating before, and it is now, you can be assured that you did the job wrong. Take the driveshaft back out, and make sure there is a Master-Spline, and lock the front half of the driveshaft correctly. You botched the job, now do it correctly.

I don’t know what kind of magic answer you are expecting from the internet, but I can say assuredly, you need to fix the **** up.


Goatman

[Henry10]

Set screw locks the shaft, splines have tolerances. Without set-screw there is play in higher revolutions. That's why you have vibration.

Middle U-joint is there to reduce the joint angles. Other parts are designed to handle stresses based on those 3 angles. Keep in mind, torque, vibration, etc formulas change as angles change.

[FlyingTog]

Originally Posted by Goatman

Hello,


What you are really asking is ‘‘Why is my driveshaft vibrating above 35 MPH?’’ Since it wasn’t vibrating before, and it is now, you can be assured that you did the job wrong. Take the driveshaft back out, and make sure there is a Master-Spline, and lock the front half of the driveshaft correctly. You botched the job, now do it correctly.

I don’t know what kind of magic answer you are expecting from the internet, but I can say assuredly, you need to fix the **** up.


Goatman

Wow, really? No ****, Sherlock. Thank you, Captain Obvious. I just explained everything I did and that I did, in fact put the master spline in the correct place (you can't assemble it if you don't line up the master spline), but you're telling me I put the splines together wrong? I also did say I didn't lock the splines with the set screw, and my actual question (not the one you said I asked) was whether or not the driveshaft actually needs the set screw holding the splines. You didn't answer my question at all. You just called me incompetent and told me to fix what I ****ed up. Thanks for no help at all and telling me what I already knew.

Also, I know for a fact I assembled everything (besides the set screw) correctly. The CSB went on properly and in the right direction and all the bolts went back in the correct ways without any problems.

Originally Posted by Henry10

Set screw locks the shaft, splines have tolerances. Without set-screw there is play in higher revolutions. That's why you have vibration.

Middle U-joint is there to reduce the joint angles. Other parts are designed to handle stresses based on those 3 angles. Keep in mind, torque, vibration, etc formulas change as angles change.

Dude, it's independent rear suspension. The angles only change so much from the engine and trans moving around on their mounts. Which is practically zero. The rear differential doesn't move. Besides, the middle u-joint is behind the center support bearing anyway, so it's not effected by engine movement much at all.

I do understand what you're saying about the set screw, though. It could certainly lock the splines in place and keep them from moving laterally as well and perpendicularly. I was only thinking about the perpendicular movement and the fact that I didn't think it would matter much. It seems as if any spline movement matters. So good point, and thanks!

Looks like my first step is to take it back apart, remove the old set screw from the inside of the driveshaft, chase the threads with a tap, rob the set screw from my parts car and reassemble it 100% properly. I'll get on that when it dries out a bit. Fingers crossed on that unless I hear otherwise from someone else.

I would still like a solid answer as to whether or not the set screw is definitely needed, (i.e. personal experience from someone) but I think Henry10 just helped me answer that question.

Also, to re-ask my edited question from the OP, can anyone confirm whether I could get away with a custom single piece driveshaft with a u-joint on either end and eliminate the center support bearing all together? I think it would work but I'm not so sure if the driveshaft would be too long and would vibrate without a center support bearing. I see tons of single piece driveshafts with only two u-joints that are way longer on trucks and bigger cars, so I'm thinking it wouldn't be a problem to have a custom single piece driveshaft made. Of course, all of those cars are solid axle cars with driveshafts that have slip yokes (or something similar) and they change angle quite a bit when the suspension moves. Not sure about a single piece on an IRS set up, though. I only have my old diesel MB to go on, and I don't remember the specific design of the driveshaft on that car...


Pete.

P.S. Thanks, Henry10. I have a definite direction to go with this, now.

[Henry10]

Like I said, the issue with a single shaft is that instead of 3 angles you will have 2 angles. Propeller / Driveshaft engineering is heavily dependent on angles. Basically, the larger the angle the higher are the stresses on joints, bearings, bushings, etc..

For example (and I don't know this in specific numbers) our cars might have a 1 degree, 2 degree, 2 degree. Single shaft might mean 2 + 3 degree, for example. So your front propeller joint will be stressed to much higher loads, so will the rear ones.

That being said, outside experimenting, I see no advantage on a single piece shaft. In fact I see a disadvantage, since a larger single unit might be required, it would increase driveline loss on this specific platform. Other cars / vehicles are engineered differently and parts are suited to that design.

Once you re-do, you should have no problems. The worst, you might need re-balance ($ 60).

[TrickMick]

Originally Posted by FlyingTog

Bump. I need help.

here is a WONDERFUL "SCREED" on DRIVESHAFT HARMONICS that I supply
to queries by customers on "Why does it DO that??"....
http://www.hotrodhotline.com/md/html..._harmonics.php

[FlyingTog]

Originally Posted by Henry10

Like I said, the issue with a single shaft is that instead of 3 angles you will have 2 angles. Propeller / Driveshaft engineering is heavily dependent on angles. Basically, the larger the angle the higher are the stresses on joints, bearings, bushings, etc..

For example (and I don't know this in specific numbers) our cars might have a 1 degree, 2 degree, 2 degree. Single shaft might mean 2 + 3 degree, for example. So your front propeller joint will be stressed to much higher loads, so will the rear ones.

That being said, outside experimenting, I see no advantage on a single piece shaft. In fact I see a disadvantage, since a larger single unit might be required, it would increase driveline loss on this specific platform. Other cars / vehicles are engineered differently and parts are suited to that design.

Once you re-do, you should have no problems. The worst, you might need re-balance ($ 60).

Good points on the angles and stresses. Not something that would cross my mind. Probably because I don't see a degree or two of increased angle on the u-joints really causing that much more stress on the output shaft of the trans or the input to the pinion gear of the diff, but I'm sure there is a mathematical way of figuring out the increased stress to the components. I doubt it would be significant, though. But that's just me. I would also see a single piece unit as lighter than the two piece shaft, so I would think driveline losses wouldn't come into play and it wight actually be a bit better. Unless you're meaning the increased angles of the u-joints increasing the turning resistance and increasing driveline losses. Which would make sense, but I still wouldn't see a few degrees effecting such things that much.

Anyway, I'm trying to fix this as cxheaply and as fast as possible, so I think I'll be okay if I just put the set screw back in... lol.

Originally Posted by TrickMick

here is a WONDERFUL "SCREED" on DRIVESHAFT HARMONICS that I supply
to queries by customers on "Why does it DO that??"....
http://www.hotrodhotline.com/md/html..._harmonics.php

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The requested document was not found on this server.

Web Server at hotrodhotline.com



Was it supposed to do that?

[Henry10]

There is really no universal right or wrong with 3 angle or 2-angle shafts. Different engineers choose one or the other based on many factors, plus other things get affected by driveshaft design.

I would also be very curious to see what results other people have on using a 2-angle on the IRS monoleaf 960s.

[TrickMick]

Originally Posted by FlyingTog

Not Found
The requested document was not found on this server.
Web Server at hotrodhotline.com
Was it supposed to do that?

weird...I just used the link and it did the same thing.....
use this "google search term": " driveshaft harmonics " and it *should come up* as the
number one hit...let me know if THAT doesn't work...

sorry for the frukup...I've been sending that for a couple of years now...DANG!

[FlyingTog]

Originally Posted by TrickMick

weird...I just used the link and it did the same thing.....
use this "google search term": " driveshaft harmonics " and it *should come up* as the
number one hit...let me know if THAT doesn't work...

sorry for the frukup...I've been sending that for a couple of years now...DANG!

lol! I thought you might have been pulling my leg or something. Haha. No worries. I found it. Here is the correct link: http://www.hotrodhotline.com/md/html..._harmonics.php

Thanks!


Pete.

P.S. I see what you did wrong. You copied the abbreviated version of the link from a post that had it hyperlinked like I just did. You need to copy the main link in the top bar of the page when you open it. You can see how it's spelled differently.

[TrickMick]

Originally Posted by FlyingTog

P.S. I see what you did wrong. You copied the abbreviated version of the link from a post that had it hyperlinked like I just did. You need to copy the main link in the top bar of the page when you open it. You can see how it's spelled differently.

YUP! *DANG*....TNX for the heads-up

back in the day my buds and I would start @ Brigantine and work the coast
down to Cape May...I *STILL* have my Dewey Weber long board....

shaka bra...no get angry, no get uptight....

[VQ]

I'm unsure why you yanks are so obsessed with using single piece driveshafts? There is a lot of issues making a single peice driveshaft on a 7/9 due to how everything is done from the factory on the floorpan IIRC.

Get it balanced, fit the set screw and it should be all good!

[Henry10]

Originally Posted by FlyingTog

Probably because I don't see a degree or two of increased angle on the u-joints really causing that much more stress on the output shaft of the trans or the input to the pinion gear of the diff, but I'm sure there is a mathematical way of figuring out the increased stress to the components. I doubt it would be significant, though.

IIRC: Min angle is 1 degree, max is 3. We can't see neither. Yet it is a big difference though.

Originally Posted by FlyingTog

I would also see a single piece unit as lighter than the two piece shaft, so I would think driveline losses wouldn't come into play and it wight actually be a bit better. Unless you're meaning the increased angles of the u-joints increasing the turning resistance and increasing driveline losses. Which would make sense, but I still wouldn't see a few degrees effecting such things that much

You would need larger U-joints with single piece. I doubt tail shaft bushings are designed to handle a single piece. Keep in mind that CSB supports and holds the shaft. Without it, its stresses will be on the tailshaft and Pinion shaft, u-joints, bearings and bushings.

[FlyingTog]

So I removed the driveshaft last night, chased the threads for the set screw in the driveshaft and chased the threads on the set screw itself. Both cleaned up perfectly and threaded together like butter. I reassembled the driveshaft into the car and hung it properly before tightening the set screw. (Last thing I did.) When I went to tighten the set screw, I realized that splines don't even extend to the set screw, so there's nothing for the set screw to hit. I vaguely remember that being the case when I did the swap back in May. (I was extremely tired the night I finished the swap. I had pulled two all-nighters getting it done in time for Carlisle.) I had to use the front half of the driveshaft from England and the rear half of the shaft that was on my car. The rear half of the shaft from England had a different diff flange. It went together no problem and the splines meshed fine (splines weren't sticking out/not contacting) and I've been driving the car daily since I put the swap together. (See my burnout videos for the stresses this driveshaft has endured since installation. If it was going too break, it would have already.) I also checked the driveshaft in my parts car for a set screw and it doesn't have one!! The automatic cars don't have set screws, and my manual swap car hasn't had a set screw the entire time it's been together, so what the ****?? I knew it didn't need the set screw. Oh yeah, I took it for another test drive and it still vibrates over 35mph.

The only thing I can think now is that when I used a hammer and a drive to knock the old center support bearing off the driveshaft and used the same method to tap the new one on, maybe one of my misses with the hammer that hit the driveshaft bent it slightly. Or I damaged the new center support bearing when I was tapping it on the driveshaft. I was extremely careful though and I use those sorts of methods all the time. Those are the only explanations I came up with. I was hitting it relatively hard to get the old bearing off, but not wailing on it perpendicular to the shaft or anything. Definitely didn't think what I was doing would have any effect on a steel driveshaft. The only other thing I could think of was that the new bearing I got was defective out of the box, but I'm going on the assumption that that isn't the case. Or possibly that I knocked a balance weight off the shaft when I was knocking the old bearing off. I didn't notice any weights come off or see any missing weights when I reassembled it, though. I have found a few local driveshaft shops so I'm prepared to take it to a shop to get it balanced or just get a new one made.

Anyone have any thoughts? At this point I'm about to just take the car to a shop, drop the ~$250 and have a shaft made.

[TrickMick]

go back and look at that screed....

get a "magnetic angle gauge" : http://www.harborfreight.com/dial-ga...der-34214.html

and set about checkin ALL of your angles....FWIF - I'd have a SERIOUS look at the FRONT shaft
in BOTH AXIS alignments (up and down / right and left)..if THAT isn't *DEAD SQUARE* you'll
get the flop you describe....
follow up w/a careful measurement of the rear half of the shaft (doing the SAME inspection but
add in the ANGLE down to the diff....

motor and trans MOUNTS all in good nick as well??
you have a "made up shaft"...PHASING is VERY important...check it carefully....

I've had NEW out the box "rubber supports" be SPOOGEY and incapable of handling
the shaft torque load....if you can - get it up on a lift and have yer mate spin it up to
the "wobble zone" and look at the shaft to make sure it's running TRUE in a
CONCENTRIC rotation and NOT "epicyclic"....

every once and awhile we'd have "SOFT MOUNT" problems on the drag boat and trust
me on this - you DON'T want the shaft going "out of true" when it's a large chunk or
rotating metal just aft of your ass....

[Henry10]

I've had driveshafts drop out before. "Hammer in the washing machine" noise is too short before shafts falls off.

Before I called myself crazy -- just checked the parts diagram. Auto cars have a set screw.

[FlyingTog]

The whole driveshaft is back together 100% as it was before this problem started. The only thing that has changed significantly is the center support bearing. The driveshaft didn't vibrate before, and now it is. I know the shaft isn't out of phase and I know all the u-joints are all solid. The trans mount is brand new, but the engine mounts are old. I have new ones waiting to go in, but I don't see how they would be causing this as they're just as old as the were a few days ago and it wasn't doing it then.

On a side note, drag boats are cool ****. I'm a marine mechanic and life long waterman myself, so I know a thing or two about boats in general and performance vessels.

I checked the front half of the shaft that came out of my car originally and there is no hole for a set screw. I don't know why there isn't, but there is not. I don't remember seeing one when I pulled the trans out of my parts car or when I swapped that trans into my mom's V90, either.

I'm pretty much at the end of my diagnosing ability without getting frustrated. I think that maybe me striking the driveshaft a few times with the hammer I was using to take the old CSB off caused a slight bend or ding in the front driveshaft and has caused the vibration. I was recommended a good driveshaft shop so I'm most likely going to take the car there today or tomorrow and let them deal with it. Hopefully it just needs a little balance or straightening and I'll be on my way for under $100. Worst case, I have them make me a custom shaft for a few hundred and I shouldn't ever have a problem again.

P.S. I was thinking about putting the car in the air and having someone accelerate it up to 35-40mph like TrimMick said so I can crawl under there and check it out first hand, but that's a little sketchy on jack stands...

[TrickMick]

1) *SUSPECT THE MOUNT*
2) *beg / borrow / steal* ten minutes of LIFT TIME it will be ILLUMINATING and you'll feel better about spending any money at a "driveline shop"
3) spoogey MOTOR MOUNTS will make the NEW TRANS mount a "pivot point" allowing weird angles in the driveline to occur (see # 2 above)
4) unlimited light hydros RULE

[FlyingTog]

Originally Posted by TrickMick

1) *SUSPECT THE MOUNT*
2) *beg / borrow / steal* ten minutes of LIFT TIME it will be ILLUMINATING and you'll feel better about spending any money at a "driveline shop"
3) spoogey MOTOR MOUNTS will make the NEW TRANS mount a "pivot point" allowing weird angles in the driveline to occur (see # 2 above)
4) unlimited light hydros RULE

I would agree about the mounts if I had only just replaced the trans mount. The trans mount has been in the car for about a month and there was no vibration after I replaced it back then. If I could get some lift time, I would, but I doubt I'll be able to. I'll hang around the driveshaft shop and be annoying to them while they check it out. Haha.

As for hydros, agreed. There is a hydrofest near me every year in the Fall and I always try to go. I'm more into jetsprint racing and river racing, though. Those guys are nuts!!

[Henry10]

Peter: so what's the moral of this story? re-balance?

[FlyingTog]

Originally Posted by Henry10

Peter: so what's the moral of this story? re-balance?

Waiting for a call from the shop. Dropped the driveshaft off to them yesterday and he said he'd be calling me by the end of the week. We'll see. I hope it can be fixed by the end of the week. I have somewhere to be this weekend.

[tomasss]

Hmm, I am following this closely - I have the same problem, solving it more than year, no find so far. I had old driveshaft with weak rubber, got it replaced with bearing, rebalanced the whole driveshaft, fitted...and got vibrations. See http://forums.turbobricks.com/showthread.php?t=234857 for inspiration...

[TrickMick]

Originally Posted by FlyingTog

Waiting for a call from the shop. Dropped the driveshaft off to them yesterday and he said he'd be calling me by the end of the week. We'll see. I hope it can be fixed by the end of the week. I have somewhere to be this weekend.

*are you SOMEWHERE* or did the driveshaft end up "weekend vacationing" at the
shop...??....

[stove]

I don't know if this applies to your scenario,
But I have recently been taking note of the FACT
that EVERY (at least '94-'98) automatic 960 I have seen
(about 20-25 cars) the front portion of the DS is assembled
In an out of "phase" manner from the factory. Hopefully this
may shed some light on your problem.