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A Bent '02. Or, The Aligning Of A Banana.


GreenSwede

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So I spent the afternoon trying to align the drive shaft. And ended up wanting to torch the thing.

 

I used the old guibo mounted with the bolts right through to see where it "wanted" to go if the guibo was mounted straight and unstressed. 

It was heading for the ground, I could barely get the CB in place with the shaft very much in the lower half of the CB. So, I shimmed the tranny as much as I could, about 1,5 cm. When I tried to lift it higher, I lifted the whole car by the tunnel. 
At this point my alignment tool, if placed along the rear half of the axle, didn't touch the front end of the axle at all. Missing it at the most front point by about 1,5-2 cm. The angle that has to be somewhere was now at the front U-joint.

 

I remembered reading "the important thing is the front end of the drive shaft, the rest isn't relevant." Or something to that effect. 

 

So I tried that, I also shimmed down the CB and got the shaft a bit more centered inside it. And took a spin, to see how the mentioned theory worked. Not well. Fine at take off and acceleration, but not at speed. At 60 I had quite a bit of rumbling from the transmission tunnel, getting worse the faster I went.

 

So I tried removing shims, a few at the time and driving in between. It was getting better, but not good. And after a while it changed a bit as the drive shaft evened out and the guibo did the bending.

 

My conclusion is that my car has taken quite a punch in the nose at some point, which probably bent the front frame rails upwards. Making it pretty much impossible to align the drive shaft properly. I need to lower the engine. Or the diff.

Both seems hard, and I really don't know what to do. I guess I'll have to get it as good as possible and keep replacing guibos until I figure it out.

 

 

It seems I can't catch a f#€%ng break and just drive.

 
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Just lower. And that would make the angle of the front U-joint even bigger. I've gotten by somewhat ok before by letting the guibo take the angle, but as you all know that is not a long term solution..

 

If I just got the engine down a bit, the angle would even out. A tiny bit there makes a lot of difference at the rear of the drive shaft.
Last time around I wacked the driver side mount downwards, but I might give the passenger side a shot. Is there a bit of play in the holes holding the bracket (between the engine and the rubber) at the engine side?

 

(a long story, I had a not-very-well-fitted header that I got to fit by adding a spacer underneath the right motor mount. It's gone now.)

 

I could maybe gain a few mm by taking the front movement stopper out and placing that underneath the base at the frame instead between the frame and the rubber. It's held by the bolts there as well..

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 "the important thing is the front end of the drive shaft, the rest isn't relevant."  

 

I just happened to chat with Le Tran the other day about this topic, and that is pretty much what he said.  Here is the gist of what he said ....

    Disconnect the driveshaft at the final drive, and loosen the bolts on the center support bearing.

    Then you start at the front.  Get the driveshaft properly bolted-up to the transmission flange, nice and tight.  Then do a left/right centering of the center bearing, then and tighten those bolts.  

    He says the key point is that because the final drive mounting holes are slotted fore-and-aft, all the slop is taken up by moving the final drive as necessary.

 

Perhaps you'll have to first-of-all disconnect the driveshaft from the final drive, then loosen the final drive mounting bolts and push it backward ??  

 

Anyway, there's an idea ...... but if "everything" is bent to crap, well ...... and maybe what I've related isn't relevant to the problem you're having.

 

Cheers,

 

Carl

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 "the important thing is the front end of the drive shaft, the rest isn't relevant."  

 

Cheers,

 

Carl

 

Maybe if the angle the U-joints ends up "normal", whatever that is. But this seems to end up in about 5 degrees. And I don't think thats ok. Or normal. At 60 to 90 mph it sure didn't feel normal.

 

And I do believe there is a reason BMW had an alignment tool for the shaft. Also, if alignment is off sideways at the CB, there's trouble. Why would vertical differences be ok, but not horizontal? I don't think the joints care.

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I guess Id determine if the car is indeed bent by getting it on a rack.  If it is Id consider spacing the front subframe if you only need 3/16 of an inch or less  But I sure wouldnt do a bandaid fix like that unless I knew for sure it was tweaked

 

No fan of bandaid fixes either. But I've really looked this time, and as I see it the engine has to come down. The only ones in town with a rack I don't trust. They tried to steal from me once. And they do crappy work.

 

The mech that replaced my front and fenders years ago said that it seemed a bit off. He had problems fitting the fenders. Like it had been crashed to some extent.

 

Of course I can't say it's bent, I'm just really frustrated. But looking at the angle of the engine and trans output it seems that way. If I'd like the shaft near the middle of the CB, I'd have to replace the bolt to longer ones so I could shim a few centimeters. And raise the tranny until it's pressed against the tunnel.

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hmmm, from a "pure geometry theory" point of view:  if you can't raise the rear-end of the transmission, theory says you can drop the front of the engine to get the angle you want.  

 

Does that theory have any practical application in what you're dealing with ??  It is just another geometric perspective to consider, and from what little I know about the front engine mounts, the answer would seem to be "no."  

    Perhaps you'll be the lucky one for which the answer is "yes."

 

Cheers,

 

Carl

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If I was to guess, I'd say the driveshaft is bad

 

If the car is that "bent", I'd take it to a frame shop to look at

(mine would maybe charge $ 40 to look at)

 

Its possible to bend things back to where they should be,

or replace the front subframe with a used one

 

You could use longer bolts in trans mount bracket, drop it down ??

 

1st stop is frame/alignment shop if it isn't the driveshaft.

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Lemmee guess- you have a 5- speed.

 

They don't fit.  You never get the guibo exactly straight.

 

It doesn't mind a degree or 3.  4 or 5, that's where things start to fatigue.

Ideally, I think you can get it to 2, but that's a close thing.

 

Have the car measured, certainly, but if the nose is punched up 5mm, I'd bet you couldn't

get your doors closed.  Or your windshield to seal.  Or....

 

The other way, of course, is to use a thinner driver's right motor mount, and lower driver's left.

As others have said, 5mm here is a coupla degrees there.

And there SHOULD be 5mm to spare in pan clearance...

 

Ours, I get close, and don't worry too much.  If the guibos die, I fuss with it some,

and change 'em, and hope for the best.

 

Yes, this includes the race car...

 

t

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 The title of the topic might be a tad exaggerated, but I was frustrated..=)

 

 

Lemmee guess- you have a 5- speed.

 

 

Nope. Stock 4-speed. The only non-stock part in the drive line is the diff, an E21 3.91 LSD.

 

If I was to guess, I'd say the driveshaft is bad

 

 

The driveshaft was rebuilt last year. New CB and U-joints and balanced.

 

All that matters is the alignment of the guibo. The rest is not relevant. That is what u-joints are for. My driveshaft has a significant kink At the center bearing. Zero issues. with a 4.44 diff behind an s14 and about 4000 miles on racetracks it it is being worked pretty hard.

 

I´m just saying it's a bit relevant. Otherwise I could have the engine standing up and a 90 degree bend on the front U-joint, as long as it's straight at the guibo. There has got to be a limit to at what angle the U-joint can work. And work well.

If I straighten out the guibo perfectly, I seem to be getting close to that limit. I think that is what the 60+ mph vibrations are is telling me.

 

Many years ago, I tried one of these in an air tool. No good. Not at speed, and not a too much angle. If I had a centre bearing holding it, it would take a lot of beating.

 

post-40090-0-99271700-1411973270_thumb.j

 

From what I've read through work the essential things is that the output and input flanges are parallell, but mostly out of consideration to life time of the U-joints. With the engine sitting too high for me to raise the tranny enough, that's not possible. Unless I raise the front end of the diff. Then the U-joints really will be bent.

 

I think I saw that here somewhere, but can't find it. Like this, anyway.

 

I think it's kind of logical, if I have an angle to start with at the output from the tranny, I get a too low dip trying to straight out the guibo causing another angle at the dip. If those angles are to large, I get vibrations.

 

 

post-40090-0-56269300-1411973818_thumb.j

 

And here, page 5-6: http://www2.dana.com/pdf/J3311-1-DSSP.pdf

This says there is the maximum angle at 5000 rpm is 3.2 degrees. And the ends should not be differing by more than 0,5-1 degree.

 

What I don't know is what to do. My conclusion is still that if I could lower the engine all would be topsy-turvy. If I can't lower the engine I guess I'll have to try and find a spot with a minimum (acceptable) amount of vibrations, and where the guibos last at least for a while so I can rest up my back between replacing them.

 

I'll probably loosen the motor mount and jump up and down on the valve cover to see if I can't get a few mm's.

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Does your fan hit the radiator ?

Dist cap too close to firewall ??

You may be able to cut down the right motor mount ?

I've never done this but guess its possible

Or the mount bracket is bent, or maybe you could bend to fit ???

You could also work on left mount or maybe cut the bracket groove deeper

I still would start with frame shop and see what they say prior to "customization"

I could do some measuring, but not as well as they

Good luck

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Does your fan hit the radiator ?

Dist cap too close to firewall ??

 

No, never had fan problems. Well, once, I bought a radiator that was built a bit wrong. The sides that is screwed to the front wasn't at the right place. That did a few mm, which made the fan hit at the lower half. Which indicates the engine is leaning backwards, actually. Never thought of it until now.

I'll take a look and check upper and lower clearance, just for fun.

 

Dist cap is close. It doesn't touch, but it's close. There's just enough room to get the clip on, and it has to be taken up a bit sideways, so to speak.

 

You may be able to cut down the right motor mount ?

I've never done this but guess its possible

Or the mount bracket is bent, or maybe you could bend to fit ???

You could also work on left mount or maybe cut the bracket groove deeper

Good luck

 

I was thinking of the right motor mount, placing the stop bracket underneath the plate at the subframe would give me a tiny bit. And maybe losen the bolts to the block to let it "seat".

 

Every mm gets me closer.

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