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What is going on here? (damaged Guibo)


Justin99

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I replaced the Guibo on my car a couple of months ago at the same time as replacing the centre bearing support that had failed completely.  The old Guibo was ok, if looking a little worn with a few minor cracks, but still serviceable.

 

Anyway, I crawled under the car this evening to see a big crack in the new guibo. Car has done less than 2000km.  Any ideas as to what has caused this?  I did have a few issues at install with tightening up the nuts attaching the gear box flange to the guibo - for some reason the original bolts on the car were of a non metric thread and I did not realise this when installing new (metric) lock nuts on the bolts. I did sort it out after two test drives,but not until the incorrect nuts had worked them selves loose twice (first time I thought I had forgotten to tighten them).  No damage was apparent at the time, and the only symptom of the nuts coming loose was the nuts/bolts of the guibo rubbing on some parts in the transmission tunnel/gearbox evident as a tapping sound)

 

The Centre bearing support seems to be in fine condition. The driveshaft does seem to have a minor kink (ie bend at the uni joint) in it at the centre bearing, probably less than 0.5 degree. 

 

Engine mounts appear to be ok.  I replaced the gear box mount at the same time I replaced the Guibo/centre bearing support. No unusual vibrations from the driveline. The car is a 71 with a 4 speed, that may or may not be original with the car. 

 

Does anyone know what might lead to the crack in an otherwise virtually new Guibo?  Happy to chalk it up to the incident above but want to check that I have not missed something else.  Also, does anyone know what the correct bolts sizes are for the guibo.  I am guessing they should all be metric, not a combination of UNF(?) and metric! 

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I had a "Made in Germany" Guibo last about 5000 miles (it was on the tranni when I bought it,  I'm not sure how many actual miles were on it before, but for sure, my 5000 miles). Replaced it with some CRAP one that lasted 1000 miles. Then I replaced it with one from "Ireland Engineering", it went about 6000 miles. Now, I bought one from "BMW", 3-times the price of "Ireland Engineering",  I'm only about 700 miles into this one, I report back at 5000 miles. 

 

From the looks of yours, you got one of those cheap Asian ones

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IMHO there are couple reasons for flex disc to fail: 1). poor quality flex disc, 2). flex disc/Guibo is under constant rotatinal stress caused by not running (rotating) true. Here are the part numbers for hatdware, but confirm for yourself by entering your VIN # into following link.

https://www.penskeparts.com/index.aspx

26111102144 HEX BOLT - M10X61 (03/66 to 07/77) (Manual Trans.)

26111106113 UNIVERSAL JOINT - D=76MM/10 (03/66 to 07/77) (Manual Trans.)

07129964672 SELF-LOCKING HEX NUT - M10 (03/66 to 07/77)

Also ensure drive shaft centering ring components are intact and has fresh long life grease in it. Self centering ring components are part of front end of the driveshaft, which goes through guibo and transmission output shaft end is inserted into it at assembly.

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Here are the steps I followed installing guibo & driveshaft;

Disconnet driveshaft from diff completely and loosen the bolts at center support bearing

Attach guibo to trans output shaft first

Fasten driveshaft to guibo

Attach diff to driveshaft end (you can loosen diff mounting hardware to move it forward if needed)

Preload the center bearing by 2mm (towards transmission) and tighten the nuts

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Torque has little to do with guibo failure as shown by properly aligned drivelines and high horsepower engines.  Where the trans shaft is not in a straight line with the forward section of the driveshaft, the rubber in the joint both stretches compressed with each revolution of the driveshaft.  At 3600rpm, that's 60 times per second!  The joint craps out.  Some things are not just plug and play, but rather plug and pray.

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I would add one thing to Buckeye's excellent synopsis-

 

after it's all installed, loosen the diff and try to push it backwards in the car.

 

You're not looking to move it enough to deform the guibo, just preload it backwards

a little bit.

 

That said, I suspect you got an inexpensive guibo....

 

t

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Happy to chalk it up to the incident above but want to check that I have not missed something else.  Also, does anyone know what the correct bolts sizes are for the guibo.  I am guessing they should all be metric, not a combination of UNF(?) and metric! 

 

You have High Tensile UNC (Unified National Course) bolts fitted which I guess are 3/8".  Yes you should have 10mm Metric Bolts with a tensile rating of at least 8.8 on the top of it.  10.8s would be better.  I use allen key inhex style bolts that are I think 12.3, with new nyloc nuts fitted. Running 165 Hp at the wheels in a track car, but not having any trouble with guibos. I have some aftermarket German brand guibo in mine.

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Thanks for all of the excellent feedback.  I like the idea or using allen key hex bolts. I think I will need to find a specialist (Australian) bolt store.

 

I will report back on the brand of the Guibo, and the condition of the centering bearing in the tail shaft nose piece when I take it all apart in the next few days. 

 

The Guibo that failed was bought from a reputable source, hence my reluctance to blame it on the equipment without ruling everything out first. 

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jg

 

Guess my posts are invisible. If you buy new hardware from BMW they should look very similar to what you already have. Those are special locking nuts.

No, not invisible.

 

 

 

You have High Tensile UNC (Unified National Course) bolts fitted which I guess are 3/8".  Yes you should have 10mm Metric Bolts with a tensile rating of at least 8.8 on the top of it.  10.8s would be better.  I use allen key inhex style bolts that are I think 12.3, with new nyloc nuts fitted. Running 165 Hp at the wheels in a track car, but not having any trouble with guibos. I have some aftermarket German brand guibo in mine.

 

AlanM is correct in his ID of the UNC bolt size. Although not ideal, I don't think the use of UNC bolt caused the failure, as the original Guibo that was on the car when I purchased it is still in good nick - aged, but in one piece (and about to do some tempoary service back on the car until I get a new replacement). 

 

I pulled the Guibo off last night.  The split is definitely terminal, went almost all the way through. No brand names or other markings on the guibo. 

 

Everything else looked ok. Nuts were not torqued up as much as I would have liked them, but nor where they loose.

 

The centering bearing in the nose of the driveshaft is ok (I cleaned and regreased it when I replaced the Guibo last time), although the bearing assembly is recessed about 2mm back from the circlip that is meant to hold it in.  I will try and bring it forward, but so far it is pretty firmly wedged towards the back.  Any tips for dissembling the centering bearing would be most welcome!

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