Driveshaft bolts - Alfa Romeo Bulletin Board & Forums
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post #1 of 41 (permalink) Old 06-19-2016, 08:09 PM Thread Starter
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Driveshaft bolts

Hello Alfisti,
I had a clanking noise coming from the rear end of the car. It was happening while disengaging clutch on low speed. I checked under the car and found out it was a rear U-joint. Removed the driveshaft and replaced the U-joints. FYI U-joints from ebspares which I bought couple years ago were 24x63.3mm with 1.5mm thick circlips and would not fit. Centerline's 24x63.1mm with 1.25mm circlips (Made in Italy on them) worked on a first try. As I was getting ready to paint the driveshaft I noticed that the M8x25 bolts that came with the car were tap bolts, not shoulder bolts and only class 8.8 (SAE 8; Grade 5). Looks like new 8mm bolts are NLA from Alfa suppliers. Do you think these Class 10.9 bolts are ok to use if the shoulder length is correct or should I look for some used ones from Alfa?
$8.40 - M8 X 1.25 X 25 Metric Hex Bolt / Cap Screw 10.9 Qty (20) [MCS825CFZ109] : NutsandBolts.com
Thanks ahead for your help
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Zaza

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post #2 of 41 (permalink) Old 06-19-2016, 08:41 PM
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Do you think these Class 10.9 bolts are ok to use if the shoulder length is correct or should I look for some used ones from Alfa?
I would think that hardware from nutsandbolts.com would be OK. But I don't love the ones shown in the link you posted. Two issues:

- The shoulder seems too short / threads too long. I think you will need to buy longer bolts (with longer shoulders) and cut them down.

- From memory, the stock bolts were 8 x 1.0, not 8 x 1.5. If fine threaded bolts are available, I would go with those.

Jay Mackro
San Juan Capistrano, CA

'65 Guilia Sprint GT
'67 Duetto
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post #3 of 41 (permalink) Old 06-19-2016, 08:43 PM
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What car/driveshaft is this? Up to 1750, it's 8mm x 1.0. 2000 uses 9mm in the driveshaft. What size are the bolt holes?

Andrew
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post #4 of 41 (permalink) Old 06-19-2016, 09:39 PM Thread Starter
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Originally Posted by Alfajay View Post
I would think that hardware from nutsandbolts.com would be OK. But I don't love the ones shown in the link you posted. Two issues:

- The shoulder seems too short / threads too long. I think you will need to buy longer bolts (with longer shoulders) and cut them down.

- From memory, the stock bolts were 8 x 1.0, not 8 x 1.5. If fine threaded bolts are available, I would go with those.
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What car/driveshaft is this? Up to 1750, it's 8mm x 1.0. 2000 uses 9mm in the driveshaft. What size are the bolt holes?

Andrew
Jay, Andrew thanks for the reply

Jay you probably meant 1.25 not 1.5. The pic of the bolt on nutsandbolts.com website seems to be a same generic for all sizes, I'll ask them what's the shoulder length on 25mm ones are. I measured flange thickness and they are roughly 6mm (wrong, see post 13 below) , so 2 of them together will need 12mm shoulder. What is the shortest shoulder lengh that I can use on these, 10mm ?

The driveshaft is for 1750 (8mm bolts) and did think it would need 1.0 fine threaded bolts, but can't find any with shoulders in 25mm length.

Zaza

Current Alfas:

2018 Stelvio Ti Sport
1987 Milano Verde
1970 Euro-spec GTV 1750

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post #5 of 41 (permalink) Old 06-19-2016, 09:50 PM Thread Starter
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Here is a pic of finished driveshaft. Hope it performs as well as it looks, fingers crossed
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Zaza

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2018 Stelvio Ti Sport
1987 Milano Verde
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post #6 of 41 (permalink) Old 06-20-2016, 12:31 AM Thread Starter
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Doing U-joints for the first time and now this makes me nervous, please bear with me.
So can I just get M8 bolt with taller than 25mm shoulder and have machine shop thread it down and cut it or does this have to be a cold rolled/formed type thread?

Zaza

Current Alfas:

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post #7 of 41 (permalink) Old 06-20-2016, 05:52 AM
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These bolts are not only clamping the two flanges together, they are also locating them. Good engineering practice is to locate them with tight fitting pins so that they cannot rotate with respect to each other. The hard shouldered bolt used by Alfa is a compromise. Most bolts are designed for clamping only and are more likely to shear. Having recently sheared a set of flywheel bolts, I would definitely buy the correct ones if you can find them. They must be very hard, have correct length shoulders and be a close fit in the holes.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #8 of 41 (permalink) Old 06-20-2016, 06:05 AM
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I have taken cars apart with every kind of hardware under the sun; proper bolts, American bolts, hardware-store grade, stainless, 8mm bolt in 9mm hole, lock nuts, no lock nuts, no lock washers, you name it. Some have had drivehshaft wobbles, some have not. Ideally you will use the right bolts with shoulders. My practical experience is, however, if the shaft is straight, balanced, and has good u-joints, it won't matter that much. I have never had a bolt break, and rarely even find them loose. Note that design of the flange has a circular internal step, so that's doing a lot of the locating and there's not much wiggle room at the bolt holes.

So yes, best you can do is best. But practically, I've never had a problem with the bolts, regardless of what I or previous owners used. I save the 9mm bolts, have a stash of them.

Andrew
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post #9 of 41 (permalink) Old 06-20-2016, 06:22 AM
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The probability of shearing the bolts may be low but the consequences could be serious. RISK = PROBABILITY * CONSEQUENCE
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #10 of 41 (permalink) Old 06-20-2016, 06:48 AM
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Quote:
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Jay you probably meant 1.25 not 1.5. The pic of the bolt on nutsandbolts.com website seems to be a same generic for all sizes, I'll ask them what's the shoulder length on 25mm ones are.
Nakagtv:

Yes, I should have typed "1.25".

You're right, most sites like nutsandbolts.com just use generic photos for all bolt lengths. But my point still holds: generic bolts have a ratio of threaded/shoulder length that will result in too short a shoulder for this application. So if you are using generic hardware, to get a long enough shoulder, you will need to buy a bolt that is too long, and cut off the excess threaded portion.

Quote:
Originally Posted by alfaparticle
These bolts are not only clamping the two flanges together, they are also locating them. Good engineering practice is to locate them with tight fitting pins so that they cannot rotate with respect to each other. The hard shouldered bolt used by Alfa is a compromise.
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Originally Posted by Andrew
Note that design of the flange has a circular internal step, so that's doing a lot of the locating and there's not much wiggle room at the bolt holes.
A good discussion!

Andrew is correct - the driveshaft flange is located radially by those flanges. The driveshaft and differential flanges fit together tightly - often when I remove the four bolts, I need the help of a mallet to get the parts to separate.

But alfaparticle has a point too - the bolts locate the two flanges rotationally. The bolts' clamping force should be high enough that friction doesn't allow them to twist relative to one another. But ideally, the bolts would fit tightly enough to prevent any relative rotation. In practice, Alfa's design conforms to industry practice.

As Andrew points out, failures in this area are rare. But as alfaparticle points out, if your front flange did fail, allowing the shaft to whip, the result could be serious.

Jay Mackro
San Juan Capistrano, CA

'65 Guilia Sprint GT
'67 Duetto
'91 164L

Last edited by Alfajay; 06-20-2016 at 10:43 AM.
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post #11 of 41 (permalink) Old 06-20-2016, 08:04 AM
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What is the shortest shoulder lengh that I can use on these, 10mm ?
8 to 10 mm is good. The root of the thread is the weakest part of the bolt and it is better if it is not at the flange joint.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #12 of 41 (permalink) Old 06-20-2016, 03:33 PM
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If you want to make sure its right, call Larry at APE. I'm sure he would the proper bolts on hand.
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post #13 of 41 (permalink) Old 06-21-2016, 09:20 AM Thread Starter
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Was away from PC, just read through all this great information. Thanks everyone for sharing, very interesting points...
After reading all the posts it's clear that original bolts are the way to go, I'll call Larry. For the sake of completeness and in case Larry ever runs out of bolts and nuts I'd like to add few points and more questions. Just trying to understand what goes into proper fastener selection, torque wrench use and thread locking on critical applications like these. I'm at the point on my mechanical restoration where I started jetting carbs, adjusting valve lashes, aligning suspension, engine driveline, correcting mistakes (some mines and others') etc and this is all very helpful.

Ed, I hope you did not get hurt Do you know what caused flywheel bolts to shear (besides the extra power and high rpms)? This is 4th time I'm reading about something like that, scary. Did this happened on your spider, what kind of damage did this cause?


First a Correction!!! I assumed that all 4 yokes were the same 6mm thickness...WRONG!
Yokes on the rear driveshaft are 6mm, yokes on the back of the front driveshaft and on the differential are around 7.5mm thick (My previous post edited) I will measure the shoulder length on Alfa bolts when I get them and will post.

Meanwhile, per Alfajay's suggestion I found some M8 zinc coated bolts at local machine shop. These are class 10.9 with longer than 25mm shoulders/shanks and they can cut and thread them 1.0. (will need replating or some vaseline after assembly to protect from corrosion) Bolts have flange heads and nuts are normal hex (same 10.9).

-I noticed a taper on the edge of the shoulder on most of the bolts that I looked at. It's where the thread begins, how important is to have this taper?

-What do you all think about the possibility of a metal fatigue/ microscopic cracks on these 40 old bolts?

-Torque spec that I found online for M8x1.0 dry threads is 28-30 ft/lb (correct?), so this is pretty close to Alfa's shop manual's torque specs (25.3-28.9 ft/lb).

-I'm planning on using split lock washer and adding medium strength blue thread locker after testing for vibration. Loosening one nut at a time and applying it.

- Great point about properly locating and aligning holes. Now that I think about it, as I was taking out 5/16-18 bolts they felt bit loose in there but dragged on something and was difficult to remove. Maybe holes vere misaligned...During the suspension rebuilt driveshaft was disconnected from the differential and put back together by a "Reputable" shop, the same one that assured me my U-joints were all good. Hmmm

I thinks this is all, for now...

Zaza

Current Alfas:

2018 Stelvio Ti Sport
1987 Milano Verde
1970 Euro-spec GTV 1750

Refreshing 1750 GTV
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post #14 of 41 (permalink) Old 06-21-2016, 09:42 AM
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If you cannot find the correct 8mm bolts then it may be possible to drill your flange holes to 9mm and use the more common 2L bolts. I can lend you a 9mm bolt if you want to compare it with your other options.

My flywheel bolts probably backed out a little enabling a differential shear torque when I got on and off the gas. They sheared on a 7000 rpm up-shift. To be fair to Alfa, the car was not designed for that, but the flywheel attachment to the crankshaft is not a good design. The shoulders of the bolts are a loose fit in the flywheel holes. The crankshaft has provision for one long shoulder bolt to pin the parts but they did not use that bolt. The clutch pressure plate is attached to the flywheel properly. Maybe Sachs had something to do with that.
I have also sheared a set of bolts on a Milano half shaft. Those bolts are such a devil to get out that I did not locktite them. My mistake.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #15 of 41 (permalink) Old 06-21-2016, 10:35 AM Thread Starter
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Thanks for the offer, but converting to 9mm holes will probably involve removing U-joints and differential yoke which I rather avoid. Sorry to hear about your incident. Did they use tab washers? Locktite?

Zaza

Current Alfas:

2018 Stelvio Ti Sport
1987 Milano Verde
1970 Euro-spec GTV 1750

Refreshing 1750 GTV
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