Prop shaft / diff flange bolts

[Nigel Riches]

My prop shaft / diff flange bolts are showing signs of wear on the threaded portion, aligned with the diff flange.

 

Mr. Caterham's build manual states to torque these very important bolts to 25 lbs/ft, which also includes the torque required to overcome the friction of the Nyloc nut, I suppose, so the actual bolt torque is comparably lower.

 

The manuals I use at work say to torque a "locking nut" tighten until one turn from closed, measure torque required to overcome nut friction and add this to the required tightening torque of the nut.

 

From a bit of digging on the 'web, it seems a grade 8 bolt, such as these, should be torqued to 47lbs/ft dry, ( for pre-tensioned and slip critical joints) so do I tighten to Mr. Caterham's direction, or to the figure given in the tables available for general nut and bolt tightening, ie 47lbs/ft + friction torque.

 

The bolts I was supplied by the pond life at the nut and bolt purveyors are actually set screws, (in UK parlance),and also only grade 5, so will be going back for round two tomorrow.

 

Happy Daze. Nigel

[Jonathan Kay]

I'd do it the way the manual says with the parts as supplied by Caterham.

 

There's an enormous literature on correct settings for the different types of threaded fastenings, but I'm not sure why you are considering doing something different in an area that you've already described as "important"...

 

Jonathan

[2GBR]

Consider using the correct Ford sierra bolts from a Ford dealer may be available still or a classic Ford site or via e-bay they have a blue locking compound on them and can be used several times before the blue compound wears away

[Nigel Riches]

Jonathon thanks for your post.

 

My concern is the fact that these bolts are showing signs of being damaged by having the tops of the threads worn away by movement in the holes in the diff flange, indicating that the "clamping force"of the bolts isn't sufficient to over come the loading from the prop shaft to the differential, and thus there is some small degree of movement under load.

 

This is my point, these are important bolts, certainly don't want a prop-shaft failure whilst giving it some beans , OK there would be some indication of impending doom of it, associated noise and drive line vibration.

 

But 25lbs/ft (inc friction in nut) against 47lbs/ft dry with plain nut, seems like a large discrepancy.

 

Tomorrow I shall take some of these nuts and bolts to work, and carry out a few checks to try and find out what torque is required to achieve 47lbs/ft against 25lbs/ft, using new Nyloc nuts.

[Nigel Riches]

2GBR.

 

Those Sierra bolts, are they 3/8 UNF, or was the Sierra a Metric motor?

 

And what torque are they pulled to in the Sierra? And I suspect they would thread into the opposite flange, ie, no nuts ☹️

 

Nigel.

[elie boone]

Do them up 1/4 before they snap 😬 I never torque those bolts, but I always check them after a test run to see if they are still tight. And yes Sierra is Metric, M 10 x 1 from memory

[Bricol]

I must admit I'm slightly confused as to why you're using a spring rate to try to torque tighten bolts

 

😬

 

My Caterham manual, circa 2001, suggests 42 lbft for the prop to diff flange bolts, with threadlock, but as you say, into a tapped flange.

 

Bri

[Nigel Riches]

I can see this could be another techie bog.

 

From other pages I've viewed it shows the bolts shank passing through both components of the joint, the thread being purely for the nut to pull both together, so if one part of the joint is only supported by tops of the threaded part of the bolt, it stands to reason the lateral loading will be higher, but may be satisfactory if a higher compression force is exerted by being torqued too 47lbs/ft + friction.

 

Not sure about, where are those Engineers who were here a while ago?

 

Nigel.

[Nigel Riches]

Bricol.

 

My car is an elderly 1982 edition, and the Caterham build manual I have from c. soaking wet, states 25lbs/ft, which is probably what I followed when I undertook a major refurb in 1997, and used the original bolts.

 

My point here is to understand why the bolts show damaged threads when torqued to the recommended torque, ( torque wrench is cal checked at work).

 

It seems to me there is movement between the two flanges, the thread damage is not circumferential, only at two diametrically opposite points, so the diff flange is moving, relative to the prop flange.

 

OK time to hit the sack, look forward to more digging tomorrow. Thanks.

 

Nigel.

 

Edited by - nigelriches on 22 Jul 2014 11:13:48

[2GBR]

If we are talking about a sierra diff here with the correct ford drive flange with as mentioned M10x1mm pitch female threads fitted with the correct as mentioned ford blue bolts And these are showing signs of wear on the thread/shank then these must have been loose for a while so need replacing and possibly the flange as well if the female threads are now worn as you wont keep these tight. No need for nylocks on rear of flange unless a last ditch measure to combat worn threads in flange.

I have never managed to get in there with a torque wrench so i remove grease nipple hard steel round dowel through the yoke and rest against chassis rail, good quality ring spanner on nut and pull down rotating around the four bolts as you do so

[Wrightpayne]

as the Sierra only started production itself in 1982 I doubt it will be one of its diffs!

 

More likely live axle.

 

 

Ian

 

[2GBR]

Thanks for that Ian, i was barking up the wrong tree well and truly Sounds like diff flange could do with a couple of locating/drive dowels fitting to take the loading of the bolts

[Jonathan Kay]

I'm confused: is either flange threaded and where was the damage to the bolts?

 

Jonathan

[elie boone]

The English axle has no tread in the flange, what u could do is to take a longer bold and cut the tread on the bolt to the desired length so that there is no tread in the flange hole.

If the tread shows damage then yes there must have been some movement, I also find it very difficult to use a torque wrench on the diff bolts as the space is too tight for a socket. You would need an open spanner on the torque wrench but then your torque setting is not correct any more. That is why I do them up as hard as I can within reason.

I have to agree some years ago there where more engineers on Blat chat and more live axles too

[Nigel Riches]

It's an Ital axle, there are no threads in either flanges, so I will probably follow Elie's advice and tighten F.T. 😳, with new nyloc nuts.

 

Johnathon. The damage on the bolt is at the threaded part, there is a short plain shank section which passes through the prop shaft flange, then the threaded part, this is where the damage is. The tops of the threads show signs of being flattens where they pass through the diff flange, hope this clarifies things for you.

 

Thank you for your replies one and all, most appreciated.

 

Regards, Nigel.

[Jonathan Kay]

Thanks

 

Jonathan