Propshaft bolts strength

[Maggie13]

The propshaft and driveshaft bolts are very expensive. They could end up £35 to £40 for 12 bolts an inch long. Are they a special strength? They are 5/16 ones. A m8 bolt would be a lot cheaper and is a better fit.

[Clive]

I would stick to inperial. But they are only high tensile bolts. Are they only an inch long? 

But I have always reused the old bolts, just fitting new nylocs. 

(And I have found 20x 5/16unf bolts, 1 1/4" long for just under £7 of fleabay)

[RobPearce]

Where did you find them "very expensive"? As Clive says, they're standard HT bolts taken from the factory's standard bolts part bin. M8 would probably work but are not as good a thread so the torque setting would be wrong. Stick with the UNF but get them from a nut and bolt shop, not a rip-off "classic car parts specialist".

[Maggie13]

I have some bolts in poor condition. They are stamped with a V. But I can't find out how strong that is. Minus the head the bolt measures 7/8, with the head 1, 1/8. I'd be afraid of it shearing and the shaft coming through the floor.

[Maggie13]

39 minutes ago, RobPearce said:

Where did you find them "very expensive"? As Clive says, they're standard HT bolts taken from the factory's standard bolts part bin. M8 would probably work but are not as good a thread so the torque setting would be wrong. Stick with the UNF but get them from a nut and bolt shop, not a rip-off "classic car parts specialist".

It was rip off classic car part specialist i was pricing them from.

[Maggie13]

Is it not also hard to get them not threaded the whole way because the bolts are so short.

[yorkshire_spam]

Propshaft bolts are about a pound each from places like Canleys/Paddocks

(+vat + postage)

[JumpingFrog]

1 hour ago, Maggie13 said:

I have some bolts in poor condition. They are stamped with a V. But I can't find out how strong that is. Minus the head the bolt measures 7/8, with the head 1, 1/8. I'd be afraid of it shearing and the shaft coming through the floor.

Informed guess here, but I believe imperial strength goes R, S, T, V, X and these roughly correspond to 8.8, 9.8, 10.9 and 12.9. X is certainly very hard and only used in special places (brake calipers). I believe R/S is roughly 8.8: https://www.namrick.co.uk/acatalog/Kev-s_Blog.html

I'm not convinced the new bolts supplied will be as strong as the originals, as a few years ago I was replacing the UJs on my car and decided to change the bolts, two of the bolts stretched while torquing them up, something I never experienced with the originals. I found some better originals and fitted those instead. The replacements I was supplied (from a classic car parts supplier), had 3 dash marks on the head, which I believe would correspond to metric 8.8. My originals were also marked 'V' grade.

The small 5/16 bolts need to be done up pretty tight relative to their size (at least in the case of driveshafts) or they quickly come loose and distort the flange and make the holes oval, so whatever is used needs to be decent. The later change to 3/8 bolts don't seem to suffer as badly, and you can buy decent 3/8 bolts cheaply from Land Rover specialists.

Edited December 30, 2022 by JumpingFrog

[Clive]

My subaru diff uses M8 bolts, which do seem small for what wpuld be a 300+bhp car. I couldn't locate genuine new bolts, but found used ones at over £30 a set! So I popped to Namricks, and bought cap (allen) head bolts, rated at 12.9. I had to buy them too long so the unthreaded shank went beyond the flange joint, and cut a bit off the threads. I torqued them up to the max M8 torque setting I could find. A similar approach may suit you? 

[drofgum]

Hi,

In the case of bolts Triumph used that have Triumph six digit part numbers there is something special about them. Stock hardware bolts had part numbers designating their size both length and diameter with a prefix that told what particular type of bolt they were. HB and BH seem to have been used interchangeably for hex head bolts. In the case of the driveshaft bolts both the smaller and the larger ones have Triumph part numbers. The smaller being 129361. the larger being 132023.

I understand that the unthreaded shank of those bolts was sized to act as a locating dowel might,  holding the flanges aligned rotationally, preventing slip that would have worn the holes oval.

Clive,

In the case of the Subaru you need to remember the full power doesn't go through either differential unit. It gets split between them , though the greater part may go through either unit. I find the diameters of the driveshafts on many moderns look small when compared to the Spitfire driveshafts.

Kind Regards,

Paul