The 340 Prop failure thread

[classicswede]

There has been a number of failed props recently and some of them have even taken out the bellhousing. With the declining numbers of 340's out there I don't think we can afford these breakages.

Now I am certain that the bulk of failure we have seen recently are due to misalignment of the engine/gearbox. This is most likely due to saggy mounts either on the engine or beabox. The other possible is rusted out gearbox support brackets and does need to be considered.

I've made a start on a laser alignment tool for setting up PU engine mounts (thank Chris C for the details on how you made yours) and will be competing it over the holidays. I'm going to make a couple and offer them out on loan. What I did notice with the dead doner prop is that the one end that had failed with the rubber had ripped apart is that the other end was displaying signs of breaking up. The failed end was the engine end.

Years gone by the more common issue was with either the splines shreading or the bond between the rubber cusion part and the alloy tube giving out. The rubbber shreading was quite rare back then.

I'm interested in everyones experiance of failed props we can come up with a long term solution.

Here are some photos of the donor prop of teh end that has signs of slight cracking

[Speedy88]

I only had one go, and the rubber fractured right down the middle, half way between the alloy and the splines.

[Dean]

Mine has done 3 props recently (only one since I've owned it) - The owner before last did a prop and bellhousing with a big clutch kick and the previous owner did his prop in just overtaking a lorry in 5th... But that's with the F7P

I did one with a 2gear clutch kick! Although when mine went - It went on the gearbox end and same as Speedy it just ripped apart right in the middle of the rubber section

I really need to align my engine so there is room for alignment with the mounts to adjust it?

Dai I have 2 bust props here if you want the ends off them to make the tools - Although 2 of the ends are ripped out they are still usable for what you need I guess!

Also - When mine went it also took some of the sirclips out in the bellhousing so the input shaft would move in/out - A bit of a pain when you have to remove the bellhousing to change them...

[Chris_C]

I've made a start on a laser alignment tool for setting up PU engine mounts (thank Chris C for the details on how you made yours) and will be competing it over the holidays. I'm going to make a couple and offer them out on loan.

I've been having a think about this and I wonder if you are chasing symptoms not problems Dai. I made the laser aligner thingy to prove to myself what the problem was, not to solve a problem. I've since seen a number of people make them and try to line the bits up, but a true solution should just align itself as my engine mounts now do. Have you updated your front engine mounts yet? If not, then we are fighting a loosing battle from the start. As the man developing parts, I see it as your role to sell bits that bolt straight on and will automatically align everything. This is how the engine mounts work from the factory, you sit the engine on all four, let gravity pull the engine to the bottom of the slots and nip everything up. It's how my rears work and how I think your system should work. For that to hold I imagine you will need to sell new uprights and rubbers for the rear mounts as a pair.

I'm interested in everyones experiance of failed props we can come up with a long term solution.

I also have a couple of theories on why the splines strip, having now done it myself. It's a bit of a shonky system in my eyes that really needs diagrams to explain, but the green book torque for the clamp bolt is right on the limit for what a high tensile of that size can take according to databooks. That says to me Volvo wanted all the clamping force they could get in that clamp. The green books also state to remove all traces of rust and dirt and coat with a named lubricant, which again says to me they didn't want a bit of crap making the torque wrench go off too early, they truely wanted *all* the force they could get on that clamp.

I did one up with a cleaned but not lubricated bolt, but a slightly dirty clamp and I've done a set of splines. This is where a diagram is useful, but think of how the forces are acting on that splined section on the prop. There are three splits to clamp, so imagine three hinged flaps that move inwards (hold the points of your thumb, 1st and 2nd fingers together to see what I mean). Have a picture to refamiliarise yourself:

All the clamping force of those splines are point loads at the furthest edge, i.e. the spline isn't acting like a true spline. If that isn't tightened up fully, then it just skips as only a small amount of spline is truly engages in a "spline fit". Again, shonky (and the same problem on the 360 setup, but there clamps are kept cleaner as inside the torque tube).

So, for the record, I've broken:
1st propshaft, rubber failure exactly half way between ali and steel tube

1 off bellhousing, which fatigued when a much less worn rubber propshaft was fitted within 6 weeks of fitment. During this letting go, it bananad the sexy propshaft by about 1.6mm, so 2nd propshaft

3rd propshaft, as I was a plonker and didn't understand why the green books stated in the method they do. FITTING PROPS AS PER GREEN BOOK IS ABSOLUTELY CRITICAL seriously, this point cannot be made strongly enough, I'd like to see a new bolt each time and a careful cleaning of the threads (maybe running a tap down? I'm toolroomy enough to know what long term damage this would cause). I'm sure I wouldn't have broken anything else if I'd not done this sillyly

I really need to align my engine so there is room for alignment with the mounts to adjust it?

You shouldn't have to realign it, just a quick check with all new parts that it is aligned. We arn't at that stage yet though, but we are getting there.

Also - When mine went it also took some of the sirclips out in the bellhousing so the input shaft would move in/out - A bit of a pain when you have to remove the bellhousing to change them...

This worries me a lot. You can change the prop without moving the bell housing with everything as it should be, it slides forward and back. I know the circlips you have removed and *really* wouldn't be happy with them not being there. I don't have a tail housing here to check, but memory says those circlips hold the bearings into the tailhousing casting. if they come loose when driving...

Sorry for the long post. The amount of these parts just getting sacrificed (I include myself in this, but I am trying to find causes and solutions too) is not sustainable. Just bolting up new bellhousing and propshafts isn't going to stop it happening again and I really want to see the performance suppliers providing a solution that *just bolts in*. As it stands, I think that will require new front poly mounts, new rear uprights and poly mounts, new gearbox mounts and some clever though in how it bolts together, how much Shore xx rubber flexs when mass of the engine is sat on it etc etc. It's all what I had to think about when making the rear upright jigs for Fake and she *does* just bolt up in the right place on the engine side at least now.

[classicswede]

The PU front mounts are at the correct length and have been for some time now as I've ointed out in a couple of other threads The reason for the setting tool is for checking rather than anything else, and both ends need to be checked as either the gearbox or engine could be out of position. Don't forget that the mounting points are the front are sloted for side to side adjustment.

I've seen far to many threads with "my prop has broken" and then not long after a order coming through for engine mounts to replace to original rubber ones.

The long term plan will be PU engine and gearbox mounts and something in the way of an upgraded prop. As you have mentioned the clamping method has no room for error the way it is and coming up a better answer that will be bolt on is what I've not as yet come up with a solution to that I'm totaly happy with.

When you put your engine mounts in and checked the positioning did you check both gearbox and engine end?

[Chris_C]

The PU front mounts are at the correct length and have been for some time now as I've ointed out in a couple of other threads

Great news on the new front mount, I'd missed that

Don't forget that the mounting points are the front are sloted for side to side adjustment.

Are they? I thought the green book stated to make sure it was slide all the way down all the slots, the slotting only being there for help in getting the stud into the hole.

The long term plan will be PU engine and gearbox mounts and something in the way of an upgraded prop. As you have mentioned the clamping method has no room for error the way it is and coming up a better answer that will be bolt on is what I've not as yet come up with a solution to that I'm totaly happy with.
When you put your engine mounts in and checked the positioning did you check both gearbox and engine end?

Long term plan sounds good. I still worry about the weight of the prop and not being able to change gear quickly due to loading on the input shaft of the box, but that will be a suck it and see thing I think.
Yes, I checked both ends, both statically and (as much as I could) dynamically. My original rubber engine mounts were not far off when the engine wasn't running, but under hard acceleration the engine could move nearly 50mm on those mounts. Gearbox is a harder test (you don't have the same leverage ratios to be able to push it about) but can be done with a 2ft bar

[filthyjohn]

Everything you guys are saying about the alignment and the clamps is true, but the actual design of the prop is at fault too. See the 3 gaps in the splined section of the prop? They allow that steel section of the prop to twist and deform slightly, perhaps even if the clamp is tight enough, but more likely if it's loose! This is the cause of any spline failure, I'm positive. Now obviously this is a problem which 360s share, though they have no alignment issues thanks to the engine being solidly mounted to the gearbox.

Those who know BMX cranks will know that only the cheap ones have a pinch bolt system, the better ones are accurate enough that they're almost an interference fit, with no chance of deformation or play. If you think that's a bad example, calculate the torque a strong rider can put through a pair of cranks, it's more than a car.

The weakness of the rubber can be exacerbated by alignment problems, but you can't ignore the fact that it's a weak design, motivated by the lower cost of avoiding a traditional two piece prop with sliding section and centre bearing. (according to this article: http://www.volvoclub.org.uk/prof_300.shtml )


"The 2.4m wheelbase was the maximum possible before a split prop shaft with intermediate bearings would be needed..."


We need better props with 700/900/BMW style cushioning doughnuts instead of this friction-fitted rubber cack.

[macplaxton]

We need better props with 700/900/BMW style cushioning doughnuts instead of this friction-fitted rubber cack.

Er, doughnuts are cack too. Ask anyone who has had a Hillman Imp.

The 3 gaps aren't an issue if the clamp is correctly tightened. If it's clamped properly I can't see how it deforms. Agree that it'll be knackered in quick order if the thing isn't done up good and proper.

There are plenty of bicycle crank / bottom bracket designs that will go south if they aren't bolted together properly too.

Going back a step, I wonder why they came round to the clamping idea with the MT. All AT props don't have split-clamps, just a tension spring at the rear. I'm also reliably informed that the AT splines are finished differently in the well 'ardness department.

I'm with Chris on the fit it in correct alignment and not dumping the clutch all the time remedy.

Anyway, these things are good for designed purpose. If used outwith there designed intent, it's no surprise they break.

[mac]

Just to point out that the prop design was influenced much more by the need to reduce the mass/inertia loadings on the gearbox during gearshifts (the need for the synchro rings to control the decoupled input mass). On a convential design ie 200/700/900 the synchro system has to handle the rotational mass of the clutch friction plate/input shaft/layshaft (assuming twin shaft arrangement). On a 300 the additional mass of the propshaft has to be controlled - hence the lightest tube and "u/js" possible (within reason and 1970s technology).

Chris talks about "point loadings" on the spline ends (which some may not fully grasp) if you consider the split clamp design it can ONLY generate point loadings as it operates almost as 3 hinged flaps (the hinge being distortion of the inner end of the lands between the spline slots, the distortion being introduced by clamp loadings). The system CANNOT produce a parallel clamping action however much torque is applied to the clamp bolt without deforming the spline lands (which the clamp simply can't do) so we are left with a non parallel spline mating giving point loads. Admittedly we do not see a large number of actual spline failures as compared to rubber failures but a poor clamping is just another issue for us to contend with.

Mac.

[Chris_C]

John, that's a much better way of saying what I was trying to re the 3 splits.

Going back a step, I wonder why they came round to the clamping idea with the MT. All AT props don't have split-clamps, just a tension spring at the rear. I'm also reliably informed that the AT splines are finished differently in the well 'ardness department.

I'm with Chris on the fit it in correct alignment and not dumping the clutch all the time remedy.

First point is super interesting, I've always assumed it's for ease of fitment. A true splined shaft could never be fitted how the green book says fit a prop, you wouldn't get the angle. I need to read the Vario green book now.

Just to point out that the prop design was influenced much more by the need to reduce the mass/inertia loadings on the gearbox during gearshifts (the need for the synchro rings to control the decoupled input mass). On a convential design ie 200/700/900 the synchro system has to handle the rotational mass of the clutch friction plate/input shaft/layshaft (assuming twin shaft arrangement). On a 300 the additional mass of the propshaft has to be controlled - hence the lightest tube and "u/js" possible (within reason and 1970s technology).

Have I spoken to you about this before? It's the theory that myself and a chap who is putting a fair bit of thought into Fake came up with, and why I'm not going the reco prop route. I'm really really happy to hear that you have the same view (I'm guessing based around knowledge rather than working out too?)

Chris talks about "point loadings" on the spline ends (which some may not fully grasp)

Again, a much better way of saying it, ta.

[mac]

We havn't actually discussed this point Chris but your thinking is spot on. (yes my comment are logic/engineering principles but also a fair bit of "factory" rubbed off on me in the "old days")

The other issue is out of balance forces - the g/box input shaft is carried ib a large main ball bearing with the inner end supported (in the main cluster) on a weak needle roller. Apply OOB forces (effectively radial leverage) to the input shaft and you will get rapid wear of the needle rollers and of the input gearset (input/layshaft pair). At the other end you can get rapid fatiguing of the clutch housing tail shaft or failure of the bell housing as well.

The heavier the prop, the worse the problems.

Mac.

[Chris_C]

Myself and other said person came from the side of

"Volvo were making the 100/200 (by the end 700) that used "proper" propshafts. Why, when Volvo added the redblock, didn't they use them"

and came up with the view that the TT is actually a really low inertia prop shaft, with no alignment issues etc etc. It all just seemed to make sense. Hence why I've been squirrelling TT bits for the last 12 months and might have some photos in the near future.

Volvo realised that propshaft couldn't deal with the redblock, which when introduced was 95ish bhp (I think I'm right in saying it was carb first). They spent a *huge* sum of pennies designing and making a new set of parts, the torque tube, to deal with the problem. The thing that surprises me is when the 1.7 was released in '86, with 10bhp less than that first redblock, they knew that it could just about get away with it without causing reliability issues. To me, it's no surprise we are in this situation, Volvo knew it 25+ years ago. Why else did the 300 never get upgraded with the B18KP engine (which was just a B172 with different carb jets and a different cam, making 95bhp for basically free)

[trabitom99]

...the redblock, which when introduced was 95ish bhp (I think I'm right in saying it was carb first)...

... correct, 1981 MY, the injected cars came with the 1983 MY changeover ...

The non-torque-tubed 1979 Oettinger cars with the bored-out B14 were supposed to have had 90 bhp, but with those cars it wasn't the prop which went first. It was the engine ...

Cheers

Tom

[pettaw]

Tbh what we're seeing here is the inevitable consequences of original materials getting old and worn. Engine mounts that are soft and brittle leading to tilting of the engine and gearbox as the mass moves around, coupled together with props with rubber doughnuts in them that have got perished and old because even the youngest and newest ones will probably be over 20 years old Add in an enthusiastic driving style probably not in keeping with what the original concept of the car was and you have the perfect cocktail.

My feeling is that we need to find a way of manufacturing them back to 'factory' spec. If we make a 'heavy duty' prop that isn't light enough or balanced properly, then its going to cause huge wear on the synchro gears of the gearbox. That lovely whining noise you can sometimes hear when you change down from 3rd to 2nd or 1st is the synchro bands accelerating the input shaft, the propshaft and the clutch shaft up to speed. The 2/7/9 can use a much heavier propshaft because it comes from the output of the gearbox, and therefore spins at a slower speed, although it does have to carry a much higher torque.

Someone mentioned the CVT system, that uses an even smaller, thinner prop which isn't clamped on at all, its simply put in place between the two shafts with a spring to keep it roughly in place. Oh and Volvo instructions say to smear 'High-tack' compound on the splines. I did try to find out exactly what that was, but I couldn't. My guess is that its some sort of weak Loctite which takes up some of the spaces in between the splines and I did think about suggesting whether Loctite in the prop splines would be something we could do for the MT props but of course it might make them a bit difficult to remove for servicing

Any custom prop manufacturer would have to understand that the prop spins at engine RPM, and therefore has to be properly balanced and light enough so that its not putting too high an inertial mass onto the input shaft of the gearbox. Otherwise you're making more problems trying to fix something else. Of course that goes hand in hand with making sure that the engine and gearbox mounts are strong enough to take the acceleration forces as the car brakes and accelerates. I don't believe that its the force from the engine that's the problem, it acts on the other axis, but rather the inertial mass lurching backwards and forwards as the car accelerates and decelerates.

Sorry for the long ramble.

[volvodspec]

what was a very big difference in lifespan on my props was changing the engine mounts for solid Delrin pieces (i had NOS OEM one's and that was simply not enough!) and strengthening the subframe; so the engine is mounted solid and can't torque the propshaft into funny angles, 200bhp+ turbo power does break one every now and then but lifespan is much better with those solid mounts

Volvo instructions say to smear 'High-tack' compound on the splines. I did try to find out exactly what that was, but I couldn't. My guess is that its some sort of weak Loctite which takes up some of the spaces in between the splines and I did think about suggesting whether Loctite in the prop splines would be something we could do for the MT props but of course it might make them a bit difficult to remove for servicing

no they aren't joking, Volvo has a special "high tack" grease, this is a thick grease that is very sticky so it won't cover the whole tunnel after the prop has been spinning around at 6000+rpm. it prevents the connection from seizing and acts as a assembly lubricant
they still supply and recommend this grease for numerous things, mainly for mounting splined couplings of fast moving parts