To: Volvo303@yahoogroups.com From: "chribrud" Date: Fri, 09 Oct 2009 09:26:18 -0000 Subject: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com I had my TGB1317 / C304 on periodical control yesterday. To make it possible to meassure the brakes on the rear axles, I had dismounted the drive axle between them. When leaving home, the car speed 'jumped', as if there was something wrong with the clutch. Later on, at least when driving home, I experienced that I lost a lot of power when using high RPM when starting. Thus I had to use moderate RPM when using 1st and 2nd gear. So it seams as the rear axles are not 100% bound to each others as I thought, because then I should not have experienced any differences. Can anyone explain this? A consequence is that lifting the rearmost axle to get shorter turning radius, the rearmost wheels might turn faster than the wheels on ground. Christian To: Volvo303@yahoogroups.com From: "Willem-Jan Markerink" Date: Fri, 09 Oct 2009 23:39:19 +0200 Subject: Re: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com On 9 Oct 2009 at 9:26, chribrud wrote: > I had my TGB1317 / C304 on periodical control yesterday. > To make it possible to meassure the brakes on the rear axles, I had > dismounted the drive axle between them. When leaving home, the car speed > 'jumped', as if there was something wrong with the clutch. Later on, at > least when driving home, I experienced that I lost a lot of power when > using high RPM when starting. Thus I had to use moderate RPM when using 1st > and 2nd gear. So it seams as the rear axles are not 100% bound to each > others as I thought, because then I should not have experienced any > differences. Can anyone explain this? A consequence is that lifting the > rearmost axle to get shorter turning radius, the rearmost wheels might turn > faster than the wheels on ground. Not sure what your exact scenario/configuration was, but if all this was indeed with the 'inter-axle' shaft removed[*], and on not so grippy roads, then my first guess is that you simply experienced wheel spin, especially in corners (where the wheels see induced/forced slip (sideways, but stiction is higher than friction, so once there is slip (regardless of direction), lateral slip/wheel-spin becomes much easier too)) (I have a theory that this phenomena even makes driving in corners with FWD engaged, on grippy roads, much easier with a 6x6 than with a 4x4, because of this forced wheel slip....once the 4 rear wheels slip a bit, it is much easier to spin them a bit more, to get rid of induced drivetrain binding) (once, after removal of engine & gearbox on mine, I drove nearly 1000km with mis-configured electrical connectors, T-case locked all the time....even without powersteering at that time, I could hardly notice it....only when I had to turn very tight corners in a garage, on smooth concrete, I realized that the tires were squealing a bit *to* much....deafening....:)) [*] BTW, which f*cking country on this planet requires you to dismantle a perfect working vehicle for a brake-test?....don't tell me they spend hours dismantling bigger trucks that way too....and how on earth do they think to do the same with a Pinzgauer 6x6, or Tatra 6x6/8x8/10x10? BTW2: what did you do with your automatic engaging front wheel drive, during hard braking, on that same roller bank? Note that this is *very* bad for your T-case/dog-clutch, locking at speed, while the shafts are not in sync. *Never* allow them to do that, so roller banks are out of the question anyway (unless they have a 2-3 axle roller bank of course (which even for trucks they don't have, AFAIK; 2 axle is max)) -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand [note: 'a-one' & 'en-el'!] To: Volvo303@yahoogroups.com From: Teppo Rapo Date: Sat, 10 Oct 2009 07:18:59 +0300 (EEST) Subject: Re: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com Willem-Jan Markerink kirjoitti 10.10.2009 kello 00:39: > > [*] BTW, which f*cking country on this planet requires you to dismantle a > perfect working vehicle for a brake-test?....don't tell me they spend > hours dismantling bigger trucks that way too....and how on earth do they > think to do the same with a Pinzgauer 6x6, or Tatra 6x6/8x8/10x10? > > BTW2: what did you do with your automatic engaging front wheel drive, > during hard braking, on that same roller bank? > Note that this is *very* bad for your T-case/dog-clutch, locking at speed, > while the shafts are not in sync. > *Never* allow them to do that, so roller banks are out of the question > anyway (unless they have a 2-3 axle roller bank of course (which even for > trucks they don't have, AFAIK; 2 axle is max)) Here, at least on station that I used to take my car into, the brake test is performed simply on the paved area with slight layer of sand on it, simple and effective. In norhtern part of finland during this summer, one station wanted to put the 6x6 on brake dyno despite all the warnings from the owner and ended up with a huge "ratteling and bang" from transfer box when brake pressure cut the solenoid line and it tried to engage and finally did. Nothing was broken though.. luckilly. -teppo Teppo Rapo +358 40 5508394 Ahkiomaantie 7 FI-96300 Rovaniemi To: Volvo303@yahoogroups.com From: Christian Brudevoll Date: Sat, 10 Oct 2009 09:13:31 +0200 Subject: Re: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com 2009/10/9 Willem-Jan Markerink > > > On 9 Oct 2009 at 9:26, chribrud wrote: > > > I had my TGB1317 / C304 on periodical control yesterday. > > To make it possible to meassure the brakes on the rear axles, I had > > dismounted the drive axle between them. When leaving home, the car speed > > 'jumped', as if there was something wrong with the clutch. Later on, at > > least when driving home, I experienced that I lost a lot of power when > > using high RPM when starting. Thus I had to use moderate RPM when using 1st > > and 2nd gear. So it seams as the rear axles are not 100% bound to each > > others as I thought, because then I should not have experienced any > > differences. Can anyone explain this? A consequence is that lifting the > > rearmost axle to get shorter turning radius, the rearmost wheels might turn > > faster than the wheels on ground. > > Not sure what your exact scenario/configuration was, but if all this was > indeed with the 'inter-axle' shaft removed[*], and on not so grippy roads, > then my first guess is that you simply experienced wheel spin, especially > in corners (where the wheels see induced/forced slip (sideways, but > stiction is higher than friction, so once there is slip (regardless of > direction), lateral slip/wheel-spin becomes much easier too)) > (I have a theory that this phenomena even makes driving in corners with > FWD engaged, on grippy roads, much easier with a 6x6 than with a 4x4, > because of this forced wheel slip....once the 4 rear wheels slip a bit, it > is much easier to spin them a bit more, to get rid of induced drivetrain > binding) > (once, after removal of engine & gearbox on mine, I drove nearly 1000km > with mis-configured electrical connectors, T-case locked all the > time....even without powersteering at that time, I could hardly notice > it....only when I had to turn very tight corners in a garage, on smooth > concrete, I realized that the tires were squealing a bit *to* > much....deafening....:)) > > [*] BTW, which f*cking country on this planet requires you to dismantle a > perfect working vehicle for a brake-test?....don't tell me they spend > hours dismantling bigger trucks that way too....and how on earth do they > think to do the same with a Pinzgauer 6x6, or Tatra 6x6/8x8/10x10? > > BTW2: what did you do with your automatic engaging front wheel drive, > during hard braking, on that same roller bank? > Note that this is *very* bad for your T-case/dog-clutch, locking at speed, > while the shafts are not in sync. > *Never* allow them to do that, so roller banks are out of the question > anyway (unless they have a 2-3 axle roller bank of course (which even for > trucks they don't have, AFAIK; 2 axle is max)) The surface was wet asphalt. My problem occurred only when accelerating right ahead. When cornering it was just slippy enough to make turning the wheel easier (like a weak servo). I think the best explanation is that one of my rear wheels were spinning, since the powered axle had only 2/7 of the vehicles weight. And since there was three wheels around it not spinning, there was no sideways gliding like on a normal four-wheel car. But I had never thought that my lazy B30 was strong enough to make the car spinning. Christian To: Volvo303@yahoogroups.com From: "Willem-Jan Markerink" Date: Sat, 10 Oct 2009 09:47:57 +0200 Subject: Re: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com On 10 Oct 2009 at 9:13, Christian Brudevoll wrote: > The surface was wet asphalt. > My problem occurred only when accelerating right ahead. > When cornering it was just slippy enough to make turning the wheel easier > (like a weak servo). > I think the best explanation is that one of my rear wheels were spinning, > since the powered axle had only 2/7 of the vehicles weight. And since there > was three wheels around it not spinning, there was no sideways gliding like > on a normal four-wheel car. > But I had never thought that my lazy B30 was strong enough to make the car > spinning. There *might* be some dynamic's involved with the axle itself, being that the front axle wants to lift up when powered, while the rear axle (when powered separately, theoretically) would want to push down.... Hmm....are those longitudinal rods not sloped down a bit, towards the axle? The middle axle is virtually pulling the vehicle by those rods (not by the spring), and if these rods are sloped downwards, it means that the axle pulls itself not just forward, but also upwards.... Btw, you *could* power the rear wheels only, to test this theory, but it requires a very even & smooth road surface: if you remove the wheels from the middle axle, the drums will still not touch the ground, hanging on the metal straps....but the margin is not very large, only advisable in emergency situations....8-)) -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand [note: 'a-one' & 'en-el'!] To: From: "John Allen" Date: Sat, 10 Oct 2009 19:34:26 +1000 Subject: RE: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com From: Volvo303@yahoogroups.com [mailto:Volvo303@yahoogroups.com] On Behalf Of Willem-Jan Markerink Sent: Saturday, 10 October 2009 5:48 PM > There *might* be some dynamic's involved with the axle itself, being that > the front axle wants to lift up when powered, while the rear axle (when > powered separately, theoretically) would want to push down.... > > Hmm....are those longitudinal rods not sloped down a bit, towards the > axle? > The middle axle is virtually pulling the vehicle by those rods (not by the > spring), and if these rods are sloped downwards, it means that the axle > pulls itself not just forward, but also upwards.... > > Btw, you *could* power the rear wheels only, to test this theory, but it > requires a very even & smooth road surface: if you remove the wheels from > the middle axle, the drums will still not touch the ground, hanging on the > metal straps....but the margin is not very large, only advisable in > emergency situations....8-)) Perhaps a broken drive axel shaft / striped splines giving one wheel drive - the difflock on the driving axel would probably need to be stuck on for this scenario to be plausible. Easy enough to check Just a thought Kind regards John Allen To: Volvo303@yahoogroups.com From: "Willem-Jan Markerink" Date: Sat, 10 Oct 2009 20:03:44 +0200 Subject: RE: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com On 10 Oct 2009 at 19:34, John Allen wrote: > Perhaps a broken drive axel shaft / striped splines giving one wheel drive - > the difflock on the driving axel would probably need to be stuck on for this > scenario to be plausible. Easy enough to check > > > > Just a thought > Another, perhaps even more exotic theory: Are 'offset' diff's[*] not also intended to compensate the dynamic/rotational forces, that create lift-up on one side/wheel, and push- down on the other side/wheel, when acellerating? (only valid with live/beam axles of course, not with independent suspension (where the diff-forces are neutralized towards the frame)) [*] out-of-center, in our case to the right (middle axle)) At first I thought 'okay, if this offset is intended, and the offset- direction in Volvo's is the same as in other vehicles, then why doesn't it compensate/neutralize as well?'....then I realized that our axles operate completely the other way around, because of the portal gearing....simply put: *somewhere* in the drive-train, the direction of rotation must be reversed, and turn both diff and half shafts in the other direction, because of the secondary reversal in the portal gearing. And the easiest way to do that is by flipping the diff itself upside-down (but not without also changing the direction/orientation/geometry of the gear teeth, between pinion and ring gear!), and keep the cardan/driveshaft rotation-direction standard, as any other 4x4 (I don't think there is much choice here, if a vehicle manufacturer wants to use somewhat standardized gearboxes!....otherwise, somewhere down the line, they would have to add another gear, to reverse the rotation-direction inside any of the boxes (or even make the engine turn the other way around....but I don't even dare to think about the confusion that might cause for the non-informed, when working on the engine....a true nightmare....:)) (normally, in a parttime 4wd with identical diff's front and rear, the front diff is powered in 'reverse', compared to the rear (cardan shafts rotating in same direction)....while the teeth geometry (also the metallurgy/teeth-side-hardening) is only optimal in one direction....such vehicles should therefore not be changed/modified to fulltime 4wd)) (it is probably also the reason why Toyota changed from 9.5" diff's both front and rear on J6 and J7 (parttime) to 8" high-pinion diff's on J8 and later (fulltime)) (high-pinion diff's are stronger in one direction (forward), but weaker in the other (in one direction the teeth 'clench' towards eachother, in the other direction they push eachother apart, bending the pinion away from the ringgear) So, where in a normal, non-portal, vehicle the offset *would* compensate/neutralize the diff-rotational forces; in our Volvo it works competely the other way around, reinforcing the 'dynamic wheel-load' inbalance....therefor significantly increasing the chance of slip. Short: diff-offset in Volvo's is based on ordinary 4x4's & their direction of diff-rotation, while our diff's rotate in reverse, thereby also reversing those dynamic/rotational forces.... Feel free to shoot at my theory, or launch even more exotic theories....:)) Willem (thinks he just created yet another chapter/file for his web- archive, adding to a long list of Volvo items/topic....:)) Jan -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand [note: 'a-one' & 'en-el'!] To: Volvo303@yahoogroups.com From: Ian Woodward Date: Mon, 12 Oct 2009 02:05:32 -0700 (PDT) Subject: RE: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com --- On Sun, 11/10/09, Willem-Jan Markerink wrote: From: Willem-Jan Markerink Received: Sunday, 11 October, 2009, 5:03 AM > Another, perhaps even more exotic theory: > > Are 'offset' diff's[*] not also intended to compensate the > dynamic/rotational forces, that create lift-up on one side/wheel, and push- > down on the other side/wheel, when acellerating? > (only valid with live/beam axles of course, not with independent > suspension (where the diff-forces are neutralized towards the frame)) > > [*] out-of-center, in our case to the right (middle axle)) > > At first I thought 'okay, if this offset is intended, and the offset- > direction in Volvo's is the same as in other vehicles, then why doesn't it > compensate/neutralize as well?'....then I realized that our axles operate > completely the other way around, because of the portal gearing....simply > put: *somewhere* in the drive-train, the direction of rotation must be > reversed, and turn both diff and half shafts in the other direction, > because of the secondary reversal in the portal gearing. > > And the easiest way to do that is by flipping the diff itself upside-down > (but not without also changing the direction/orientation/geometry of the > gear teeth, between pinion and ring gear!), and keep the cardan/driveshaft > rotation-direction standard, as any other 4x4 (I don't think there is much > choice here, if a vehicle manufacturer wants to use somewhat standardized > gearboxes!....otherwise, somewhere down the line, they would have to add > another gear, to reverse the rotation-direction inside any of the boxes > (or even make the engine turn the other way around....but I don't even > dare to think about the confusion that might cause for the non-informed, > when working on the engine....a true nightmare....:)) > > (normally, in a parttime 4wd with identical diff's front and rear, the > front diff is powered in 'reverse', compared to the rear (cardan shafts > rotating in same direction)....while the teeth geometry (also the > metallurgy/teeth-side-hardening) is only optimal in one direction....such > vehicles should therefore not be changed/modified to fulltime 4wd)) > (it is probably also the reason why Toyota changed from 9.5" diff's both > front and rear on J6 and J7 (parttime) to 8" high-pinion diff's on J8 and > later (fulltime)) > (high-pinion diff's are stronger in one direction (forward), but weaker in > the other (in one direction the teeth 'clench' towards eachother, in the > other direction they push eachother apart, bending the pinion away from > the ringgear) > > So, where in a normal, non-portal, vehicle the offset *would* > compensate/neutralize the diff-rotational forces; in our Volvo it works > competely the other way around, reinforcing the 'dynamic wheel-load' > inbalance....therefor significantly increasing the chance of slip. > > Short: diff-offset in Volvo's is based on ordinary 4x4's & their direction > of diff-rotation, while our diff's rotate in reverse, thereby also > reversing those dynamic/rotational forces.... > > Feel free to shoot at my theory, or launch even more exotic > theories....:)) > > > Willem (thinks he just created yet another chapter/file for his web- > archive, adding to a long list of Volvo items/topic....:)) Jan I have removed the rear propshaft on my 6x6 son only the front axle is driven. It is amazing how little grip I have.=A0 I need to engage FWD just to get up a slight gravel drive, and on wet tarmac in 1st and 2nd (and 3rd sometimes!) it takes just the slightest application of throttle and the wheels spin. It's very smooth though.=A0 No jumping at all. Ian. To: Volvo303@yahoogroups.com From: "Willem-Jan Markerink" Date: Mon, 12 Oct 2009 12:29:03 +0200 Subject: RE: [Volvo303] Surprising boggie characteristics Reply-To: Volvo303@yahoogroups.com On 12 Oct 2009 at 2:05, Ian Woodward wrote: > I have removed the rear propshaft on my 6x6 son only the front axle is > driven.=A0 It is amazing how little grip I have.=A0 I need to engage FWD just > to get up a slight gravel drive, and on wet tarmac in 1st and 2nd (and 3rd > sometimes!) it takes just the slightest application of throttle and the > wheels spin.=A0 It's very smooth though.=A0 No jumping at all. Ian. That is probably because only one wheel is spinning....try locking the rear axle(s), and see if it still spins so easily (probably not, especially if my theory about rotational-forces is correct), and *if* it spins, whether it is still smooth (probably not). -- Bye, Willem-Jan Markerink The desire to understand=20 is sometimes far less intelligent than the inability to understand [note: 'a-one' & 'en-el'!]