Bouncy Rear-End

Discuss other problems here.

Moderator: Moderators

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Bouncy Rear-End

Postby Monty-4 » Thu May 26, 2016 12:01 pm

Oooer!

The rear-end of my Morris has developed a habit of bouncing up and down - noticeable at low speed. My first thought is that it might be related to me finishing the renewal of the suspension setup - it had new standard leaf springs last year and I've refreshed the damper oil with SAE40 more recently.

I've had a look and it doesn't look like anything has rusted out so I don't think it's the axle twisting - could it be that SAE40 is a bit too much? The rear-end is pretty stiff and I can hear the contents of my toolbox rattling around when going over potholes now!
68' 4-door Saloon, another 'Monty'.

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Thu May 26, 2016 1:36 pm

No! The SAE 40 is perfect - assuming you didn't use 10W40 which is hopeless. I assume also the car is not sitting on the bump stops at the rear? You can cut 1" off the stops which greatly improves the suspension travel and compliance. Did you load up the suspension before tightening all the fixings? Perhaps try loosening them - driving around - then retightening -again with the suspension loaded - ie a trolley jack under the rear axle lifting the wheels off the ground. The bouncing is more likely to be coming from the clutch or perhaps knackered engine or gearbox mountings. Is the wire restraint in place (and 'not quite' tight) on the gearbox cross member - and is the engine steady bar ok ?
ImageImage
Image

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Thu May 26, 2016 2:02 pm

The car isn't on the stops and the rear is sitting quite high. Definitely SE40 and the front-end is great.

I didn't load up the suspension when doing the springs last year. Which fixing should I loosen (slightly I'm guessing)? The spring front and rear hangers and also the nuts around the U bolts?

Will also check the gearbox mounts tonight!

Thanks bmc!
68' 4-door Saloon, another 'Monty'.

oliver90owner
Minor Addict
Posts: 528
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Bouncy Rear-End

Postby oliver90owner » Thu May 26, 2016 2:41 pm

Harshness of the suspension depends on the oil viscosity in the dampers and their condition, amongst others.

The trouble with SAE viscosity is that it is measured at elevated temperatures ( ie hot oil).

10W in the designator means it acts like SAE10 at cool temps. This means the viscosity rating at cold for straight SAE oils is something different. That means your oil viscosity at ambient temperatures might depend on its supplier. Less-worn dampers may be better served with 30 weight - and your rears may be less worn than your fronts.

Tighening suspension bushes while the axle is in the mid point of travel is important, too, but I would be trying thinner oil as you state this was the last change you made.

RAB

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Thu May 26, 2016 5:16 pm

The dampers will be fine -the suspension is just 'tight' - the dampers only 'damp' - the springs determine the harshness. I assume it's on 5 leaves - or did you fit 7 leaf springs? And poly bushes ??Did you grease them when fitting?
ImageImage
Image

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Thu May 26, 2016 7:11 pm

Just 5 springs with rubber bushes that already look a little knackered. I don't recall if I used grease so probably not.

First point of action may be to redo the bushes with grease AND tighten under load.
68' 4-door Saloon, another 'Monty'.

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Thu May 26, 2016 10:40 pm

No grease with rubber - but 'white' grease is often used with poly, although I don't see why ordinary lithium / moly grease shouldn't be used.
ImageImage
Image

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Sat May 28, 2016 6:10 pm

Loosened the nuts and then re-tightened with the axle jacked up and I'd say the back-end feels a little more relaxed now. The gearbox steady looked okay - could do with being a little tighter perhaps as there is a noticeable curve?

New clutch and a bottom-end rebuild (running out of adjustment and <20psi hot idle) are both on *the list* but will have to wait until car #2 is back on the road!
68' 4-door Saloon, another 'Monty'.

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Sat May 28, 2016 7:35 pm

The wee cable sounds about right - problems can arise if it's done up tight.
ImageImage
Image

john newton
Minor Friendly
Posts: 48
Joined: Sun Dec 08, 2013 3:05 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby john newton » Tue May 31, 2016 3:45 pm

how was suspension before topping up? are units dodgy re,cons or somehow heavy duty ? if they are too stiff it will be like on solid suspension and will bounce over a chalk mark, re john

john newton
Minor Friendly
Posts: 48
Joined: Sun Dec 08, 2013 3:05 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby john newton » Tue May 31, 2016 3:51 pm

another quick one. i fitted new bump stops and new springs from a well known supplier.. the car sat lower and bump stops hammered chassis even over small bumps . bought second hand stops and springs, sorted, re john

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Tue May 31, 2016 5:35 pm

Dampers are original and don't appear to leak, new leaves were from well known supplier in east of England. It's not sitting on the stops - far from it in fact, the car has a forward lean.

It does still feel a bit stiff and skittery at the back. Tyres are Toyo 155 radials and I've tried 28, 30 and 32psi.
68' 4-door Saloon, another 'Monty'.

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Tue May 31, 2016 9:26 pm

Suspect the tyres if they are on 3" wide wheels!
ImageImage
Image

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Tue May 31, 2016 9:59 pm

I gather they'd be 3.5" as standard 1968 saloon wheels, could be wrong of course. The tyres seemed fine when I had suspension as soft as a downy pillow - would they only manifest their true trampoline-like nature once the suspension has become stiffer?
68' 4-door Saloon, another 'Monty'.

panky
Minor Legend
Posts: 1545
Joined: Wed Aug 20, 2014 4:12 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby panky » Tue May 31, 2016 10:16 pm

Just throwing something into the ring here, and I suspect it might sound daft, but are the new springs the same length as the old ones? could it be that the shackles have flattened out against the under body and have 'locked'.
Image

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Wed Jun 01, 2016 7:28 pm

Wheels are only 3" I'm afraid - with 6" wide tyres on them ....well outside any 'fitting chart' recommendation. However - perhaps with that make they would be better at a lower pressure - stand by for the jelly wobble effect....
ImageImage
Image

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Wed Jun 08, 2016 7:57 pm

Best balance seems to be ~32psi front and rear. Anything below and it feels like driving on blancmange.

Can't afford a set of 145s right now, or wider wheels I suppose, so I'm stuck bouncing for a while unless somebody wants to swap!

[frame]Image[/frame]
68' 4-door Saloon, another 'Monty'.

ManyMinors
Minor Legend
Posts: 1060
Joined: Tue Nov 11, 2014 9:41 am
MMOC Member: No

Re: Bouncy Rear-End

Postby ManyMinors » Wed Jun 08, 2016 9:26 pm

bmcecosse wrote:Wheels are only 3" I'm afraid - with 6" wide tyres on them ....well outside any 'fitting chart' recommendation.
That is rather simplistic and misleading isn't it. If recommended wheel & tyres sizes were that straightforward then the original recommended tyre sizes for the Minor would have been 3.00x14 crossply or 075x14 radial rather than 5.20x14 and 145x14.
As it is, a 155x14 is just 10mm wider than the recommended size is it not? Not so vastly oversize, and fitted to a good proportion of Minors on the roads. The Toyo does have a rather soft sidewall and when I had them on my own MInor the general handling of the car was not as good as with some other makes. I currently have 155x14 Nankangs fitted which are inexpensive and a decent improvement. I did not experience "bouncing" particularly and since all that has been changed on this car is the suspension, then i would suggest that is where the problem lies. Different tyres can alter the road behavior of a car of course but the tyres have not been changed have they? I do slightly prefer the drive of my other Minor which is fitted with 145x14 Bridgestone tyres but there is really little in it and the Bridgestones are quite a bit more expensive.

Monty-4
Minor Fan
Posts: 288
Joined: Sun Oct 26, 2014 7:17 pm
MMOC Member: Yes

Re: Bouncy Rear-End

Postby Monty-4 » Wed Jun 08, 2016 10:08 pm

Interesting.

Could it be that stiffening of the suspension has led to the sloppy characteristics of the tyre becoming more apparent? Makes sense to me.

That said I still have to get under the car and check the gearbox mounts. Last and most unpleasant check saved 'till last...
68' 4-door Saloon, another 'Monty'.

bmcecosse
Minor Maniac
Posts: 46561
Joined: Wed Feb 16, 2005 11:24 pm
MMOC Member: No

Re: Bouncy Rear-End

Postby bmcecosse » Thu Jun 09, 2016 1:00 pm

The original tyres were 5.00 X 14 crossplies - not even ideal then , but seemed to be what was acceptable back in the day. Then 5.20 became the norm. When radials came along much more attention was focused on tyre/rim widths. I suppose the nearest radial would be a 125 X14 (Citroen 2CV had 125 x 15 radials) or 135 I suppose. But not many about - and I think for 'trailer' use only. Look at any tyre/rim chart these days - and nowhere does it ever suggest a relationship of anything like 6" tyre on 3" rim.... Wider/better wheels are the answer... They are also 'money in the bank' because the value will never go down!
ImageImage
Image


Who is online

Users browsing this forum: No registered users and 1 guest