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MG MGB Technical - BGT front Springs.
|Just a quickie: '73 BGT back on the road after 6 years faffing about with incompetent painter; everything spick and span and lovely to drive again - BUT - she wallows a bit at the front end. I'll be checking the coil springs for free length at the weekend and comparing them with the table on Paul's website; and as recommended in the archives I'll free the shocker arms and see how they feel for resistance.|
Question is: would it be more likely to be tired coil-springs or tired shock absorbers that create the wallowing front end? I'm sure others have been here before me.
BTW, the front rideheight is 14.25" each side and rear is 15". I use the elongated shackles at the back, and would like to put in front coils that bring the height down half an inch. Thanks for any advice. John.
|J P Hall|
|Wallowing just sounds like un, or under damping. Technically the springs ARE the shock absorbers, the dampers control compression and rebound of the springs. Make sure the dampers are topped up and not leaking. You can get a good idea of how well the dampers are working by compressing the spring (push lean or sit on a wing) then take the weight off. The spring should return to height without any "bounce" Where are you measuring the ride height?|
What Allen said about the dampers (front & back) would be good for starters. I had a similar situation a few years back (a wobble at speed) that I also thought originated in the front of the car, and eventually traced it to the tightness of rear spring assembly in the shackle pins and U-bolts. Worth a look mate.
|Larry C '74 B/GT|
|I think you could expect a small amount of over-rebound when taking the weight off, then settling back to its static position.|
It depends if by 'wallowing' John means roll in the corners (normal, judging by the attached publicity photo ...), or a) having to continually correct the steering over undulations or b) when using the throttle. a) can be caused by one dead damper (I'm with the springs being the shock absorbers too), b) by loose U-bolts and rear axle steering as Larry indicates.
|Interesting - I hadn't thought about the rear set-up possibly causing (or contributing to) wallowing at the front. By "wallowing" I mean a soft rise-and-fall of the front end, not side-to-side.|
So I'll also look at the rear end in case anything is loose. The rear has good quality tubular shocks.
Allan I measure ride height from centre of wheel to bottom edge of the side strips.And yes, I put a small dent in one side-strip when putting on new ones!
I'll report back after weekend investigation.Thanks all ... John.
|J P Hall|
|Just a reminder. Topping off shocks does not mean filling them all the way to the rim. There needs to be an air gap to allow for expansion.|
|"expect a small amount of over-rebound when taking the weight off, then settling back to its static position"|
was the standard (UK) method of test for MOT
|Update: the free length of the (yellow) coils is 24.5cms; the shock absorbers give good resistance by hand for the full length of travel when going down, but there is a difference on the upstroke: about 1 inch of travel is not damped, then the dampening effect kicks in for the remainder of the upstroke.This is the case whether the arms are pushed from the bottom-most position, or whether I start mid-travel and push them up to the top.|
So does it sound like lack of fluid or maybe deterioration of fluid? I'm thinking take the shockers off, drain and refill to specification and see if the undamped portion of travel goes away. Any comments gratefully received. Regards, John.
|J P Hall|
|John, Worth a try, especially if you can hear it "squishing" on the 1" "lost motion". If you are going to re-fill, use motorcycle fork oil, SEA 20. It's synthetic and much more heat stable. The down stroke is the rebound, the up is the compression, 1 " of travel without damping represents quite a proportion of a dampers normal travel on reasonable surfaces, hence the "wallowing".|
|If the 1" lost motion occurs wherever the arm changes direction (as seems to be the caae) then the dampers are faulty, and as Allan says will definitely be contributing to 'wallowing'|
|John, thinking about it again, if that 1" of travel is the "normal' range of movement, then that would be the most worn area of the piston/cylinder. Maybe they are just worn out.|
|Looks like a really good result after the weekend's fettling:|
Remove shock absorbers, drain, flush and fill - both now operate without any free play. No leaking. New top link bushes.
Replaced 24.5cm coil springs with 23cm, stiffer rated (500lb) springs.
New sway-bar bushes and drop-links.
Replace old-skool spring-pan bushes with V8 style. A bugger to press in, but worth it.
"While I'm at it" : new brake pads and brake hoses.
The front end (without any road testing yet) now sits at 13 7/8", which is about where I wanted it. Road testing will settle it a bit, and probably feel firmer with the different springs and new bushes.
Thanks all for your comments to my original post. I love this BBS! regards, John.
|J P Hall|
Thanks for the follow-up on this as sometimes we never find out if, or when an issue gets sorted. It's been twenty-five years since I re-worked the suspension on our B/GT, and your post (almost) makes me want to delve into in and install the nylon bush kit I bought to do an upgrade a while back. Almost ;-)
PS; I used dish soap to install my V8 style bushes.
|Larry C '74 B/GT|
|When you built the car did you wait until the front nsuspension was fully loaded before you tightened the nuts retaining the wishbores?|
|R J Marshall|
|Laz - I hear you brother; yes, I use Fairy Liquid with good results normally - those V8 bushes are just a pig to press in. I have new spring-pan arms coming, which should be easier to work with.|
RJM, quite right - previous owner didn't, but I definitely did keep the wishbones loose until she settled on full weight. Thanks for the reminder!
I will say that the shorter and stiffer springs have made the world of difference to the way the car "sits" at the front - no wallowing at all, and nice and firm but not harsh on the corners. I'm of the school that is quite happy with the lever-arm shock absorbers, as long as they are working properly.
|J P Hall|
|Nothing at all wrong with Armstrongs, but they do work better, not withstanding wear issues that is, with synthetic fork oil rather than the original mineral oil. Less viscosity variation with temperature and temperature rises with use. |
Washing up liquid contains salt so I avoid using it, preferring baby shampoo or pure soap.
|FWIW the WSM only advises mineral oil when the correct fluid is not available, and then only 20W, and even then NOT for low-temperature operation. I've always used hydraulic jack fluid and never noticed any issues with variability. Some recommend motor cycle fork oil as it's said to contain a seal-swelling agent.|
|Paul the "drop off" in damping was quite pronounced, both on the 1800 and the V8 on my regular trips to Lancashire until I put Synthetic fork oil in. But the 1800 has now departed and the V8 is on Hoyle.|
This thread was discussed between 27/10/2016 and 11/11/2016
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