Q. There is a dimension listed in the MkIV workshop manual for the curve in the rear suspension leaf springs. My question is how much clearance does this give between the axle housing and the bump stop mounted on the chassis?
I recently replaced the rear leaf springs on a MkIV and the axle housing practically sitting on the bottom bump stops. Not an issue if you have rear seat passengers but hits the bump stops hard, on rebound, if only the driver is in the car.
Can anyone see how much clearance they have on their car with no occupants.
Regards, Graham
Hello Graham - just curious, are your shock absorbers working (correctly filled) ? I am thinking this may be the problem, since with passenger weight okay, but no weight, springs rebounding travel greatly increased if no shock control - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 10/15/2020 1808hrs. EDT USA.
You can expect the axle casing to sit quite firmly on the rebound stops. This is normal.
Peter
Thanks for that. Regarding the shock absorbers yes they are functioning correctly. More restriction as the shock link travels up (chassis moving downward) but I wonder if just a slightly more viscous grade of fluid would help slow the rebound.
Regards.
Hi Graham,
Here are a few pics of my car - only about 5 to 10 mm between axle casing and bump stop. Original car 60000 miles. I don’t have any bumping with or without passengers.
Cheers
Darryl
Excellent. Thanks for taking the time to send those. Regards, Graham
Jordy’s IPhone
I have nothing but a gap of about an inch there on my '38 SS.
But apparently I am supposed to have something called a 3302 Buffer.
Now in British slang I might be called a buffer, but anyway they apparently fell out long ago.
But I am surprised that there should be no gap at all. Surely it must be felt when the axle rebounds after hitting a large bump.
Perhaps this is one reason why the Mark V was considered so much better for ride quality, not being underslung here like the previous models.
The rebound stop is a big fat rectangular block of rubber bonded to a brass strip that is bolted to the chassis. If you don’t have them then the axle will hit the chassis with a very solid thump when you go over a big bump.
Peter
Ok Peter, thanks for the picture. I guess I haven’t hit any big bumps yet.
I see a flat strip of steel, not brass, on each side, held on by the same 4 bolts that hold the check strap loop above. I guess the rubber blocks must have been on those strips.
Your chassis number falls into the third group so I suppose you have Buffer 48835 with clip plate, apparently slightly different.
The rubber blocks for my check straps are also gone, so it looks like a good winter project is shaping up.
There may be a mistake in the 2-1/2 Litre Parts Catalogue regarding the chassis numbers using the 38532 Buffer.
I checked the 3-1/2 SPC and the chassis number groups do not overlap.
So I suspect the 2-1/2 chassis numbers for the 38532 buffer should run from 40448 to 40858 and 46061 to 46136.
This sort of typesetting mistake occurs quite frequently in the XK120 SPC, so it is well to be aware of the possibility of informational mistakes here as well.
I found one of the rubber blocks from my check strap in a box of loose parts that came with the car, so at least I know what it looks like.
Does it really matter? There are earlier two part buffers and later one part but they do the same thing and to be honest I don’t thing the axle should ever be touching them unless you plan on doing the Peking to Paris Rally.
Quite so, Peter. I suspect these are two stages of improvement in the original design, and the latest is probably superior, although it doesn’t say “supersedes” so there may be a difference in the way they fit. There was some corresponding change in the chassis frame at the same point as the change from the second to the third buffer, relating to the change of shock absorbers.
Hi Rob, I was surprised that you hadn’t experienced the axle crashing onto the chassis. I wonder if your rear springs need lubricated? Although rather messy I have a tool for separating spring leaves and injecting grease. The combination of more compliant springs and good working dampers did improve the ride and handling in my car.
Peter
Now that’s a clever tool I hadn’t seen before. I suppose the wedge tips swivel; they would have to as you crank the screw in.
I oiled my springs, there is a 1" gap without the missing rubber buffers, and I’ve only driven suburban streets with no potholes. 