Diff Mounting and Knocking

[William2]

I have a knocking sound coming from the rear of the car when going over uneven ground so I thought I would check the diff mounting. Everything seemed ok but I only have a clearance between the front of the diff and the lower chassis of about 50 thou. Is that enough? I have taken a photo to show how I have assembled the upper diff mounts with the sprint strengthening angle bracket and also an 1/8" thick penny washer. Is that how it should be or are you supposed not to fit the washer?

[Hawksfield]

William

You don't fit the big washer if you fit the stiffing bracket, See the manual if you have one

[elanner]

William (and Hawksfield),

According to the manual, section R.7, the brace plus one of the thick washers is correct. That's how I installed mine (3 times, no less!). The manual also states that "it is possible that no washers will be necessary."

Do you mean 50 thou under the aluminium diff carrier/case, or under the nose of the diff, below the pinion bearing?

There's not much clearance under the carrier. I've just eyeballed mine and 50 thou sounds about right. There's no room for a finger, but perhaps a couple of matchsticks. The carrier has enough clearance that it's definitely not going to foul the chassis unless one of the Frustacones fails.

Under the nose of the diff there's a big gap to the chassis. Eyeballing mine looks like 3/8"-1/2". If the nose is too low doesn't that suggest something wrong with the torque rods?

Nick

[William2]

Hi Nick and John, thanks for your replies. The 50 thou gap I have is at the lowest point of the diff where the alloy carrier and cast iron diff housing join. At the very rear of the diff under the alloy housing I have about 1/4" clearance. I am going to check that the tie rods are correctly assembled regarding the washers, etc. It sounds like I could remove the large washer if necessary. Regards, William.

[William2]

Just removed the tie bars and found that I hadn't fitted the cup washers either side of the diff mounts!! Silly boy. Maybe that will raise the diff a little.

[Hawksfield]

William

The clearance you have at the closest point to the chassis I feel is too close (0.050") my clearance is nowhere near as close as that I will measure mine and let you know. Just got down and dirty I have one large washer And I can get a 8mm drill just through the space. My lowest point is as you say at the joint between the diff and the carrier.

You need to check your alignments or your clearance
Good luck

[William2]

John, I currently have the Sprint stiffening brace on my car plus one thick washer. I wonder if I should do what the manual suggests and remove the washer which will then give me at least an 1/8" of clearance. I have noticed that the stiffening bar won't spread the load on the rubber mounts as effectively as having washers due to it's narrower width. Has anyone else gone ahead and removed said washer?? As a point of interest I couldn't see any torque figure for the upper diff mounts in the manual.

[Hawksfield]

William

I have new diff mounts fitted from PM and tightened by hand with a standard ring spanner, I have found different mounting inserts in the past, see my post post269640.html#p269640. The diff only hangs on the mountings and the torque rods check fore and aft movement, rotation controlled by top mounts
I have found that the mountings can change the height. check out yours.
There is no torque setting in the manual that I can see.

Another check to make is the state of the chassis tray below the diff this can get deformed and close up the gap if damaged.

[rgh0]

My Elan just has the stiffening bracket and no large washers. Been that way for 30 years without a problem and the diff gets a hammering with lots of drop the clutch starts. Clearance under the diff would be about 4 mm.

cheers
Rohan

[ElanDNA]

I have a knocking sound coming from the rear of the car when going over uneven ground so I thought I would check the diff mounting. Everything seemed ok but I only have a clearance between the front of the diff and the lower chassis of about 50 thou. Is that enough? I have taken a photo to show how I have assembled the upper diff mounts with the sprint strengthening angle bracket and also an 1/8" thick penny washer. Is that how it should be or are you supposed not to fit the washer?

Hi
Do it like me and you have silence.
The Lip-seal from the gearbox say to you "thank you" too
Urs

[rgh0]

The Frustacons that the diff hangs on have a inner steel tube the centre bolt goes through that sets the height the diff hangs at versus the mount and chassis when the diff bolt and washers are tightened up and the rubber is compressed. These tubes appear to vary in length with the new replacement units. Previously someone posted three different lengths they has found in various frustacons and I checked and found 2 different lengths in the ones I had.

You may need to trim this steel tube to get the clearance you want if you want to use a diff brace and at least one large washer.

cheers
Rohan

[tedtaylor]

Here's my Sprint with stiffening bracket and NO washers (as per shop manual).

[William2]

Followed all your helpful advice and removed the single large washer either side. Have now got about 5mm diff clearance. Will go out for a road test when the rain stops!

[elanner]

Just to correct my earlier error - so much for me being able to eyeball 50 thou. Not a chance!

I was under my Elan yesterday to change the diff oil and decided to measure the gap. Well, my entire feeler gauge set of 100 thou slipped under the diff easily, with plenty of space to spare. I couldn't find anything else to measure it with so would now estimate 1/8" or so. This with one washer and stiffening bracket.

Nick

[661]

Plenty of room with a high back chassis!

Not very useful, apologies, but a shameless excuse to post some pictures.