Herald Differential

[all mod cons]

Has anyone taken a differential apart?

I've been replacing the UV joins on my 1965 Herald 1200. At the same time I decided to change the diff as mine was very noisy when in first and reverse gears.

I sourced a reconditioned diff for this model (I was told) before I took the diff off my Herald - and now that I have them side by side on the garage floor I can see a difference in the shape of the front mounting plate.  

I've attached a couple of photos.  The dirty one (from my car) has a straight mounting plate. The recon one (green) has a bent mounting plate on one side.

So, my question is - am I being too simplistic by thinking that I can just take the mounting plate off my diff and fit it on to the new one? The Haynes book shows one oil seal at this end. Have any of you guys had experience in this area? Any advice before I have a go - or do you reckon I need another complete diff?

        

[Deleted User]

The mounting plate should be straight, like your old diff, not bent like the new one.

Looking at the pictures, you have another problem as well.

The new diff is for a car fitted with a swing spring (MKIV Spit or late MKIII GT6) and not for a car with a fixed spring - it has 4 holes for studs, not six like on your old diff.

It also looks like the input flange is the larger version, so will not mate with your propshaft unless you change the end of the propshaft.

[Nick Jones]

Kevin is right.  Top one is a herald diff. 4.11:1 ratio and 'small' flanges.  Also has 6 bolts to hold the fixed spring in place.

Bottom one is a Spitfire Mk4 or 1500 (or possibly GT6) diff so ratio could be 3.89:1, 3.63:1 or (unlikely) 3.27:1.  It will have the larger flanges and does only have 4 bolts to hold the spring on as it is from a swing spring car.

None of these things is a show stopper and it is possible to modify to fit - BUT you may find it easier to source the correct diff.  

Another question - you say it's noisy in 1st and reverse - are you sure it's the diff?  Any noises they make are usually apparent at higher speeds whereas the Herald gearbox has straight cut 1st and reverse gears which are noisy by design.... maybe that your diff is ok in any case?

Nick

[heraldcoupe]

I would also be concerned about the bent front plate. The damage most likely happened when the diff was dropped, there aren;t many other possibilities fot that kind of damage to have occurred.
If the input flange took any of the impact, that loading will be transmitted directly to the internals of the diff.
Cheers,
Bill.

[all mod cons]

Thanks for identifying the new diff Kevin, Nick and Bill.

So I've got the wrong one. Also, from what you've said, even if it is a Spit or GT6 unit, the front plate is still not correct and had been bent into that shape. I kind of assumed that there may be some cars where the mountings are in those positions. Obviously not then.
It must have been a hell of a drop to bend it that much.

I was considering having a go at modifying it to fit - but I guess it would be better to keep hunting for the right one and trying to sell the new one on to a Spitfire owner.

Nick - I suspected the noises were from the diff as when I moved off in first or reverse, the back end appeared to be really noisy. It didn't sound like the gearbox, but I suppose the noise could have been transmitted to sound like it was at the back.
For this reason and the fact that my diff looked like it was leaking oil (out the top or so it seems as the spring was covered with oil at the point where it sits on the diff), plus the fact that I needed to do the UV joints, - I decided to change the diff at the same time.

If you are correct - in that it could be a noisy first and reverse gear - then maybe I'll clean up my old diff and put it back on - then have a look at the gearbox. Any thoughts on why the diff would lose oil from that hole in the top (shown in the picture... the one under  the spring)?
    

[Richard B]

That hole is the breather for the diff. Maybe the unit has been over filled?

[herald948]

all_mod_cons wrote:

Any thoughts on why the diff would lose oil from that hole in the top (shown in the picture... the one under  the spring)?
    

These can "lose" oil from lots of places from something as simple as a plugged vent. It's rather more visible in the photo of the clean diff with the bent mount; it's nothing more than a hole (upper left in the photo) with a cotter pin stuck in it. The pin is supposed to move about just enough to keep the vent clear, but the diffs can get pretty crusted up with grime. I've done nothing more than scrape that caked grime away from the vent and have virtually eliminated leaks from several diffs!

[Nick Jones]

Difficult to identify noises on a forum with sound or vid clips.....  As I said before, the Herald has straight cut gears on first and reverse and these will always be noisier than the other gears (more like the reverse noise on most other cars).
If the noise shuts up as soon as you stick it in second, it's not the diff.
In my experience, diffs that sound bad at low speed sound much worse when you speed up!

As a rough condition check on your old one;  do all shafts turn smoothly and freely?  Graunching, roughness or tight spots are not good news.  If you hold both output shafts still, how much rotational freeplay (backlash) do you have when rotating the input flange?  A few degress is normal, 1/4 turn is not a great sign....  Do any of the shafts, especially the input shaft have any sideways movement or axial movement?  A hint is usually ok (although a sign of wear) but any more is not a great sign either.

As to oil leaks, well, it's a piece of old Triumph.  It has to leak, it's in its contract.. :P.  But seriously, it probably means the breather is blocked.  This is a simple jiggle pin located under 35 years accumulation of crud on the right rear mounting eye and when blocked it allows the diff casing to pressurise as it warms up and pushes oil out wherever, including up the threads of the spring mounting studs, which is, I think, where the oil you are referring to has come from.

Cheers

Nick

[all mod cons]

I'm learning a lot in such a short time from you guys...

Right, decision made. I'll clean up the old diff, ensuing the breather pin hole is free, change the oil and put it back on.

In response to your points Nick, the noise stops immediately I select second gear.
I've just been out to the garage to check the diff and held the two output shafts rigid. There is then only a tiny amount of play on the input shaft, 2-3mm movement maxmimum. They all turn freely with no grindng or rought spots and no sideways movement.
The oil was coming out of the hole you see in the picture I think. The one that Andy says is the vent.

[Deleted User]

heraldcoupe wrote:

I would also be concerned about the bent front plate. The damage most likely happened when the diff was dropped, there aren;t many other possibilities fot that kind of damage to have occurred.
If the input flange took any of the impact, that loading will be transmitted directly to the internals of the diff.
Cheers,
Bill.

A sideswipe into the rear quarter of the original car could do it....

Personally, I'd run a mile from any chassis component that looked like that.