Replacing the differential

[DieselSpider]

Just having a similar issue were the diff was getting progressively noisier and has since failed. I decided to swap out the third member and am keeping the old one as a back up (repairing it later). I purchased mine from autoricambi and had it shipped to Aus. While replacing it I will be swapping out the rear wheel bearings as well as I don't know how long ago they were done. Will also be going from 4.3 to 3.9 as one of the PO's has swapped the diff and axial to to earlier model spider at some point. Will be good to get a better Highway run with less RPM's and better economy.

How complete was the unit? Plug and play or are there additional parts/setup required? I see some specifying that they are "Complete: Headspaced and shimmed, 3.90 ring and pinion with the bearings installed". Was a new third member to axle housing gasket included?

Vics has it for $40 than AR more however if its more completely setup then its worth it.



Mine is pinging and more than likely a 4.30 which is not that great with the Diesel as that originally was in a car with a 3.38 so I am hoping that going to a 3.90 will be a more livable compromise.

[Squidders]

Whilst it hasn't been installed as yet. However I believe its a straight swap out for the existing one I have. The gasket was extra and only $4.30. Send Csaba a message I am sure he can confirm it.

[vandor]

Yes, it's complete, ready to bolt in. One only needs a gasket.

[DieselSpider]

Yes, it's complete, ready to bolt in. One only needs a gasket.

When will it become available again since its currently shown as on back order?

Looking over the number below do you feel that the change from the 4.30 to the 3.90 will make a reasonable difference? Since they are on back order is it possible to get one with a ratio closer to the original 3.36 or with the larger diameter tires on the Spider should I stick with the 3.90?

The 4FB1 Diesel Engine and MSG5t Transmission came from a Chevette with a curb weight of 2293 lbs which ran on P155/80 R 13 tires and had a 3.36 final drive ratio. The engine naturally aspirated put out 51 hp and 72 ft-lb or torque however I have no idea what it now generates with the turbo charger on it. Fuel economy is higher than EPA estimates for the Chevette at about 40 mpg in the city if I behave and 35 mpg driving a bit more aggressively.

The transmission ratios are listed as:
I - 3.76 (12.63)
II - 2.18 (7.32)
III - 1.36 (4.57)
IV - 1 (3.36)
V - 0.86 (2.89)
R - 3.76

Speed range (max speed on gears, top gear value theor.) however with the current I believe 4:30 third member mph appear to be limited to around 2/3 whats listed below:
(km/h/mph)
I: 48 / 30
II: 83 / 52
III: 132 / 82
IV: 180 / 112
V: 209 / 130

These numbers were from:
http://www.automobile-catalog.com/auta_perf1.php

[vandor]

> When will it become available again since its currently shown as on back order?

Less than a month, with any luck.

>Looking over the number below do you feel that the change from the 4.30 to the 3.90 will make a reasonable difference?

It's a ~10% difference, you have to judge for yourself if that is enough of a change to make it worth while.

> is it possible to get one with a ratio closer to the original 3.36

I'm not aware of new gears being available with anything longer than 3.90:1. If you want something longer you may
consider the 3.58 ratio (used rear end) from an automatic Spider.
If the Spider has smaller diameter tires then they will make it seem like the rear end ratio is shorter (numerically higher).

[DieselSpider]

The current diff is rattling, chattering and pinging so it needs servicing one way or another.

[Exit98]

ASLives,

You don't say where you hail from. If it's East coast/West coast there maybe a group around.

When my 76 rear gave up the ghost (4.10) I got a later (3.90) from one of the NJ guy's parts car. Sure it was a crap shoot but the rears tend to be pretty stout and the price was right. I'm no mechanic but with some good help it was a simple swap and I was off and running. Still going good 5 years later.

See Brad's post above for the details and other parts needed, none if its a like for like. Even if you don't want to do it yourself if you can find a used unit a willing local mechanic could have it done in a couple hours.

Good lluck.

[Squidders]

Now having had the diff in a couple of days and just driving locally so far. There is a difference in the rev range for the spider which is noticable and first gear seems to get a higher speed due to the lower revs and only a minor acceleration drop. With the previous 4.3 ratio diff in the car, first gear would rev out and need changing in my mind way too soon,. I haven't tried the freeway yet to see what rev range might be at 80, 90, 100, 110+. My guess is it will cruise at close to around 2700 - 3100, instead of 3100 to 3600 RPM in the mentioned speed ranges.

The car feels much easier to drive which is a combination of a new diff and the 3.9 Ratio.

[wubie317]

Yes, it's complete, ready to bolt in. One only needs a gasket.

The diff on my '77 needs replacing too. So, if I purchase this and have limited mechanic skill/space is the process that simple? Or is there much more to it than I should get myself into?

[vandor]

> I haven't tried the freeway yet to see what rev range might be

Remember, that unless you replace the speedometer drive and gear in the transmission, the speedometer will be off. On most SPiders it is ~5% fast, but with this rear end it will be ~5% slow! It you will be going at a higher speed than indicated.
There are free apps for smartphones for GPS based speedometer, I use them to check speedometer accuracy.

[vandor]

> So, if I purchase this and have limited mechanic skill/space is the process that simple?

The only difficult part is getting the large circlips out that hold the axles in place. One needs a small to meadim 45 degree needle nose pliers and a small flatblade screwdriver. Compress the circlip with the pliers and work the opposite side out with the screwdriver.

[DieselSpider]

> So, if I purchase this and have limited mechanic skill/space is the process that simple?

The only difficult part is getting the large circlips out that hold the axles in place. One needs a small to meadim 45 degree needle nose pliers and a small flatblade screwdriver. Compress the circlip with the pliers and work the opposite side out with the screwdriver.

I hadn't looked that closely at how the axle shafts were held in place so I was expecting a 4 bolt flange and such. This appears to be best done with the rear axle removed from the car then if you do not have a lift.

I checked Spider Roadster and they show the following breakdown which looks like after you remove all the brake parts along with the backing plates you have to get between the flange on the end of the axle shaft and the axle housing to clean out any rust and debris from the open end of the housing to get at the circlip so it can be freed for removal and then need an angled pair of snap ring pliers to compress the snap ring (7b) for removal.

Once the snap ring is out then the axle shaft along with the items in part group 24 should slide out as a unit.

Are parts 4 & 5 behind the retainer and do they remain in the axle housing after you remove the shaft or am I looking at this incorrectly?

Is the retainer split?

I would be inclined to replace the bearings and seals when I have this apart to replace the third member. Also the it appears it would be prudent to replace the circlip since it appears to be the only thing keeping the axle shaft in place and would cause quite a problem if it failed. The caliper bracket should prevent it from completely flying out but with some damage to the rotor and caliper.

I am thinking that to do this following best practice you should remove the rear axle from the car to clean it up and work it on a bench.

The following parts would then be needed to do the full overhaul:

27 - Third Member
14 - Third Member Gasket
04 - Seal (2)
05 - O-ring (2)
06 - Retainer (2)
07 - Bearing (2)
7a - Dust Shield (2)
7b - CirClip (2)

[Redline]

I'm curious, a reputable seller in Germany sells complete units, but specifically say that they are not ready to install and need (loosely translated) the "contact pattern" checked and adjusted (point of load application between the gears). Is this normal, relevant? Are the units for sale in the US already set up somehow?

[Squidders]

> I haven't tried the freeway yet to see what rev range might be

Remember, that unless you replace the speedometer drive and gear in the transmission, the speedometer will be off. On most SPiders it is ~5% fast, but with this rear end it will be ~5% slow! It you will be going at a higher speed than indicated.
There are free apps for smartphones for GPS based speedometer, I use them to check speedometer accuracy.

My speedo was already out by approx 7 Km/h faster. I think this replacement may bring it back to being more accurate. The rear axle and diff was replaced at least once to an earlier front loading style.

[vandor]

> but specifically say that they are not ready to install and need (loosely translated) the "contact pattern" checked and adjusted

If it needs that, then what is the point of buying a complete unit? To change the pinion gear shim the unit has to be completely disassembled and a new crush-sleeve used on reassembly.
The only ones I've ever seen that were bad were gear sets, not complete diffs, where the manufacturer 'forgot' to do the last machining operation. But this was ~10 years ago.