Gearboxes and differentials

[andyowl]

Following the major failure of the differential on my competition Bagheera I am now fitting an old one I have had for some years just to get me back "on the road". I have been studying some correspondence we had on the old Matra Cars Forum and there is more to changing gearboxes and differentials than is first obvious.

In February 2004 I was trying to identify the four gearboxes I had in my parts store. (This is a grand way to describe the mess of old Bagheera parts I keep in the roof space of my garage. I have cleared away a lot of Series 1 parts but I had received a request from a USA member to source a suitable gearbox for his Bagheera).

I kept the printout from a very helpful email but I do not now know who sent it to me. I think it may have been Spyros but if it was someone else please accept my apologies and thanks.

To summarise...

These Simca derived gearboxes all have serial numbers. There were (at least) three different final drive ratios at various times. There may have been other ratios as well fitted to other models but I don't have information on those.

The "Information" page in the parts book has a confusing table which gives an explanation of the serial numbers and shows that all Bagheeras have 17 teeth on the gearbox output matched with either 59, 61 or 63 teeth on the differential input. Because the distance between the two shafts remains the same the 17 teeth gearbox output pinions must each have different diameters and therefore different size teeth! You MUST use matching gearbox and differential gears.

The output pinions carry identifying codes which which can tell you which diff input they are intended to match. These markings consist of concentric rings on the end of the pinion and sometimes a stamped figure. I do not know what this code means although it would be very useful to find out.

Once the differential and gearbox have become separated how can one match them again? It would be easy to count the teeth on the differential but how do you decide which 17 teeth gearbox pinion is correct for that diff?

I am going to try taking some measurements of the gearbox pinion diameter and relate that to the markings. I am today going to separate my gearbox and broken differential and I will start there. If anyone else would like to do some checking on their spare boxes and diffs it would be most helpful! We can then collate the answers and produce a table for everyone else.

Andy

[lewisman]

I fitted a lower ratio diff from a 1300 to my Bagheera to lower the gearing as I was more interested in acceleration than top speed.  Unfortunately I cannot remember where the gearbox came from (possibly a Ranco or maybe even a Horizon). I never had any problems with the combination of box and diff.

[andyowl]

Interesting!
- Did you notice any improvement in acceleration?
- Was there an increase in the noise level?

Andy

[lewisman]

I thought that it felt a bit faster "off the line" and it was running a bit more revs at motorway speeds - not a day to day problem for me!

[andyowl]

Apologies, but I mistakenly placed this message in the "Roll Cage wanted" thread. It should have been here!

....I regret to say that the continued growling from the "new" gearbox and diff is probably my fault, not that of a previous owner! Talking to friends and my son about the problems reminded me that we saw some damaged shims when we separated the "new" gearbox and diff before we installed them in the car. They were separated because a) I wanted to minimise the weight to be lifted when re-fitting them and b) I wanted to check the diameter of the gearbox output pinion and the number of teeth on the diff "crown wheel" - more of this later.

The damaged shims were between the gearbox and the diff itself and they govern the meshing of the output pinion and the diff crown wheel. When we put them in the car, in my haste, I forgot about the need to re-fit shims and check the pre-load in the diff.

There is a second pre-load with its own shims and my understanding is that the tapered bearings that support the "bridge" or cage (the four gear wheels that allow the road wheels to turn at different rates when going around a corner) require to fit tightly, but not too tightly, And I didn't check those either. So a double fault on my part I am sorry to say. If either pre-load is not correct bad noises or worse may result!

Interestingly if the Bridge preload is too tight that may result in a split diferential casing. Sounds familiar??

I am travelling in the west of England at present but when I return I plan to take both gearbox and diff off again (getting better at doing that!) and get them examined professionally to check whether they are good enough to be re-used in a competition car with sticky tyres, 25mm wheel spacers and a supercharger! I have another gearbox which was factory re-conditioned (they say) and maybe I should be using that in Baggy Joe. Perhaps this is the "rainy day" I was keeping it for?

As usual, any comments you may have or gearbox & diff experience you would like to share would be most welcome.

Out of my depth again. What a lot there is to learn!

Andy Owler (Matra-less for the moment!)

.

[valross]

The output pinions carry identifying codes which which can tell you which diff input they are intended to match. These markings consist of concentric rings on the end of the pinion and sometimes a stamped figure. I do not know what this code means although it would be very useful to find out.

The official Peugeot workshop manual identifies the markings on the end of the pinion and on the crownwheel:

no ring  -  16 x 63
one ring - 16 x 65
two rings - 17 x 63
three rings - 17 x 61
four rings - 17 x 59

Lasse H

[Spyros]

Wonderfull !

[andyowl]

Lasse... That is brilliant. Thank you very much.

I'm off to check my gearboxes.

Saved me a lot of itme.

Thanks again.

Andy Owler

PS Gearbox and diff coming out (again) as well speak.