4 speed manual to OD conversion

[Meonstoke]

Hi,

I've been trawling the Upgrade forum and I came across a few mentions of folks converting their standard 4 speed manual to have overdrive. That surprised me as I always thought that the V12 torque would place too much strain on a transmission with O/D. I have to admit that if an O/D conversion (with the original gearbox) is reliably possible that would be the option I would go for. (It works great on my S1 XJ6 with the O/D switch on the gearstick knob.) My OTS has a 3.31 differential so you can understand why I am missing that "5" gear or overdrive option. If I can avoid an engine out job for a 5 speed gearbox that would indeed be fine.

Are there any transmission specialists based in the UK or on mainland Europe who are known to be experienced in O/D conversions / upgrades?

All thoughts / suggestions welcome. Thanks.

M.

[JJC]

If you decide to go the 5 speed route, which I did on my 1973 Series 3, it is not necessary to pull engine. Much simpler then that. Send me a pm and I'll tell ya how its done. BTW, the 5 speed simply transforms the car. 75mph on 2000 rpm's. Fantastic.

JJ

[Ole-xke1974]

Hi,

I've been trawling the Upgrade forum and I came across a few mentions of folks converting their standard 4 speed manual to have overdrive. That surprised me as I always thought that the V12 torque would place too much strain on a transmission with O/D. I have to admit that if an O/D conversion (with the original gearbox) is reliably possible that would be the option I would go for. (It works great on my S1 XJ6 with the O/D switch on the gearstick knob.) My OTS has a 3.31 differential so you can understand why I am missing that "5" gear or overdrive option. If I can avoid an engine out job for a 5 speed gearbox that would indeed be fine.

Are there any transmission specialists based in the UK or on mainland Europe who are known to be experienced in O/D conversions / upgrades?

All thoughts / suggestions welcome. Thanks.

M.

Works wonders, once you have the gearbox and O/D sorted out.

I had my O/D rebuilt by these guys:
https://www.overdrive-repairs.co.uk/

The 4-speed done in the US.

[lowact]

For the o/drive option, I am in the process of this, reco’d Laycock de Normanville Compact type A unit is sitting on the bench waiting for me to get a round tuit. The same as was fitted to XJ6 S1 and S2 cars.
You will find in the S3 forum that UK companies advertising expertise are of ODSpares in Rugby, Warwickshire and Overdrive Repair Services in Halfway, Sheffield. My overdrive was reconditioned by Tony Arditto (Sydney, Aus.) using parts supplied by David Twigger of ODSpares, I was very happy with the service, including David’s ability to source parts including a new gearbox mainshaft.
Re yr torque limit question, I would be interested if the advice you get is different to what I have interpreted on this subject.
There are claims of uprated OD clutch springs that “should” be fitted to these (LdA) ODs if engine is V12. My understanding is that there were only two spring stiffnesses and that XJ6 ODs (mine) had the stiffest springs.
Below are torque curves for XJ6, V12 and V12HE, the latter is where I’m headed. Despite that there will be 432 Nm = 40% more torque than in the car the OD came out of (305 Nm), I’m told that the LdA overdrives are plenty strong enough..
The torque curves are of course at WOT (wide open throttle). I could be burbling along at 3250 rpm in OD (= 150 kph = 90 mph) with the throttle only partly depressed and therefore not be producing anywhere near 432 Nm. To produce this max torque I would need to find me a hill steep enough so that, when flat out in OD, I couldn’t rev harder than 3250 rpm …

[mgcjag]

Hi....just to add you cannot simply add an o/d unit to your existing gearbox......you need a gearbox that either has or had a compact o/d unit fitted.....an xj6 unit is ideal.....Steve

[angelw]

Steve Wrote:

Hi....just to add you cannot simply add an o/d unit to your existing gearbox......you need a gearbox that either has or had a compact o/d unit fitted.....an xj6 unit is ideal.....Steve

Hello Steve,
The difference is the Main Shaft. Accordingly, if you can get hold of Gearbox Main Shaft for use with the Laycock de Normanville A Type Compact Overdrive, then the existing 4 Speed Gearbox of the S3 E Type can be converted. I'm fairly sure that is what Colin did.

If an XJ6 Gearbox equipped with an Overdrive is used instead of converting the original Gearbox, the Top Cover of the XJ6 will have to be replaced with the Top Cover from the E Type Gearbox.

Regards,

Bill

[Meonstoke]

Gents,

Thanks a lot for all your advice and comments. I'll check out the UK companies mentioned.

M.

[Ole-xke1974]

Apart from the main shaft being O/D specific, I'm pretty sure that the flange between the gearbox and the O/D is specific to the O/D configuration as well. Something to consider if you want to ad the O/D to your existing box.
If you have a well working manual box in your E, you could also consider the cheaper and much quicker solution of a changed diff ratio. Say from 3.31 to 2.88. That would give you ~15% drop in top gear RPM (and the other 3 gears) with a theoretically slower acceleration.
PS: My gear box w O/D came from an XJ S2 and was uprated to 4.2 specification (stiffer springs).

[angelw]

Ole-xke1974 Wrote:

Apart from the main shaft being O/D specific, I'm pretty sure that the flange between the gearbox and the O/D is specific to the O/D configuration as well. Something to consider if you want to ad the O/D to your existing box.

What flange? Following is a picture of the Rear Face of an S2 E Type Gearbox. This is out of a 2 Seater Coupe, hence the short Main Shaft. The only difference between the S2 and S3 Gearbox Housing is the mounting point on the housing for the Clutch Slave Cylinder (S3) as opposed to the mounting point on the Bell Housing for the S2.



There is no flange between the Gearbox and Gearbox extension of a non-overdrive gearbox. For short and long wheel base E Types, the Oil Pump Drive ring is held firm against the inner race of the Main Shaft rear bearing and in turn, the bearing inner race against Reverse Gear, via the Companion Flange nut being tightened.

There is a separate plate between the Gearbox rear face and the OD unit, but if the OD has been sourced from an XJ6, the assembly will bolt onto the E Type Gearbox once its been fitted with the OD Main Shaft.

The system is different with a Gearbox equipped with an OD. In this case, the OD compatible Main Shaft is threaded near the rear bearing and a nut is used to hold the bearing inner race and Reverse Gear firmly in place. The OD unit then bolts to the back surface of the Gear Box in the same manner as does the Gear Box extensions of the non-overdrive, short and long wheel base cars.

Regards,

Bill

[PeterCrespin]

Gents,

Thanks a lot for all your advice and comments. I'll check out the UK companies mentioned.

M.

I went to the ex Laycock people in Sheffield and asked them to upgrade the OD as part of the refurb. They asked why did I wan a competition upgrade? I said I might end up using it in an S3 OTS I had and they said not to waste my money as the E wasn't that heavy a car. I then said it wasn't definite and I might use it in a race car so they eventually agreed. When you have to persuade a seller to accept extra spending you know you're unlikely to get ripped off.

[Ole-xke1974]

There is no flange between the Gearbox and Gearbox extension of a non-overdrive gearbox. For short and long wheel base E Types, the Oil Pump Drive ring is held firm against the inner race of the Main Shaft rear bearing and in turn, the bearing inner race against Reverse Gear, via the Companion Flange nut being tightened.

There is a separate plate between the Gearbox rear face and the OD unit, but if the OD has been sourced from an XJ6, the assembly will bolt onto the E Type Gearbox once its been fitted with the OD Main Shaft.

It is that plate I am referring to.
On a std 4 speed box that flange is not there and its not attached to the O/D, its bolted to the gearbox.
I think we are saying the same, but differently.

[lowact]

Hello Peter. Can you tell us what the “competition upgrade” comprises, specifically what is different to the OD that was fitted to Jaguar 4.2L XJ6’s? Do you know spring rates and materials?

[jagwit]

Colin,

I find specifically your V12 HE torque graphs rather interesting! Below the dyno graphs of my ex E-type which had the 11:1 HE + EFI conversion. This run was done at 1800m AMSL where normally aspirated engines lose between 15-20% of the power compared to sea level.

On my graph you will see that they did two runs. The first only started around 2000rpm but then I told them to start at 1000rpm which they still got wrong (only "mad people" are interested in torque at 1000rpm....)

E-type HE EFI Dyno.jpg (111.82 KiB) Viewed 5775 times

Now some observations:
1) The SHAPE of the two curves is what attracts my attention.
2) Your torque graph seems a lot more curved - not just because the graphs are scaled differently but it really seems as if your engine needs to rev to deliver torque. I've plotted the main points on the same graph to eliminate the graph scaling effect below.
3) It again shows how things can vary from dyno to dyno; My dyno graph has a correction factor called "Ambient" and was set at 23%. No idea what the implication is of that.
4) This car could run next to a '00 4.0 supercharged XKR - but neither could outrun the other, not at this altitude and not at sea level either;

Colin vs Philip.png (7.33 KiB) Viewed 5775 times

[PeterCrespin]

Hello Peter. Can you tell us what the “competition upgrade” comprises, specifically what is different to the OD that was fitted to Jaguar 4.2L XJ6’s? Do you know spring rates and materials?

I did ask re upgrade but it was ten years ago. I think it was a combination of better or more friction material and higher pressure

[lowact]

Hello Phil. The performance curves I posted are not my cars, not even real, they are copied from automobile-catalog, this uses car dynamics simulation software i.e https://www.automobile-catalog.com/simulation.php

[jagwit]

Hello Phil. The performance curves I posted are not my cars, not even real, they are copied from automobile-catalog, this uses car dynamics simulation software i.e https://www.automobile-catalog.com/simulation.php

In that case, I can be more direct. I think those curves are seriously flawed.

I was blown away by how flat the torque curve on my S3 OTS was. But it did confirm how the car felt - strong, very strong, from idle to 5500rpm. This is why my XJS is so happy with its Tremec 5-sp doing 2000rpm @ 120km/h. I recon it would be just as happy if it could do 1500rpm @ 120km/h.

I installed a GM 4L60e into my 7.2L Jensen Interceptor and the car loves it. If I could somehow know that the 4L60e (or 700R4 or 4L60) would physically fit into the S3 and be mated successfully to the pre-HE V12, I would immediately start doing the conversion....