49 replies to this topic

[Marks LXTorana]

Hi everyone,
I have been sitting back since joining the forum, reading and studying where and what I can. When I bought my LX I knew it was a bit of a mystery bag so it is a slow process of discovery. The speedo runs about 20kph above the actual road speed, so I would like to change the speedo cable drive gear accordingly. From what I can tell, I have a T5 gearbox (5 speed) which is mated to a VN efi V8, although if someone can confirm based on the photos it would be appreciated.


I have contacted Holden to ask for the price of a speedo cable gear and they keep telling me it is an electrical output, yet clearly mine has the gear drive!


Also from the photo you will see I have a 20 tooth gear drive. On the end of the drive it has the I.D.: 20A-CA.


The rear tyres are 265/50-15 and I am not sure of the diff ratio, I think it is 3.55? It is a 9" diff so where is the ratio shown?


From reading different posts and web sites, I understand my "driven" gear can be changed up or down 1 or 2 teeth without changing the driving gear on the output shaft (if that makes sense??) therefore I do not need to remove the rear housing from the gearbox. Looking at some supplier web sites, they refer to black (manual) and orange (auto) 20 tooth gears although mine seems brown???

So in summary, maybe you can help with the following list of questions:
1) Is it a T5?
2) If the speedo is reading high, do I need less teeth?
3) Can I just replace the cable gear shown in the photo or do I need to replace the mating ring gear on the output shaft?
4) Is the colour of the gear important or do I just count the teeth?
5) Is the diff ratio marked somewhere on the outside of the diff centre?

Thanks anyone for your help in advance!

[myss427]

Holden's were all electric, that gear is a ford type out of a 90's mustang T5. Go to Dellow or Jegs, Mal wood want's $50 for one! Colour should be Maroon or white for a 20km drop.

[Marks LXTorana]

Thanks both for the replies. Interesting news about the gearbox! I assume the rear housing and output shaft was changed when the engine/gearbox was prepared for the car. I need to take a trip to Rare Spares anyway so I might check their website first.

So does anyone know if I need to change the internal gears or just the one in the picture? Thanks again.

[v6 torana]

Mark

I have been through the same exercise in my LC (T700, 9 inch), spent heaps of time trying to locate the correct driven/drive gears. In the end opted for a $100 Garmin GPS and use it as my speedo (very accurate).

V6TORANA

[Uncle Chop Chop]

I also bought a GPS unit for that very reason.

[Marks LXTorana]

I used my GPS to check the speedo. Sounds like a common issue with no easy fix other than trial and error......

Thanks everyone.

[S pack]

Some interesting reading here about the T5's fitted to American cars.
http://www.moderndri.../t5_history.htm

The following is an extract from the article about the Ford speedo drive gears.

1990 to 1993 the stock Ford production V-8 WC T-5 was upgraded with stronger 3.35 gear set by increasing the nickel content to produce a harder, stronger gear. 2nd and 3rd gear ratios were decreased slightly to provide more torque to the rear wheels. Synchro linings on 3rd & 4th were improved by changing from fiber linings to carbon fiber to further improve the friction surface resulting in better high rpm shifts. A longer throw shifter was installed to "make shifting easier". The speedo drive gear was changed from 7 tooth to 8 tooth. The 8 tooth was a step backwards when installing lower rear axle ratio greater than 3.55 as the driven gear is limited to 21tooth count. Yes, 23 tooth gears are available but do not last long as the teeth are thin and do not mesh correctly. Torque rating jumped to 300ft/lbs.

Edited by S pack, 03 January 2013 - 09:59 PM.

[Marks LXTorana]

Thanks everyone.

So I went for a drive yesterday with the GPS down the M4 motorway. I checked the speedo readings at 60, 80, 90, 100 and 110kph. Short term I might just mark the speedo cover with very small strips of white contact at the key speeds. The speedo is doing 155kph at 110 so the error increases with the speed. I also noticed the engine is super smooth at 80 although by 110 it is above its ideal cruising rpm's so I am going to work out the current ratio (I understand it is somewhere between 3.55 and 3.96?) and drop it down to get a more suitable highway rpm. Doing that will again change the speedo output and so best leave that problem until after the diff has been sorted.

Also I know it is a limited slip (the inside chirps if I am doing a u-turn, and I have tested the sideways abilities just once.....) although I do not know if it is a mini spool or what. Ahh the excitement of buying an unknown...!

[ls2lxhatch]

Open Centre
Jack one wheel off the ground and turn the wheel ten revolutions counting the number of tailshaft revolutions (make sure the other wheel does not turn). If the tailshaft turns 15.04 times then you have (15.04 * 2) / 10 = 3.08 centre.

LSD Centre
Jack both wheels off the ground and turn the one wheel ten revolutions counting the number of tailshaft revolutions (make sure that both wheels turn at the same speed). If the tailshaft turns 30.08 times then you have 30.08 / 10 = 3.08 centre.

You can also use string taped to the tailshaft to count the revolutions.
http://www.gmh-toran...showtopic=10732

You can fit a ratio box or drive joint to solve the speedo errors. Flexible Drive Agencies list the ratio boxes as drive joints. Flexible Drive Agencies make both standard speedo cables and a cable to suit the ratio box.

Method of Calculating Drive Joint Ratio

1. Drive vehicle on a measured course of ~ 5 km. The longer the course, the more accurate the test.
2. Note distance measured on the odometer.
3. The Drive Joint Ratio can then be calculated as follows:

Actual Distance Travelled / Odometer Reading = Drive Joint Ratio

If it turns out that you drove for 5 km and the odometer read 5.5 km then you would fit a 5/5.5 (0.9090) ratio drive joint.

Edited by dattoman, 05 January 2013 - 03:20 PM.

[Bernie]

As stated earlier Flexible drive agencies will make you a ratio box for your speedo drive .Give them what speed it is showing and what speed you are doing and they can make the box to suit .Not very exp either.Can be inductive type as well

Bernie

Edited by Bernie, 05 January 2013 - 10:06 PM.

[Marks LXTorana]

Thanks everyone, I have decided to look into a lower ratio diff first (3 or 3.08). This should bring the speedo back closer to where it should be although I know I will still need to address the error at some stage. I am keen to calculate the current diff ratio, considering I am running a 5 speed overdrive and chunky 15" tyres on the back!

I appreciate everyone's input and will let you know the results of the "string test".

[SmacT]

My two cents - that speedo cable looks very much like a Dellow item (I just bought one) which deletes the electronic drive of a T5 and makes it mechanical. I'd give Dellow Conversions a ring, tell them the problem and they may have a solution.

[Marks LXTorana]

Ok, firstly thanks for the tip on using the string test - works a treat. After 10 turns of the wheel (both wheels jacked up and spinning the same direction, most definitely an lsd), i got just a smidge over 41 turns of the string which suggests I have a 4.11 ratio. So the million dollar question is what ratio should I drop it to, so it can make the most of the 5 speed gearbox and cruise comfortably on weekend runs??? I am starting to think a 3.00 is too low...

So then my options are:

• Swap mine for a 2nd hand centre
• Do a rebuild with new gears myself
• Pay a shop to rebuild it with new gears
• Leave it as is.

I do not want to leave it as I want to use the car for weekend drives. From Sydney, any direction requires a highway cruise. I do not want to spend the money for a professional rebuild although I haven't rebuilt a diff before (and dont have a press for the bearings which I think I will need) and I could end up with a noisy diff with too much or too little backlash. Therefore I will be on the lookout for a suitable lsd centre to buy or swap. Next I need to take an axle out to check the splines.

[ls2lxhatch]

This calculator will calculate different speeds for gearbox, diff and tyre combinations. It should also confirm the diff ratio you currently have.

GearCalc

Edited by ls2lxhatch, 20 January 2013 - 12:09 PM.

[Marks LXTorana]

This calculator will calculate different speeds for gearbox, diff and tyre combinations. It should also confirm the diff ratio you currently have.

GearCalc

Excellent! Easy to use and great to compare how changes to the diff/wheels impact the revs.
Thanks heaps !

[Marks LXTorana]

Cool thanks nemo! I am now on the look out for a lower diff centre ratio, which will impact on the speedo reading. This will certainly come in handy for after the diff has been changed.