Print Page - Speedo Gears???

Just replaced original diff with a 3.55 ratio. I am quite plesed with the performance other than a whine in top gear at about 30-40 miles / hour. Looks like I will need to take it out and replace bearings (thought???). Anyway the question is, is there any replacement speedo gears that I can put in the old crash box to change the speedo reading back to the right speed? I know you can change the tension on the rear cluster of the speedo, but I don't want to do this if speedo gears can be purchased. If I had to change the tension of the spring at the rear of the speedo to bring it back to the right speed, does this also change the odometer back to the correct reading??

Many thanks to a great informative site. Keep up the good work.

Rod

Rod,

I went through this a year ago when I changed the original 3.89 diff in my EJ for a 3.36.

The 3.55 is 10% taller than the original 3.89 so to correct the speedo and odometer you need to fit a gear with 10% fewer teeth. Changing the tension on the spring in the speedo will only fix the speedo- not the odometer. I am not sure what speedo gear you have in your car but in the EJ the standard one is green and has 21 teeth. If yours is the same you would need to find a gear with 19 teeth if such a beast exists to fit your gearbox.

The solution in the EJ was a bit more complex. With the 3.36 the difference is 15% from standard meaning I would have needed a gear with 18 teeth. Unfortunately I couldn't find one and I suspect they don't exist to fit the original gearbox. The solution in the EJ was to fit an EH speedo which gives a 20% higher speedo (and odometer) reading for the same speedo cable rpm. To get back to 15% I fitted a speedo gear with 22 teeth (5% more) which just happens to be the standard EH speedo gear which is blue. That works OK in the EJ because the EH speedo is easily interchangeable- the only differences being the speedo markings (50 mph with needle straight up in the EJ, 60 mph straight up in EH). The result- accurate speedo and odo and only a real expert would know that it is an EH rather than an EJ speedo.

If I had fitted a 3.55 I could have achieved the same result with the EH speedo and a speedo gear with 23 teeth (red, I think).

If you can't find a 19 tooth gear or you don't have an EJ, the next best option is probably to get a speedo adjuster box from the Castlemaine Rod shop. Basically they are a little gearbox that is fitted somewhere along your speedo cable between the gearbox and the speedo. You could get one to speed up the input by 10%.

Hope this helps

David ;D

Many Thanks for your reply David.
I have two speedo gears that have different number of teeth.The first one has 23 teeth and has Holden and the part number 7409427. This is interesting as the number in the parts catalogue is 7495945. The second one has 22 teeth and the only markings are GMH and 15. The gears are not colored. I am unsure of the number of teeth in the gearbox at the moment.
These gears are from the crash box which I initially assumed was standard FE / FC vintage. Why is there a difference between the number of teeth? Were Vans and Station Wagons different or did later model boxes have differnt number teeth.
I hope this offers a basis for further discussions.
Thanks once again.

Rod

The FX/FJ box had a different gear to the FE/EK because the FX/FJ had 15 inch wheels. Fitting the gear from the FX/FJ box will be closer to right than the FE/EK gear if you are running a 3.55 diff, but not exactly right.

The FE/FC box has a serial number starting with "L" whilst the FX/FJ box has no letter prefix.
The FB/EK box has a serial number starting with "B"

Ken

What model do you have Rod?

From what you and Ken have said I guess that the speedo gears in FX-EK gearboxes are a different type to those in EJ-HK and would not fit these later boxes. If anyone could confirm or deny I would be interested.

I guess, Rod, you will need to work out how many teeth there are on your current speedo gear to work out what will correct the speedo/odo. Unless someone else knows and can save you crawling under your car to pull it out.

I have had another thought that might be useful too. I think that automatic EKs had the 3.55 diff ratio and that the speedo unit itself (the bit in the dash) is actually different to the manual to account for the higher diff ratio. If you have a manual FB or EK swapping the speedo for an auto one might solve your problem. If an EK speedo will fit an FE/FC then it could solve the problem for these models (perhaps I am really displaying my ignorance of FE-EK instrumentation here!). I don't think that the speedo gear from the auto box will fit into a manual gearbox (can't recall where I got that idea from so I could be completely wrong but I am fairly confident I'm not).

Thanks for the info, Ken, on FX/FJ having a different speedo gear due to 15in wheels. Is the difference due to the wheels corrected solely by the speedo gear or is there a different input shaft:speedo reading ratio in FX/FJ compared to later models. For example in FE/FC when the speedo cable it doing 1,000rpm the speedo reading should be 50mph. Is it the same in the FX/FJ. I think this gearing was retained in the EJ but went to 60mph at 1000rpm in the EH.

Rivetting stuff! Something for the wife and I to ponder over a candlelit dinner I'm sure.

Sorry, I get a bit carried away sometimes.

David

David

Dave,

Please feel free to get as carried away as you like! I've had questions along these lines asked of me before, and I don't know the definitive answer. I'd like to, though.

For what it's worth, whilst the FB-EK speedo looks different to the FE/FC one in operation (it has a moving bar rather than a needle), it bolts up exactly the same, and they're quite interchangeable - I have an EK one in my car, as it happens. When idle, it looks like an FE one with the needle missing! If the EK auto one is different inside the speedo unit itself, then that is an interesting wrinkle.

It's also worth bearing in mind that these speedos are calibrated to suit cross-ply tyres, which have a considerably wider diameter than equivalent radials, so even a correct setup is not going to give the correct speed. (Why do some people insist on calling cross-plies 'conventional tyres'? They're certainly not the convention in this day and age! Do these people refer to a bus as a 'charabanc'? Of course not.)

Anyway, I'm interested if anyone has an opinion or more knowledge on this subject.

RET

Back to the trusty parts book ;D

No 3.55 diff for EK auto - All diffs to EJ were 3.89
No different speedo head for EK auto
The EK auto has the same speedo drive gear as the EJ

The speedo gear for FX to EK (except auto) will not fit later models.

FX and FJ speed corrected soley by the different speedo gear.
I believe all FX to EK speedos will work in any of the FX to EK vehicles.
As Richard has said, the EK one certainly works in FC.

Really there is very little option to fix incorrect speedo reading when using the original box. You need an EJ onwards box so that you can select different gear ratios at will to suit your need as EJ Dave has suggested.

Ken

Hi guys,

was wondering if anyone knows whether the speedo drive gear (worm gear) is the same in all boxes and what number of teeth it has (a bit hard to count as they wrap right around the worm)?

I am putting a HT Trimatic behind a 186 in my FC, so I guess I have the luxury of more adjusting gears to choose from...currently have a blue 22 tooth gear.

I have measured my wheel diam, using a 3.89:1 diff centre, I can calc the gearbox output shaft rpm for 50 mph....if I can find out the ratio of the speedo drive gear:driven gear in the gearbox, I can determine the speedo cable rpm, and see how close it is to Dave's 1000 rpm for 50 mph.....and see how far out the speedo is likely to be.

I guess another issue is whether or not the speedo driven gear turns at the same rpm as the output shaft....so many unknowns!!!

Any comments would be appreciated...

cheers....Brad

Brad,

be careful about basing you calculations on 1000 rpm giving 50mph in your car. This was the case in FE/FC and, from previous posts in this string it appears that all speedos to EJ had the same calibration. This changed with the EH when the calibration changed to 60mph at 1000rpm (based on my calculations i.e. subject to challenge). I have no idea what happened post EH. HD-HR had the same wheel diameter and diff ratios as EH but HK-T-G went to 14 inch wheels so the engineers could have gone one of several routes to adjust the speedo.

Interesting thought about the worm gear. I guess that the speed of the driven gear could be altered by changing the pitch of the worm. Therefore the cable speed would not have to be the same as the output shaft. Substantially changing the pitch on the worm would probably mean that the original driven gear would not mesh too well (teeth too close together or far apart to neatly mesh with the worm).

David

my fc has a celica 5 speed, EK speedo, an hr diff with an un-standard centre (can't remember what), and 14" wheels that actually are about 2cm larger in diameter than good o'l crossplys.

my very technical solution of speedo calibration was to have a friend drive next to me on the freeway and signal when he hit certain speeds. ;D

i worked out that i double the number on the speedo and add 10!

not very techy i know, but it adds to the overall 'character' of the car i think. ::) he he

just trying to add a bit of humour to this technical discussion.

i love this site. you always learn something new and interesting. i check it out every day.

simon

Thanks guys....I do appreciate the humour...as was said earlier in this string, just the stuff to discuss with your other half over a candlelit dinner....

having looked at my manuals it appears to me that the speedo worm gear is indeed on the output shaft of the gearbox.

I had a double think about the changes to design since the FC as you suggest Dave, but then I thought that if I'm using an FC speedo head, the 1000 rpm is still valid to make it read correctly at 50 mph...then hopefully, I could achieve 1000 rpm on the speedo cable by selection of a driven gear with the appropriate number of teeth to get approx 1000 rpm. All I need to know is the number of teeth on my speedo drive gear to get the reduction ratio...given that it is a HT Trimatic, I may just have to investigate it further for myself....I'll post any solutions I come up with.

if all this fails, of course, I'll resort to Simon's method...

thanks....Brad

Brad,

another thought. Simon's method actually has some merit (aside from the very compelling one of character- doesn't usually carry much sway with the missus though, candlelit dinner or not). If you could follow someone and get them to signal when you are doing 50mph you could work out what your speedo is reading. If you know the difference between your reading and the actual speed and you know the number of teeth on your current speedo gear you can work out what speedo gear would correct the speedo. Hopefully your answer will be one that exists to fit your gearbox.

If you want some guidance with the calculations I would be happy to help out. It can get a bit confusing (it was for me anyway).

David

i don't know about 200ks +, but i'll never forget my first ride in a vey original and very battered EK farm ute that my friend just bought in high school. we took it out to the local drag strip (with a grey motor! :P ) and just floored it to see how fast it would go.

the faster we went, the more the whole car shook, and the harder we laughed. we actually backed off because the whole car was shaking so violently, that we thought the guards were going to fly off (every bolt on pannel was jumping around like crazy!).

we started to see melting colours like in 2001 a space odyssey!

:o

in this kind of scenario, it seemed to be best to listen to the structural integrity of the car and the laws of physics, rather than look at the speedo (it was vibrating too much to see anyway!)

we were lucky the whole car didn't disintegrate around us i think. but you know what being 18 is like. damn funny at the time though!

Hi again,

just another detail on speedo gears (in case you're interested)...

I counted the teeth on the speedo drive gear in my HT Trimatic today...8 teeth...so for the "blue" driven gear this gives a ratio of 0.3636:1.....

previously I had calc'd that for a wheel circumference of 8 ft 4 ins through a 3.89:1 diff centre, the tailshaft rpm was 2689 for 50 mph.....so the speedo drive gear to driven gear ratio of 0.3636:1 gives me 978 rpm on the speedo cable for 50 mph......pretty close to the 1000 rpm calibration given by Dave above (only 2% low, underestimating the real speed).

no need to change the driven gear......woohoo!! I've got enough bits to look for without having to chase that one up!! Will be interesting to see if the calcs hold up when I get it on the road and test it for real!!

Brad W

Finally got around and changed the speedo gear. The original gear was a 23 tooth gear and I have replaced it with a 22 tooth gear.

From what I have ascertained this gear has adjusted the speed to within one or two km/h for the 3.55 using another car as a guide. Tried to use the speed detectors out on the highway but for some reason it would not register. I tried numerous times; possible the ute is not a large enough object to detect.

Following on from Ken I assume that the new 22 tooth gear is from a FX / FJ. So for anyone who wants to agjust the speed with a 3.55 diff the 22 tooth is awfully close. Hope its of interest.

Rod

GIDDAY EVERYBODY

JUST THOUGHT I WOULD RESURRECT THIS STRING BECAUSE I AM PLANNING TO FIT A 2.78 DIFF TO THE HT MANUAL WHICH I AM CURRENTLY DRIVING UNTIL "EFFIE" FINALLY SEES THE LIGHT OF DAY. NOT SURE WHAT CURRENT DIFF RATIO IS BUT HAS A RED GEAR GOING INTO THE BOX[3SP ALL SYNC]. IS IT AS SIMPLE AS JUST FINDING THE RIGHT GEAR? IF SO WHERE DO I START BECAUSE INITIAL ENQUIRIES FROM PARTS SUPPLIERS HAVE DRAWN A BLANK.IS GETTING IT CALIBRATED THE GO? IF SO WHERE?[I AM SITUATED IN DANDENONG RANGES]

ANY HELP WOULD BE MUCH APPRECIATED

DENIS

Denis,

if you can check your current diff ratio and the number of teeth on the red speedo gear I should be able to work it out. The diff ratio should be stamped on the flange attached to the yoke. I know the number of teeth on a red gear from a crash box but don't know if it is the same as in an all-synchro box. Does anyone else know if they are the same?

Also, is the speedo accurate with the current diff and speedo gear?

And are you sure you want to go to a 2.78? That's a pretty tall ratio with a 3 speed.

David

gidday dave

thanks for the reply. i will get out and under the car tommorrow and let you know about diff ratio and teeth.

the speedo is currently accurate to within a bees genitalia so that should be a good starting point i suppose.

the 3 speed is only a short term thing as i also have an m20 ready to go in but not the time to do the whole job at once due to the daily driver status of the car.

thanks again

denis

Denis

Following from HQ Spare Parts Book(Same Three Speed Box).

Diff Ratio Tyre Size Gear Colour # Teeth

3.08:1 F78-14 Pink 19

3.08:1 All other tyre White 20

3.36:1 7.35 x 14
EB78S-14
195 x 14 Green 21

3.36:1 6.95 x 14
185 x14
70 x 14 Dark Blue 22

3.55:1 195 x 14
78 x 14 Dark Blue 22

3.55:1 6.95 x 14
185 x 14
70 x 14
7.35 x 14 Red 23

Drive Gear Part Number 7437317

2.78:1 ratiois for Trimatic box

Diff Ratio Tyre Size Gear Colour # Teeth

2.78:1 F78-14
7.35 x 14 Pink 19

2.78:1 6.95 x 14
185 x 14
70 x 14
7.35 x 14
1.95 x 14 White 20

Drive Gear Part Number 5258493

Hope the above helps
John M

By my calculations you would need a gear with 18 teeth to give you the same speedo reading you have now. A 19 tooth (pink) gear may be the best you can do.

I worked this out by dividing 3.55 by 2.78 = 0.78. That is, your speedo will only read 78% of what it does now at the same actual speed. To correct the speedo you need a gear with 0.78 times the number of teeth you have now (23). This comes to 18. If you use a 19 tooth gear your speedo will read 5% lower than it does now. That is you will be going 5% faster than the speedo is telling you. This is not much but enough that you probably shouldn't allow yourself quite as much 'error' over the speed limit.

Good luck

David

PS. It sounds as though the speedo gears in the all synchro box may be the same as in the EJ-HK crash box- the tooth numbers are the same at least. Can anyone confirm or deny that they are the same?

G'Day Denis
To follow upon what dave has said, to change from your red 23 tooth item to a pink 19 tooth would also require the changing of the drive gear in the gearbox (Different part numbers ) more than likely different number of teeth.
The other alternatives is to have a correction box made up by CRS or have your speedo re calibrated by a instrument tech.
Good Luck
John M

gidday john and dave

thanks for your input. all i can say is that there are more champions on this site than you would find at an olympic games ;D ;D ;D

i assume john you are talking about the internal gear in the box and not the plastic one on the end of the cable. sounds like a lot of work. may ring mr hadfield and suss him out about a correction box otherwise does any one know an approximate cost of callibration?

thanks again

denis

G'Day Denis
Yep the drive gear is on the shaft within the rear extension housing, not really that hard to change. Just drop the rear housing off and it is held to the shaft with a spring type clip slide one off the other on and put extension housing back on.
Re calibration a lot easier but more expensive, not sure of cost but to have calibration checked and certified (required by rego and engineers) costs Approx. $180 in ACT.
John M

Just thought I'd bring this thread to the top again because it answers some questions in the 'diff centres' thread just below. It seems that the FX-FJ gearboxes did have a different speedo gear to FE-EK- see Ken's reply (about 4th in thread- including part numbers!!). In an FC with a 3.55 diff and an FX-FJ speedo gear it seems the speedo reads pretty close to right. This assumes tyre diameters same as the originals.

David

Rusty,

As per the Sydney Torana Club site here are the choices:

3.98:1 (4cyl 56bhp with four-speed manual).
4.125:1 (all other four-cylinder).
3.08:1, 3.36:1, 3.55:1 (six-cylinder) (LSD optional).

All of these diff centres will have an effect on your speedo reading, as will your wheel rim and tyre size.

Send me a P.M with your specs and I'll work it all out for you.

Cheers,

Craig.

FE-FC Holden Discussion Forum

Technical Board => Modification Help => Topic started by: Rod on July 25, 2002, 10:57:28 AM