LT77 gearboxes

[ssc1]

i have just got a recon gearbox for the 400se and i'm worried that it may be the wrong type, i took off a preffix 28a D variant and have now got a preffix 34a G variant , i realise that the G variant has stronger bearings but are concerned that the 34a bit will mean that the ratios are all wrong , the transmission company that sold it stated that there was only one tooth difference in it compared to the 28a, does anybody know anything about these boxes before i fit the thing or am i just worrying for nothing...

[GreenV8S]

I would have thought your transmission specialists would be the best people to ask. They should be able to tell you the gear ratios of the old and new 'boxes so you can judge for yourself. If you know what the mph/rpm in each gear used to be you could use this to double check their figures for the old one.

I don't know if the V8S used the same gearing as yours, but for what it's worth the original gearing on mine was 7, 11, 17, 21, 27 mph/thousand rpm (indicated).

[adam quantrill]

You can check the ratios yourself by putting it in each gear and rotating input shaft after marking it. Do 10 turns for each gear, should be fairly accurate. If you wind some string round the output shaft it'll do the counting for you!

I had an 'F' suffix on the 350i which seemed to last reasonably well....

[jchase]

21? that doesn't sound right, its not a prime number!

(okay, I know nothing about transmissions - I'll get me coat...)

-Jim

[ssc1]

hi adam , was the F suffix box in your 350i presuffix 28a or what was it , as i say this one i have is G which according to RPI should be ok for the 400 , i just forgot to ask about the first part of the part number which it seems is important and mine is 34a , i have emailed them just to check as i dont want to fit the box and then find out that the ratios are all wrong, i could try the turning it and counting the turns in each gear but i dont have the numbers from a 28a type box to compare with..

[adam quantrill]

Serial number is 34A0318527F

Wonderful thing, these PDA's!

The only thing I never fathomed was that the speedo drive was too slow for the speedo. For the first time in years I saw the 350i crack 100 on the clock! (Private road, professional driver, etc etc m'lud). And I was using the highest speedo drive gear I could find.

So you might have to get a different speedo drive gear.

[ssc1]

thanks for that adam so you are also using a 34a so mine must be ok then , so i'll fit the thing , you should also have a black speedo drive ring in your box and an orange gear from that or the speedo will be wrong, anyway thanks for all that , by the time i get the car back on the road it will be winter as i can only do a bit every so often( still on big course)
regards ian

[adam quantrill]

Yeah I was on the black gear, that having the highest ratio. I also have a green one and an orange one.

THe black one is now in the 350i on a new box and reads accurately.

[ssc1]

is your new box the 34a or the 28a type

[adam quantrill]

It's certainly not a 34a. I'm wondering if the 34a has a different speedo drive ratio on the output shaft...

It's not a showstopper as you can always use the rev counter and work from there.

[jchase]

I have a friend who is building a kit-car who plans to stick a magnet on the prop shaft and run a push bike speedo/odometer. Apparently the whole set-up is £10 and can be calibrated for the SVA. I'll let you know if it passes.

-Jim

[ssc1]

i take it then apart from the speedo problem that the gears were ok for the car then , the chap that built the box up said that it was only on tooth diff from the 28a box , so i will count the turns as you sugested and check it that way , and the black gear goes on the output shaft for this car as i have been informed .

[adam quantrill]

Yeah it was fine, lasted 30 or 40k miles until I destroyed the synchros on 3rd, 4th and 5th.

I just worked from the tacho for speed.

[ssc1]

sorry to go on about this damn box , but when trying to find out the ratios say first gear should be about 3.32:1 , now is that 3.32 turns of the crank to 1 turn of the output shaft, if so this box ratios are no good .it should be

first 3.32;1 I GET 3.90:1

second 2.09:1 i get 2.70:1

third 1.40:1 i get 1.50:1

forth 1.00:1 i get 1.00:1

fith 0.79:1 i get 0.80:1
or am i doing it wrong , this is what happens when i try to save money and trust a company that sells on ebay.....

[wedg1e]

ssc, since the first two ratios are higher I'd say it was to shift a bigger load: how about the LDV/ Sherpa van?
I just checked the Range Rover manual and their box ratios are more like the SD1 than what you have.

[wedgeman]

Hi Ian - this may help...

"As it was used in such a wide range of vehicles there are a number of different alternatives. This means that not all SD1 boxes are suitable for a V8 conversion. For example the Rover 2000 and 2300 SD1’s could be fitted with a 4 speed version. The Van versions had another with totally unsuitable low gearing, but great for hauling heavy loads! When searching for an SD1 gearbox look on the right lower side and you will see a machined surface onto which is stamped the gearbox number. The start of the number will give the identity of the gearbox and this is what you need. For example G19A refers to SD1 3500 SE and VP models, which of course is very suitable. I do not have a full list of numbers but some common ones are: -

G16A SD1 2000 (Could be 4 speed)

G17A SD1 2300/2600 5 speed

G19A SD1 3500 SE/VP 5 speed

G22A SD1 3500 Police spec 5 speed

G23A SD1 2600 Police spec 5 speed

G26A SD1 2400 Diesel 5 speed

G27A SD1 2000 Later model 5 speed

G28A SD1 Vitesse 5 speed

In addition the Sherpa van range use gearboxes with G30A numbers and these should be avoided. There were also versions used in the TR7 range and these are 5 speed and have the right ratios to be used with a V8. Land Rover products also use versions of the gearbox, but with 4-wheel drive applications that see a transfer gearbox attached where the end housing fits on the rear wheel drive applications. Many internal parts are the same though. Numbers have reached into the G50’s so this indicates the various options for this gearbox."

That any use?

Cheers - Howard

[adam quantrill]

Looks like a much wider ratio on 1st and 2nd. Now you could use this two ways....

1. Use a longer diff, this will take 1st and 2nd up to 60 mph as before but give you a better top end if you increase overall horsepower.

2. Stay with the same diff but use 2nd for 0-60 runs and 1st if you're being kind to the car.

Not sure which way to call this one...

[ssc1]

thats ok adam and thanks guys , the chap that builds the boxes is going to rebuild my old one and i'll give him this 34a back as its not going to be suitable , he does a good job and at a fair price alot cheaper than others , but i wont knowe what the quality is like till get the box back and they do come with three months warranty , not much yes but cheap..and he says he uses top quality bearings , as i say i'll let you know who he is if it turns out ok and if it dont ....

[ssc1]

anyway back to the same old problem , the company doing the job has a 20a or 22a cant remember but they are going to put the 28a D variant internals in it which will be fully rebuilt , i dont mind as long as i get the right spec at the end of the day , i have to wait a week or two as its a one man operation but he does know his boxes ....

>> Edited by ssc1 on Saturday 17th September 11:19

>> Edited by ssc1 on Saturday 17th September 12:28