80 series - Anyone fitted a taller 5th gear?

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mad_mat222
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80 series - Anyone fitted a taller 5th gear?

Unread post by mad_mat222 » July 28th, 2013, 1:33 pm

Has anyone had any experience with changing 5th gear to make it a bit taller. At the moment I think I'm on about 2800 rpm for a 100 kmh with 33" tyres. To my knowledge everything else is stock as a rock . I don't want to change diff ratios because or slow speed work is a must. Just want to be able to stretch the legs without revving the ring out of the poor old girl.

It's a '92 mod 80 series with 1hdt donk so has the power to turn a taller gear. Most of the other threads and forums deal with diff ratios that effect every gear which is not what I'm after. Cheers

mydmax
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mydmax » July 28th, 2013, 3:39 pm

IS the tacho really correct??

Are you going by the speedo 100kmh or a GPS 100kmh???

A 60 series at 100kmh measure by both Speedo and GPS is nowhere near those revs. Something is wrong.

What diff gears have been altered to what ratio for it to do that?

mad_mat222
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mad_mat222 » July 28th, 2013, 8:26 pm

Not a clue never got under and found out but like I said pretty certain it's stock as a rock. I will try the GPS though. I will get around to jacking up the wheel and finding out the ratios. Any advice on the fifth gear?

acheshifter
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by acheshifter » July 29th, 2013, 6:43 pm

Can't help you with the taller gear question, but have to agree with mydmax re the revs at 100kmh. My 1hz 80 with 33's does it at 2450rpm, as does a mates 1hdfte 100 series, 2800 is too high for that speed. My advice would be to get all that checked first mate

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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mydmax » July 29th, 2013, 9:09 pm

Wheel size has no bearing on revs and registered road speed on the speedo.

Sounds like someone has fitted higher than stock ratio diff/s ie. bigger numbers/lower gearing.

GPS will confirm that. I agree 2450 is about right.

Do a fluoro light strobe check on the front pulley and see if reading 3000rpm is 3000rpm. Also syncs with 1500rpm nicely too.

mad_mat222
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mad_mat222 » July 30th, 2013, 3:39 pm

Double checked its sitting on 2600. Still to high. Would like to see at about 2200rpm

Aaron Schubert
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by Aaron Schubert » July 30th, 2013, 6:10 pm

They are quite tall. Mine, running standard tyres sits at around 3k at 110 and 2800-2900 at 100km/h.

I wonder whether Toyota did it intentionally, knowing they can handle the high revs.

Are they all of your youtube videos? Awesome work!

Aaron
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My 80 Series Landcruiser

acheshifter
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by acheshifter » July 30th, 2013, 8:05 pm

Actually, tyre size does have an effect on revs at a given speed. 33's over 32's about 5%, as reflected in speedo accuracy when you change up to 33's.

This is because the circumference of the larger tyre is greater and so covers a greater distance for each revolution. Therefore, you are doing less revs for 100 km/h with 33's over 32's. In effect alters (raises) the overall gearing slightly.

Standard gearing on the Cruisers will see 2450rpm give or take, as the connection between pistons and wheels is a physical one, the gearing has to be lowered at some stage in the drive train to increase the revs at a given speed. Unless, the clutch is slipping, but I reckon you'd notice that.

Now, all this time I have assumed (always risky I know) that we are talking about a manual transmission, The gearing may be different in the auto, I will have to check.

mydmax
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mydmax » July 30th, 2013, 9:03 pm

Acheshifter
Thanks for the tyre size bit but I mentioned the speedo reading doesn't change with the revs no matter what size tyre is on there. In fact it will be the same on blocks in the garage with the wheels off the vehicle and will still indicate the same revs at he same speedo speed. That's why it was suggested checking the rev counter so it can then be aligned with speedo, gearing and tyre sizes so there is no unseen/hidden factor present.

acheshifter
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by acheshifter » July 30th, 2013, 9:35 pm

Absolutely agree mydmax, you will simply be travelling faster than indicated with larger tyres. I should have read your post more thoroughly... Doh!

hey mad-matt222, is you 80 manual or auto mate?

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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by Aaron Schubert » July 31st, 2013, 6:43 am

acheshifter
2450rpm at what speed? Mine is a manual 1990 1HDT, and revs in between 2800 and 3000 from 100 to 110. Everything is stock on it

Aaron
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acheshifter
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by acheshifter » July 31st, 2013, 6:45 pm

Wow, those are big numbers for 100 km/h everyone I know with a diesel Tojo, be it an 80, 100, or Troopy, 1hz or 1hdfte is around 2450 @ 100 km/h

All very interesting stuff hey? As we were discussing before, rpm and road speed are directly related by gearing, so, if tachos and speedos on all vehicles mentioned are somewhere near the mark, I suspect our trucks must be geared differently.

mad_mat222
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mad_mat222 » July 31st, 2013, 7:16 pm

Mine is a manual. I noticed big difference in speed and loss of bit of power with the bigger tyres but still to high in my opinion at 2600. With the running gear on the v8 s they are doing way less. Obviously diff ratios will raise all gear but that's not a good thing and putsmheaps more stress on the diff which in turn puts more stress on the drive shafts that put more stress etc etc. so if not owing anything slightly decreasing ration of 5 th is a good option and keeps you smack bang in the torque curve just purring along.

mydmax
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by mydmax » July 31st, 2013, 9:08 pm

mad_mat222
When you say you double checked what did you check?
Do you know if the rev counter is actually indicating the correct revs the engine is doing? If not everything is up in the air and no definite decision can be arrived at.
Did you "flouro lamp" and strobe a large painted white spot on the crank pulley? If you haven't you won't know how accurate the revs indication really is.

240v ac makes a fluoro go on and off 50 times a second. A white spot on your crank shaft will be going past at 50 times a second when the engine is revving at exactly 3000rpm.
If the White spot appears to stop moving at 3000rpm or slows right down so you can see it slowly go past, it means the crank is spinning at 3000rpm. If the tacho reads 3000rpm when the spot stops/slows from moving one way or the other you then know the tacho is correct or can work out the error.
Then you can start talking gearing and tyres and road speed etc.

Cheers
mydmax

acheshifter
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Re: 80 series - Anyone fitted a taller 5th gear?

Unread post by acheshifter » July 31st, 2013, 10:33 pm

You blokes are lucky, my 80 is a poverty pack model, and when Toyota say poverty they mean poverty! No tacho as standard! I don't know what they were thinking releasing a diesel without one. I fitted up a Tiny Tach from the US, they operate by way of a transducer clamped to one of the injector lines. 100% accurate, confirmed while on the Dyno having the turbo fitted.

At the end of the day, it probably doesn't matter too much about the actual numbers, as long as the motor isn't labouring. A non-turbo 1hz will suffer with 33's on, that was what cemented the decision to fit up the snail. Hills on the highway will always require frequent cog swapping naturally aspirated, but the old girl always purred along nicely at 100 on the flat.

If you fit a taller 5th gear it will have the same effect as fitting even larger tyres (when in top gear anyway), yes it will lower the rpm for the same cruising speed, but the motor will be doing it harder and have you changing down even more at the very mention of an incline or headwind. We generally fit larger tyres for better diff clearance at the expense of a bit of acceleration, and if anything, reduce the gearing to bring it back to stock to ease the load on the motor. Fitting an EGT gauge when doing the turbo has taught me lots about how wind and hills affect the load on the motor, it's not unusual for me to see the exhaust gas temp rise by 100 degrees when driving into a decent headwind. Even though it will sail up the hills without dropping speed with the turbo, swapping back to 4th keeps it in the sweet spot - more rpm, less load, much less heat, happy days!

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