wat is going wrong with my drive train??

[lilcrash]

hey, after driving around in my celica for a few hours i noticed something weird. my car tops out at 130kmph, and my speedo seams to be about 20 km out. my engine also sits at about 3500-4000 and 4-5psi boost when we are doing an estimated 100kmph. could it just be my diff being the wrong ratio?? my drive train is as below-

3tgte - w56 - diff??? -185/55r14tyres

if it is my diff wat sort of diff should i look for to replace it??

thank you

[ace]

At a guess yeah it sounds like the diff, is it the standard T series celica diff? In that case its probs a 4.1 or 4.3....
Why'd you use a W56, doesn't that have weird Truck ratios too?
I dunno much about this stuff though.
Ace

[thechuckster]

From <http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/Gearboxes.html>, some ratios:
W56
4.091 - 3.954 - 2.141 - 1.384 - 1 - 0.850
W58
3.768 - 3.285 - 1.894 - 1.275 - 1 - 0.783
W57
3.768 - 3.285 - 1.894 - 1.275 - 1 - 0.861

You'll be running a little higher than normal in 5th gear (MA61 with W58 is about 2750-2850rpm in 5th at 100k) - but not by >1000rpm.

I'd say you've got a combination of:
-way wrong diff ratio
-wrong gears for the speedo output on the gearbox.

Before pointing the finger at the gearbox, what is the diff code for your diff (e.g. what does the plate on the firewall say)?

Also, find a mate with an accurate speedo, borrow 2 UHF radios and go for a speed test on the toowoomba highway- he/she reads sticks to agreed speeds and ou note down what you're reading.

[lilcrash]

its just how the car was when i got it, i dont think it is the original diff as it is purple and the rest is black.

if i got the diff from my other car do u think it would be better cause it used to red line at 160-170. it is a 2tgeu, t50 and a stock diff, its speedo was pretty good too.

laterdays

[EnFlaMEd]

Ide definately be looking at speedo gear. My cars speedo is out by 12kph and the factory tacho by about 600rpm. When your at the dyno next ask them for roadspeed to be indiciated on your printout.

[urantia]

not of any great use to the thread. *apologies in advance*

I changed my 15" rims with 16"'s. And my 3.9 diff to 4.3 ratio diff, converted to a manual Gearbox. My speedo is out maybe 2-3km/h at 100km/h, 60km/h is perfect as well as 50km/h. I must of fluked getting the higher ratio diff and larger tyres to bring it back to pretty much correct calibration for the speedo.

[lilcrash]

im not worried about the speedo, im worried about my car sitting on red line before the end of the 1/4 mile, like by the end of the 1/4 most cars are doing ova 100 and ive only got 120-130 to play with. my honda pulled a 17.7 and it was doing 137 so im guessing that my diff is going to slow me down a lot. should i just be going with my original idea and go to arb and get a diffrent ratio air locker put in my diff housing?? wat ration should i be running?? 3.9, 3.7 or lower??

[thechuckster]

you need to find out what diff you have before heading off to ARB to purchase a locker or elsewhere to purchase over-priced ring/pinion gearsets.

If you have a T-series diff, then ARB isn't going to have a locker that fits your diff.

Unless you've majorly modified the rear suspension in your TA (it is a TA celica?) - then the plaque on the firewall IS going to give you a good idea of the the type of diff, and possibly the ratio. Painting a diff doesn't mean its been changed mechanically.

So.. can you list the transmission and diff code?

cheers,
Charles.

[lilcrash]

ok here is the numbers, trans axle - 5F1 T292

its got a stock rear end but i think its got a screwed up diff ratio

laterdays

[thechuckster]

well it's either 4.1 or 4.3 - combine the higher one with the very ordinary 5th gear and you've got a drag car with an easy launch but a low trap speed.

Assuming the diff is still a T series, i think you want the centre out of an RA60 (code T312) which is a 3.9.

Have you considered finding an alternative gearbox?

[lilcrash]

thank you. so basically the 4.3 will get up to speed fast and the 3.9 will have a slower 0-100 but have a higher top speed??

will the T312 bolt straight in??

i havent thought of a gearbox change as i didnt think it would be easy to find another one, wat would u recomend to put in??

thankyou

[thechuckster]

if i've got my diff ratios around the right way - yes - except that the 4.3 would let the engine rev up quicker and you'd have a lower top speed

easy way to check the ratio:
chock front wheels
put arse of car in the air
put gearbox in nuetral
but marks on edge of tyre and tailshaft
you rotate tailshaft, mate looks at a tyre
count number of times you rotate shaft for 10 tyre rotations
divide that by 10, should give you the approximate ratio.

the T312 (if you can find one) "should" bolt in (pull axles out, remove entire centre, bold new entire centre in, re-fit axles...sounds so easy? )

put a W58 or W57 in - they have taller 5th gears and first gear isn't so short.

[lilcrash]

is there a way to actually tell wat gear box i have?? like i was told my front suspension/brakes were upgraded and it isnt, so im not 100% on wat the gear box is.

thanx and laterdays

[Andrew162]

not of any great use to the thread. *apologies in advance*

I changed my 15" rims with 16"'s. And my 3.9 diff to 4.3 ratio diff, converted to a manual Gearbox. My speedo is out maybe 2-3km/h at 100km/h, 60km/h is perfect as well as 50km/h. I must of fluked getting the higher ratio diff and larger tyres to bring it back to pretty much correct calibration for the speedo.

I had a similar issue in the RAV, after changing the wheels over from stock 16's to 17's, and having comparably similar tyres (rotation-wise), the new setup was 20mm shorter than the stock fitment, thus making the speedo slightly faster (about 2%). Then I changed over the engine and gearbox for all GT-Four gear, that's ST205 box, all driveshafts and 185 diff as well. This throws out the speedo even more (by about 10% total) and the gear settings aren't that overly different, except the 1st gear isn't as short and 5th gear is taller (a PROPER 5th gear!!). While I didn't take the RAV down the quarter mile, I'm pretty sure that it would have had a good take-off and trap speed.

Again, not that relevant, but just my 2c...

[thechuckster]

is there a way to actually tell wat gear box i have?? like i was told my front suspension/brakes were upgraded and it isnt, so im not 100% on wat the gear box is.

only way to work out what gearbox you have is the same process
- rotate input shaft and count how roations of output shaft
- repeat for each gear
is a PITA if the gearbox is still in the car.

pictures would help confirm that it is a w55/6/7/8 gearbox - but there's no other obvious identifying marks to distinguish one from the other.

cheers,
Charles