5 speed strength

J

johosjokers

Daily Driver
at what point (hp wise) does the stock tranny lay down?
ETA, what effect does an a/c comp. have on a hi rpm engine? if using a modern comp. can i assume none?
thanks, john
 
Last edited:
It's not Hp that will kill the transmission more like torque and traction.
It's the differential centre that is the weak link, and that doesn't like hard drag racing launches, but will survive just fine with 120/130 crank hp and spirited driving or race track work... it just doesn't like hard starts, especially if you have plenty of tyre grip.

SteveC
 
helical cut gears are very strong and quiet by design, straight cut lose less power thru transmission, so that's why race and rally cars use straight cut gears.

I think Matt posted a while back about a straight cut set he bought for his race car, worked great but didn't last due to insufficient hardening...

The Fiat gears are plenty strong, made with good steel, and hardened well for long life which is why OE gearbox parts are damn expensive. Unless your talking something out of Italy from a reputable tuning house, then I would be wondering about the overall quality... basically, if it's cheap there's a good reason. But buy one if you want to, and in 12 months time tell us how it works out for you...

Like I said it's the diff centre that's prone to break anyway... I built a trans for a customer and he bought a C&B LSD for me to install, had a machined billet diff centre, no way that would break in a hurry ... basically it's to do with the design, the small diff bearings of the five speed limit the material around that area... that's why the four speed diff is so much stronger, it uses much larger diameter bearings and gives more 'meat' around that area in the stock casting.

SteveC
 
Interesting Steve

I was previously not too worried about my gearbox as leaving big black marks on the road is something I grew out of decades ago. Now with all this talk of weak gearboxes I am thinking otherwise.

I have read and seen images of cracked Fiat X1/9 5 Speed alloy intermediate plates and housings but this is the very first time I have heard that the diff is a weak link, So Steve I guess the open diff is probably just as weak as the BE3 Pewgoat transaxel. Question is are we talking the same bad Pewgoat habit of the spider (planet) gears splitting / ramping on the pinion shaft jamming the side gears and cracking the diff casing?


The roll pin in the BE3 Pewgoat trannies, which retains the spider gear cross shaft, falls out.... this then lets the spider gear shaft 'migrate' out of the crown wheel carrier and when it drops out far enough it will 'whack' the side of the casing.... sometimes this results in the shaft ripping a hole in the casing... other times it merely whacks the shaft back in (until it creeps out again)... Sometimes it results in the spider gear shaft breaking and wrecking the whole tranny.

In this example the smaller spider in the diff that would have split in two and taken the rest of the GB out.

http://www.aussiefrogs.com/forum/at...23d1375604168-shes-just-gone-bang-gearbox.jpg



A Quaife ATB LSD is in my 205, I drive it hard every day and to be honest I now wish I had one in my X1/9 for the same simple reason, it gives the confidence that it is not likely to let go if you give it a bit of biff. The ATB unit is likely around twice the weight of the stock diff but the advantages out-way the disadvantages by FAR IMHO.

Finding a 5 Speed gearbox is hard ( I have been unsuccessful to date to find a spare ). I'm guessing a standard diff reco is an expensive job anyway so before I finish the Punto GT engine I'm thinking get the ATB LSD fitting new bearings in the current GB and being done with it?

So question is will the Quaife QDH2K unit for the Uno / Punto fit in the 5 Speed X 1/9 without machining?
 
I

Have sock HP/torque and autox on toyo R888 I do hard launch my car haven't had a problum yet . Like Steve said it not a problum to you start making high HP and torque .
 
johosjokers said:
at what point (hp wise) does the stock tranny lay down?
ETA, what effect does an a/c comp. have on a hi rpm engine? if using a modern comp. can i assume none?
thanks, john
Click to expand...

For the a/c part - a modern compressor should cut out when it's running at high rpm. I say this, because a fellow racer had a mid 90's showroom stock Mustang race car, and "tried" running the AC during race conditions (on a hot day) - it didn't work, but it cooled him down plenty on mock grid.

For the transmission part - Steve has good points on the bearing OD being smaller on the 5spd. My race car was 135hp at the crank - I ran a stock 5spd, one with 3:59:1 and the 4.08:1. I didn't have problems with the bearings at all. The transmission was very reliable - EXCEPT the syncro rings and engagement rings (gear side and engagement sleeve). Bah, I'd wear those out fairly quickly, perhaps I was a little aggressive on the upshifts. I was using a GL1 gear oil, maybe not the best, but it worked. Unfortunately I used EP GL5 on my first gearbox and the syncros didn't work well as a result, ending in very rounded teeth on the syncro engagement teeth of the ring and gear.

What will be your final application? As mentioned in this thread, standing starts aren't so great - but I never subjected mine to that.


On another note, my friend's X1/9 race car (Boig's old FP car), producing 165hp ran a PBS straight cut gearbox - but when that blew up, they replaced it with a welded diff 5spd and ground and welded gear set - meaning, they started off with 5spd gears, ground them off and welded on straight cuts for the ratios they needed. The transmission lasted long enough, but the syncros were the weak link here. Ultimately they repaired the PBS box - which fits into a 4spd housing, 5forward gears, no functioning reverse with LSD.


heh, my other friend who also ran an X1/9 race car forgot to "fill" the transaxle while doing a fluid change. He ran two laps, and BOOM! his 5spd gearbox literally exploded.. oh... the agony!
 
I used the stock 5-speed in my DM autocross car with 140 hp for about 7 years. Before that the tranny was in my Street-prepared car for 4 years with many autocrosses and Pro Solos without any problems. I wasn't brutal with it and never missed a shift. Sustained high RPMs, like for road racing, above 8,000 will take its told on this transmission though.
 
Diff bearings and crown wheel PCD for the bottom change Uno gearbox is the same as the X19 five speed...not sure about tipo/punto style top change, but I think Bacci list different parts for the late box... never had one apart myself so I'm not sure what the differences are...never seen the quaife listing.

Had several X19's to 120rwhp NA, and with careful use had no transmission issues... have seen and repaired several gearboxes that broke the keyway out of the input shaft on the fifth gear... but that design was changed for later gearboxes to a spline, Fiat obviously realised that the design was an issue...a couple weren't even improved engines just totally stock...so obviously a weak design with a severe stress riser at the sharp edge at the bottom of the keyways...design changed in 1981.. but the first batch of five speeds in australia were actually 1979 manufacture and re complianced as 1982's... and had the keyway style transmissions...which broke.

Had one gearbox on a lower powered car sieze fourth gear onto the lay shaft... which took out fourth and fifth gears ... I have read several anecdotal reports about oil starvation to the plain bush/bearing when used for road racing... I could be G force related as the oil in the gearbox can also move just like oil in a sump... fast left turns would move the oil away from fourth/fifth and could lead to supply issues...

Later gearbox casing have a different design that looks like an attempt to distribute more oil towards these points at 4/5 in the transmission... but as I said I have only seen one gearbox that died like this with a gear bush seizure... I had put it down to the wrong oil (had EP oil in the trans) which failed to lubricate properly, as EP oil tends to froth and foam in a non EP application, but for sure diagnosing broken transmissions is a lot of guesswork

I have seen several 5 speed diff housings that cracked in higher powered/high grip and turbo cars... the uno has a built in clutch... wheelspin when weight transfers away from the front... you don't get that in an X19 and all that load breaks the cast diff centre... if you have one apart you'll see the 'windows' in the casting and that's where the crack propagate from...four speed has lots more meat in this area.... but yes it's likely that torque - which will make the spiders ride up on the side gears - puts undue stress on the cast iron diff casting and makes it crack.

SteveC
 
Thank you Steve

I understand what you are saying about the diff centers as this is exactly what happens in in my little Frenchie when you bump up the power and run fatter, stickier tyres - in Froggie circles it is well known the ATF diff solves this problem.

The old Mk1 uno block was pushing out a bit more but I have been treating the gear box like Czech Bohemia Crystal. The car is plated as an 81 so the PO could have made a mixie blob with either an early or late 5 speed I'm guessing.

I have next to zero (worthwhile) knowledge of the standard 5 speed as I have been a useless twat at sourcing another one to rebuild/beef/play with up so what you have said is extremely useful. The key-way vs spline change in the later 5 speed is good to know in my ongoing search for another box. 4 speeds I have three of for the project car but no 5 speed spare for the road going X uno (soon Punto).

If the Crown wheel PCD in the bottom change Uno box is the same as the X I will look into the drawings at Quaife and see if the package size is the same, might fit, it may be a way ahead.

Merry Christmas to you and the kids.
 
pretty sure your car began life as a 1300/four speed, aust spec mk 2, so gearbox internals are anyone's guess, though I think mario monachaio built the car originally, so he may know what went into it... could easily have been unoT internals...he had a front cut from a mk1 sitting in his workshop for years and I think that's where your engine came from originally.

I have a distant and vague recollection of selling mario a pair of 5 speed X casings from a damaged gearbox many moons ago... all unoT are splined fifth gear AFAIK.

SteveC
 
A memory like an elephant

Yes that's the one,

Mario is the one who guaranteed the internals were UnoT.

Spun a big end bearing after a (small) compressor upgrade in that engine.

You have a PM
 
You must log in or register to reply here.
Back
Top