73 transmission on a 79 block?

[ga.spyder]

We are building a 2 liter motor for our Lemons racer.Hi_comp pistons,big valves,1800 head,hotter cams,ported and polished head and dual carb manifold by a professional.The tranny out of our 73 has been fantastic,and we want to mate it to this motor.Any issue doing this?

[csi2000s]

I've been running a 72 transmission mated to a 2 litre block in my 1974 spider for the last 20 years with no problems at all. That combo was fitted to the car when I bought it. I had no idea the engine was a 2 litre until I checked the engine number. I knew very little about Fiats then.
I had both units rebuilt at the same time and the transmission just keeps going and going.The engine is fitted with hi comp pistons,1800 head with hot cams and twin 40mm DCOE Webers so It has a bit of power and the early trans loves it!

[Fi8spider]

Hi ga.

The fact of the matter is that you'll be giving the trans a hard time being a race car.
A lot will depend on how you treat the gearbox, obviously repeated hard take off's i.e dropping the clutch will increase the risk. I have used my Spider with a hot 1756cc on the track on a number of occasions and I like the 124 5 speed for it's slick gear delivery, I mainly run super sprints where a rolling start applys so I don't really give it that much hurry curry but when I do I can hear those bearings drone on down shiftand when pulling away hard in 2nd or 3rd.

I have retired the Spider from track duties about a year ago and replaced it with a 131 2000 series 3 with the "big bearing" gear box. It has a longer throw on shift however the feel is a lot more at home on the track than the 124 box.

In saying all this and taking into consideration your parts bin I would say use the 124 trans for now, heck it's a LeMons car, isn't it all about running to a modest budget? Use a quality oil that can withstand the temps you'll be subjecting it too and who knows it'll probably do you many many race meetings of good service, actually it wouldn't suprise me if it does.

If I had to choose between the two trannies (124 or 131) for a purpose built Fiat racer I'd pick the 131 box simply because it was built to withstand more HP.

[Fi8spider]

dpost.

[ga.spyder]

Thanks guys,I was pretty sure there wasnt a issue.I may have a line on a 131 tranny.We would definitely go that way,if possible.As you say,its a stronger unit.We do all rolling starts also.The trans has done 3 races now,with no problem.I drop the oil after each race,and refill with Pennzoil Synchromesh

[Fi8spider]

Are you dropping the oil after every race because it's a mineral oil?

I'm using Castrox Syntrax 75w/90 with great results in both the 131 and 124.
http://www.msds.castrol.com.au/msds.asp ... 55704-AU07

[engineerted]

Craig,

There is nothing wrong in using a 124 box for racing. Myself and Jim S. have been using one for years without problems. The 131 does have steel syncros but the issure is fabracating the drive shaft, mouning, enlarging the tunnel in the body and finding parts, seals etc. Keep it simple, easy to have a spare 124 trans on hand if something does go wrong.

I run Redline 1qt. MT-90 plus 1qt Valvoline straight 50w racing oil in the gear box. I like this combo better than the syncromesh

Ted

[BEEK]

i abused 124 boxes in my nascar fiats for years, only had one that started popping out of 3rd, which was the gear we ran in. new hub and fork and syncro , back in business

[ga.spyder]

Thanks guys,we are planning on keeping and using the 124 tranny.It has servred us well.I change the oil for every race because we are running 24 hour endurance races.Since we had been doing that,we felt the extra cost of synthetic just not worth it.The car sits for months between events,so changing it and the diff before events seemed good preventative maint.