odxr

Will this harm the OD unit?I got a very beat 1987 that I am building into an on/off road buggy.I want to flat tow it behind a motorhome with just a towbar.Old school stick shift cars could be towed with the trans in neutral.Has any members on here rebuilt the OD unit and know how it works?

FOURSPEEDVETTE

No problem will occur to the O/D unit. It's controlled by an electrical switch that turns it on or off. Being that your post sounds like you may traveling a long distance(?), because of the motor home, you may want to just flatbed the car. I was never a fan of towing any car with a towbar. It's a lot safer to tow a car flatbed style for everyone else on the road also. Good luck with your project!

c4cruiser

Either rent a flatbed trailer or use a tow dolly that will carry the front wheels off the ground. There is no way to use a "tow bar" as there are no places to hook it up to the front of the car.

The manual trans can be left in Neutral and it won't hurt the trans or the OD. One thing you should do is to check the fluid level in the OD unit. Towing so that the rear wheels spin will also cause circulation of the ATF within the OD unit. The fluid will also run thru the two cooling lines to the radiator and back.

Tom400CFI

What lubricates:
The tail shaft bushing
The main shaft bearings in the trans?

Does the OD unit have an oil pump for the TS bushing like a 4wd T-case? If not...

In the trans, everything is typically lubed by splash from the counter shaft gears in the sump, plus oil runs from them onto the main shaft gears and sprays everywhere. When towing, the input shaft, counter shaft and all gears are stationary. The main shaft is spinning ~3000 RPM (at hwy speed) inside the input shaft, 1st, 2nd and 3rd gears. I don't think that the oil level is high enough to reach the spinning shift collars to sling oil. I think the bearings in the main shaft/gears will run dry eventually.

bjankuski

I agree but am not 100% sure so this really needs to be looked into.

bjankuski

After checking some diagrams on the transmission design I do not believe you can tow the car with the wheels spinning for any long distance. The main shaft will be spinning but the countershaft and gears will be stopped, this will eventually cause the failure of the bearings in the stopped gears and the tailshaft housing.

The attached link shows the power flow a manual transmission (Not a Doug Nash) and you can see when the car is in neutral and the engine is off the mainshaft will be rotating and the countershaft and gears will be stopped. That means the bearing on the mainshaft gears 2, 3, and 4 will be rotating while not getting any lubrication.

https://www.cartechbooks.com/techtip...ons-explained/

hcbph

Never liked to flat tow a vehicle anyway without pulling the driveshaft.

s carter

The O/Ds pump is on the Tail Shaft/Out Put Shaft, so as long as the Drive shaft is moving and the Direct Clutches and other component's working correctly Fluid is sliding around the OD unit and T-10 Out board side of trans is spinning also. so all is being Lubed.

Does This Still make me a Fan of Wheels on Ground Towing for long Distance, Not Really but it can be done, but not Recommended for any Distance or Speed.

bjankuski

This is the part that has me concerned, the countershaft is not spinning and that is what throws the oil up to lubricate the bearing in each gear on the mainshaft. The overdrive unit may be fine but the 4 speed will not be?

Tom400CFI

I agree. ^

Unless the oil level in the T10 is high enough to touch the shifting collars (and I don't think that it is), the bearings on the main shaft will not be lubed.

s carter

If I not Mistaken the Direct Clutches just do a Pass Thru of OD, One simple test to put it all to rest. Get Both rear wheels off the ground. We all Know in gear the wheels will not move, so have a Friend Step on the Clutch and they move Hence a pass thru to clutch. Face it you park your car in gear it Don't Roll

Tom400CFI

You're not "getting it".

You are right, that the OD does "Pass Thru" as you put it. In other words, as far as the transmission is concerned, we can simply pretend that the OD is nothing more than an output shaft. If the wheels turn, the trans main shaft will turn. No doubting that.

The problem is, in the trans, no part of the main shaft touches oil (I don't think). So...if it's turning, but not touching oil...

s carter

Your probably Rite the Counter shaft doesn't see any action in Neutral , I will admit i am having a bit of trouble running the Flow with car running counter shaft is moving. Rolling it's stopping at the Syncro's

I just remembered As a rule when I was driving a tow Truck if we were dragging a Heavy truck much more than 30 Miles on back roads or any Highway we pulled the Shaft or 1 Axle, Just for this reason.

Churchkey

Remove the driveshaft.