Driveline locking up in reverse

[Garys1969RR]

I was running the 69 RoadRunner through the 1/4 mile at Bandimere last nite. Made 2 passes, ran approx 13.70 at 103 MPH. This with street tires, 16", with good width and tread. Ran fine, no problems. So I bolted on some M/T slicks, and it slowed to 13.86 at 100 MPH! I was expecting a faster time slip. The slicks are about 2" smaller diameter. (30.5) " . Plus when I went to cool the motor after this run with the slicks on, and tried to back up, the drivetrain locked up in reverse only! But forward speeds were fine. I even made 3 more passes with the slicks on. So when I back up, it locks at anywhere from immediately to 15 feet back. And the car ran slower the next 3 passes, to 13.94 at 99 MPH last run. So I am thinking possibly the trans rear sprag 1 way clutch? Or the 3.91 sure grip differential ? Or even some kind of rear brake problem locking it up when backing up? It is definitely the drive train preventing the reverse movement, and not the front tires. Any one ever have this happen? If so what was the problem? HELP! ! ! :icon_neutral:

 

[Garys1969RR]

Oh yea, this is a 727 torque flite with an 11 " converter.

 

[khryslerkid]

Do you have some play in your ring and pinion?

 

[Garys1969RR]

No, about .010" backlash on the ring and pinion. Have had this gearset in there for about a month. No probs till last nite

 

[khryslerkid]

.006-.010 is the correct amount of backlash. Let's think simple things first. Brake shoes aren't too tight? I'm sure you are checking the ease of turning the rear wheels, listing for any weird sounds or binding.

Here is a good link for rear specs. http://www.moparmusclemagazine.com/...08_mopar_8_3_4_rear_gear_buildup/viewall.html

 

[rrowdy]

One time years ago this happened to one of my drag cars which had drums in the rear. Turned out it was a broken shoe retaining spring which allowed the Front shoe to pivot against the drum in reverse only.

I'd try that first as it's easy to check.

Good luck!

 

[Garys1969RR]

Ok thanks, will check it out on tuesday. Sounds like that could be the problem.

 

[Garys1969RR]

Found the problem, the return spring was in the wrong hole. Plus a stud had got left and stuck in there, not allowing the shoes to completely re tract. Like they say in Misourri, " It don't pay to be in no hurry" LOL

 

[khryslerkid]

Glad you found your problem. Those simple things can seem to be something major. I learned many years ago to think simple things first! I could tell you stories all day. Let us know how it does next time you take it to the strip...

 

[Meep-Meep]

Well, look on the bright side. You were running 13's with the brakes on!

 

[Garys1969RR]

Thanks, Meep Meep, today I changed the left front wheel studs to right hand threads! Thats the Last one. Now you can remove any wheel on the car with a 13/16 socket! Also the front brakes have no adjuster so I backed them off until there was no drag. Wonder if I should do this to the rear brakes also? Have heard many drag racers switch from disc brakes to drum to reduce drag, as disc brakes always have some pad pressure on the discs, creating drag.