I have been rebuilding 700s out of my home garage for a while now and have had fairly good results but a 1990 unit out of a full size Blazer w/350 TBI that I recently rebuilt has issues that I cant find a solution to.
The problem(s) are that when the gear selector is put into OD the trans engauges 2nd gear until the throttle is slightly applied which causes it to immediately down shift into 1st with a "clunk". The vehicle doesnt have to be moving to do this either as you can make it happen by holding the brakes, selecting OD, and slightly applying the throttle. If you manually select 3rd, 2nd, or 1st this problem doesnt occur just when selecting OD.
The other problem (related to the above?) is that while road testing the vehicle when the trans shifts from 3rd to 4th it binds up causing the vehicle to slow until the speed is slow enough that the trans down shifts back to 3rd then all is fine again.
Other than the two problems listed the trans works fine, shift points are right on the money, shift feel is fine, TCC apply is good, etc. I rebuilt the unit using a Transtar kit, new Daaco TC, pump clearance mic'd fine, total end play is .029", all clutch stack clearances were well within spec, air checked input drum (no leaks), etc. The only mods that were done to the trans, which I perform on all trans's that are destined for full size trucks, is the TC check ball in the input shaft was deleted, PR
valve land ground off, .420" boost valve (unit had a .400" originally), load release springs deleted and #44 hole in seperator plate drilled to .093" per the ATSG manual when deleting these springs.
I swapped the unit out at the customers house for another fresh unit I had on hand that was built the same and brought the defective unit home for tear down. Upon tear down the only thing I can find is that the 2-4 band is burned which I kind of expected. Other than that the clutches look new, all seals/gaskets are fine, no valves in the VB
were stuck/sticky, all servo/accume springs fine, etc. Other than the burnt band the trans looks new.
Anything thoughts on what to check? I thought that maybe I put the forward sprag togeather backwards after cleaning it but after checking it the sprag was assembled correctly. Im kinda stumped on whats wrong.
TIA for any help.
BTW, the unit in question was a replacement from the salvage yard that burnt completely up due to the customer not adjusting the TV cable when he installed it (he thought it was the "kick down" cable...UGH). He removed the trans and brought it to me for rebuilding and once he had reinstalled it I adjusted the TV cable for him. Once that was done and upon testing is when I found the 2nd gear start/4th bind up issues. I forgot my line pressure gauge at home (DOH) so I never got to check the line pressure while the unit was running and the customer was over an hours drive from my garage so getting line pressure readings didnt happen.