When i put it in reverse it really slams in gear, but when i go to drive it`s smooth.
Normal or a sign i need a checkup?
This is my first car with TH 400.

 

Your TH400 has a modulator valve that has a short neoprene vacuum hose attached to it. Its very common for the oil-soaked hose at the modulator to come off which causes the symptoms you are describing. Its also possible the modulator valve has gone bad and needs to be replaced.

 

The key word here is "slams". On cold start-up the shift to reverse can be a bit "abrupt" at cold idle RPMs (~1200-1500) but that is normal. As is a smoother shift to "D" after the choke has kicked down. You haven't said if this is a cold or hot engine situation.

 

[QUOTE=paul 74;1590234040]The key word here is "slams". On cold start-up the shift to reverse can be a bit "abrupt" at cold idle RPMs (~1200-1500) but that is normal. As is a smoother shift to "D" after the choke has kicked down. You haven't said if this is a cold or hot engine situation.[/QUOTE


It is the same issue cold or hot.

 

What's the idle rpm? If yours is 800 or more you will get a jolt or feel as if it's slamming into gear. More noticeable in reverse than drive. If it's not a high idle speed, check the cushions on the differential plate.

 

Good advice, your hot idle should be 600 RPM. The cushion on the rear differential is a often a problem spot. Replace with rubber, not poly.

 

My 73 would clank into (any) gear, mostly when first starting out and worse in reverse. I ended up breaking the left stub axle about 2 months ago that put me on the side of the road. After about ~$800 in diff repair and a bunch of more $’s in other pieces parts, the TH400 now shifts perfectly with no more clanking noise!

Regarding those poly bushing, I bought ploy’s for all the rear suspension parts, but only ended up using the big ones for the diff cross member and the strut rods. The diff CM poly’s went in fine with no fitment issues, however, the strut rod ones did not fit without modification. I measure the old steel bushing vs. the brass looking ones that came with the poly’s and the new ones were about a 1/8” too long which I filed down and also had to cut about 1/8” off one each of the inside poly material to make them fit flat on camber bracket and spindle supports.

From everything I read on the forum prior to ordering the poly parts it sounded like most everyone was using poly, it wasn’t until later research I saw that others were adamant about staying with rubber. From my little experience with poly I was not impressed. I ended up keeping mostly rubber bushing on everything else.

Just my $.02 from my limited experience